build_id: Provide ld-embedded build-ids

This patch enables the Elf to be built with the build-id
and provide in the Xen hypervisor the code to extract it.

The man-page for ld --build-id says it is:

"Request the creation of a ".note.gnu.build-id" ELF note
section or a ".build-id" COFF section.  The contents of the
note are unique bits identifying this linked file. style can be
"uuid" to use 128 random bits, "sha1" to use a 160-bit SHA1 hash
on the normative parts of the output contents, ..."

One can also retrieve the value of the build-id by doing
'readelf -n xen-syms'.

For EFI builds we re-use the same build-id that the xen-syms
was built with.

The version of ld that first implemented --build-id is v2.18.
We check for to see if the linker supports the --build-id
parameter and if so use it.

For x86 we have two binaries - the xen-syms and the xen - an
smaller version with lots of sections removed. To make it possible
for readelf -n xen we also modify mkelf32 and xen.lds.S to include
the PT_NOTE ELF section.

The EFI binary is more complicated. We only build one type of
binary and expanding the amount of sections the EFI binary has to
include an .note one is pointless - as there is no concept of
PT_NOTE. The best we can do is move this .note in the .rodata section.

Further development wise should move it to .buildid section
so that DataDirectory debug data nor CodeView can view it.
(The author has no clue what those are).

Note that in earlier patches the linker script had:

 __note_gnu_build_id_start = .;
 *(.rodata.note.gnu.build-id)
 __note_gnu_build_id_end = .;
 *(.note)
 *(.note.*)

Which meant you could have different ELF notes _outside_ the
__note_gnu_build_id_end. However for EFI builds we take the whole
.note* section and jam it in the EFI to be between
__note_gnu_build_id_start and __note_gnu_build_id_end.
To not make this happend we make on the ELF build the section
be called .note.gnu.build-id  (instead of just .note).
If there is a need for a different type of note other folks
can add it as a different section name.

Note that we do call --binary-id=sha1 on all linker invocations.
We have to do to enforce that the symbol offsets don't changes
(the side effect is that we we would have multiple binary ids -
except that the last one is the final one).

Without this working the symbol table embedded in Xen ends
up incorrect - some of the values it contains would be offset by the
size of the included build id.

This obviously causes problems when resolving symbols.

We also define the NT_GNU_BUILD_ID in the elfstructs.h as we
need to use it in various places.

Suggested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Martin Pohlack <mpohlack@amazon.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

Config.mk

@@ -135,6 +135,17 @@ endef
 check-$(gcc) = $(call cc-ver-check,CC,0x040100,"Xen requires at least gcc-4.1")
 $(eval $(check-y))
 
+ld-ver-build-id = $(shell $(1) --build-id 2>&1 | \
+					grep -q build-id && echo n || echo y)
+
+export XEN_HAS_BUILD_ID ?= n
+ifeq ($(call ld-ver-build-id,$(LD)),n)
+build_id_linker :=
+else
+CFLAGS += -DBUILD_ID
+build_id_linker := --build-id=sha1
+endif
+
 # as-insn: Check whether assembler supports an instruction.
 # Usage: cflags-y += $(call as-insn "insn",option-yes,option-no)
 as-insn = $(if $(shell echo 'void _(void) { asm volatile ( $(2) ); }' \

xen/arch/arm/Makefile

@@ -93,7 +93,7 @@ $(TARGET)-syms: prelink.o xen.lds $(BASEDIR)/common/symbols-dummy.o
 	$(NM) -pa --format=sysv $(@D)/.$(@F).1 \
 		| $(BASEDIR)/tools/symbols --sysv --sort >$(@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_linker) \
 	    $(@D)/.$(@F).1.o -o $@
 	rm -f $(@D)/.$(@F).[0-9]*
 

xen/arch/arm/xen.lds.S

@@ -22,6 +22,9 @@ OUTPUT_ARCH(FORMAT)
 PHDRS
 {
   text PT_LOAD /* XXX should be AT ( XEN_PHYS_START ) */ ;
+#if defined(BUILD_ID)
+  note PT_NOTE ;
+#endif
 }
 SECTIONS
 {
@@ -57,10 +60,18 @@ SECTIONS
        *(.lockprofile.data)
        __lock_profile_end = .;
 #endif
-
-        _erodata = .;          /* End of read-only data */
   } :text
 
