binutils causes GLIBC ifunc breakage on PowerPC64 ELFv2

binutils causes GLIBC ifunc breakage on PowerPC64 ELFv2

[Aurelien Jarno]

Hi,

Building GNU libc using binutils HEAD, I have noticed that the following
tests fails on PowerPC64 ELFv2:

| FAIL: elf/ifuncmain1staticpic
| FAIL: elf/ifuncmain4
| FAIL: elf/ifuncmain5staticpic

The last one segfault, while two first ones actually fails to build:

| gcc -nostdlib -nostartfiles -o /build/glibc/glibc-build/elf/ifuncmain4    -Wl,-z,combreloc -Wl,-z,relro -Wl,--hash-style=both /build/glibc/glibc-build/csu/crt1.o /build/glibc/glibc-build/csu/crti.o `gcc  --print-file-name=crtbegin.o` /build/glibc/glibc-build/elf/ifuncmain4.o  -Wl,-dynamic-linker=/lib64/ld64.so.2 -Wl,-rpath-link=/build/glibc/glibc-build:/build/glibc/glibc-build/math:/build/glibc/glibc-build/elf:/build/glibc/glibc-build/dlfcn:/build/glibc/glibc-build/nss:/build/glibc/glibc-build/nis:/build/glibc/glibc-build/rt:/build/glibc/glibc-build/resolv:/build/glibc/glibc-build/crypt:/build/glibc/glibc-build/nptl /build/glibc/glibc-build/libc.so.6 /build/glibc/glibc-build/libc_nonshared.a -Wl,--as-needed /build/glibc/glibc-build/elf/ld.so -Wl,--no-as-needed -lgcc -Wl,--as-needed -lgcc_s  -Wl,--no-as-needed `gcc  --print-file-name=crtend.o` /build/glibc/glibc-build/csu/crtn.o
| /build/glibc/toolchain/bin/ld: BFD (GNU Binutils) 2.24.51.20140817 internal error, aborting at elf64-ppc.c line 14483 in ppc64_elf_relocate_section
| 
| /build/glibc/toolchain/bin/ld: Please report this bug.
| 
| collect2: error: ld returned 1 exit status

| gcc -pie -Wl,-O1 -nostdlib -nostartfiles -o /build/glibc/glibc-build/elf/ifuncmain1vispie    -Wl,-z,combreloc -Wl,-z,relro -Wl,--hash-style=both /build/glibc/glibc-build/csu/Scrt1.o /build/glibc/glibc-build/csu/crti.o `gcc  --print-file-name=crtbeginS.o` /build/glibc/glibc-build/elf/ifuncmain1vispie.o /build/glibc/glibc-build/elf/ifuncmod1.so  -Wl,-dynamic-linker=/lib64/ld64.so.2 -Wl,-rpath-link=/build/glibc/glibc-build:/build/glibc/glibc-build/math:/build/glibc/glibc-build/elf:/build/glibc/glibc-build/dlfcn:/build/glibc/glibc-build/nss:/build/glibc/glibc-build/nis:/build/glibc/glibc-build/rt:/build/glibc/glibc-build/resolv:/build/glibc/glibc-build/crypt:/build/glibc/glibc-build/nptl /build/glibc/glibc-build/libc.so.6 /build/glibc/glibc-build/libc_nonshared.a -Wl,--as-needed /build/glibc/glibc-build/elf/ld.so -Wl,--no-as-needed -lgcc -Wl,--as-needed -lgcc_s  -Wl,--no-as-needed `gcc  --print-file-name=crtendS.o` /build/glibc/glibc-build/csu/crtn.o
| /build/glibc/toolchain/bin/ld: BFD (GNU Binutils) 2.24.51.20140817 internal error, aborting at elf64-ppc.c line 14483 in ppc64_elf_relocate_section
|
| /build/glibc/toolchain/bin/ld: Please report this bug.
| 
| collect2: error: ld returned 1 exit status

Bisecting the issue I have found the problem has been introduced by this
commit:

| commit d1eca1e41ddae8c3cd925be827640de919301432
| Author: Alan Modra <amodra@gmail.com>
| Date:   Wed Jul 2 15:07:18 2014 +0930
| 
|     Taking an undefined function's address in an executable
| 
|     doesn't always mean you need to define a function symbol on plt code.
|     If all references are in read-write sections, then using dynamic relocs
|     is OK.
| 
|     bfd/
|         * elf32-ppc.c (ppc_elf_adjust_dynamic_symbol): Clear
|         pointer_equality_needed when !readonly_dynrelocs.
|         * elf64-ppc.c (ppc64_elf_adjust_dynamic_symbol): Likewise.
|     ld/testsuite/
|         * ld-powerpc/ambiguousv1.d: Match symbol table too.
|         * ld-powerpc/ambiguousv2.d: Likewise.
|         * ld-powerpc/ambiguousv1b.d: New.
|         * ld-powerpc/ambiguousv2b.d: New.
|         * ld-powerpc/powerpc.exp: Run new tests.

