[PATCH v2 00/12] Add build ID to stacktraces

[PATCH v2 00/12] 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 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>

Stephen Boyd (12):
  buildid: Add API to parse build ID out of buffer
  buildid: Add method to get running kernel's build ID
  dump_stack: Add vmlinux build ID to stack traces
  module: Add printk format to add module build ID to stacktraces
  arm64: stacktrace: Use %pSb for backtrace printing
  x86/dumpstack: Use %pSb 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 |  9 +++
 arch/arm64/kernel/stacktrace.c            |  2 +-
 arch/x86/kernel/dumpstack.c               |  4 +-
 include/linux/buildid.h                   |  3 +
 include/linux/crash_core.h                |  6 +-
 include/linux/kallsyms.h                  | 13 +++-
 include/linux/module.h                    |  6 +-
 kernel/crash_core.c                       | 41 +----------
 kernel/kallsyms.c                         | 73 ++++++++++++++-----
 kernel/module.c                           | 24 +++++-
 lib/buildid.c                             | 75 +++++++++++++++----
 lib/dump_stack.c                          |  5 +-
 lib/vsprintf.c                            |  6 +-
 scripts/decode_stacktrace.sh              | 89 +++++++++++++++++++----
 14 files changed, 251 insertions(+), 105 deletions(-)


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

[PATCH v2 04/12] module: Add printk format 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 a new printk
format '%p[sS][br]' for "pointer symbolic 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 |  9 +++
 include/linux/kallsyms.h                  | 13 +++-
 include/linux/module.h                    |  6 +-
 kernel/kallsyms.c                         | 73 ++++++++++++++++-------
 kernel/module.c                           | 24 +++++++-
 lib/vsprintf.c                            |  6 +-
 6 files changed, 106 insertions(+), 25 deletions(-)

diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index 160e710d992f..c0844cb275eb 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst
@@ -114,6 +114,15 @@ 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.
+
+::
+	%pS	versatile_init+0x0/0x110 [module_name]
+	%pSb	versatile_init+0x0/0x110 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
+	%pSr	versatile_init+0x9/0x110 [module_name ed5019fdf5e53be37cb1ba7899292d7e143b259e]
+		(with __builtin_extract_return_addr() translation)
+
 Probed Pointers from BPF / tracing
 ----------------------------------
 
diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index 465060acc981..9f489aaa4127 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;
@@ -91,6 +93,7 @@ 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_stacktrace(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);
 
@@ -128,6 +131,12 @@ static inline int sprint_symbol(char *buffer, unsigned long addr)
 	return 0;
 }
 
+static inline int sprint_symbol_stacktrace(char *buffer, unsigned long address)
+{
+	*buffer = '\0';
+	return 0;
+}
+
 static inline int sprint_symbol_no_offset(char *buffer, unsigned long addr)
 {
 	*buffer = '\0';
diff --git a/include/linux/module.h b/include/linux/module.h
index 59f094fa6f74..0d17c7eb4c8a 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, 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..e77a1b6680a9 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,
+				    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;
+	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 +391,12 @@ 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);
+		if (add_buildid && buildid)
+			len += sprintf(buffer + len, " %20phN", buildid);
+		len += sprintf(buffer + len, "]");
+	}
 
 	return len;
 }
@@ -398,10 +414,27 @@ 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_stacktrace - 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_stacktrace(char *buffer, unsigned long address)
+{
+	return __sprint_symbol(buffer, address, 0, 1, 1);
+}
+EXPORT_SYMBOL_GPL(sprint_symbol_stacktrace);
+
 /**
  * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer
  * @buffer: buffer to be stored
@@ -415,7 +448,7 @@ 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 +468,7 @@ 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);
 }
 
 /* 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..9e9cb502fb33 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, 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..9cd62e84e4aa 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -961,13 +961,15 @@ char *symbol_string(char *buf, char *end, void *ptr,
 	char sym[KSYM_SYMBOL_LEN];
 #endif
 
-	if (fmt[1] == 'R')
+	if (fmt[1] == 'R' || fmt[1] == 'r')
 		ptr = __builtin_extract_return_addr(ptr);
 	value = (unsigned long)ptr;
 
 #ifdef CONFIG_KALLSYMS
 	if (*fmt == 'B')
 		sprint_backtrace(sym, value);
+	else if (*fmt == 'S' && (fmt[1] == 'b' || fmt[1] == 'r'))
+		sprint_symbol_stacktrace(sym, value);
 	else if (*fmt != 's')
 		sprint_symbol(sym, value);
 	else
@@ -2129,6 +2131,8 @@ 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
+ * - '[Ss]r' as above with __builtin_extract_return_addr() translation and module build ID
+ * - '[Ss]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
-- 
https://chromeos.dev

Re: [PATCH v2 00/12] Add build ID to stacktraces

[Christoph Hellwig]

On Tue, Mar 23, 2021 at 07:04:31PM -0700, Stephen Boyd wrote:
>  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]

Yikes.  No, please do not make the backtraces a complete mess for
something that serves absolutely no need.

