[PATCH v4 00/13] Add build ID to stacktraces

[PATCH v4 00/13] Add build ID to stacktraces

[Stephen Boyd]

This series adds the kernel's build ID[1] to the stacktrace header printed
in oops messages, warnings, etc. and the build ID for any module that
appears in the stacktrace after the module name. The goal is to make the
stacktrace more self-contained and descriptive by including the relevant
build IDs in the kernel logs when something goes wrong. This can be used
by post processing tools like script/decode_stacktrace.sh and kernel
developers to easily locate the debug info associated with a kernel
crash and line up what line and file things started falling apart at.

To show how this can be used I've included a patch to
decode_stacktrace.sh that downloads the debuginfo from a debuginfod
server.

This also includes some patches to make the buildid.c file use more
const arguments and consolidate logic into buildid.c from kdump. These
are left to the end as they were mostly cleanup patches. I don't know
who exactly maintains this so I guess Andrew is the best option to merge
all this code.

Here's an example lkdtm stacktrace on arm64.

 WARNING: CPU: 4 PID: 3255 at drivers/misc/lkdtm/bugs.c:83 lkdtm_WARNING+0x28/0x30 [lkdtm]
 Modules linked in: lkdtm rfcomm algif_hash algif_skcipher af_alg xt_cgroup uinput xt_MASQUERADE
 CPU: 4 PID: 3255 Comm: bash Not tainted 5.11 #3 aa23f7a1231c229de205662d5a9e0d4c580f19a1
 Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
 pstate: 00400009 (nzcv daif +PAN -UAO -TCO BTYPE=--)
 pc : lkdtm_WARNING+0x28/0x30 [lkdtm]
 lr : lkdtm_do_action+0x24/0x40 [lkdtm]
 sp : ffffffc0134fbca0
 x29: ffffffc0134fbca0 x28: ffffff92d53ba240
 x27: 0000000000000000 x26: 0000000000000000
 x25: 0000000000000000 x24: ffffffe3622352c0
 x23: 0000000000000020 x22: ffffffe362233366
 x21: ffffffe3622352e0 x20: ffffffc0134fbde0
 x19: 0000000000000008 x18: 0000000000000000
 x17: ffffff929b6536fc x16: 0000000000000000
 x15: 0000000000000000 x14: 0000000000000012
 x13: ffffffe380ed892c x12: ffffffe381d05068
 x11: 0000000000000000 x10: 0000000000000000
 x9 : 0000000000000001 x8 : ffffffe362237000
 x7 : aaaaaaaaaaaaaaaa x6 : 0000000000000000
 x5 : 0000000000000000 x4 : 0000000000000001
 x3 : 0000000000000008 x2 : ffffff93fef25a70
 x1 : ffffff93fef15788 x0 : ffffffe3622352e0
 Call trace:
  lkdtm_WARNING+0x28/0x30 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
  direct_entry+0x16c/0x1b4 [lkdtm ed5019fdf5e53be37cb1ba7899292d7e143b259e]
  full_proxy_write+0x74/0xa4
  vfs_write+0xec/0x2e8
  ksys_write+0x84/0xf0
  __arm64_sys_write+0x24/0x30
  el0_svc_common+0xf4/0x1c0
  do_el0_svc_compat+0x28/0x3c
  el0_svc_compat+0x10/0x1c
  el0_sync_compat_handler+0xa8/0xcc
  el0_sync_compat+0x178/0x180
 ---[ end trace 3d95032303e59e68 ]---

Changes from v3 (https://lore.kernel.org/r/20210331030520.3816265-1-swboyd@chromium.org):
 * Fixed compilation warnings due to config changes
 * Fixed kernel-doc on init_vmlinx_build_id()
 * Totally removed add_build_id_vmcoreinfo()
 * Added another printk format %pBb to help x86 print backtraces
 * Some BUILD_BUG_ON() checks to make sure the buildid doesn't get bigger or smaller

Changes from v2 (https://lore.kernel.org/r/20210324020443.1815557-1-swboyd@chromium.org):
 * Renamed symbol printing function to indicate build IDness
 * Put build ID information behind Kconfig knob
 * Build ID for vmlinux is calculated in early init instead of on demand
 * printk format is %pS[R]b

Changes from v1 (https://lore.kernel.org/r/20210301174749.1269154-1-swboyd@chromium.org):
 * New printk format %pSb and %pSr
 * Return binary format instead of hex format string from build ID APIs
 * Some new patches to cleanup buildid/decode_stacktrace.sh
 * A new patch to decode_stacktrace.sh to parse output

[1] https://fedoraproject.org/wiki/Releases/FeatureBuildId

Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Evan Green <evgreen@chromium.org>
Cc: Hsin-Yi Wang <hsinyi@chromium.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: <kexec@lists.infradead.org>
Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: <linux-arm-kernel@lists.infradead.org>
Cc: <linux-doc@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: <x86@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: peter enderborg <peter.enderborg@sony.com>


Stephen Boyd (13):
  buildid: Only consider GNU notes for build ID parsing
  buildid: Add API to parse build ID out of buffer
  buildid: Stash away kernels build ID on init
  dump_stack: Add vmlinux build ID to stack traces
  module: Add printk formats to add module build ID to stacktraces
  arm64: stacktrace: Use %pSb for backtrace printing
  x86/dumpstack: Use %pSb/%pBb for backtrace printing
  scripts/decode_stacktrace.sh: Support debuginfod
  scripts/decode_stacktrace.sh: Silence stderr messages from
    addr2line/nm
  scripts/decode_stacktrace.sh: Indicate 'auto' can be used for base
    path
  buildid: Mark some arguments const
  buildid: Fix kernel-doc notation
  kdump: Use vmlinux_build_id to simplify

 Documentation/core-api/printk-formats.rst | 11 +++
 arch/arm64/kernel/stacktrace.c            |  2 +-
 arch/x86/kernel/dumpstack.c               |  6 +-
 include/linux/buildid.h                   |  4 +
 include/linux/crash_core.h                |  7 +-
 include/linux/kallsyms.h                  | 20 ++++-
 include/linux/module.h                    |  6 +-
 init/main.c                               |  1 +
 kernel/crash_core.c                       | 50 +-----------
 kernel/kallsyms.c                         | 95 ++++++++++++++++++-----
 kernel/module.c                           | 24 +++++-
 lib/Kconfig.debug                         | 11 +++
 lib/buildid.c                             | 72 +++++++++++++----
 lib/dump_stack.c                          | 13 +++-
 lib/vsprintf.c                            |  8 +-
 scripts/decode_stacktrace.sh              | 89 +++++++++++++++++----
 16 files changed, 304 insertions(+), 115 deletions(-)


base-commit: a38fd8748464831584a19438cbb3082b5a2dab15
-- 
https://chromeos.dev

[PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Stephen Boyd]

Let's make kernel stacktraces easier to identify by including the build
ID[1] of a module if the stacktrace is printing a symbol from a module.
This makes it simpler for developers to locate a kernel module's full
debuginfo for a particular stacktrace. Combined with
scripts/decode_stracktrace.sh, a developer can download the matching
debuginfo from a debuginfod[2] server and find the exact file and line
number for the functions plus offsets in a stacktrace that match the
module. This is especially useful for pstore crash debugging where the
kernel crashes are recorded in something like console-ramoops and the
recovery kernel/modules are different or the debuginfo doesn't exist on
the device due to space concerns (the debuginfo can be too large for
space limited devices).

Originally, I put this on the %pS format, but that was quickly rejected
given that %pS is used in other places such as ftrace where build IDs
aren't meaningful. There was some discussions on the list to put every
module build ID into the "Modules linked in:" section of the stacktrace
message but that quickly becomes very hard to read once you have more
than three or four modules linked in. It also provides too much
information when we don't expect each module to be traversed in a
stacktrace. Having the build ID for modules that aren't important just
makes things messy. Splitting it to multiple lines for each module
quickly explodes the number of lines printed in an oops too, possibly
wrapping the warning off the console. And finally, trying to stash away
each module used in a callstack to provide the ID of each symbol printed
is cumbersome and would require changes to each architecture to stash
away modules and return their build IDs once unwinding has completed.

Instead, we opt for the simpler approach of introducing new printk
formats '%pS[R]b' for "pointer symbolic backtrace with module build ID"
and '%pBb' for "pointer backtrace with module build ID" and then
updating the few places in the architecture layer where the stacktrace
is printed to use this new format.

Example:

 WARNING: CPU: 3 PID: 3373 at drivers/misc/lkdtm/bugs.c:83 lkdtm_WARNING+0x28/0x30 [lkdtm]
 Modules linked in: lkdtm rfcomm algif_hash algif_skcipher af_alg xt_cgroup uinput xt_MASQUERADE hci_uart <modules trimmed>
 CPU: 3 PID: 3373 Comm: bash Not tainted 5.11 #12 a8c0d47f7051f3e6670ceaea724af66a39c6cec8
 Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
 pstate: 00400009 (nzcv daif +PAN -UAO -TCO BTYPE=--)
 pc : lkdtm_WARNING+0x28/0x30 [lkdtm]
 lr : lkdtm_do_action+0x24/0x40 [lkdtm]
 sp : ffffffc013febca0
 x29: ffffffc013febca0 x28: ffffff88d9438040
 x27: 0000000000000000 x26: 0000000000000000
 x25: 0000000000000000 x24: ffffffdd0e9772c0
 x23: 0000000000000020 x22: ffffffdd0e975366
 x21: ffffffdd0e9772e0 x20: ffffffc013febde0
 x19: 0000000000000008 x18: 0000000000000000
 x17: 0000000000000000 x16: 0000000000000037
 x15: ffffffdd102ab174 x14: 0000000000000003
 x13: 0000000000000004 x12: 0000000000000000
 x11: 0000000000000000 x10: 0000000000000000
 x9 : 0000000000000001 x8 : ffffffdd0e979000
 x7 : 0000000000000000 x6 : ffffffdd10ff6b54
 x5 : 0000000000000000 x4 : 0000000000000000
 x3 : ffffffc013feb938 x2 : ffffff89fef05a70
 x1 : ffffff89feef5788 x0 : ffffffdd0e9772e0
 Call trace:
  lkdtm_WARNING+0x28/0x30 [lkdtm 6c2215028606bda50de823490723dc4bc5bf46f9]
  direct_entry+0x16c/0x1b4 [lkdtm 6c2215028606bda50de823490723dc4bc5bf46f9]
  full_proxy_write+0x74/0xa4
  vfs_write+0xec/0x2e8
  ksys_write+0x84/0xf0
  __arm64_sys_write+0x24/0x30
  el0_svc_common+0xf4/0x1c0
  do_el0_svc_compat+0x28/0x3c
  el0_svc_compat+0x10/0x1c
  el0_sync_compat_handler+0xa8/0xcc
  el0_sync_compat+0x178/0x180
 ---[ end trace f89bc7f5417cbcc6 ]---

Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Evan Green <evgreen@chromium.org>
Cc: Hsin-Yi Wang <hsinyi@chromium.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: <linux-doc@vger.kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Link: https://fedoraproject.org/wiki/Releases/FeatureBuildId [1]
Link: https://sourceware.org/elfutils/Debuginfod.html [2]
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
---
 Documentation/core-api/printk-formats.rst | 11 +++
 include/linux/kallsyms.h                  | 20 ++++-
 include/linux/module.h                    |  6 +-
 kernel/kallsyms.c                         | 95 ++++++++++++++++++-----
 kernel/module.c                           | 24 +++++-
 lib/vsprintf.c                            |  8 +-
 6 files changed, 139 insertions(+), 25 deletions(-)

diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index 160e710d992f..5f60533f2a56 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -114,6 +114,17 @@ used when printing stack backtraces. The specifier takes into
 consideration the effect of compiler optimisations which may occur
 when tail-calls are used and marked with the noreturn GCC attribute.
 
