From 68d36578e9a840c088e0f73c41416ff9b30cb79b Mon Sep 17 00:00:00 2001
From: Valerii Chernous <vchernou@cisco.com>
Date: Thu, 28 Oct 2021 05:19:19 -0700
Subject: [PATCH] ignore build-id for linker inputs if new requested

Issue description:
building of glibc 2.32 and later with option "-Wl,--build-id" produce libc.so.6
with section ".note.gnu.build-id" that have invalid(double, 0x48) section size.
It happens because glibc use sublibraries for linking libc.so.6
ld produce this sublibraries with build-id section and on last
linking stage loads this sections as input for linking.
ld should create new(valid) ".note.gnu.build-id" into function
ldelf_setup_build_id on last linking stage but it skip creating because
build-id section already exists.
As result libc.so.6 contain ".note.gnu.build-id" with build-ids from
sublibraries and without valid build-id
Howto solved:
Ignoring ".note.gnu.build-id" on linker input fix this problem.
Linker input doesn't have invalid build-id sections on ldelf_setup_build_id
stage and create new(proper) one for output library/binary

Clang have it's own fix for this issue:
https://reviews.llvm.org/D42823
https://bugs.llvm.org/show_bug.cgi?id=36203

howto reproduce:
yocto:
cd GLIBC_RECIPE_WORKDIR
export CMD_PREFIX="./recipe-sysroot-native/usr/bin/x86_64-iosxe-linux/x86_64-iosxe-linux"; export GCC="$CMD_PREFIX-gcc"; export RELF="$CMD_PREFIX-readelf"
echo "void f1(){}" >f1.c
echo "void f2(){}" >f2.c
$GCC f1.c -c -o f1.o
$GCC f2.c -c -o f2.o
$GCC f1.o -Wl,--build-id -nostdlib -nostartfiles -r -o f1
$GCC f2.o -Wl,--build-id -nostdlib -nostartfiles -r -o f2
$GCC ./f1 ./f2 -shared -Wl,--build-id -nostdlib -nostartfiles -o f.so
$RELF -S f.so | grep -E -A1 "note.gnu.bu"

ubuntu:
echo "void f1(){}" >f1.c
echo "void f2(){}" >f2.c
gcc f1.c -c -o f1.o
gcc f2.c -c -o f2.o
gcc f1.o -Wl,--build-id -nostdlib -nostartfiles -r -o f1
gcc f2.o -Wl,--build-id -nostdlib -nostartfiles -r -o f2
gcc ./f1 ./f2 -shared -Wl,--build-id -nostdlib -nostartfiles -o f.so
readelf -S f.so | grep -E -A1 "note.gnu.bu"

output:
without fix
  [ 1] .note.gnu.bu[...] NOTE             0000000000000238  00000238
       0000000000000048  0000000000000000   A       0     0     4
with fix
  [ 1] .note.gnu.bu[...] NOTE             0000000000000238  00000238
       0000000000000024  0000000000000000   A       0     0     4

Signed-off-by: Valerii Chernous <vchernou@cisco.com>
---
 bfd/bfd-in2.h | 2 ++
 bfd/elf.c     | 4 ++++
 ld/ldfile.c   | 5 +++++
 3 files changed, 11 insertions(+)

diff --git a/bfd/bfd-in2.h b/bfd/bfd-in2.h
index 7b7a329cd62..5a91e14f6f9 100644
--- a/bfd/bfd-in2.h
+++ b/bfd/bfd-in2.h
@@ -6851,6 +6851,8 @@ struct bfd
 
   /* For input BFDs, the build ID, if the object has one. */
   const struct bfd_build_id *build_id;
+  /* linker set this flag if create build-id requested by cmd line or default */
+  int is_new_build_id_requested;
 };
 
 static inline const char *
diff --git a/bfd/elf.c b/bfd/elf.c
index cfdb94922f3..24a1dc44731 100644
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -2100,6 +2100,10 @@ bfd_section_from_shdr (bfd *abfd, unsigned int shindex)
     case SHT_PREINIT_ARRAY:	/* .preinit_array section.  */
     case SHT_GNU_LIBLIST:	/* .gnu.liblist section.  */
     case SHT_GNU_HASH:		/* .gnu.hash section.  */
+
+    /* skip .note.gnu.build-id section for linker input if create new one requested */
+      if (hdr->sh_type == SHT_NOTE && abfd->is_linker_input == 1 && abfd->is_new_build_id_requested == 1 && strncmp(name, ".note.gnu.build-id", strlen(".note.gnu.build-id")) == 0 )
+	goto success;
       ret = _bfd_elf_make_section_from_shdr (abfd, hdr, name, shindex);
       goto success;
 
diff --git a/ld/ldfile.c b/ld/ldfile.c
index 22271fd6810..e28cf297057 100644
--- a/ld/ldfile.c
+++ b/ld/ldfile.c
@@ -34,6 +34,7 @@
 #include "ldemul.h"
 #include "libiberty.h"
 #include "filenames.h"
+#include "ldelf.h"
 #if BFD_SUPPORTS_PLUGINS
 #include "plugin-api.h"
 #include "plugin.h"
@@ -155,6 +156,10 @@ ldfile_try_open_bfd (const char *attempt,
     entry->the_bfd->lto_output = 1;
 #endif
 
+  /* if new build-id required, inform bfd/elf.c about it */
+  if (ldelf_emit_note_gnu_build_id != NULL)
+    entry->the_bfd->is_new_build_id_requested = 1;
+
   /* If we are searching for this file, see if the architecture is
      compatible with the output file.  If it isn't, keep searching.
      If we can't open the file as an object file, stop the search
-- 
2.26.2.Cisco