Re: [PATCH v2 04/12] module: Add printk format to add module build ID to stacktraces

[Rasmus Villemoes]

On 24/03/2021 03.04, Stephen Boyd wrote:

> @@ -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, unsigned char **modbuildid,

It's an existing defect with modname, but surely this should take a
"const unsigned char **modbuildid", no?

>  			    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..9cd62e84e4aa 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -961,13 +961,15 @@ char *symbol_string(char *buf, char *end, void *ptr,
>  	char sym[KSYM_SYMBOL_LEN];
>  #endif
>  
> -	if (fmt[1] == 'R')
> +	if (fmt[1] == 'R' || fmt[1] == 'r')
>  		ptr = __builtin_extract_return_addr(ptr);
>  	value = (unsigned long)ptr;
>  
>  #ifdef CONFIG_KALLSYMS
>  	if (*fmt == 'B')
>  		sprint_backtrace(sym, value);
> +	else if (*fmt == 'S' && (fmt[1] == 'b' || fmt[1] == 'r'))
> +		sprint_symbol_stacktrace(sym, value);
>  	else if (*fmt != 's')
>  		sprint_symbol(sym, value);
>  	else
> @@ -2129,6 +2131,8 @@ 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
> + * - '[Ss]r' as above with __builtin_extract_return_addr() translation and module build ID
> + * - '[Ss]b' as above with module build ID (for use in backtraces)

The code doesn't quite match the comment. The lowercase s is not handled
(i.e., there's no way to say "without offset, with build ID"). You don't
have to fix the code to support that right now, the whole kallsyms
vsprintf code needs to be reworked inside-out anyway (having vsnprint
call sprint_symbol* which builds the output using snprintf() calls makes
me cringe), so please just replace [Ss] by S to make the comment match
the code - I notice that you did only document the S variant in
printk-formats.rst.

Is there any reason you didn't just make b an optional flag that could
be specified with or without R? I suppose the parsing is more difficult
with several orthogonal flags (see escaped_string()), but it's a little
easier to understand. Dunno, it's not like we're gonna think of 10 other
things that could be printed for a symbol, so perhaps it's fine.

Rasmus

Re: [PATCH v2 00/12] Add build ID to stacktraces

[Stephen Boyd]

HTML mail?

Quoting Konstantin Khlebnikov (2021-03-24 01:23:55)
> 24.03.2021, 05:04, "Stephen Boyd" <swboyd@chromium.org>:
>  
> Looks too noisy for me. Maybe print id in the line "Modules linked in:"?
> I suppose only out-of-tree modules need this?
>  

Please see this note in patch 4:

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.

Re: [PATCH v2 04/12] module: Add printk format to add module build ID to stacktraces

[Stephen Boyd]

Quoting Rasmus Villemoes (2021-03-24 02:57:13)
> On 24/03/2021 03.04, Stephen Boyd wrote:
> 
> > @@ -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, unsigned char **modbuildid,
> 
> It's an existing defect with modname, but surely this should take a
> "const unsigned char **modbuildid", no?

Sure.