+If the pointer is within a module, the module name and optionally build ID is
+printed after the symbol name with an extra ``b`` appended to the end of the
+specifier.
+
+::
+	%pS	versatile_init+0x0/0x110 [module_name]
+	%pSb	versatile_init+0x0/0x110 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
+	%pSRb	versatile_init+0x9/0x110 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
+		(with __builtin_extract_return_addr() translation)
+	%pBb	prev_fn_of_versatile_init+0x88/0x88 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
+
 Probed Pointers from BPF / tracing
 ----------------------------------
 
diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index 465060acc981..f760cb839775 100644
--- a/include/linux/kallsyms.h
+++ b/include/linux/kallsyms.h
@@ -7,6 +7,7 @@
 #define _LINUX_KALLSYMS_H
 
 #include <linux/errno.h>
+#include <linux/buildid.h>
 #include <linux/kernel.h>
 #include <linux/stddef.h>
 #include <linux/mm.h>
@@ -15,8 +16,9 @@
 #include <asm/sections.h>
 
 #define KSYM_NAME_LEN 128
-#define KSYM_SYMBOL_LEN (sizeof("%s+%#lx/%#lx [%s]") + (KSYM_NAME_LEN - 1) + \
-			 2*(BITS_PER_LONG*3/10) + (MODULE_NAME_LEN - 1) + 1)
+#define KSYM_SYMBOL_LEN (sizeof("%s+%#lx/%#lx [%s %s]") + (KSYM_NAME_LEN - 1) + \
+			 2*(BITS_PER_LONG*3/10) + (MODULE_NAME_LEN - 1) + \
+			 (BUILD_ID_SIZE_MAX * 2) + 1)
 
 struct cred;
 struct module;
@@ -91,8 +93,10 @@ const char *kallsyms_lookup(unsigned long addr,
 
 /* Look up a kernel symbol and return it in a text buffer. */
 extern int sprint_symbol(char *buffer, unsigned long address);
+extern int sprint_symbol_build_id(char *buffer, unsigned long address);
 extern int sprint_symbol_no_offset(char *buffer, unsigned long address);
 extern int sprint_backtrace(char *buffer, unsigned long address);
+extern int sprint_backtrace_build_id(char *buffer, unsigned long address);
 
 int lookup_symbol_name(unsigned long addr, char *symname);
 int lookup_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name);
@@ -128,6 +132,12 @@ static inline int sprint_symbol(char *buffer, unsigned long addr)
 	return 0;
 }
 
+static inline int sprint_symbol_build_id(char *buffer, unsigned long address)
+{
+	*buffer = '\0';
+	return 0;
+}
+
 static inline int sprint_symbol_no_offset(char *buffer, unsigned long addr)
 {
 	*buffer = '\0';
@@ -140,6 +150,12 @@ static inline int sprint_backtrace(char *buffer, unsigned long addr)
 	return 0;
 }
 
+static inline int sprint_backtrace_build_id(char *buffer, unsigned long addr)
+{
+	*buffer = '\0';
+	return 0;
+}
+
 static inline int lookup_symbol_name(unsigned long addr, char *symname)
 {
 	return -ERANGE;
diff --git a/include/linux/module.h b/include/linux/module.h
index 59f094fa6f74..4bf869f6c944 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -11,6 +11,7 @@
 
 #include <linux/list.h>
 #include <linux/stat.h>
+#include <linux/buildid.h>
 #include <linux/compiler.h>
 #include <linux/cache.h>
 #include <linux/kmod.h>
@@ -367,6 +368,9 @@ struct module {
 	/* Unique handle for this module */
 	char name[MODULE_NAME_LEN];
 
+	/* Module build ID */
+	unsigned char build_id[BUILD_ID_SIZE_MAX];
+
 	/* Sysfs stuff. */
 	struct module_kobject mkobj;
 	struct module_attribute *modinfo_attrs;
@@ -630,7 +634,7 @@ void *dereference_module_function_descriptor(struct module *mod, void *ptr);
 const char *module_address_lookup(unsigned long addr,
 			    unsigned long *symbolsize,
 			    unsigned long *offset,
-			    char **modname,
+			    char **modname, const unsigned char **modbuildid,
 			    char *namebuf);
 int lookup_module_symbol_name(unsigned long addr, char *symname);
 int lookup_module_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name);
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 8043a90aa50e..b835992e76c2 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -273,21 +273,13 @@ int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
 		get_symbol_pos(addr, symbolsize, offset);
 		return 1;
 	}
-	return !!module_address_lookup(addr, symbolsize, offset, NULL, namebuf) ||
+	return !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf) ||
 	       !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
 }
 
-/*
- * Lookup an address
- * - modname is set to NULL if it's in the kernel.
- * - We guarantee that the returned name is valid until we reschedule even if.
- *   It resides in a module.
- * - We also guarantee that modname will be valid until rescheduled.
- */
-const char *kallsyms_lookup(unsigned long addr,
-			    unsigned long *symbolsize,
-			    unsigned long *offset,
-			    char **modname, char *namebuf)
+const char *kallsyms_lookup_buildid(unsigned long addr, unsigned long *symbolsize,
+				    unsigned long *offset, char **modname,
+				    const unsigned char **modbuildid, char *namebuf)
 {
 	const char *ret;
 
@@ -303,12 +295,14 @@ const char *kallsyms_lookup(unsigned long addr,
 				       namebuf, KSYM_NAME_LEN);
 		if (modname)
 			*modname = NULL;
+		if (modbuildid)
+			*modbuildid = NULL;
 		return namebuf;
 	}
 
 	/* See if it's in a module or a BPF JITed image. */
 	ret = module_address_lookup(addr, symbolsize, offset,
-				    modname, namebuf);
+				    modname, modbuildid, namebuf);
 	if (!ret)
 		ret = bpf_address_lookup(addr, symbolsize,
 					 offset, modname, namebuf);
@@ -319,6 +313,22 @@ const char *kallsyms_lookup(unsigned long addr,
 	return ret;
 }
 
+/*
+ * Lookup an address
+ * - modname is set to NULL if it's in the kernel.
+ * - We guarantee that the returned name is valid until we reschedule even if.
+ *   It resides in a module.
+ * - We also guarantee that modname will be valid until rescheduled.
+ */
+const char *kallsyms_lookup(unsigned long addr,
+			    unsigned long *symbolsize,
+			    unsigned long *offset,
+			    char **modname, char *namebuf)
+{
+	return kallsyms_lookup_buildid(addr, symbolsize, offset, modname,
+				       NULL, namebuf);
+}
+
 int lookup_symbol_name(unsigned long addr, char *symname)
 {
 	symname[0] = '\0';
@@ -359,15 +369,17 @@ int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
 
 /* Look up a kernel symbol and return it in a text buffer. */
 static int __sprint_symbol(char *buffer, unsigned long address,
-			   int symbol_offset, int add_offset)
+			   int symbol_offset, int add_offset, int add_buildid)
 {
 	char *modname;
+	const unsigned char *buildid;
 	const char *name;
 	unsigned long offset, size;
 	int len;
 
 	address += symbol_offset;
-	name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
+	name = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid,
+				       buffer);
 	if (!name)
 		return sprintf(buffer, "0x%lx", address - symbol_offset);
 
@@ -379,8 +391,14 @@ static int __sprint_symbol(char *buffer, unsigned long address,
 	if (add_offset)
 		len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
 
-	if (modname)
-		len += sprintf(buffer + len, " [%s]", modname);
+	if (modname) {
+		len += sprintf(buffer + len, " [%s", modname);
+		/* build ID should match length of sprintf below */
+		BUILD_BUG_ON(BUILD_ID_SIZE_MAX != 20);
+		if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) && add_buildid && buildid)
+			len += sprintf(buffer + len, " %20phN", buildid);
+		len += sprintf(buffer + len, "]");
+	}
 
 	return len;
 }
@@ -398,10 +416,27 @@ static int __sprint_symbol(char *buffer, unsigned long address,
  */
 int sprint_symbol(char *buffer, unsigned long address)
 {
-	return __sprint_symbol(buffer, address, 0, 1);
+	return __sprint_symbol(buffer, address, 0, 1, 0);
 }
 EXPORT_SYMBOL_GPL(sprint_symbol);
 
+/**
+ * sprint_symbol_build_id - Look up a kernel symbol and return it in a text buffer
+ * @buffer: buffer to be stored
+ * @address: address to lookup
+ *
+ * This function looks up a kernel symbol with @address and stores its name,
+ * offset, size, module name and module build ID to @buffer if possible. If no
+ * symbol was found, just saves its @address as is.
+ *
+ * This function returns the number of bytes stored in @buffer.
+ */
+int sprint_symbol_build_id(char *buffer, unsigned long address)
+{
+	return __sprint_symbol(buffer, address, 0, 1, 1);
+}
+EXPORT_SYMBOL_GPL(sprint_symbol_build_id);
+
 /**
  * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
  * @buffer: buffer to be stored
@@ -415,7 +450,7 @@ EXPORT_SYMBOL_GPL(sprint_symbol);
  */
 int sprint_symbol_no_offset(char *buffer, unsigned long address)
 {
-	return __sprint_symbol(buffer, address, 0, 0);
+	return __sprint_symbol(buffer, address, 0, 0, 0);
 }
 EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
 
