Message ID | 20200205060922.5pbgm5hfj2r6vrl2@google.com |
---|---|
State | New |
Headers | show |
Series | Improve IFUNC check | expand |
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 And for the PIE case: | Relocation section '.rela.dyn' at offset 0x290 contains 1 entry: | Offset Info Type Sym. Value Sym. Name + Addend | 0000001021a0 0000000000f9 R_SPARC_IRELATIVE 2c0 | | Relocation section '.rela.plt' at offset 0x2a8 contains 1 entry: | Offset Info Type Sym. Value Sym. Name + Addend | 000000102180 0000000000f8 R_SPARC_JMP_IREL 2c0 Looks like you might want to slightly adjust the regex. Also note that this is BZ#25506, to add to the commit message.
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? As my lld R_RISCV_IRELATIVE patch (https://reviews.llvm.org/D74022) shows # DIS64: _start: # DIS64-NEXT: 1264: auipc a0, 0 # DIS64-NEXT: addi a0, a0, 12 # DIS64: Disassembly of section .iplt: # DIS64: 00001270 func: ## 64-bit: &.got.plt[func]-. = 0x3370-0x1270 = 4096*2+256 # DIS64-NEXT: auipc t3, 2 # DIS64-NEXT: ld t3, 256(t3) # DIS64-NEXT: jalr t1, t3 # DIS64-NEXT: nop The idea is to create an IPLT entry and bind absolute/PC-relative relocations to that address. The IPLT entry needs a .got.plt slot, which is relocated by an R_*_IRELATIVE at runtime. It is R_*_IRELATIVE because no symbol index is needed. R_SPARC_JMP_IREL looks strange. I hope someone can explain. >And for the PIE case: > >| Relocation section '.rela.dyn' at offset 0x290 contains 1 entry: >| Offset Info Type Sym. Value Sym. Name + Addend >| 0000001021a0 0000000000f9 R_SPARC_IRELATIVE 2c0 >| >| Relocation section '.rela.plt' at offset 0x2a8 contains 1 entry: >| Offset Info Type Sym. Value Sym. Name + Addend >| 000000102180 0000000000f8 R_SPARC_JMP_IREL 2c0 > >Looks like you might want to slightly adjust the regex. > >Also note that this is BZ#25506, to add to the commit message. > >-- >Aurelien Jarno GPG: 4096R/1DDD8C9B >aurelien@aurel32.net http://www.aurel32.net
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.
diff --git a/configure b/configure index b959d2d988..0107f0dec5 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 && { libc_cv_ld_gnu_indirect_function=yes } fi diff --git a/configure.ac b/configure.ac index 49b900c1ed..1fbaf65951 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 && { libc_cv_ld_gnu_indirect_function=yes } fi