Patchwork [v2] Improve IFUNC check

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Submitter Fangrui Song
Date Feb. 10, 2020, 7:14 p.m.
Message ID <20200210191425.52xvvdot7kunt2gc@google.com>
Download mbox | patch
Permalink /patch/37867/
State New
Headers show

Comments

Fangrui Song - Feb. 10, 2020, 7:14 p.m.
On 2020-02-08, Aurelien Jarno wrote:
>On 2020-02-06 10:53, Fangrui Song wrote:
>> On 2020-02-06, Aurelien Jarno wrote:
>> > Hi,
>> >
>> > On 2020-02-04 22:09, Fangrui Song wrote:
>> > > GNU ld's RISCV port does not support IFUNC. ld -no-pie produces no
>> > > relocation and the test passed incorrectly. Be more rigid by testing
>> > > IRELATIVE explicitly.
>> >
>> > Thanks for your patch and sorry for the time to answer, I was testing it
>> > on many architectures. First of all I confirm it fixes the issue when
>> > building glibc with PIE on mips* and riscv64. I also confirm it
>> > introduces no regression on aarch64, armv5, armv7, hppa, m68k, powerpc,
>> > ppc64, ppc64le, s390x and x86_64.
>> >
>> > However it wrongly detects that IFUNC is not supported on sparc64 when
>> > PIE is not in use. Here is the output of of readelf for the non-PIE
>> > case:
>> >
>> > | Relocation section '.rela.dyn' at offset 0x110 contains 1 entry:
>> > |   Offset          Info           Type           Sym. Value    Sym. Name + Addend
>> > | 000000200280  0000000000f8 R_SPARC_JMP_IREL                     100128
>>
>> sparc64 -no-pie does not produce an R_SPARC_IRELATIVE. This looks weird.
>> All other archs emit an R_*_IRELATIVE.
>>
>> Can you dump the assembly (including .text and .[i]plt)?
>> Or can someone with sparc64 experience answer why sparc64 is different
>> here?
>
>Here is the dump of the .iplt section:
>Disassembly of section .iplt:
>
>0000000000200200 <.iplt>:
>        ...
>  200280:       03 00 00 80     sethi  %hi(0x20000), %g1
>  200284:       30 6f ff e7     b,a   %xcc, 200220 <__start+0x1000f8>
>  200288:       01 00 00 00     nop
>  20028c:       01 00 00 00     nop
>  200290:       01 00 00 00     nop
>  200294:       01 00 00 00     nop
>  200298:       01 00 00 00     nop
>  20029c:       01 00 00 00     nop
>
>There is no .text nor .plt section.
>
>-- 
>Aurelien Jarno                          GPG: 4096R/1DDD8C9B
>aurelien@aurel32.net                 http://www.aurel32.net

Attached PATCH v2.