+#if defined(BUILD_ID)
+  . = ALIGN(4);
+  .note.gnu.build-id : {
+       __note_gnu_build_id_start = .;
+       *(.note.gnu.build-id)
+       __note_gnu_build_id_end = .;
+  } :note :text
+#endif
+  _erodata = .;                /* End of read-only data */
+
   .data : {                    /* Data */
        . = ALIGN(PAGE_SIZE);
        *(.data.page_aligned)

xen/arch/x86/Makefile

@@ -74,6 +74,12 @@ efi-y := $(shell if [ ! -r $(BASEDIR)/include/xen/compile.h -o \
                       -O $(BASEDIR)/include/xen/compile.h ]; then \
                          echo '$(TARGET).efi'; fi)
 
+ifneq ($(build_id_linker),)
+notes_phdrs = --notes
+else
+notes_phdrs =
+endif
+
 ifdef CONFIG_XSPLICE
 all_symbols = --all-symbols
 ifdef CONFIG_FAST_SYMBOL_LOOKUP
@@ -84,7 +90,7 @@ all_symbols =
 endif
 
 $(TARGET): $(TARGET)-syms $(efi-y) boot/mkelf32
-	./boot/mkelf32 $(TARGET)-syms $(TARGET) 0x100000 \
+	./boot/mkelf32 $(notes_phdrs) $(TARGET)-syms $(TARGET) 0x100000 \
 	`$(NM) -nr $(TARGET)-syms | head -n 1 | sed -e 's/^\([^ ]*\).*/0x\1/'`
 
 .PHONY: tests
@@ -119,22 +125,28 @@ $(BASEDIR)/common/symbols-dummy.o:
 	$(MAKE) -f $(BASEDIR)/Rules.mk -C $(BASEDIR)/common symbols-dummy.o
 
 $(TARGET)-syms: prelink.o xen.lds $(BASEDIR)/common/symbols-dummy.o
-	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o \
+	$(LD) $(LDFLAGS) -T xen.lds -N prelink.o $(build_id_linker) \
 	    $(BASEDIR)/common/symbols-dummy.o -o $(@D)/.$(@F).0
 	$(NM) -pa --format=sysv $(@D)/.$(@F).0 \
 		| $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort \
 		>$(@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_linker) \
 	    $(@D)/.$(@F).0.o -o $(@D)/.$(@F).1
 	$(NM) -pa --format=sysv $(@D)/.$(@F).1 \
 		| $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort --warn-dup \
 		>$(@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_linker) \
 	    $(@D)/.$(@F).1.o -o $@
 	rm -f $(@D)/.$(@F).[0-9]*
 