@@ -435,7 +470,27 @@ EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
  */
 int sprint_backtrace(char *buffer, unsigned long address)
 {
-	return __sprint_symbol(buffer, address, -1, 1);
+	return __sprint_symbol(buffer, address, -1, 1, 0);
+}
+
+/**
+ * sprint_backtrace_build_id - Look up a backtrace symbol and return it in a text buffer
+ * @buffer: buffer to be stored
+ * @address: address to lookup
+ *
+ * This function is for stack backtrace and does the same thing as
+ * sprint_symbol() but with modified/decreased @address. If there is a
+ * tail-call to the function marked "noreturn", gcc optimized out code after
+ * the call so that the stack-saved return address could point outside of the
+ * caller. This function ensures that kallsyms will find the original caller
+ * by decreasing @address. This function also appends the module build ID to
+ * the @buffer if @address is within a kernel module.
+ *
+ * This function returns the number of bytes stored in @buffer.
+ */
+int sprint_backtrace_build_id(char *buffer, unsigned long address)
+{
+	return __sprint_symbol(buffer, address, -1, 1, 1);
 }
 
 /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
diff --git a/kernel/module.c b/kernel/module.c
index 30479355ab85..6f5bc1b046a5 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -13,6 +13,7 @@
 #include <linux/trace_events.h>
 #include <linux/init.h>
 #include <linux/kallsyms.h>
+#include <linux/buildid.h>
 #include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/sysfs.h>
@@ -2770,6 +2771,20 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
 	}
 	mod->core_kallsyms.num_symtab = ndst;
 }
+
+static void init_build_id(struct module *mod, const struct load_info *info)
+{
+	const Elf_Shdr *sechdr;
+	unsigned int i;
+
+	for (i = 0; i < info->hdr->e_shnum; i++) {
+		sechdr = &info->sechdrs[i];
+		if (!sect_empty(sechdr) && sechdr->sh_type == SHT_NOTE &&
+		    !build_id_parse_buf((void *)sechdr->sh_addr, mod->build_id,
+					sechdr->sh_size))
+			break;
+	}
+}
 #else
 static inline void layout_symtab(struct module *mod, struct load_info *info)
 {
@@ -2778,6 +2793,10 @@ static inline void layout_symtab(struct module *mod, struct load_info *info)
 static void add_kallsyms(struct module *mod, const struct load_info *info)
 {
 }
+
+static void init_build_id(struct module *mod, const struct load_info *info)
+{
+}
 #endif /* CONFIG_KALLSYMS */
 
 static void dynamic_debug_setup(struct module *mod, struct _ddebug *debug, unsigned int num)
@@ -4004,6 +4023,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
 		goto free_arch_cleanup;
 	}
 
+	init_build_id(mod, info);
 	dynamic_debug_setup(mod, info->debug, info->num_debug);
 
 	/* Ftrace init must be called in the MODULE_STATE_UNFORMED state */
@@ -4235,7 +4255,7 @@ void * __weak dereference_module_function_descriptor(struct module *mod,
 const char *module_address_lookup(unsigned long addr,
 			    unsigned long *size,
 			    unsigned long *offset,
-			    char **modname,
+			    char **modname, const unsigned char **modbuildid,
 			    char *namebuf)
 {
 	const char *ret = NULL;
@@ -4246,6 +4266,8 @@ const char *module_address_lookup(unsigned long addr,
 	if (mod) {
 		if (modname)
 			*modname = mod->name;
+		if (modbuildid)
+			*modbuildid = mod->build_id;
 
 		ret = find_kallsyms_symbol(mod, addr, size, offset);
 	}
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 41ddc353ebb8..fee5282ebb0a 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -966,8 +966,12 @@ char *symbol_string(char *buf, char *end, void *ptr,
 	value = (unsigned long)ptr;
 
 #ifdef CONFIG_KALLSYMS
-	if (*fmt == 'B')
+	if (*fmt == 'B' && fmt[1] == 'b')
+		sprint_backtrace_build_id(sym, value);
+	else if (*fmt == 'B')
 		sprint_backtrace(sym, value);
+	else if (*fmt == 'S' && (fmt[1] == 'b' || (fmt[1] == 'R' && fmt[2] == 'b')))
+		sprint_symbol_build_id(sym, value);
 	else if (*fmt != 's')
 		sprint_symbol(sym, value);
 	else
@@ -2129,9 +2133,11 @@ early_param("no_hash_pointers", no_hash_pointers_enable);
  * - 'S' For symbolic direct pointers (or function descriptors) with offset
  * - 's' For symbolic direct pointers (or function descriptors) without offset
  * - '[Ss]R' as above with __builtin_extract_return_addr() translation
+ * - 'S[R]b' as above with module build ID (for use in backtraces)
  * - '[Ff]' %pf and %pF were obsoleted and later removed in favor of
  *	    %ps and %pS. Be careful when re-using these specifiers.
  * - 'B' For backtraced symbolic direct pointers with offset
+ * - 'Bb' as above with module build ID (for use in backtraces)
  * - 'R' For decoded struct resource, e.g., [mem 0x0-0x1f 64bit pref]
  * - 'r' For raw struct resource, e.g., [mem 0x0-0x1f flags 0x201]
  * - 'b[l]' For a bitmap, the number of bits is determined by the field
-- 
https://chromeos.dev

Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Andy Shevchenko]

On Fri, Apr 09, 2021 at 06:52:52PM -0700, Stephen Boyd wrote:
> Let's make kernel stacktraces easier to identify by including the build
> ID[1] of a module if the stacktrace is printing a symbol from a module.
> This makes it simpler for developers to locate a kernel module's full
> debuginfo for a particular stacktrace. Combined with
> scripts/decode_stracktrace.sh, a developer can download the matching
> debuginfo from a debuginfod[2] server and find the exact file and line
> number for the functions plus offsets in a stacktrace that match the
> module. This is especially useful for pstore crash debugging where the
> kernel crashes are recorded in something like console-ramoops and the
> recovery kernel/modules are different or the debuginfo doesn't exist on
> the device due to space concerns (the debuginfo can be too large for
> space limited devices).
> 
> Originally, I put this on the %pS format, but that was quickly rejected
> given that %pS is used in other places such as ftrace where build IDs
> aren't meaningful. There was some discussions on the list to put every
> module build ID into the "Modules linked in:" section of the stacktrace
> message but that quickly becomes very hard to read once you have more
> than three or four modules linked in. It also provides too much
> information when we don't expect each module to be traversed in a
> stacktrace. Having the build ID for modules that aren't important just
> makes things messy. Splitting it to multiple lines for each module
> quickly explodes the number of lines printed in an oops too, possibly
> wrapping the warning off the console. And finally, trying to stash away
> each module used in a callstack to provide the ID of each symbol printed
> is cumbersome and would require changes to each architecture to stash
> away modules and return their build IDs once unwinding has completed.
> 
> Instead, we opt for the simpler approach of introducing new printk
> formats '%pS[R]b' for "pointer symbolic backtrace with module build ID"
> and '%pBb' for "pointer backtrace with module build ID" and then
> updating the few places in the architecture layer where the stacktrace
> is printed to use this new format.
> 
> Example:

Can you trim a bit the example, so we will see only important lines.
In such case you may provide "before" and "after" variants.

...

> -	if (modname)
> -		len += sprintf(buffer + len, " [%s]", modname);
> +	if (modname) {
> +		len += sprintf(buffer + len, " [%s", modname);

> +		/* build ID should match length of sprintf below */
> +		BUILD_BUG_ON(BUILD_ID_SIZE_MAX != 20);

First of all, why not static_assert() defined near to the actual macro?

> +		if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) && add_buildid && buildid)
> +			len += sprintf(buffer + len, " %20phN", buildid);

			len += sprintf(buffer + len, " %*phN", BUILD_ID_SIZE_MAX, buildid);

?

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Stephen Boyd]

Quoting Andy Shevchenko (2021-04-12 04:58:02)
> On Fri, Apr 09, 2021 at 06:52:52PM -0700, Stephen Boyd wrote:
> > Let's make kernel stacktraces easier to identify by including the build
> > ID[1] of a module if the stacktrace is printing a symbol from a module.
> > This makes it simpler for developers to locate a kernel module's full
> > debuginfo for a particular stacktrace. Combined with
> > scripts/decode_stracktrace.sh, a developer can download the matching
> > debuginfo from a debuginfod[2] server and find the exact file and line
> > number for the functions plus offsets in a stacktrace that match the
> > module. This is especially useful for pstore crash debugging where the
> > kernel crashes are recorded in something like console-ramoops and the
> > recovery kernel/modules are different or the debuginfo doesn't exist on
> > the device due to space concerns (the debuginfo can be too large for
> > space limited devices).
> > 
> > Originally, I put this on the %pS format, but that was quickly rejected
> > given that %pS is used in other places such as ftrace where build IDs
> > aren't meaningful. There was some discussions on the list to put every
> > module build ID into the "Modules linked in:" section of the stacktrace
> > message but that quickly becomes very hard to read once you have more
> > than three or four modules linked in. It also provides too much
> > information when we don't expect each module to be traversed in a
> > stacktrace. Having the build ID for modules that aren't important just
> > makes things messy. Splitting it to multiple lines for each module
> > quickly explodes the number of lines printed in an oops too, possibly
> > wrapping the warning off the console. And finally, trying to stash away
> > each module used in a callstack to provide the ID of each symbol printed
> > is cumbersome and would require changes to each architecture to stash
> > away modules and return their build IDs once unwinding has completed.
> > 
> > Instead, we opt for the simpler approach of introducing new printk
> > formats '%pS[R]b' for "pointer symbolic backtrace with module build ID"
> > and '%pBb' for "pointer backtrace with module build ID" and then
> > updating the few places in the architecture layer where the stacktrace
> > is printed to use this new format.
> > 
> > Example:
> 
> Can you trim a bit the example, so we will see only important lines.
> In such case you may provide "before" and "after" variants.
> 
> ...
> 
> > -     if (modname)
> > -             len += sprintf(buffer + len, " [%s]", modname);
> > +     if (modname) {
> > +             len += sprintf(buffer + len, " [%s", modname);
> 
> > +             /* build ID should match length of sprintf below */
> > +             BUILD_BUG_ON(BUILD_ID_SIZE_MAX != 20);
> 
> First of all, why not static_assert() defined near to the actual macro?

Which macro? BUILD_ID_SIZE_MAX? I tried static_assert() and it didn't
work for me but maybe I missed something. Why is static_assert()
preferred?