> 
> >                           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..9cd62e84e4aa 100644
> > --- a/lib/vsprintf.c
> > +++ b/lib/vsprintf.c
> > @@ -961,13 +961,15 @@ char *symbol_string(char *buf, char *end, void *ptr,
> >       char sym[KSYM_SYMBOL_LEN];
> >  #endif
> >  
> > -     if (fmt[1] == 'R')
> > +     if (fmt[1] == 'R' || fmt[1] == 'r')
> >               ptr = __builtin_extract_return_addr(ptr);
> >       value = (unsigned long)ptr;
> >  
> >  #ifdef CONFIG_KALLSYMS
> >       if (*fmt == 'B')
> >               sprint_backtrace(sym, value);
> > +     else if (*fmt == 'S' && (fmt[1] == 'b' || fmt[1] == 'r'))
> > +             sprint_symbol_stacktrace(sym, value);
> >       else if (*fmt != 's')
> >               sprint_symbol(sym, value);
> >       else
> > @@ -2129,6 +2131,8 @@ 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
> > + * - '[Ss]r' as above with __builtin_extract_return_addr() translation and module build ID
> > + * - '[Ss]b' as above with module build ID (for use in backtraces)
> 
> The code doesn't quite match the comment. The lowercase s is not handled
> (i.e., there's no way to say "without offset, with build ID"). You don't
> have to fix the code to support that right now, the whole kallsyms
> vsprintf code needs to be reworked inside-out anyway (having vsnprint
> call sprint_symbol* which builds the output using snprintf() calls makes
> me cringe), so please just replace [Ss] by S to make the comment match
> the code - I notice that you did only document the S variant in
> printk-formats.rst.

No problem. Will fix this comment.

> 
> Is there any reason you didn't just make b an optional flag that could
> be specified with or without R? I suppose the parsing is more difficult
> with several orthogonal flags (see escaped_string()), but it's a little
> easier to understand. Dunno, it's not like we're gonna think of 10 other
> things that could be printed for a symbol, so perhaps it's fine.
> 

I think I follow. So %pSb or %pSRb? If it's easier to understand then
sure. I was trying to avoid checking another character beyond fmt[1] but
it should be fine if fmt[1] is already 'R'.

Re: [PATCH v2 04/12] module: Add printk format to add module build ID to stacktraces

[Rasmus Villemoes]

On 24/03/2021 20.11, Stephen Boyd wrote:
> Quoting Rasmus Villemoes (2021-03-24 02:57:13)

>>
>> Is there any reason you didn't just make b an optional flag that could
>> be specified with or without R? I suppose the parsing is more difficult
>> with several orthogonal flags (see escaped_string()), but it's a little
>> easier to understand. Dunno, it's not like we're gonna think of 10 other
>> things that could be printed for a symbol, so perhaps it's fine.
>>
> 
> I think I follow. So %pSb or %pSRb? If it's easier to understand then
> sure. I was trying to avoid checking another character beyond fmt[1] but
> it should be fine if fmt[1] is already 'R'.
> 

I don't know. On the one hand, it seems sensible to allow such "flag"
modifiers to appear independently and in any order. Because what if some
day we think of some other property of the symbol we might want to
provide access to via a "z" flag; when to allow all combinations of the
R, b and z functionality we'd have to use four more random letters to
stand for various combinations of those flags. On the other hand,
vsprintf.c is already a complete wild west of odd conventions for
%p<foo>, and it's not like symbol_string() gets extended every other
release, and I can certainly understand the desire to keep the parsing
of fmt minimal. So 'r' to mean 'Rb' is ok by me if you prefer that.

Rasmus

Re: [PATCH v2 04/12] module: Add printk format to add module build ID to stacktraces

[Stephen Boyd]

Quoting Rasmus Villemoes (2021-03-24 15:21:34)
> On 24/03/2021 20.11, Stephen Boyd wrote:
> > Quoting Rasmus Villemoes (2021-03-24 02:57:13)
> 
> >>
> >> Is there any reason you didn't just make b an optional flag that could
> >> be specified with or without R? I suppose the parsing is more difficult
> >> with several orthogonal flags (see escaped_string()), but it's a little
> >> easier to understand. Dunno, it's not like we're gonna think of 10 other
> >> things that could be printed for a symbol, so perhaps it's fine.
> >>
> > 
> > I think I follow. So %pSb or %pSRb? If it's easier to understand then
> > sure. I was trying to avoid checking another character beyond fmt[1] but
> > it should be fine if fmt[1] is already 'R'.
> > 
> 
> I don't know. On the one hand, it seems sensible to allow such "flag"
> modifiers to appear independently and in any order. Because what if some
> day we think of some other property of the symbol we might want to
> provide access to via a "z" flag; when to allow all combinations of the
> R, b and z functionality we'd have to use four more random letters to
> stand for various combinations of those flags. On the other hand,
> vsprintf.c is already a complete wild west of odd conventions for
> %p<foo>, and it's not like symbol_string() gets extended every other
> release, and I can certainly understand the desire to keep the parsing
> of fmt minimal. So 'r' to mean 'Rb' is ok by me if you prefer that.