+note.o: $(TARGET)-syms
+	$(OBJCOPY) -O binary --only-section=.note.gnu.build-id  $(BASEDIR)/xen-syms $@.bin
+	$(OBJCOPY) -I binary -O elf64-x86-64 -B i386:x86-64 \
+		--rename-section=.data=.note.gnu.build-id -S $@.bin $@
+	rm -f $@.bin
+
 EFI_LDFLAGS = $(patsubst -m%,-mi386pep,$(LDFLAGS)) --subsystem=10
 EFI_LDFLAGS += --image-base=$(1) --stack=0,0 --heap=0,0 --strip-debug
 EFI_LDFLAGS += --section-alignment=0x200000 --file-alignment=0x20
@@ -147,6 +159,13 @@ $(TARGET).efi: VIRT_BASE = 0x$(shell $(NM) efi/relocs-dummy.o | sed -n 's, A VIR
 $(TARGET).efi: ALT_BASE = 0x$(shell $(NM) efi/relocs-dummy.o | sed -n 's, A ALT_START$$,,p')
 # Don't use $(wildcard ...) here - at least make 3.80 expands this too early!
 $(TARGET).efi: guard = $(if $(shell echo efi/dis* | grep disabled),:)
+ifneq ($(build_id_linker),)
+$(TARGET).efi: note.o
+note_file := note.o
+else
+note_file :=
+endif
+
 $(TARGET).efi: prelink-efi.o efi.lds efi/relocs-dummy.o $(BASEDIR)/common/symbols-dummy.o efi/mkreloc
 	$(foreach base, $(VIRT_BASE) $(ALT_BASE), \
 	          $(guard) $(LD) $(call EFI_LDFLAGS,$(base)) -T efi.lds -N $< efi/relocs-dummy.o \
@@ -163,7 +182,7 @@ $(TARGET).efi: prelink-efi.o efi.lds efi/relocs-dummy.o $(BASEDIR)/common/symbol
 		| $(guard) $(BASEDIR)/tools/symbols $(all_symbols) --sysv --sort >$(@D)/.$(@F).1s.S
 	$(guard) $(MAKE) -f $(BASEDIR)/Rules.mk $(@D)/.$(@F).1r.o $(@D)/.$(@F).1s.o
 	$(guard) $(LD) $(call EFI_LDFLAGS,$(VIRT_BASE)) -T efi.lds -N $< \
-	                $(@D)/.$(@F).1r.o $(@D)/.$(@F).1s.o -o $@
+	                $(@D)/.$(@F).1r.o $(@D)/.$(@F).1s.o $(note_file) -o $@
 	if $(guard) false; then rm -f $@; echo 'EFI support disabled'; fi
 	rm -f $(@D)/.$(@F).[0-9]*
 
@@ -195,4 +214,5 @@ clean::
 	rm -f $(BASEDIR)/.xen-syms.[0-9]* boot/.*.d
 	rm -f $(BASEDIR)/.xen.efi.[0-9]* efi/*.o efi/.*.d efi/*.efi efi/disabled efi/mkreloc
 	rm -f boot/reloc.S boot/reloc.lnk boot/reloc.bin
+	rm -f note.o
 	$(MAKE) -f $(BASEDIR)/Rules.mk -C test clean

xen/arch/x86/boot/mkelf32.c

@@ -45,9 +45,9 @@ static Elf32_Ehdr out_ehdr = {
     0,                                       /* e_flags */
     sizeof(Elf32_Ehdr),                      /* e_ehsize */
     sizeof(Elf32_Phdr),                      /* e_phentsize */
-    1,                                       /* e_phnum */
+    1,  /* modify based on num_phdrs */      /* e_phnum */
     sizeof(Elf32_Shdr),                      /* e_shentsize */
-    3,                                       /* e_shnum */
+    3,  /* modify based on num_phdrs */      /* e_shnum */
     2                                        /* e_shstrndx */
 };
 
@@ -61,8 +61,20 @@ static Elf32_Phdr out_phdr = {
     PF_R|PF_W|PF_X,                          /* p_flags */
     64                                       /* p_align */
 };
+static Elf32_Phdr note_phdr = {
+    PT_NOTE,                                 /* p_type */
+    DYNAMICALLY_FILLED,                      /* p_offset */
+    DYNAMICALLY_FILLED,                      /* p_vaddr */
+    DYNAMICALLY_FILLED,                      /* p_paddr */
+    DYNAMICALLY_FILLED,                      /* p_filesz */
+    DYNAMICALLY_FILLED,                      /* p_memsz */
+    PF_R,                                    /* p_flags */
+    4                                        /* p_align */
+};
 
 static u8 out_shstrtab[] = "\0.text\0.shstrtab";
+/* If num_phdrs >= 2, we need to tack the .note. */
+static u8 out_shstrtab_extra[] = ".note\0";
 
 static Elf32_Shdr out_shdr[] = {
     { 0 },
@@ -90,6 +102,23 @@ static Elf32_Shdr out_shdr[] = {
     }
 };
 