> 
> > +             if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) && add_buildid && buildid)
> > +                     len += sprintf(buffer + len, " %20phN", buildid);
> 
>                         len += sprintf(buffer + len, " %*phN", BUILD_ID_SIZE_MAX, buildid);
> 

Are you suggesting to use sprintf format here so that the size is part
of the printf? Sounds good to me. Thanks.

Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Andy Shevchenko]

On Mon, Apr 12, 2021 at 12:29:05PM -0700, Stephen Boyd wrote:
> Quoting Andy Shevchenko (2021-04-12 04:58:02)
> > On Fri, Apr 09, 2021 at 06:52:52PM -0700, Stephen Boyd wrote:
> > > Let's make kernel stacktraces easier to identify by including the build
> > > ID[1] of a module if the stacktrace is printing a symbol from a module.
> > > This makes it simpler for developers to locate a kernel module's full
> > > debuginfo for a particular stacktrace. Combined with
> > > scripts/decode_stracktrace.sh, a developer can download the matching
> > > debuginfo from a debuginfod[2] server and find the exact file and line
> > > number for the functions plus offsets in a stacktrace that match the
> > > module. This is especially useful for pstore crash debugging where the
> > > kernel crashes are recorded in something like console-ramoops and the
> > > recovery kernel/modules are different or the debuginfo doesn't exist on
> > > the device due to space concerns (the debuginfo can be too large for
> > > space limited devices).
> > > 
> > > Originally, I put this on the %pS format, but that was quickly rejected
> > > given that %pS is used in other places such as ftrace where build IDs
> > > aren't meaningful. There was some discussions on the list to put every
> > > module build ID into the "Modules linked in:" section of the stacktrace
> > > message but that quickly becomes very hard to read once you have more
> > > than three or four modules linked in. It also provides too much
> > > information when we don't expect each module to be traversed in a
> > > stacktrace. Having the build ID for modules that aren't important just
> > > makes things messy. Splitting it to multiple lines for each module
> > > quickly explodes the number of lines printed in an oops too, possibly
> > > wrapping the warning off the console. And finally, trying to stash away
> > > each module used in a callstack to provide the ID of each symbol printed
> > > is cumbersome and would require changes to each architecture to stash
> > > away modules and return their build IDs once unwinding has completed.
> > > 
> > > Instead, we opt for the simpler approach of introducing new printk
> > > formats '%pS[R]b' for "pointer symbolic backtrace with module build ID"
> > > and '%pBb' for "pointer backtrace with module build ID" and then
> > > updating the few places in the architecture layer where the stacktrace
> > > is printed to use this new format.
> > > 
> > > Example:
> > 
> > Can you trim a bit the example, so we will see only important lines.
> > In such case you may provide "before" and "after" variants.
> > 
> > ...
> > 
> > > -     if (modname)
> > > -             len += sprintf(buffer + len, " [%s]", modname);
> > > +     if (modname) {
> > > +             len += sprintf(buffer + len, " [%s", modname);
> > 
> > > +             /* build ID should match length of sprintf below */
> > > +             BUILD_BUG_ON(BUILD_ID_SIZE_MAX != 20);
> > 
> > First of all, why not static_assert() defined near to the actual macro?
> 
> Which macro? BUILD_ID_SIZE_MAX?

Yes.

> I tried static_assert() and it didn't
> work for me but maybe I missed something.

Sounds weird. static_assert() is a good one. Check, for example, lib/vsprintf.c
on how to use it.

> Why is static_assert()
> preferred?

Because it's cleaner way to achieve it and as a bonus it can be put outside of
the functions (be in the header or so).

> > > +             if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) && add_buildid && buildid)
> > > +                     len += sprintf(buffer + len, " %20phN", buildid);
> > 
> >                         len += sprintf(buffer + len, " %*phN", BUILD_ID_SIZE_MAX, buildid);
> > 
> 
> Are you suggesting to use sprintf format here so that the size is part
> of the printf? Sounds good to me. Thanks.

I prefer %20phN when the size is carved in stone (for example by
specification), but if you are really expecting that it may be
changed in the future, use variadic approach as I showed above.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Petr Mladek]

On Fri 2021-04-09 18:52:52, Stephen Boyd wrote:
> Let's make kernel stacktraces easier to identify by including the build
> ID[1] of a module if the stacktrace is printing a symbol from a module.
> This makes it simpler for developers to locate a kernel module's full
> debuginfo for a particular stacktrace. Combined with
> scripts/decode_stracktrace.sh, a developer can download the matching
> debuginfo from a debuginfod[2] server and find the exact file and line
> number for the functions plus offsets in a stacktrace that match the
> module. This is especially useful for pstore crash debugging where the
> kernel crashes are recorded in something like console-ramoops and the
> recovery kernel/modules are different or the debuginfo doesn't exist on
> the device due to space concerns (the debuginfo can be too large for
> space limited devices).
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 59f094fa6f74..4bf869f6c944 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -11,6 +11,7 @@
>  
>  #include <linux/list.h>
>  #include <linux/stat.h>
> +#include <linux/buildid.h>
>  #include <linux/compiler.h>
>  #include <linux/cache.h>
>  #include <linux/kmod.h>
> @@ -367,6 +368,9 @@ struct module {
>  	/* Unique handle for this module */
>  	char name[MODULE_NAME_LEN];
>  
> +	/* Module build ID */
> +	unsigned char build_id[BUILD_ID_SIZE_MAX];

Do we want to initialize/store the ID even when
CONFIG_STACKTRACE_BUILD_ID is disabled and nobody would
use it?

Most struct module members are added only when the related feature
is enabled.

I am not sure how it would complicate the code. It is possible
that it is not worth it. Well, I could imagine that the API
will always pass the buildid parameter and
module_address_lookup() might do something like

#ifndef CONFIG_STACKTRACE_BUILD_ID
static char empty_build_id[BUILD_ID_SIZE_MAX];
#endif

		if (modbuildid) {
			if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID))
				*modbuildid = mod->build_id;
			else
				*modbuildid = empty_build_id;

IMHO, this is primary a call for Jessica as the module code maintainer.

Otherwise, I am fine with this patch. And it works as expected.

Best Regards,
Petr

Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Petr Mladek]

On Tue 2021-04-13 13:56:31, Andy Shevchenko wrote:
> On Mon, Apr 12, 2021 at 12:29:05PM -0700, Stephen Boyd wrote:
> > Quoting Andy Shevchenko (2021-04-12 04:58:02)
> > > On Fri, Apr 09, 2021 at 06:52:52PM -0700, Stephen Boyd wrote:
> > > > Let's make kernel stacktraces easier to identify by including the build
> > > > ID[1] of a module if the stacktrace is printing a symbol from a module.
> > > > This makes it simpler for developers to locate a kernel module's full
> > > > debuginfo for a particular stacktrace. Combined with
> > > > scripts/decode_stracktrace.sh, a developer can download the matching
> > > > debuginfo from a debuginfod[2] server and find the exact file and line
> > > > number for the functions plus offsets in a stacktrace that match the
> > > > module. This is especially useful for pstore crash debugging where the
> > > > kernel crashes are recorded in something like console-ramoops and the
> > > > recovery kernel/modules are different or the debuginfo doesn't exist on
> > > > the device due to space concerns (the debuginfo can be too large for
> > > > space limited devices).
> > > > 
> > > > Originally, I put this on the %pS format, but that was quickly rejected
> > > > given that %pS is used in other places such as ftrace where build IDs
> > > > aren't meaningful. There was some discussions on the list to put every
> > > > module build ID into the "Modules linked in:" section of the stacktrace
> > > > message but that quickly becomes very hard to read once you have more
> > > > than three or four modules linked in. It also provides too much
> > > > information when we don't expect each module to be traversed in a
> > > > stacktrace. Having the build ID for modules that aren't important just
> > > > makes things messy. Splitting it to multiple lines for each module
> > > > quickly explodes the number of lines printed in an oops too, possibly
> > > > wrapping the warning off the console. And finally, trying to stash away
> > > > each module used in a callstack to provide the ID of each symbol printed
> > > > is cumbersome and would require changes to each architecture to stash
> > > > away modules and return their build IDs once unwinding has completed.
> > > > 
> > > > Instead, we opt for the simpler approach of introducing new printk
> > > > formats '%pS[R]b' for "pointer symbolic backtrace with module build ID"
> > > > and '%pBb' for "pointer backtrace with module build ID" and then
> > > > updating the few places in the architecture layer where the stacktrace
> > > > is printed to use this new format.
> > > > 
> > > > Example:
> > > 
> > > Can you trim a bit the example, so we will see only important lines.
> > > In such case you may provide "before" and "after" variants.
> > > 
> > > ...
> > > 
> > > > -     if (modname)
> > > > -             len += sprintf(buffer + len, " [%s]", modname);
> > > > +     if (modname) {
> > > > +             len += sprintf(buffer + len, " [%s", modname);
> > > 
> > > > +             /* build ID should match length of sprintf below */
> > > > +             BUILD_BUG_ON(BUILD_ID_SIZE_MAX != 20);
> > > 
> > > First of all, why not static_assert() defined near to the actual macro?
> > 
> > Which macro? BUILD_ID_SIZE_MAX?
> 
> Yes.
> 
> > I tried static_assert() and it didn't
> > work for me but maybe I missed something.

I guess that you wanted to use it inside macro definition:

#define VMCOREINFO_BUILD_ID(value) \
	static_assert(ARRAY_SIZE(value) == BUILD_ID_SIZE_MAX); \
	vmcoreinfo_append_str("BUILD-ID=%20phN\n", value)

Instead, you should do it outside the macro:

static_assert(ARRAY_SIZE(value) == BUILD_ID_SIZE_MAX);
#define VMCOREINFO_BUILD_ID(value) \
	vmcoreinfo_append_str("BUILD-ID=%20phN\n", value)

> Sounds weird. static_assert() is a good one. Check, for example, lib/vsprintf.c
> on how to use it.
> 
> > Why is static_assert()
> > preferred?

I guess that it is because it is enough and more efficient for
checks of constant values (no computation of the value).

> Because it's cleaner way to achieve it and as a bonus it can be put outside of
> the functions (be in the header or so).
> 
> > > > +             if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) && add_buildid && buildid)
> > > > +                     len += sprintf(buffer + len, " %20phN", buildid);
> > > 
> > >                         len += sprintf(buffer + len, " %*phN", BUILD_ID_SIZE_MAX, buildid);
> > > 
> > 
> > Are you suggesting to use sprintf format here so that the size is part
> > of the printf? Sounds good to me. Thanks.
> 
> I prefer %20phN when the size is carved in stone (for example by
> specification), but if you are really expecting that it may be
> changed in the future, use variadic approach as I showed above.