sparc64 has a non-conventional R_SPARC_JMP_IREL, along with conventional
R_SPARC_IRELATIVE.
Aurelien Jarno - Feb. 10, 2020, 10:19 p.m.
On 2020-02-10 11:14, Fangrui Song wrote:
> On 2020-02-08, Aurelien Jarno wrote:
> > On 2020-02-06 10:53, Fangrui Song wrote:
> > > On 2020-02-06, Aurelien Jarno wrote:
> > > > Hi,
> > > >
> > > > On 2020-02-04 22:09, Fangrui Song wrote:
> > > > > GNU ld's RISCV port does not support IFUNC. ld -no-pie produces no
> > > > > relocation and the test passed incorrectly. Be more rigid by testing
> > > > > IRELATIVE explicitly.
> > > >
> > > > Thanks for your patch and sorry for the time to answer, I was testing it
> > > > on many architectures. First of all I confirm it fixes the issue when
> > > > building glibc with PIE on mips* and riscv64. I also confirm it
> > > > introduces no regression on aarch64, armv5, armv7, hppa, m68k, powerpc,
> > > > ppc64, ppc64le, s390x and x86_64.
> > > >
> > > > However it wrongly detects that IFUNC is not supported on sparc64 when
> > > > PIE is not in use. Here is the output of of readelf for the non-PIE
> > > > case:
> > > >
> > > > | Relocation section '.rela.dyn' at offset 0x110 contains 1 entry:
> > > > |   Offset          Info           Type           Sym. Value    Sym. Name + Addend
> > > > | 000000200280  0000000000f8 R_SPARC_JMP_IREL                     100128
> > > 
> > > sparc64 -no-pie does not produce an R_SPARC_IRELATIVE. This looks weird.
> > > All other archs emit an R_*_IRELATIVE.
> > > 
> > > Can you dump the assembly (including .text and .[i]plt)?
> > > Or can someone with sparc64 experience answer why sparc64 is different
> > > here?
> > 
> > Here is the dump of the .iplt section:
> > Disassembly of section .iplt:
> > 
> > 0000000000200200 <.iplt>:
> >        ...
> >  200280:       03 00 00 80     sethi  %hi(0x20000), %g1
> >  200284:       30 6f ff e7     b,a   %xcc, 200220 <__start+0x1000f8>
> >  200288:       01 00 00 00     nop
> >  20028c:       01 00 00 00     nop
> >  200290:       01 00 00 00     nop
> >  200294:       01 00 00 00     nop
> >  200298:       01 00 00 00     nop
> >  20029c:       01 00 00 00     nop
> > 
> > There is no .text nor .plt section.
> > 
> > -- 
> > Aurelien Jarno                          GPG: 4096R/1DDD8C9B
> > aurelien@aurel32.net                 http://www.aurel32.net
> 
> Attached PATCH v2.
> 
> sparc64 has a non-conventional R_SPARC_JMP_IREL, along with conventional
> R_SPARC_IRELATIVE.

Thanks for the new version. I confirm it fixes the problem on sparc and
that it still works on other architectures.

Tested-by: Aurelien Jarno <aurelien@aurel32.net>

Patch

From 624b3a0c9e4f2f421227bb3f331723dfe807f157 Mon Sep 17 00:00:00 2001
From: Fangrui Song <maskray@google.com>
Date: Tue, 4 Feb 2020 21:55:44 -0800
Subject: [PATCH] Improve IFUNC check [BZ #25506]

GNU ld does not support IFUNC but does not produces a relocation.
The test passed incorrectly. Be more rigid by testing IRELATIVE
explicitly.
---
 configure    | 2 +-
 configure.ac | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/configure b/configure
index b959d2d988..3b98ec312f 100755
--- a/configure
+++ b/configure
@@ -4035,7 +4035,7 @@  if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS \
 	    -o conftest conftest.S 1>&5 2>&5; then
   # Do a link to see if the backend supports IFUNC relocs.
   $READELF -r conftest 1>&5
-  LC_ALL=C $READELF -r conftest | grep 'no relocations' >/dev/null || {
+  LC_ALL=C $READELF -Wr conftest | grep -q 'IRELATIVE\|R_SPARC_JMP_IREL' && {
     libc_cv_ld_gnu_indirect_function=yes
   }
 fi
diff --git a/configure.ac b/configure.ac
index 49b900c1ed..e20034f301 100644
--- a/configure.ac
+++ b/configure.ac
@@ -649,7 +649,7 @@  if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS \
 	    -o conftest conftest.S 1>&AS_MESSAGE_LOG_FD 2>&AS_MESSAGE_LOG_FD; then
   # Do a link to see if the backend supports IFUNC relocs.
   $READELF -r conftest 1>&AS_MESSAGE_LOG_FD
-  LC_ALL=C $READELF -r conftest | grep 'no relocations' >/dev/null || {
+  LC_ALL=C $READELF -Wr conftest | grep -q 'IRELATIVE\|R_SPARC_JMP_IREL' && {
     libc_cv_ld_gnu_indirect_function=yes
   }
 fi
-- 
2.25.0.341.g760bfbb309-goog