+/*
+ * The 17 points to the '.note' in the out_shstrtab and out_shstrtab_extra
+ * laid out in the file.
+ */
+static Elf32_Shdr out_shdr_note = {
+      17,                                    /* sh_name */
+      SHT_NOTE,                              /* sh_type */
+      0,                                     /* sh_flags */
+      DYNAMICALLY_FILLED,                    /* sh_addr */
+      DYNAMICALLY_FILLED,                    /* sh_offset */
+      DYNAMICALLY_FILLED,                    /* sh_size */
+      0,                                     /* sh_link */
+      0,                                     /* sh_info */
+      4,                                     /* sh_addralign */
+      0                                      /* sh_entsize */
+};
+
 /* Some system header files define these macros and pollute our namespace. */
 #undef swap16
 #undef swap32
@@ -228,28 +257,34 @@ static void do_read(int fd, void *data, int len)
 int main(int argc, char **argv)
 {
     u64        final_exec_addr;
-    u32        loadbase, dat_siz, mem_siz;
+    u32        loadbase, dat_siz, mem_siz, note_base, note_sz, offset;
     char      *inimage, *outimage;
     int        infd, outfd;
     char       buffer[1024];
-    int        bytes, todo, i;
+    int        bytes, todo, i = 1;
+    int        num_phdrs = 1;
 
     Elf32_Ehdr in32_ehdr;
 
     Elf64_Ehdr in64_ehdr;
     Elf64_Phdr in64_phdr;
 
-    if ( argc != 5 )
+    if ( argc < 5 )
     {
-        fprintf(stderr, "Usage: mkelf32 <in-image> <out-image> "
+        fprintf(stderr, "Usage: mkelf32 [--notes] <in-image> <out-image> "
                 "<load-base> <final-exec-addr>\n");
         return 1;
     }
 
-    inimage  = argv[1];
+    if ( !strcmp(argv[1], "--notes") )
-    outimage = argv[2];
+    {
-    loadbase = strtoul(argv[3], NULL, 16);
+        i = 2;
-    final_exec_addr = strtoull(argv[4], NULL, 16);
+        num_phdrs = 2;
+    }
+    inimage  = argv[i++];
+    outimage = argv[i++];
+    loadbase = strtoul(argv[i++], NULL, 16);
+    final_exec_addr = strtoull(argv[i++], NULL, 16);
 
     infd = open(inimage, O_RDONLY);
     if ( infd == -1 )
@@ -285,11 +320,10 @@ int main(int argc, char **argv)
                 (int)in64_ehdr.e_phentsize, (int)sizeof(in64_phdr));
         return 1;
     }
-
+    if ( in64_ehdr.e_phnum != num_phdrs )
-    if ( in64_ehdr.e_phnum != 1 )
     {
-        fprintf(stderr, "Expect precisly 1 program header; found %d.\n",
+        fprintf(stderr, "Expect precisly %d program header; found %d.\n",
-                (int)in64_ehdr.e_phnum);
+                num_phdrs, (int)in64_ehdr.e_phnum);
         return 1;
     }
 
@@ -304,6 +338,32 @@ int main(int argc, char **argv)
     /*mem_siz = (u32)in64_phdr.p_memsz;*/
     mem_siz = (u32)(final_exec_addr - in64_phdr.p_vaddr);
 
+    note_sz = note_base = offset = 0;
+    if ( num_phdrs > 1 )
+    {
+        offset = in64_phdr.p_offset;
+        note_base = in64_phdr.p_vaddr;
+
+        (void)lseek(infd, in64_ehdr.e_phoff+sizeof(in64_phdr), SEEK_SET);
+        do_read(infd, &in64_phdr, sizeof(in64_phdr));
+        endianadjust_phdr64(&in64_phdr);
+
+        (void)lseek(infd, offset, SEEK_SET);
+
+        note_sz = in64_phdr.p_memsz;
+        note_base = in64_phdr.p_vaddr - note_base;
+
+        if ( in64_phdr.p_offset > dat_siz || offset > in64_phdr.p_offset )
+        {
+            fprintf(stderr, "Expected .note section within .text section!\n" \
+                    "Offset %ld not within %d!\n",
+                    in64_phdr.p_offset, dat_siz);
+            return 1;
+        }
+        /* Gets us the absolute offset within the .text section. */
+        offset = in64_phdr.p_offset - offset;
+    }
+
     /*
      * End the image on a page boundary. This gets round alignment bugs
      * in the boot- or chain-loader (e.g., kexec on the XenoBoot CD).
@@ -322,6 +382,31 @@ int main(int argc, char **argv)
     out_shdr[1].sh_size   = dat_siz;
     out_shdr[2].sh_offset = RAW_OFFSET + dat_siz + sizeof(out_shdr);
 