I would consider this written in stone (last famous words ;-) and use
%20phN with the static_assert().

Best Regards,
Petr

Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Stephen Boyd]

Quoting Petr Mladek (2021-04-13 08:16:20)
> On Tue 2021-04-13 13:56:31, Andy Shevchenko wrote:
> > On Mon, Apr 12, 2021 at 12:29:05PM -0700, Stephen Boyd wrote:
> > > Quoting Andy Shevchenko (2021-04-12 04:58:02)
> > > > 
> > > > First of all, why not static_assert() defined near to the actual macro?
> > > 
> > > Which macro? BUILD_ID_SIZE_MAX?
> > 
> > Yes.
> > 
> > > I tried static_assert() and it didn't
> > > work for me but maybe I missed something.
> 
> I guess that you wanted to use it inside macro definition:
> 
> #define VMCOREINFO_BUILD_ID(value) \
>         static_assert(ARRAY_SIZE(value) == BUILD_ID_SIZE_MAX); \
>         vmcoreinfo_append_str("BUILD-ID=%20phN\n", value)
> 
> Instead, you should do it outside the macro:
> 
> static_assert(ARRAY_SIZE(value) == BUILD_ID_SIZE_MAX);
> #define VMCOREINFO_BUILD_ID(value) \
>         vmcoreinfo_append_str("BUILD-ID=%20phN\n", value)

In this example "value" is not defined because it's an argument to the
macro. How can this work?

From what I can tell static_assert() is for the case that you want to
assert something at the global scope level. BUILD_BUG_ON() can't be used
at global scope. I see the usage is usually to assert struct members and
alignment of those members. In turn, static_assert() can't be used at
function level scope. Each has a use and in this case I want to assert
at function level scope to be as close as possible to the place that
would need to change.

> 
> > Sounds weird. static_assert() is a good one. Check, for example, lib/vsprintf.c
> > on how to use it.
> > 
> > > Why is static_assert()
> > > preferred?
> 
> I guess that it is because it is enough and more efficient for
> checks of constant values (no computation of the value).
> 
> > Because it's cleaner way to achieve it and as a bonus it can be put outside of
> > the functions (be in the header or so).

Ok, but I'm still not sure what it would be enforcing. In this case we
need to have it near the sprintf line so that we know to fix the 20 in
there should it ever change to be larger. If it's defined next to the
BUILD_ID_SIZE_MAX macro then it does practically nothing to help future
developers know what to change.

> > 
> > > > > +             if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) && add_buildid && buildid)
> > > > > +                     len += sprintf(buffer + len, " %20phN", buildid);
> > > > 
> > > >                         len += sprintf(buffer + len, " %*phN", BUILD_ID_SIZE_MAX, buildid);
> > > > 
> > > 
> > > Are you suggesting to use sprintf format here so that the size is part
> > > of the printf? Sounds good to me. Thanks.
> > 
> > I prefer %20phN when the size is carved in stone (for example by
> > specification), but if you are really expecting that it may be
> > changed in the future, use variadic approach as I showed above.
> 
> I would consider this written in stone (last famous words ;-) and use
> %20phN with the static_assert().
> 

Yes it is pretty much written in stone. The build ID can be an md5sum
instead of SHA1, and thus 16 bytes instead of 20 bytes for the 160-bit
SHA1 form. This is rare, and the code in buildid.c is padding it out
with zeroes in the case that the note is smaller than 20 bytes in
length. Within the kernel we can always assume the buffer is
BUILD_ID_SIZE_MAX. How about this patch?

----8<-----
diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index 2174dab16ba9..042c9c034fba 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -39,7 +39,7 @@ phys_addr_t paddr_vmcoreinfo_note(void);
 #define VMCOREINFO_OSRELEASE(value) \
 	vmcoreinfo_append_str("OSRELEASE=%s\n", value)
 #define VMCOREINFO_BUILD_ID(value) \
-	BUILD_BUG_ON(ARRAY_SIZE(value) != BUILD_ID_SIZE_MAX); \
+	BUILD_BUG_ON(ARRAY_SIZE(value) != 20); \
 	vmcoreinfo_append_str("BUILD-ID=%20phN\n", value)
 #define VMCOREINFO_PAGESIZE(value) \
 	vmcoreinfo_append_str("PAGESIZE=%ld\n", value)
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index b835992e76c2..5d9c7ac80633 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -25,7 +25,10 @@
 #include <linux/filter.h>
 #include <linux/ftrace.h>
 #include <linux/kprobes.h>
+#include <linux/build_bug.h>
 #include <linux/compiler.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
 
 /*
  * These will be re-linked against their real values
@@ -394,7 +397,7 @@ static int __sprint_symbol(char *buffer, unsigned long address,
 	if (modname) {
 		len += sprintf(buffer + len, " [%s", modname);
 		/* build ID should match length of sprintf below */
-		BUILD_BUG_ON(BUILD_ID_SIZE_MAX != 20);
+		BUILD_BUG_ON(sizeof(typeof_member(struct module, build_id)) != 20);
 		if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) && add_buildid && buildid)
 			len += sprintf(buffer + len, " %20phN", buildid);
 		len += sprintf(buffer + len, "]");

Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Stephen Boyd]

Quoting Stephen Boyd (2021-04-13 13:10:05)
> Quoting Petr Mladek (2021-04-13 08:16:20)
> > On Tue 2021-04-13 13:56:31, Andy Shevchenko wrote:
> > > On Mon, Apr 12, 2021 at 12:29:05PM -0700, Stephen Boyd wrote:
> > > > Quoting Andy Shevchenko (2021-04-12 04:58:02)
> > > > > 
> > > > > First of all, why not static_assert() defined near to the actual macro?
> > > > 
> > > > Which macro? BUILD_ID_SIZE_MAX?
> > > 
> > > Yes.
> > > 
> > > > I tried static_assert() and it didn't
> > > > work for me but maybe I missed something.
> > 
> > I guess that you wanted to use it inside macro definition:
> > 
> > #define VMCOREINFO_BUILD_ID(value) \
> >         static_assert(ARRAY_SIZE(value) == BUILD_ID_SIZE_MAX); \
> >         vmcoreinfo_append_str("BUILD-ID=%20phN\n", value)
> > 
> > Instead, you should do it outside the macro:
> > 
> > static_assert(ARRAY_SIZE(value) == BUILD_ID_SIZE_MAX);
> > #define VMCOREINFO_BUILD_ID(value) \
> >         vmcoreinfo_append_str("BUILD-ID=%20phN\n", value)
> 
> In this example "value" is not defined because it's an argument to the
> macro. How can this work?
> 
> From what I can tell static_assert() is for the case that you want to
> assert something at the global scope level. BUILD_BUG_ON() can't be used
> at global scope. I see the usage is usually to assert struct members and
> alignment of those members. In turn, static_assert() can't be used at
> function level scope. Each has a use and in this case I want to assert
> at function level scope to be as close as possible to the place that
> would need to change.
> 

Good news. I can do this to force a basic block and then GCC doesn't complain.

---8<---
diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index 2174dab16ba9..de62a722431e 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -38,9 +38,12 @@ phys_addr_t paddr_vmcoreinfo_note(void);

 #define VMCOREINFO_OSRELEASE(value) \
        vmcoreinfo_append_str("OSRELEASE=%s\n", value)
-#define VMCOREINFO_BUILD_ID(value) \
-       BUILD_BUG_ON(ARRAY_SIZE(value) != BUILD_ID_SIZE_MAX); \
-       vmcoreinfo_append_str("BUILD-ID=%20phN\n", value)
+#define VMCOREINFO_BUILD_ID()                                          \
+       ({                                                              \
+               static_assert(sizeof(vmlinux_build_id) == 20);          \
+               vmcoreinfo_append_str("BUILD-ID=%20phN\n", vmlinux_build_id); \
+       })
+
 #define VMCOREINFO_PAGESIZE(value) \
        vmcoreinfo_append_str("PAGESIZE=%ld\n", value)

Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Stephen Boyd]

Quoting Petr Mladek (2021-04-13 08:01:14)
> On Fri 2021-04-09 18:52:52, Stephen Boyd wrote:
> > Let's make kernel stacktraces easier to identify by including the build
> > ID[1] of a module if the stacktrace is printing a symbol from a module.
> > This makes it simpler for developers to locate a kernel module's full
> > debuginfo for a particular stacktrace. Combined with
> > scripts/decode_stracktrace.sh, a developer can download the matching
> > debuginfo from a debuginfod[2] server and find the exact file and line
> > number for the functions plus offsets in a stacktrace that match the
> > module. This is especially useful for pstore crash debugging where the
> > kernel crashes are recorded in something like console-ramoops and the
> > recovery kernel/modules are different or the debuginfo doesn't exist on
> > the device due to space concerns (the debuginfo can be too large for
> > space limited devices).
> > 
> > diff --git a/include/linux/module.h b/include/linux/module.h
> > index 59f094fa6f74..4bf869f6c944 100644
> > --- a/include/linux/module.h
> > +++ b/include/linux/module.h
> > @@ -11,6 +11,7 @@
> >  
> >  #include <linux/list.h>
> >  #include <linux/stat.h>
> > +#include <linux/buildid.h>
> >  #include <linux/compiler.h>
> >  #include <linux/cache.h>
> >  #include <linux/kmod.h>
> > @@ -367,6 +368,9 @@ struct module {
> >       /* Unique handle for this module */
> >       char name[MODULE_NAME_LEN];
> >  
> > +     /* Module build ID */
> > +     unsigned char build_id[BUILD_ID_SIZE_MAX];
> 
> Do we want to initialize/store the ID even when
> CONFIG_STACKTRACE_BUILD_ID is disabled and nobody would
> use it?
> 
> Most struct module members are added only when the related feature
> is enabled.
> 
> I am not sure how it would complicate the code. It is possible
> that it is not worth it. Well, I could imagine that the API
> will always pass the buildid parameter and
> module_address_lookup() might do something like
> 
> #ifndef CONFIG_STACKTRACE_BUILD_ID
> static char empty_build_id[BUILD_ID_SIZE_MAX];
> #endif
> 
>                 if (modbuildid) {
>                         if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID))
>                                 *modbuildid = mod->build_id;
>                         else
>                                 *modbuildid = empty_build_id;
> 
> IMHO, this is primary a call for Jessica as the module code maintainer.
> 
> Otherwise, I am fine with this patch. And it works as expected.
> 

Does declaring mod->build_id as zero length work well enough?

