[PATCH] xsplice: Use ld-embedded build-ids

[Martin Pohlack <mpohlack@amazon.de>]

Todo:
  * Should be moved to sysctl to only allow Dom0 access
  * Maybe convert to binary transport to userland instead of printable form

* use ld to actually embed the build ID
* convert to textual representation in hypervisor and report in
  printable form

Signed-off-by: Martin Pohlack <mpohlack@amazon.de>
---
 xen/arch/x86/Makefile        |  4 ++--
 xen/arch/x86/xen.lds.S       |  5 +++++
 xen/common/kernel.c          | 33 +++++++++++++++++++++++++++++----
 xen/common/version.c         |  5 -----
 xen/include/xen/compile.h.in |  1 -
 5 files changed, 36 insertions(+), 12 deletions(-)

diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 5f24951..f724bd8 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -108,11 +108,11 @@ $(TARGET)-syms: prelink.o xen.lds $(BASEDIR)/common/symbols-dummy.o
 	    $(BASEDIR)/common/symbols-dummy.o -o $(@D)/.$(@F).0
 	$(NM) -n $(@D)/.$(@F).0 | $(BASEDIR)/tools/symbols >$(@D)/.$(@F).0.S
 	$(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).0.o
-	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o \
+	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o --build-id=sha1 \
 	    $(@D)/.$(@F).0.o -o $(@D)/.$(@F).1
 	$(NM) -n $(@D)/.$(@F).1 | $(BASEDIR)/tools/symbols >$(@D)/.$(@F).1.S
 	$(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).1.o
-	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o \
+	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o --build-id=sha1 \
 	    $(@D)/.$(@F).1.o -o $@
 	rm -f $(@D)/.$(@F).[0-9]*
 
diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
index 6553cff..2176782 100644
--- a/xen/arch/x86/xen.lds.S
+++ b/xen/arch/x86/xen.lds.S
@@ -67,6 +67,11 @@ SECTIONS
        *(.rodata.*)
   } :text
 
+  .note.gnu.build-id : {
+      __note_gnu_build_id_start = .;
+      *(.note.gnu.build-id)
+  } :text
+
   . = ALIGN(SMP_CACHE_BYTES);
   .data.read_mostly : {
        /* Exception table */
diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index e9d41b6..9814585 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -6,9 +6,11 @@
 
 #include <xen/init.h>
 #include <xen/lib.h>
+#include <xen/elf.h>
 #include <xen/errno.h>
 #include <xen/version.h>
 #include <xen/sched.h>
+#include <xen/types.h>
 #include <xen/paging.h>
 #include <xen/nmi.h>
 #include <xen/guest_access.h>
@@ -227,6 +229,10 @@ void __init do_initcalls(void)
  * Simple hypercalls.
  */
 
+#define NT_GNU_BUILD_ID 3
+
+extern char * __note_gnu_build_id_start;  /* defined in linker script */
+
 DO(xen_version)(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
 {
     switch ( cmd )
@@ -360,11 +366,30 @@ DO(xen_version)(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
 
     case XENVER_build_id:
     {
-        xen_build_id_t build_id;
+        xen_build_id_t ascii_id;
+        Elf_Note * n = (Elf_Note *)&__note_gnu_build_id_start;
+        char * binary_id;
+        int i;
+
+        memset(ascii_id, 0, sizeof(ascii_id));
+
+        /* check if we really have a build-id */
+        if ( NT_GNU_BUILD_ID != n->type )
+            return 0;
+
+        /* sanity check, name should be "GNU" for ld-generated build-id */
+        if ( 0 != strncmp(ELFNOTE_NAME(n), "GNU", n->namesz))
+            return 0;
+
+        binary_id = (char *)ELFNOTE_DESC(n);
+
+        /* convert to printable format */
+        for (i = 0; i < n->descsz && (i + 1) * 2 < sizeof(xen_build_id_t); i++)
+        {
+            snprintf(&ascii_id[i * 2], 3, "%02hhx", binary_id[i]);
+        }
 
-        memset(build_id, 0, sizeof(build_id));
-        safe_strcpy(build_id, xen_build_id());
-        if ( copy_to_guest(arg, build_id, ARRAY_SIZE(build_id)) )
+        if ( copy_to_guest(arg, ascii_id, ARRAY_SIZE(ascii_id)) )
             return -EFAULT;
         return 0;
     }
diff --git a/xen/common/version.c b/xen/common/version.c
index 5c3dbb0..b152e27 100644
--- a/xen/common/version.c
+++ b/xen/common/version.c
@@ -55,8 +55,3 @@ const char *xen_banner(void)
 {
     return XEN_BANNER;
 }
-
-const char *xen_build_id(void)
-{
-    return XEN_BUILD_ID;
-}
diff --git a/xen/include/xen/compile.h.in b/xen/include/xen/compile.h.in
index 939685e..440ecb2 100644
--- a/xen/include/xen/compile.h.in
+++ b/xen/include/xen/compile.h.in
@@ -10,5 +10,4 @@
 #define XEN_EXTRAVERSION	"@@extraversion@@"
 
 #define XEN_CHANGESET		"@@changeset@@"
-#define XEN_BUILD_ID        "@@changeset@@"
 #define XEN_BANNER		\
-- 
2.5.0

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