Reverting this commit on top on current binutils HEAD makes the GNU libc
testsuite to pass. Do you have an idea what could be the problem? I
guess you will be able to reproduce by yourself, if not don't hesitate
to ask for more details.

Thanks,
Aurelien

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net

Re: binutils causes GLIBC ifunc breakage on PowerPC64 ELFv2

[Alan Modra]

On Sun, Aug 17, 2014 at 04:10:05PM +0200, Aurelien Jarno wrote:
> Bisecting the issue I have found the problem has been introduced by this
> commit:
> 
> | commit d1eca1e41ddae8c3cd925be827640de919301432
> | Author: Alan Modra <amodra@gmail.com>
> | Date:   Wed Jul 2 15:07:18 2014 +0930
> | 
> |     Taking an undefined function's address in an executable
> | 
> |     doesn't always mean you need to define a function symbol on plt code.
> |     If all references are in read-write sections, then using dynamic relocs
> |     is OK.

Thanks for tracking this down.

This probably could be fixed by making changes in relocate_section for
ifunc, but it's simpler to disable this optimisation for ifunc.

	* elf64-ppc.c (ppc64_elf_adjust_dynamic_symbol): Don't attempt to
	use dynrelocs for ifunc.
	* elf32-ppc.c (ppc_elf_adjust_dynamic_symbol): Similarly.

diff --git a/bfd/elf64-ppc.c b/bfd/elf64-ppc.c
index 0efc602..ca2dd4c 100644
--- a/bfd/elf64-ppc.c
+++ b/bfd/elf64-ppc.c
@@ -7002,6 +7002,7 @@ ppc64_elf_adjust_dynamic_symbol (struct bfd_link_info *info,
 	     executable on a global entry stub.  A dynamic reloc can
 	     be used instead.  */
 	  if (h->pointer_equality_needed
+	      && h->type != STT_GNU_IFUNC
 	      && !readonly_dynrelocs (h))
 	    {
 	      h->pointer_equality_needed = 0;
diff --git a/bfd/elf32-ppc.c b/bfd/elf32-ppc.c
index e20e804..97f4724 100644
--- a/bfd/elf32-ppc.c
+++ b/bfd/elf32-ppc.c
@@ -5512,9 +5512,12 @@ ppc_elf_adjust_dynamic_symbol (struct bfd_link_info *info,
 	{
 	  /* Taking a function's address in a read/write section
 	     doesn't require us to define the function symbol in the
-	     executable on a global entry stub.  A dynamic reloc can
+	     executable on a plt call stub.  A dynamic reloc can
 	     be used instead.  */
 	  if (h->pointer_equality_needed
+	      && h->type != STT_GNU_IFUNC
+	      && !htab->is_vxworks
+	      && !ppc_elf_hash_entry (h)->has_sda_refs
 	      && !readonly_dynrelocs (h))
 	    {
 	      h->pointer_equality_needed = 0;

-- 
Alan Modra

Re: binutils causes GLIBC ifunc breakage on PowerPC64 ELFv2

[Aurelien Jarno]

On Mon, Aug 18, 2014 at 08:57:55PM +0930, Alan Modra wrote:
> On Sun, Aug 17, 2014 at 04:10:05PM +0200, Aurelien Jarno wrote:
> > Bisecting the issue I have found the problem has been introduced by this
> > commit:
> > 
> > | commit d1eca1e41ddae8c3cd925be827640de919301432
> > | Author: Alan Modra <amodra@gmail.com>
> > | Date:   Wed Jul 2 15:07:18 2014 +0930
> > | 
> > |     Taking an undefined function's address in an executable
> > | 
> > |     doesn't always mean you need to define a function symbol on plt code.
> > |     If all references are in read-write sections, then using dynamic relocs
> > |     is OK.
> 
> Thanks for tracking this down.
> 
> This probably could be fixed by making changes in relocate_section for
> ifunc, but it's simpler to disable this optimisation for ifunc.
> 
> 	* elf64-ppc.c (ppc64_elf_adjust_dynamic_symbol): Don't attempt to
> 	use dynrelocs for ifunc.
> 	* elf32-ppc.c (ppc_elf_adjust_dynamic_symbol): Similarly.

Thanks for the quick patch. I confirm it fixes the problem for elf64.
Unfortunately I don't have a full toolchain ready to test the elf32
case.

Aurelien

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net