----8<----
diff --git a/include/linux/module.h b/include/linux/module.h
index 4bf869f6c944..03b2f6af093a 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -359,6 +359,12 @@ struct klp_modinfo {
 };
 #endif
 
+#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
+#define MODULE_BUILD_ID_LEN BUILD_ID_SIZE_MAX
+#else
+#define MODULE_BUILD_ID_LEN 0
+#endif
+
 struct module {
 	enum module_state state;
 
@@ -369,7 +375,7 @@ struct module {
 	char name[MODULE_NAME_LEN];
 
 	/* Module build ID */
-	unsigned char build_id[BUILD_ID_SIZE_MAX];
+	unsigned char build_id[MODULE_BUILD_ID_LEN];
 
 	/* Sysfs stuff. */
 	struct module_kobject mkobj;
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index b835992e76c2..ebd5b30c3039 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -25,7 +25,10 @@
 #include <linux/filter.h>
 #include <linux/ftrace.h>
 #include <linux/kprobes.h>
+#include <linux/build_bug.h>
 #include <linux/compiler.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
 
 /*
  * These will be re-linked against their real values
@@ -393,10 +396,13 @@ static int __sprint_symbol(char *buffer, unsigned long address,
 
 	if (modname) {
 		len += sprintf(buffer + len, " [%s", modname);
-		/* build ID should match length of sprintf below */
-		BUILD_BUG_ON(BUILD_ID_SIZE_MAX != 20);
-		if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) && add_buildid && buildid)
+#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
+		if (add_buildid && buildid) {
+			/* build ID should match length of sprintf */
+			static_assert(MODULE_BUILD_ID_LEN == 20);
 			len += sprintf(buffer + len, " %20phN", buildid);
+		}
+#endif
 		len += sprintf(buffer + len, "]");
 	}
 
diff --git a/kernel/module.c b/kernel/module.c
index 6f5bc1b046a5..a0d222fbd281 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2771,7 +2771,17 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
 	}
 	mod->core_kallsyms.num_symtab = ndst;
 }
+#else
+static inline void layout_symtab(struct module *mod, struct load_info *info)
+{
+}
+
+static void add_kallsyms(struct module *mod, const struct load_info *info)
+{
+}
+#endif /* CONFIG_KALLSYMS */
 
+#if IS_ENABLED(CONFIG_KALLSYMS) && IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
 static void init_build_id(struct module *mod, const struct load_info *info)
 {
 	const Elf_Shdr *sechdr;
@@ -2786,18 +2796,10 @@ static void init_build_id(struct module *mod, const struct load_info *info)
 	}
 }
 #else
-static inline void layout_symtab(struct module *mod, struct load_info *info)
-{
-}
-
-static void add_kallsyms(struct module *mod, const struct load_info *info)
-{
-}
-
 static void init_build_id(struct module *mod, const struct load_info *info)
 {
 }
-#endif /* CONFIG_KALLSYMS */
+#endif
 
 static void dynamic_debug_setup(struct module *mod, struct _ddebug *debug, unsigned int num)
 {

Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Petr Mladek]

On Tue 2021-04-13 15:57:49, Stephen Boyd wrote:
> Quoting Petr Mladek (2021-04-13 08:01:14)
> > On Fri 2021-04-09 18:52:52, Stephen Boyd wrote:
> > > Let's make kernel stacktraces easier to identify by including the build
> > > ID[1] of a module if the stacktrace is printing a symbol from a module.
> > > This makes it simpler for developers to locate a kernel module's full
> > > debuginfo for a particular stacktrace. Combined with
> > > scripts/decode_stracktrace.sh, a developer can download the matching
> > > debuginfo from a debuginfod[2] server and find the exact file and line
> > > number for the functions plus offsets in a stacktrace that match the
> > > module. This is especially useful for pstore crash debugging where the
> > > kernel crashes are recorded in something like console-ramoops and the
> > > recovery kernel/modules are different or the debuginfo doesn't exist on
> > > the device due to space concerns (the debuginfo can be too large for
> > > space limited devices).
> > > 
> > > diff --git a/include/linux/module.h b/include/linux/module.h
> > > index 59f094fa6f74..4bf869f6c944 100644
> > > --- a/include/linux/module.h
> > > +++ b/include/linux/module.h
> > > @@ -11,6 +11,7 @@
> > >  
> > >  #include <linux/list.h>
> > >  #include <linux/stat.h>
> > > +#include <linux/buildid.h>
> > >  #include <linux/compiler.h>
> > >  #include <linux/cache.h>
> > >  #include <linux/kmod.h>
> > > @@ -367,6 +368,9 @@ struct module {
> > >       /* Unique handle for this module */
> > >       char name[MODULE_NAME_LEN];
> > >  
> > > +     /* Module build ID */
> > > +     unsigned char build_id[BUILD_ID_SIZE_MAX];
> > 
> > Do we want to initialize/store the ID even when
> > CONFIG_STACKTRACE_BUILD_ID is disabled and nobody would
> > use it?
> > 
> > Most struct module members are added only when the related feature
> > is enabled.
> > 
> > I am not sure how it would complicate the code. It is possible
> > that it is not worth it. Well, I could imagine that the API
> > will always pass the buildid parameter and
> > module_address_lookup() might do something like
> > 
> > #ifndef CONFIG_STACKTRACE_BUILD_ID
> > static char empty_build_id[BUILD_ID_SIZE_MAX];
> > #endif
> > 
> >                 if (modbuildid) {
> >                         if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID))
> >                                 *modbuildid = mod->build_id;
> >                         else
> >                                 *modbuildid = empty_build_id;
> > 
> > IMHO, this is primary a call for Jessica as the module code maintainer.
> > 
> > Otherwise, I am fine with this patch. And it works as expected.
> > 
> 
> Does declaring mod->build_id as zero length work well enough?

It might be fine because it would actually never get displayed.
But yeah, it is kind of hack. The idea was to avoid too many
#ifdefs in the code.

I think that it is Jessica's call what she would prefer.

Best Regards,
Petr

Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Jessica Yu]