+    if ( num_phdrs > 1 )
+    {
+        /* We have two of them! */
+        out_ehdr.e_phnum = num_phdrs;
+        /* Extra .note section. */
+        out_ehdr.e_shnum++;
+
+        /* Fill out the PT_NOTE program header. */
+        note_phdr.p_vaddr   = note_base;
+        note_phdr.p_paddr   = note_base;
+        note_phdr.p_filesz  = note_sz;
+        note_phdr.p_memsz   = note_sz;
+        note_phdr.p_offset  = offset;
+
+        /* Tack on the .note\0 */
+        out_shdr[2].sh_size += sizeof(out_shstrtab_extra);
+        /* And move it past the .note section. */
+        out_shdr[2].sh_offset += sizeof(out_shdr_note);
+
+        /* Fill out the .note section. */
+        out_shdr_note.sh_size = note_sz;
+        out_shdr_note.sh_addr = note_base;
+        out_shdr_note.sh_offset = RAW_OFFSET + offset;
+    }
+
     outfd = open(outimage, O_WRONLY|O_CREAT|O_TRUNC, 0775);
     if ( outfd == -1 )
     {
@@ -335,8 +420,14 @@ int main(int argc, char **argv)
 
     endianadjust_phdr32(&out_phdr);
     do_write(outfd, &out_phdr, sizeof(out_phdr));
-    
+
-    if ( (bytes = RAW_OFFSET - sizeof(out_ehdr) - sizeof(out_phdr)) < 0 )
+    if ( num_phdrs > 1 )
+    {
+        endianadjust_phdr32(&note_phdr);
+        do_write(outfd, &note_phdr, sizeof(note_phdr));
+    }
+
+    if ( (bytes = RAW_OFFSET - sizeof(out_ehdr) - (num_phdrs * sizeof(out_phdr)) ) < 0 )
     {
         fprintf(stderr, "Header overflow.\n");
         return 1;
@@ -355,9 +446,22 @@ int main(int argc, char **argv)
         endianadjust_shdr32(&out_shdr[i]);
     do_write(outfd, &out_shdr[0], sizeof(out_shdr));
 
-    do_write(outfd, out_shstrtab, sizeof(out_shstrtab));
+    if ( num_phdrs > 1 )
-    do_write(outfd, buffer, 4-((sizeof(out_shstrtab)+dat_siz)&3));
+    {
-
+        endianadjust_shdr32(&out_shdr_note);
+        /* Append the .note section. */
+        do_write(outfd, &out_shdr_note, sizeof(out_shdr_note));
+        /* The normal strings - .text\0.. */
+        do_write(outfd, out_shstrtab, sizeof(out_shstrtab));
+        /* Our .note */
+        do_write(outfd, out_shstrtab_extra, sizeof(out_shstrtab_extra));
+        do_write(outfd, buffer, 4-((sizeof(out_shstrtab)+sizeof(out_shstrtab_extra)+dat_siz)&3));
+    }
+    else
+    {
+        do_write(outfd, out_shstrtab, sizeof(out_shstrtab));
+        do_write(outfd, buffer, 4-((sizeof(out_shstrtab)+dat_siz)&3));
+    }
     close(infd);
     close(outfd);
 

xen/arch/x86/xen.lds.S

@@ -31,6 +31,9 @@ OUTPUT_ARCH(i386:x86-64)
 PHDRS
 {
   text PT_LOAD ;
+#if defined(BUILD_ID) && !defined(EFI)
+  note PT_NOTE ;
+#endif
 }
 SECTIONS
 {
@@ -79,6 +82,16 @@ SECTIONS
        *(.rodata)
        *(.rodata.*)
 