I'm inclined to use %pSb and %pSRb. The code looks to simpler and I
suppose we can worry about different ordering/combination problems if it
comes to it.

---8<---
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 41ddc353ebb8..0e94cba5ba20 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -968,6 +968,8 @@ char *symbol_string(char *buf, char *end, void *ptr,
 #ifdef CONFIG_KALLSYMS
        if (*fmt == 'B')
                sprint_backtrace(sym, value);
+       else if (*fmt == 'S' && (fmt[1] == 'b' || (fmt[1] == 'R' && fmt[2] == 'b')))
+               sprint_symbol_stacktrace(sym, value);
        else if (*fmt != 's')
                sprint_symbol(sym, value);
        else

Re: [PATCH v2 00/12] Add build ID to stacktraces

[peter enderborg]

On 3/24/21 9:55 AM, Christoph Hellwig wrote:
> On Tue, Mar 23, 2021 at 07:04:31PM -0700, Stephen Boyd wrote:
>>  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]
> Yikes.  No, please do not make the backtraces a complete mess for
> something that serves absolutely no need.

Would a "verbose" flag be acceptable solution?    Something like write 1 to /sys/kernel/debug/verbose_stack to get the extra info.

I think I see a need for it.

Re: [PATCH v2 00/12] Add build ID to stacktraces

[peter enderborg]

On 3/24/21 3:04 AM, Stephen Boyd wrote:
> 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 ]---

How will this work with the ftrace?

Re: [PATCH v2 00/12] Add build ID to stacktraces

[Stephen Boyd]

Quoting peter enderborg (2021-03-25 04:14:31)
> >   el0_sync_compat_handler+0xa8/0xcc
> >   el0_sync_compat+0x178/0x180
> >  ---[ end trace 3d95032303e59e68 ]---
> 
> How will this work with the ftrace?
> 

It won't affect ftrace, if that's the question you're asking.

Re: [PATCH v2 00/12] Add build ID to stacktraces

[Stephen Boyd]

Quoting peter enderborg (2021-03-25 04:06:17)
> On 3/24/21 9:55 AM, Christoph Hellwig wrote:
> > On Tue, Mar 23, 2021 at 07:04:31PM -0700, Stephen Boyd wrote:
> >>  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]
> > Yikes.  No, please do not make the backtraces a complete mess for
> > something that serves absolutely no need.

It serves a need. Please look at the patches to understand that I'm
adding the buildid to automatically find the associated debug
information on distros.

> 
> Would a "verbose" flag be acceptable solution?    Something like write 1 to /sys/kernel/debug/verbose_stack to get the extra info.
> 
> I think I see a need for it.
> 

Or a kernel config option and a commandline parameter? That would be OK
for me as I said on v1 of this series. I'll add that in for the next
patch series given all the distaste for some more hex characters next to
the module name.

Re: [PATCH v2 04/12] module: Add printk format to add module build ID to stacktraces

[Petr Mladek]

On Tue 2021-03-23 19:04:35, 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.
> 
> 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

I tested it with "echo l >/proc/sysrq-trigger" and I got the following
output:

[   71.905593] CPU: 0 PID: 1762 Comm: bash Kdump: loaded Not tainted 5.12.0-rc5-default+ #167 00000080ffffffff0000000000000000
00000000

It does not looks like an unique build-id.
Any idea what was going wrong?

> --- a/include/linux/kallsyms.h
> +++ b/include/linux/kallsyms.h
> @@ -91,6 +93,7 @@ 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_stacktrace(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);

Could we use a more clear name? It is hard to guess what is
the difference between sprint_*_stacktrace() and sprint_backtrace().

What about sprint_symbol_build_id() ?


> diff --git a/kernel/module.c b/kernel/module.c
> index 30479355ab85..9e9cb502fb33 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;
> +	}

Just to be sure. Is this really reliable way how to find the build ID,
please?