+++ Stephen Boyd [09/04/21 18:52 -0700]:
>Let's make kernel stacktraces easier to identify by including the build
>ID[1] of a module if the stacktrace is printing a symbol from a module.
>This makes it simpler for developers to locate a kernel module's full
>debuginfo for a particular stacktrace. Combined with
>scripts/decode_stracktrace.sh, a developer can download the matching
>debuginfo from a debuginfod[2] server and find the exact file and line
>number for the functions plus offsets in a stacktrace that match the
>module. This is especially useful for pstore crash debugging where the
>kernel crashes are recorded in something like console-ramoops and the
>recovery kernel/modules are different or the debuginfo doesn't exist on
>the device due to space concerns (the debuginfo can be too large for
>space limited devices).
>
>Originally, I put this on the %pS format, but that was quickly rejected
>given that %pS is used in other places such as ftrace where build IDs
>aren't meaningful. There was some discussions on the list to put every
>module build ID into the "Modules linked in:" section of the stacktrace
>message but that quickly becomes very hard to read once you have more
>than three or four modules linked in. It also provides too much
>information when we don't expect each module to be traversed in a
>stacktrace. Having the build ID for modules that aren't important just
>makes things messy. Splitting it to multiple lines for each module
>quickly explodes the number of lines printed in an oops too, possibly
>wrapping the warning off the console. And finally, trying to stash away
>each module used in a callstack to provide the ID of each symbol printed
>is cumbersome and would require changes to each architecture to stash
>away modules and return their build IDs once unwinding has completed.
>
>Instead, we opt for the simpler approach of introducing new printk
>formats '%pS[R]b' for "pointer symbolic backtrace with module build ID"
>and '%pBb' for "pointer backtrace with module build ID" and then
>updating the few places in the architecture layer where the stacktrace
>is printed to use this new format.
>
>Example:
>
> WARNING: CPU: 3 PID: 3373 at drivers/misc/lkdtm/bugs.c:83 lkdtm_WARNING+0x28/0x30 [lkdtm]
> Modules linked in: lkdtm rfcomm algif_hash algif_skcipher af_alg xt_cgroup uinput xt_MASQUERADE hci_uart <modules trimmed>
> CPU: 3 PID: 3373 Comm: bash Not tainted 5.11 #12 a8c0d47f7051f3e6670ceaea724af66a39c6cec8
> Hardware name: Google Lazor (rev3+) with KB Backlight (DT)
> pstate: 00400009 (nzcv daif +PAN -UAO -TCO BTYPE=--)
> pc : lkdtm_WARNING+0x28/0x30 [lkdtm]
> lr : lkdtm_do_action+0x24/0x40 [lkdtm]
> sp : ffffffc013febca0
> x29: ffffffc013febca0 x28: ffffff88d9438040
> x27: 0000000000000000 x26: 0000000000000000
> x25: 0000000000000000 x24: ffffffdd0e9772c0
> x23: 0000000000000020 x22: ffffffdd0e975366
> x21: ffffffdd0e9772e0 x20: ffffffc013febde0
> x19: 0000000000000008 x18: 0000000000000000
> x17: 0000000000000000 x16: 0000000000000037
> x15: ffffffdd102ab174 x14: 0000000000000003
> x13: 0000000000000004 x12: 0000000000000000
> x11: 0000000000000000 x10: 0000000000000000
> x9 : 0000000000000001 x8 : ffffffdd0e979000
> x7 : 0000000000000000 x6 : ffffffdd10ff6b54
> x5 : 0000000000000000 x4 : 0000000000000000
> x3 : ffffffc013feb938 x2 : ffffff89fef05a70
> x1 : ffffff89feef5788 x0 : ffffffdd0e9772e0
> Call trace:
>  lkdtm_WARNING+0x28/0x30 [lkdtm 6c2215028606bda50de823490723dc4bc5bf46f9]
>  direct_entry+0x16c/0x1b4 [lkdtm 6c2215028606bda50de823490723dc4bc5bf46f9]
>  full_proxy_write+0x74/0xa4
>  vfs_write+0xec/0x2e8
>  ksys_write+0x84/0xf0
>  __arm64_sys_write+0x24/0x30
>  el0_svc_common+0xf4/0x1c0
>  do_el0_svc_compat+0x28/0x3c
>  el0_svc_compat+0x10/0x1c
>  el0_sync_compat_handler+0xa8/0xcc
>  el0_sync_compat+0x178/0x180
> ---[ end trace f89bc7f5417cbcc6 ]---
>
>Cc: Jiri Olsa <jolsa@kernel.org>
>Cc: Alexei Starovoitov <ast@kernel.org>
>Cc: Jessica Yu <jeyu@kernel.org>
>Cc: Evan Green <evgreen@chromium.org>
>Cc: Hsin-Yi Wang <hsinyi@chromium.org>
>Cc: Petr Mladek <pmladek@suse.com>
>Cc: Steven Rostedt <rostedt@goodmis.org>
>Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
>Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
>Cc: <linux-doc@vger.kernel.org>
>Cc: Matthew Wilcox <willy@infradead.org>
>Link: https://fedoraproject.org/wiki/Releases/FeatureBuildId [1]
>Link: https://sourceware.org/elfutils/Debuginfod.html [2]
>Signed-off-by: Stephen Boyd <swboyd@chromium.org>
>---
> Documentation/core-api/printk-formats.rst | 11 +++
> include/linux/kallsyms.h                  | 20 ++++-
> include/linux/module.h                    |  6 +-
> kernel/kallsyms.c                         | 95 ++++++++++++++++++-----
> kernel/module.c                           | 24 +++++-
> lib/vsprintf.c                            |  8 +-
> 6 files changed, 139 insertions(+), 25 deletions(-)
>
>diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
>index 160e710d992f..5f60533f2a56 100644
>--- a/Documentation/core-api/printk-formats.rst
>+++ b/Documentation/core-api/printk-formats.rst
>@@ -114,6 +114,17 @@ used when printing stack backtraces. The specifier takes into
> consideration the effect of compiler optimisations which may occur
> when tail-calls are used and marked with the noreturn GCC attribute.
>
>+If the pointer is within a module, the module name and optionally build ID is
>+printed after the symbol name with an extra ``b`` appended to the end of the
>+specifier.
>+
>+::
>+	%pS	versatile_init+0x0/0x110 [module_name]
>+	%pSb	versatile_init+0x0/0x110 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
>+	%pSRb	versatile_init+0x9/0x110 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
>+		(with __builtin_extract_return_addr() translation)
>+	%pBb	prev_fn_of_versatile_init+0x88/0x88 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
>+
> Probed Pointers from BPF / tracing
> ----------------------------------
>
>diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
>index 465060acc981..f760cb839775 100644
>--- a/include/linux/kallsyms.h
>+++ b/include/linux/kallsyms.h
>@@ -7,6 +7,7 @@
> #define _LINUX_KALLSYMS_H
>
> #include <linux/errno.h>
>+#include <linux/buildid.h>
> #include <linux/kernel.h>
> #include <linux/stddef.h>
> #include <linux/mm.h>
>@@ -15,8 +16,9 @@
> #include <asm/sections.h>
>
> #define KSYM_NAME_LEN 128
>-#define KSYM_SYMBOL_LEN (sizeof("%s+%#lx/%#lx [%s]") + (KSYM_NAME_LEN - 1) + \
>-			 2*(BITS_PER_LONG*3/10) + (MODULE_NAME_LEN - 1) + 1)
>+#define KSYM_SYMBOL_LEN (sizeof("%s+%#lx/%#lx [%s %s]") + (KSYM_NAME_LEN - 1) + \
>+			 2*(BITS_PER_LONG*3/10) + (MODULE_NAME_LEN - 1) + \
>+			 (BUILD_ID_SIZE_MAX * 2) + 1)
>
> struct cred;
> struct module;
>@@ -91,8 +93,10 @@ const char *kallsyms_lookup(unsigned long addr,
>
> /* Look up a kernel symbol and return it in a text buffer. */
> extern int sprint_symbol(char *buffer, unsigned long address);
>+extern int sprint_symbol_build_id(char *buffer, unsigned long address);
> extern int sprint_symbol_no_offset(char *buffer, unsigned long address);
> extern int sprint_backtrace(char *buffer, unsigned long address);
>+extern int sprint_backtrace_build_id(char *buffer, unsigned long address);
>
> int lookup_symbol_name(unsigned long addr, char *symname);
> int lookup_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name);
>@@ -128,6 +132,12 @@ static inline int sprint_symbol(char *buffer, unsigned long addr)
> 	return 0;
> }
>
>+static inline int sprint_symbol_build_id(char *buffer, unsigned long address)
>+{
>+	*buffer = '\0';
>+	return 0;
>+}
>+
> static inline int sprint_symbol_no_offset(char *buffer, unsigned long addr)
> {
> 	*buffer = '\0';
>@@ -140,6 +150,12 @@ static inline int sprint_backtrace(char *buffer, unsigned long addr)
> 	return 0;
> }
>
>+static inline int sprint_backtrace_build_id(char *buffer, unsigned long addr)
>+{
>+	*buffer = '\0';
>+	return 0;
>+}
>+
> static inline int lookup_symbol_name(unsigned long addr, char *symname)
> {
> 	return -ERANGE;
>diff --git a/include/linux/module.h b/include/linux/module.h
>index 59f094fa6f74..4bf869f6c944 100644
>--- a/include/linux/module.h
>+++ b/include/linux/module.h
>@@ -11,6 +11,7 @@
>
> #include <linux/list.h>
> #include <linux/stat.h>
>+#include <linux/buildid.h>
> #include <linux/compiler.h>
> #include <linux/cache.h>
> #include <linux/kmod.h>
>@@ -367,6 +368,9 @@ struct module {
> 	/* Unique handle for this module */
> 	char name[MODULE_NAME_LEN];
>
>+	/* Module build ID */
>+	unsigned char build_id[BUILD_ID_SIZE_MAX];

Hi Stephen,

Since this field is not used when !CONFIG_STACKTRACE_BUILD_ID, I
would prefer to wrap this in an ifdef, similar to the other
CONFIG-dependent fields in struct module. This makes it explicit under
what conditions (i.e. config) the field is meant to be used.

>+
> 	/* Sysfs stuff. */
> 	struct module_kobject mkobj;
> 	struct module_attribute *modinfo_attrs;
>@@ -630,7 +634,7 @@ void *dereference_module_function_descriptor(struct module *mod, void *ptr);
> const char *module_address_lookup(unsigned long addr,
> 			    unsigned long *symbolsize,
> 			    unsigned long *offset,
>-			    char **modname,
>+			    char **modname, const unsigned char **modbuildid,
> 			    char *namebuf);
> int lookup_module_symbol_name(unsigned long addr, char *symname);
> int lookup_module_symbol_attrs(unsigned long addr, unsigned long *size, unsigned long *offset, char *modname, char *name);
>diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
>index 8043a90aa50e..b835992e76c2 100644
>--- a/kernel/kallsyms.c
>+++ b/kernel/kallsyms.c
>@@ -273,21 +273,13 @@ int kallsyms_lookup_size_offset(unsigned long addr, unsigned long *symbolsize,
> 		get_symbol_pos(addr, symbolsize, offset);
> 		return 1;
> 	}
>-	return !!module_address_lookup(addr, symbolsize, offset, NULL, namebuf) ||
>+	return !!module_address_lookup(addr, symbolsize, offset, NULL, NULL, namebuf) ||
> 	       !!__bpf_address_lookup(addr, symbolsize, offset, namebuf);
> }
>
>-/*
>- * Lookup an address
>- * - modname is set to NULL if it's in the kernel.
>- * - We guarantee that the returned name is valid until we reschedule even if.
>- *   It resides in a module.
>- * - We also guarantee that modname will be valid until rescheduled.
>- */
>-const char *kallsyms_lookup(unsigned long addr,
>-			    unsigned long *symbolsize,
>-			    unsigned long *offset,
>-			    char **modname, char *namebuf)
>+const char *kallsyms_lookup_buildid(unsigned long addr, unsigned long *symbolsize,
>+				    unsigned long *offset, char **modname,
>+				    const unsigned char **modbuildid, char *namebuf)
> {
> 	const char *ret;
>
>@@ -303,12 +295,14 @@ const char *kallsyms_lookup(unsigned long addr,
> 				       namebuf, KSYM_NAME_LEN);
> 		if (modname)
> 			*modname = NULL;
>+		if (modbuildid)
>+			*modbuildid = NULL;
> 		return namebuf;
> 	}
>
> 	/* See if it's in a module or a BPF JITed image. */
> 	ret = module_address_lookup(addr, symbolsize, offset,
>-				    modname, namebuf);
>+				    modname, modbuildid, namebuf);
> 	if (!ret)
> 		ret = bpf_address_lookup(addr, symbolsize,
> 					 offset, modname, namebuf);
>@@ -319,6 +313,22 @@ const char *kallsyms_lookup(unsigned long addr,
> 	return ret;
> }
>
>+/*
>+ * Lookup an address
>+ * - modname is set to NULL if it's in the kernel.
>+ * - We guarantee that the returned name is valid until we reschedule even if.
>+ *   It resides in a module.
>+ * - We also guarantee that modname will be valid until rescheduled.
>+ */
>+const char *kallsyms_lookup(unsigned long addr,
>+			    unsigned long *symbolsize,
>+			    unsigned long *offset,
>+			    char **modname, char *namebuf)
>+{
>+	return kallsyms_lookup_buildid(addr, symbolsize, offset, modname,
>+				       NULL, namebuf);
>+}
>+
> int lookup_symbol_name(unsigned long addr, char *symname)
> {
> 	symname[0] = '\0';
>@@ -359,15 +369,17 @@ int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
>
> /* Look up a kernel symbol and return it in a text buffer. */
> static int __sprint_symbol(char *buffer, unsigned long address,
>-			   int symbol_offset, int add_offset)
>+			   int symbol_offset, int add_offset, int add_buildid)
> {
> 	char *modname;
>+	const unsigned char *buildid;
> 	const char *name;
> 	unsigned long offset, size;
> 	int len;
>
> 	address += symbol_offset;
>-	name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
>+	name = kallsyms_lookup_buildid(address, &size, &offset, &modname, &buildid,
>+				       buffer);
> 	if (!name)
> 		return sprintf(buffer, "0x%lx", address - symbol_offset);
>
>@@ -379,8 +391,14 @@ static int __sprint_symbol(char *buffer, unsigned long address,
> 	if (add_offset)
> 		len += sprintf(buffer + len, "+%#lx/%#lx", offset, size);
>
>-	if (modname)
>-		len += sprintf(buffer + len, " [%s]", modname);
>+	if (modname) {
>+		len += sprintf(buffer + len, " [%s", modname);
>+		/* build ID should match length of sprintf below */
>+		BUILD_BUG_ON(BUILD_ID_SIZE_MAX != 20);
>+		if (IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) && add_buildid && buildid)
>+			len += sprintf(buffer + len, " %20phN", buildid);
>+		len += sprintf(buffer + len, "]");
>+	}
>
> 	return len;
> }
>@@ -398,10 +416,27 @@ static int __sprint_symbol(char *buffer, unsigned long address,
>  */
> int sprint_symbol(char *buffer, unsigned long address)
> {
>-	return __sprint_symbol(buffer, address, 0, 1);
>+	return __sprint_symbol(buffer, address, 0, 1, 0);
> }
> EXPORT_SYMBOL_GPL(sprint_symbol);
>
>+/**
>+ * sprint_symbol_build_id - Look up a kernel symbol and return it in a text buffer
>+ * @buffer: buffer to be stored
>+ * @address: address to lookup
>+ *
>+ * This function looks up a kernel symbol with @address and stores its name,
>+ * offset, size, module name and module build ID to @buffer if possible. If no
>+ * symbol was found, just saves its @address as is.
>+ *
>+ * This function returns the number of bytes stored in @buffer.
>+ */
>+int sprint_symbol_build_id(char *buffer, unsigned long address)
>+{
>+	return __sprint_symbol(buffer, address, 0, 1, 1);
>+}
>+EXPORT_SYMBOL_GPL(sprint_symbol_build_id);
>+
> /**
>  * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
>  * @buffer: buffer to be stored
>@@ -415,7 +450,7 @@ EXPORT_SYMBOL_GPL(sprint_symbol);
>  */
> int sprint_symbol_no_offset(char *buffer, unsigned long address)
> {
>-	return __sprint_symbol(buffer, address, 0, 0);
>+	return __sprint_symbol(buffer, address, 0, 0, 0);
> }
> EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
>
>@@ -435,7 +470,27 @@ EXPORT_SYMBOL_GPL(sprint_symbol_no_offset);
>  */
> int sprint_backtrace(char *buffer, unsigned long address)
> {
>-	return __sprint_symbol(buffer, address, -1, 1);
>+	return __sprint_symbol(buffer, address, -1, 1, 0);
>+}
>+
>+/**
>+ * sprint_backtrace_build_id - Look up a backtrace symbol and return it in a text buffer
>+ * @buffer: buffer to be stored
>+ * @address: address to lookup
>+ *
>+ * This function is for stack backtrace and does the same thing as
>+ * sprint_symbol() but with modified/decreased @address. If there is a
>+ * tail-call to the function marked "noreturn", gcc optimized out code after
>+ * the call so that the stack-saved return address could point outside of the
>+ * caller. This function ensures that kallsyms will find the original caller
>+ * by decreasing @address. This function also appends the module build ID to
>+ * the @buffer if @address is within a kernel module.
>+ *
>+ * This function returns the number of bytes stored in @buffer.
>+ */
>+int sprint_backtrace_build_id(char *buffer, unsigned long address)
>+{
>+	return __sprint_symbol(buffer, address, -1, 1, 1);
> }
>
> /* To avoid using get_symbol_offset for every symbol, we carry prefix along. */
>diff --git a/kernel/module.c b/kernel/module.c
>index 30479355ab85..6f5bc1b046a5 100644
>--- a/kernel/module.c
>+++ b/kernel/module.c
>@@ -13,6 +13,7 @@
> #include <linux/trace_events.h>
> #include <linux/init.h>
> #include <linux/kallsyms.h>
>+#include <linux/buildid.h>
> #include <linux/file.h>
> #include <linux/fs.h>
> #include <linux/sysfs.h>
>@@ -2770,6 +2771,20 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
> 	}
> 	mod->core_kallsyms.num_symtab = ndst;
> }
>+
>+static void init_build_id(struct module *mod, const struct load_info *info)
>+{
>+	const Elf_Shdr *sechdr;
>+	unsigned int i;
>+
>+	for (i = 0; i < info->hdr->e_shnum; i++) {
>+		sechdr = &info->sechdrs[i];
>+		if (!sect_empty(sechdr) && sechdr->sh_type == SHT_NOTE &&
>+		    !build_id_parse_buf((void *)sechdr->sh_addr, mod->build_id,
>+					sechdr->sh_size))
>+			break;
>+	}