+#if defined(BUILD_ID) && defined(EFI)
+/*
+ * No mechanism to put an PT_NOTE in the EFI file - so put
+ * it in .rodata section. (notes.o supplies us with .note.gnu.build-id).
+ */
+       . = ALIGN(4);
+       __note_gnu_build_id_start = .;
+       *(.note.gnu.build-id)
+       __note_gnu_build_id_end = .;
+#endif
        . = ALIGN(8);
        /* Exception table */
        __start___ex_table = .;
@@ -96,9 +109,24 @@ SECTIONS
        *(.lockprofile.data)
        __lock_profile_end = .;
 #endif
-       _erodata = .;
   } :text
 
+#if defined(BUILD_ID) && !defined(EFI)
+/*
+ * What a strange section name. The reason is that on ELF builds this section
+ * is extracted to notes.o (which then is ingested in the EFI file). But the
+ * compiler may want to inject other things in the .note which we don't care
+ * about - hence this unique name.
+ */
+  . = ALIGN(4);
+  .note.gnu.build-id : {
+       __note_gnu_build_id_start = .;
+       *(.note.gnu.build-id)
+       __note_gnu_build_id_end = .;
+  } :note :text
+#endif
+  _erodata = .;
+
 #ifdef EFI
   . = ALIGN(MB(2));
 #else

xen/common/version.c

@@ -1,6 +1,13 @@
 #include <xen/compile.h>
+#include <xen/init.h>
+#include <xen/errno.h>
+#include <xen/string.h>
+#include <xen/types.h>
+#include <xen/elf.h>
 #include <xen/version.h>
 
+#include <asm/cache.h>
+
 const char *xen_compile_date(void)
 {
     return XEN_COMPILE_DATE;
@@ -61,6 +68,51 @@ const char *xen_deny(void)
     return "<denied>";
 }
 
+static const void *build_id_p __read_mostly;
+static unsigned int build_id_len __read_mostly;
+
+int xen_build_id(const void **p, unsigned int *len)
+{
+    if ( !build_id_len )
+        return -ENODATA;
+
+    *len = build_id_len;
+    *p = build_id_p;
+
+    return 0;
+}
+
+#ifdef BUILD_ID
+/* Defined in linker script. */
+extern const Elf_Note __note_gnu_build_id_start[], __note_gnu_build_id_end[];
+
+static int __init xen_build_init(void)
+{
+    const Elf_Note *n = __note_gnu_build_id_start;
+
+    /* --build-id invoked with wrong parameters. */
+    if ( __note_gnu_build_id_end <= &n[0] )
+        return -ENODATA;
+
+    /* Check for full Note header. */
+    if ( &n[1] > __note_gnu_build_id_end )
+        return -ENODATA;;
+
+    /* Check if we really have a build-id. */
+    if ( NT_GNU_BUILD_ID != n->type )
+        return -ENODATA;
+
+    /* Sanity check, name should be "GNU" for ld-generated build-id. */
+    if ( strncmp(ELFNOTE_NAME(n), "GNU", n->namesz) != 0 )
+        return -ENODATA;
+
+    build_id_len = n->descsz;
+    build_id_p = ELFNOTE_DESC(n);
+
+    return 0;
+}
+__initcall(xen_build_init);
+#endif
 /*
  * Local variables:
  * mode: C

xen/include/xen/elfstructs.h

@@ -40,6 +40,9 @@ typedef uint32_t	Elf64_Word;
 typedef int64_t		Elf64_Sxword;
 typedef uint64_t	Elf64_Xword;
 
+/* Unique build id string format when using --build-id. */
+#define NT_GNU_BUILD_ID 3
+
 /*
  * e_ident[] identification indexes
  * See http://www.caldera.com/developers/gabi/2000-07-17/ch4.eheader.html 

xen/include/xen/version.h

@@ -13,5 +13,6 @@ const char *xen_extra_version(void);
 const char *xen_changeset(void);
 const char *xen_banner(void);
 const char *xen_deny(void);
+int xen_build_id(const void **p, unsigned int *len);
 
 #endif /* __XEN_VERSION_H__ */