> +}
>  #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)
>  {
>  }

Best Regards,
Petr

Re: [PATCH v2 04/12] module: Add printk format to add module build ID to stacktraces

[Petr Mladek]

On Wed 2021-03-24 15:28:43, Stephen Boyd wrote:
> Quoting Rasmus Villemoes (2021-03-24 15:21:34)
> > On 24/03/2021 20.11, Stephen Boyd wrote:
> > > Quoting Rasmus Villemoes (2021-03-24 02:57:13)
> > 
> > >>
> > >> Is there any reason you didn't just make b an optional flag that could
> > >> be specified with or without R? I suppose the parsing is more difficult
> > >> with several orthogonal flags (see escaped_string()), but it's a little
> > >> easier to understand. Dunno, it's not like we're gonna think of 10 other
> > >> things that could be printed for a symbol, so perhaps it's fine.
> > >>
> > > 
> > > I think I follow. So %pSb or %pSRb? If it's easier to understand then
> > > sure. I was trying to avoid checking another character beyond fmt[1] but
> > > it should be fine if fmt[1] is already 'R'.
> 
> I'm inclined to use %pSb and %pSRb. The code looks to simpler and I
> suppose we can worry about different ordering/combination problems if it
> comes to it.
>
> ---8<---
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 41ddc353ebb8..0e94cba5ba20 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -968,6 +968,8 @@ char *symbol_string(char *buf, char *end, void *ptr,
>  #ifdef CONFIG_KALLSYMS
>         if (*fmt == 'B')
>                 sprint_backtrace(sym, value);
> +       else if (*fmt == 'S' && (fmt[1] == 'b' || (fmt[1] == 'R' && fmt[2] == 'b')))
> +               sprint_symbol_stacktrace(sym, value);
>         else if (*fmt != 's')
>                 sprint_symbol(sym, value);
>         else

I prefer the extra "b" flag as well. It helps me to understand and
memorize[*] the meaning.

[*] at least short-time memorize ;-)

Best Regards,
Petr

Re: [PATCH v2 00/12] Add build ID to stacktraces

[Petr Mladek]

On Thu 2021-03-25 16:21:46, Stephen Boyd wrote:
> Quoting peter enderborg (2021-03-25 04:06:17)
> > On 3/24/21 9:55 AM, Christoph Hellwig wrote:
> > > On Tue, Mar 23, 2021 at 07:04:31PM -0700, Stephen Boyd wrote:
> > >>  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]
> > > Yikes.  No, please do not make the backtraces a complete mess for
> > > something that serves absolutely no need.
> 
> It serves a need. Please look at the patches to understand that I'm
> adding the buildid to automatically find the associated debug
> information on distros.
> 
> > 
> > Would a "verbose" flag be acceptable solution?    Something like write 1 to /sys/kernel/debug/verbose_stack to get the extra info.
> > 
> > I think I see a need for it.
> > 
> 
> Or a kernel config option and a commandline parameter? That would be OK
> for me as I said on v1 of this series. I'll add that in for the next
> patch series given all the distaste for some more hex characters next to
> the module name.

IMHO, a build configure option would fit the best here.

It does not make sense to show the ID when the kernel vendor does
not have a service to download the related binaries. But it makes
sense to show the buildid by default when the provider/distro has
the service and want to use the ID when handling bug reports.

We could always add boot/run time options when people really need it.

Best Regards,
Petr

Re: [PATCH v2 04/12] module: Add printk format to add module build ID to stacktraces

[Stephen Boyd]

Quoting Petr Mladek (2021-03-30 03:29:24)
> On Tue 2021-03-23 19:04:35, 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.
> > 
> > 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
> 
> I tested it with "echo l >/proc/sysrq-trigger" and I got the following
> output:
> 
> [   71.905593] CPU: 0 PID: 1762 Comm: bash Kdump: loaded Not tainted 5.12.0-rc5-default+ #167 00000080ffffffff0000000000000000
> 00000000
> 
> It does not looks like an unique build-id.
> Any idea what was going wrong?

Hmm not sure. What does 'hexdump /sys/kernel/notes' show or 'file
vmlinux' parse out of the kernel image?

> 
> > --- a/include/linux/kallsyms.h
> > +++ b/include/linux/kallsyms.h
> > @@ -91,6 +93,7 @@ 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_stacktrace(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);
> 
> Could we use a more clear name? It is hard to guess what is
> the difference between sprint_*_stacktrace() and sprint_backtrace().
> 
> What about sprint_symbol_build_id() ?

Sure.

> 
> 
> > diff --git a/kernel/module.c b/kernel/module.c
> > index 30479355ab85..9e9cb502fb33 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;
> > +     }
> 
> Just to be sure. Is this really reliable way how to find the build ID,
> please?
> 

The build ID is always part of a note section, so if we parse the notes
and find a build ID type of section (see nhdr->n_type == BUILD_ID) with
a GNU name then we know we have the right section and will be able to
parse the ID out of the buffer.