If mod->build_id is not used when !CONFIG_STACKTRACE_BUILD_ID, then we
don't need to look for it. I would be fine with wrapping the function
body in an ifdef (similar to what we currently do in
del_usage_links() and do_mod_ctors()).

>+}
> #else
> static inline void layout_symtab(struct module *mod, struct load_info *info)
> {
>@@ -2778,6 +2793,10 @@ static inline void layout_symtab(struct module *mod, struct load_info *info)
> static void add_kallsyms(struct module *mod, const struct load_info *info)
> {
> }
>+
>+static void init_build_id(struct module *mod, const struct load_info *info)
>+{
>+}
> #endif /* CONFIG_KALLSYMS */
>
> static void dynamic_debug_setup(struct module *mod, struct _ddebug *debug, unsigned int num)
>@@ -4004,6 +4023,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
> 		goto free_arch_cleanup;
> 	}
>
>+	init_build_id(mod, info);
> 	dynamic_debug_setup(mod, info->debug, info->num_debug);
>
> 	/* Ftrace init must be called in the MODULE_STATE_UNFORMED state */
>@@ -4235,7 +4255,7 @@ void * __weak dereference_module_function_descriptor(struct module *mod,
> const char *module_address_lookup(unsigned long addr,
> 			    unsigned long *size,
> 			    unsigned long *offset,
>-			    char **modname,
>+			    char **modname, const unsigned char **modbuildid,
> 			    char *namebuf)
> {
> 	const char *ret = NULL;
>@@ -4246,6 +4266,8 @@ const char *module_address_lookup(unsigned long addr,
> 	if (mod) {
> 		if (modname)
> 			*modname = mod->name;
>+		if (modbuildid)
>+			*modbuildid = mod->build_id;

Then maybe we can set *modbuildid = NULL in the case of
!CONFIG_STACKTRACE_BUILD_ID, similar to the kernel case in
kallsyms_lookup_buildid().


Thanks!

Jessica

Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Stephen Boyd]

Quoting Jessica Yu (2021-04-15 06:04:35)
> +++ Stephen Boyd [09/04/21 18:52 -0700]:
> >diff --git a/include/linux/module.h b/include/linux/module.h
> >index 59f094fa6f74..4bf869f6c944 100644
> >--- a/include/linux/module.h
> >+++ b/include/linux/module.h
> >@@ -11,6 +11,7 @@
> >
> > #include <linux/list.h>
> > #include <linux/stat.h>
> >+#include <linux/buildid.h>
> > #include <linux/compiler.h>
> > #include <linux/cache.h>
> > #include <linux/kmod.h>
> >@@ -367,6 +368,9 @@ struct module {
> >       /* Unique handle for this module */
> >       char name[MODULE_NAME_LEN];
> >
> >+      /* Module build ID */
> >+      unsigned char build_id[BUILD_ID_SIZE_MAX];
> 
> Hi Stephen,
> 
> Since this field is not used when !CONFIG_STACKTRACE_BUILD_ID, I
> would prefer to wrap this in an ifdef, similar to the other
> CONFIG-dependent fields in struct module. This makes it explicit under
> what conditions (i.e. config) the field is meant to be used.

Ok will do.

> >diff --git a/kernel/module.c b/kernel/module.c
> >index 30479355ab85..6f5bc1b046a5 100644
> >--- a/kernel/module.c
> >+++ b/kernel/module.c
> >@@ -2770,6 +2771,20 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
> >       }
> >       mod->core_kallsyms.num_symtab = ndst;
> > }
> >+
> >+static void init_build_id(struct module *mod, const struct load_info *info)
> >+{
> >+      const Elf_Shdr *sechdr;
> >+      unsigned int i;
> >+
> >+      for (i = 0; i < info->hdr->e_shnum; i++) {
> >+              sechdr = &info->sechdrs[i];
> >+              if (!sect_empty(sechdr) && sechdr->sh_type == SHT_NOTE &&
> >+                  !build_id_parse_buf((void *)sechdr->sh_addr, mod->build_id,
> >+                                      sechdr->sh_size))
> >+                      break;
> >+      }
> 
> If mod->build_id is not used when !CONFIG_STACKTRACE_BUILD_ID, then we
> don't need to look for it. I would be fine with wrapping the function
> body in an ifdef (similar to what we currently do in
> del_usage_links() and do_mod_ctors()).

Ok, done.

> 
> >+}
> > #else
> > static inline void layout_symtab(struct module *mod, struct load_info *info)
> > {
> >@@ -2778,6 +2793,10 @@ static inline void layout_symtab(struct module *mod, struct load_info *info)
> > static void add_kallsyms(struct module *mod, const struct load_info *info)
> > {
> > }
> >+
> >+static void init_build_id(struct module *mod, const struct load_info *info)
> >+{
> >+}
> > #endif /* CONFIG_KALLSYMS */
> >
> > static void dynamic_debug_setup(struct module *mod, struct _ddebug *debug, unsigned int num)
> >@@ -4004,6 +4023,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
> >               goto free_arch_cleanup;
> >       }
> >
> >+      init_build_id(mod, info);
> >       dynamic_debug_setup(mod, info->debug, info->num_debug);
> >
> >       /* Ftrace init must be called in the MODULE_STATE_UNFORMED state */
> >@@ -4235,7 +4255,7 @@ void * __weak dereference_module_function_descriptor(struct module *mod,
> > const char *module_address_lookup(unsigned long addr,
> >                           unsigned long *size,
> >                           unsigned long *offset,
> >-                          char **modname,
> >+                          char **modname, const unsigned char **modbuildid,
> >                           char *namebuf)
> > {
> >       const char *ret = NULL;
> >@@ -4246,6 +4266,8 @@ const char *module_address_lookup(unsigned long addr,
> >       if (mod) {
> >               if (modname)
> >                       *modname = mod->name;
> >+              if (modbuildid)
> >+                      *modbuildid = mod->build_id;
> 
> Then maybe we can set *modbuildid = NULL in the case of
> !CONFIG_STACKTRACE_BUILD_ID, similar to the kernel case in
> kallsyms_lookup_buildid().
> 

Sounds good. It means that some more ifdefs are probably required vs.
making the array size be 0 when the config is disabled but that isn't a
big problem for me. I'm reworking the code now and will test and then
send v5 shortly. Thanks!

Re: [PATCH v4 05/13] module: Add printk formats to add module build ID to stacktraces

[Jessica Yu]

+++ Stephen Boyd [17/04/21 18:52 -0700]:
[snip]
>Sounds good. It means that some more ifdefs are probably required vs.
>making the array size be 0 when the config is disabled but that isn't a
>big problem for me. I'm reworking the code now and will test and then
>send v5 shortly. Thanks!

Great, thanks a lot Stephen!

Jessica