Message ID | CAMe9rOr9ewbZEj_AY_pLv8GUWju=ZxVNbOgQ1FxO_6Z5vL8EXQ@mail.gmail.com |
---|---|
State | New, archived |
Headers | show |
On 02/20/2016 12:49 AM, H.J. Lu wrote: > +#ifndef DL_RUNTIME_UNALIGNED_VEC_SIZE > +/* The maximum size in bytes of unaligned vector load and store in the > + dynamic linker. Since SSE optimized memory/string functions with > + aligned SSE register load and store are used in the dynamic linker, > + we must set this to 8 so that _dl_runtime_resolve_sse will align the > + stack before calling _dl_fixup. */ > +# define DL_RUNTIME_UNALIGNED_VEC_SIZE 8 The comment doesn't really explain the situation. If all programs actually fallowed the psABI, we wouldn't need this. I think it's easier at this point to change the psABI to say that __tls_getaddr can be called with an 8-byte-aligned stack. And DL_RUNTIME_UNALIGNED_VEC_SIZE etc. can be removed. Florian
"H.J. Lu" <hjl.tools@gmail.com> writes: > -#ifndef DL_RUNIME_UNALIGNED_VEC_SIZE > -/* The maximum size of unaligned vector load and store. */ > -# define DL_RUNIME_UNALIGNED_VEC_SIZE 16 > +#ifndef DL_RUNTIME_UNALIGNED_VEC_SIZE > +/* The maximum size in bytes of unaligned vector load and store in the > + dynamic linker. Since SSE optimized memory/string functions with > + aligned SSE register load and store are used in the dynamic linker, > + we must set this to 8 so that _dl_runtime_resolve_sse will align the > + stack before calling _dl_fixup. */ > +# define DL_RUNTIME_UNALIGNED_VEC_SIZE 8 > #endif Why isn't DL_RUNTIME_UNALIGNED_VEC_SIZE unconditionally defined? Andreas.
On 2016.02.20 at 09:38 +0100, Florian Weimer wrote: > On 02/20/2016 12:49 AM, H.J. Lu wrote: > > +#ifndef DL_RUNTIME_UNALIGNED_VEC_SIZE > > +/* The maximum size in bytes of unaligned vector load and store in the > > + dynamic linker. Since SSE optimized memory/string functions with > > + aligned SSE register load and store are used in the dynamic linker, > > + we must set this to 8 so that _dl_runtime_resolve_sse will align the > > + stack before calling _dl_fixup. */ > > +# define DL_RUNTIME_UNALIGNED_VEC_SIZE 8 > > The comment doesn't really explain the situation. If all programs > actually fallowed the psABI, we wouldn't need this. > > I think it's easier at this point to change the psABI to say that > __tls_getaddr can be called with an 8-byte-aligned stack. I think this would be an overreaction. It is actually quite hard to hit the issue in practice. You would have to build glibc with gcc-6 and -O3, to get the SSE instructions that require proper alignment in the dynamic linker. And then you have to use it with an old and buggy libstc++ from gcc-4.9.3. One could argue that it isn't really the job of the dynamic linker to fix unaligned stacks.
On 02/20/2016 10:16 AM, Markus Trippelsdorf wrote: > On 2016.02.20 at 09:38 +0100, Florian Weimer wrote: >> On 02/20/2016 12:49 AM, H.J. Lu wrote: >>> +#ifndef DL_RUNTIME_UNALIGNED_VEC_SIZE >>> +/* The maximum size in bytes of unaligned vector load and store in the >>> + dynamic linker. Since SSE optimized memory/string functions with >>> + aligned SSE register load and store are used in the dynamic linker, >>> + we must set this to 8 so that _dl_runtime_resolve_sse will align the >>> + stack before calling _dl_fixup. */ >>> +# define DL_RUNTIME_UNALIGNED_VEC_SIZE 8 >> >> The comment doesn't really explain the situation. If all programs >> actually fallowed the psABI, we wouldn't need this. >> >> I think it's easier at this point to change the psABI to say that >> __tls_getaddr can be called with an 8-byte-aligned stack. > > I think this would be an overreaction. I don't know. If glibc will keep this compatibility code indefinitely, it's easy for other toolchains to make the same mistake. > It is actually quite hard to hit the issue in practice. You would have > to build glibc with gcc-6 and -O3, to get the SSE instructions that > require proper alignment in the dynamic linker. We will gradually get more SSE instructions in glibc, including the dynamic linker. > And then you have to use it with an old and buggy libstc++ from > gcc-4.9.3. I assume that could happen with TLS support in binaries from older compilers. > One could argue that it isn't really the job of the dynamic linker to > fix unaligned stacks. Correct, so why are we doing it? It would be pretty drastic to tell users to throw away their old binaries because they were built with a buggy toolchain. Florian
On Sat, Feb 20, 2016 at 4:05 AM, Florian Weimer <fweimer@redhat.com> wrote: > On 02/20/2016 10:16 AM, Markus Trippelsdorf wrote: >> On 2016.02.20 at 09:38 +0100, Florian Weimer wrote: >>> On 02/20/2016 12:49 AM, H.J. Lu wrote: >>>> +#ifndef DL_RUNTIME_UNALIGNED_VEC_SIZE >>>> +/* The maximum size in bytes of unaligned vector load and store in the >>>> + dynamic linker. Since SSE optimized memory/string functions with >>>> + aligned SSE register load and store are used in the dynamic linker, >>>> + we must set this to 8 so that _dl_runtime_resolve_sse will align the >>>> + stack before calling _dl_fixup. */ >>>> +# define DL_RUNTIME_UNALIGNED_VEC_SIZE 8 >>> >>> The comment doesn't really explain the situation. If all programs >>> actually fallowed the psABI, we wouldn't need this. >>> >>> I think it's easier at this point to change the psABI to say that >>> __tls_getaddr can be called with an 8-byte-aligned stack. >> >> I think this would be an overreaction. > > I don't know. If glibc will keep this compatibility code indefinitely, > it's easy for other toolchains to make the same mistake. > On one hand, we are realigning stack in glibc anyway, may be forever, and compiler doesn't need to keep stack aligned to 16 bytes when calling __tls_getaddr. Also we realign stack in AVX and AVX512 machines anyway and TLS isn't completely specified in the x86-64 psABI. On the other hand, it is odd to change psABI after 10 years just because one compiler has a bug in its TLS implementation. If we change the x86-64 psABI for this, I will update i386 psABI specify that __tls_getaddr has 4-byte incoming stack alignment. FYI, I am backporting it to 2.23 branch.
From 8d9c92017d85f23ba6a2b3614b2f2bcf1820d6f0 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" <hjl.tools@gmail.com> Date: Fri, 19 Feb 2016 15:43:45 -0800 Subject: [PATCH] [x86_64] Set DL_RUNTIME_UNALIGNED_VEC_SIZE to 8 Due to GCC bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58066 __tls_get_addr may be called with 8-byte stack alignment. Although this bug has been fixed in GCC 4.9.4, 5.3 and 6, we can't assume that stack will be always aligned at 16 bytes. Since SSE optimized memory/string functions with aligned SSE register load and store are used in the dynamic linker, we must set DL_RUNTIME_UNALIGNED_VEC_SIZE to 8 so that _dl_runtime_resolve_sse will align the stack before calling _dl_fixup: Dump of assembler code for function _dl_runtime_resolve_sse: 0x00007ffff7deea90 <+0>: push %rbx 0x00007ffff7deea91 <+1>: mov %rsp,%rbx 0x00007ffff7deea94 <+4>: and $0xfffffffffffffff0,%rsp ^^^^^^^^^^^ Align stack to 16 bytes 0x00007ffff7deea98 <+8>: sub $0x100,%rsp 0x00007ffff7deea9f <+15>: mov %rax,0xc0(%rsp) 0x00007ffff7deeaa7 <+23>: mov %rcx,0xc8(%rsp) 0x00007ffff7deeaaf <+31>: mov %rdx,0xd0(%rsp) 0x00007ffff7deeab7 <+39>: mov %rsi,0xd8(%rsp) 0x00007ffff7deeabf <+47>: mov %rdi,0xe0(%rsp) 0x00007ffff7deeac7 <+55>: mov %r8,0xe8(%rsp) 0x00007ffff7deeacf <+63>: mov %r9,0xf0(%rsp) 0x00007ffff7deead7 <+71>: movaps %xmm0,(%rsp) 0x00007ffff7deeadb <+75>: movaps %xmm1,0x10(%rsp) 0x00007ffff7deeae0 <+80>: movaps %xmm2,0x20(%rsp) 0x00007ffff7deeae5 <+85>: movaps %xmm3,0x30(%rsp) 0x00007ffff7deeaea <+90>: movaps %xmm4,0x40(%rsp) 0x00007ffff7deeaef <+95>: movaps %xmm5,0x50(%rsp) 0x00007ffff7deeaf4 <+100>: movaps %xmm6,0x60(%rsp) 0x00007ffff7deeaf9 <+105>: movaps %xmm7,0x70(%rsp) [BZ #19679] * sysdeps/x86_64/dl-trampoline.S (DL_RUNIME_UNALIGNED_VEC_SIZE): Renamed to ... (DL_RUNTIME_UNALIGNED_VEC_SIZE): This. Set to 8. (DL_RUNIME_RESOLVE_REALIGN_STACK): Renamed to ... (DL_RUNTIME_RESOLVE_REALIGN_STACK): This. Updated. (DL_RUNIME_RESOLVE_REALIGN_STACK): Renamed to ... (DL_RUNTIME_RESOLVE_REALIGN_STACK): This. * sysdeps/x86_64/dl-trampoline.h (DL_RUNIME_RESOLVE_REALIGN_STACK): Renamed to ... (DL_RUNTIME_RESOLVE_REALIGN_STACK): This. --- ChangeLog | 14 ++++++++++++++ sysdeps/x86_64/dl-trampoline.S | 20 ++++++++++++-------- sysdeps/x86_64/dl-trampoline.h | 6 +++--- 3 files changed, 29 insertions(+), 11 deletions(-) diff --git a/ChangeLog b/ChangeLog index 1ed0e7b..db05bdc 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,17 @@ +2016-02-19 H.J. Lu <hongjiu.lu@intel.com> + + [BZ #19679] + * sysdeps/x86_64/dl-trampoline.S (DL_RUNIME_UNALIGNED_VEC_SIZE): + Renamed to ... + (DL_RUNTIME_UNALIGNED_VEC_SIZE): This. Set to 8. + (DL_RUNIME_RESOLVE_REALIGN_STACK): Renamed to ... + (DL_RUNTIME_RESOLVE_REALIGN_STACK): This. Updated. + (DL_RUNIME_RESOLVE_REALIGN_STACK): Renamed to ... + (DL_RUNTIME_RESOLVE_REALIGN_STACK): This. + * sysdeps/x86_64/dl-trampoline.h + (DL_RUNIME_RESOLVE_REALIGN_STACK): Renamed to ... + (DL_RUNTIME_RESOLVE_REALIGN_STACK): This. + 2016-02-19 Mark Wielaard <mjw@redhat.com> * elf/elf.h: Add NT_ARM_SYSTEM_CALL. diff --git a/sysdeps/x86_64/dl-trampoline.S b/sysdeps/x86_64/dl-trampoline.S index 9fb6b13..39b8771 100644 --- a/sysdeps/x86_64/dl-trampoline.S +++ b/sysdeps/x86_64/dl-trampoline.S @@ -33,15 +33,19 @@ # define DL_STACK_ALIGNMENT 8 #endif -#ifndef DL_RUNIME_UNALIGNED_VEC_SIZE -/* The maximum size of unaligned vector load and store. */ -# define DL_RUNIME_UNALIGNED_VEC_SIZE 16 +#ifndef DL_RUNTIME_UNALIGNED_VEC_SIZE +/* The maximum size in bytes of unaligned vector load and store in the + dynamic linker. Since SSE optimized memory/string functions with + aligned SSE register load and store are used in the dynamic linker, + we must set this to 8 so that _dl_runtime_resolve_sse will align the + stack before calling _dl_fixup. */ +# define DL_RUNTIME_UNALIGNED_VEC_SIZE 8 #endif /* True if _dl_runtime_resolve should align stack to VEC_SIZE bytes. */ -#define DL_RUNIME_RESOLVE_REALIGN_STACK \ +#define DL_RUNTIME_RESOLVE_REALIGN_STACK \ (VEC_SIZE > DL_STACK_ALIGNMENT \ - && VEC_SIZE > DL_RUNIME_UNALIGNED_VEC_SIZE) + && VEC_SIZE > DL_RUNTIME_UNALIGNED_VEC_SIZE) /* Align vector register save area to 16 bytes. */ #define REGISTER_SAVE_VEC_OFF 0 @@ -76,7 +80,7 @@ #ifdef HAVE_AVX512_ASM_SUPPORT # define VEC_SIZE 64 # define VMOVA vmovdqa64 -# if DL_RUNIME_RESOLVE_REALIGN_STACK || VEC_SIZE <= DL_STACK_ALIGNMENT +# if DL_RUNTIME_RESOLVE_REALIGN_STACK || VEC_SIZE <= DL_STACK_ALIGNMENT # define VMOV vmovdqa64 # else # define VMOV vmovdqu64 @@ -100,7 +104,7 @@ strong_alias (_dl_runtime_profile_avx, _dl_runtime_profile_avx512) #define VEC_SIZE 32 #define VMOVA vmovdqa -#if DL_RUNIME_RESOLVE_REALIGN_STACK || VEC_SIZE <= DL_STACK_ALIGNMENT +#if DL_RUNTIME_RESOLVE_REALIGN_STACK || VEC_SIZE <= DL_STACK_ALIGNMENT # define VMOV vmovdqa #else # define VMOV vmovdqu @@ -119,7 +123,7 @@ strong_alias (_dl_runtime_profile_avx, _dl_runtime_profile_avx512) /* movaps/movups is 1-byte shorter. */ #define VEC_SIZE 16 #define VMOVA movaps -#if DL_RUNIME_RESOLVE_REALIGN_STACK || VEC_SIZE <= DL_STACK_ALIGNMENT +#if DL_RUNTIME_RESOLVE_REALIGN_STACK || VEC_SIZE <= DL_STACK_ALIGNMENT # define VMOV movaps #else # define VMOV movups diff --git a/sysdeps/x86_64/dl-trampoline.h b/sysdeps/x86_64/dl-trampoline.h index f419183..b90836a 100644 --- a/sysdeps/x86_64/dl-trampoline.h +++ b/sysdeps/x86_64/dl-trampoline.h @@ -30,7 +30,7 @@ #undef REGISTER_SAVE_AREA #undef LOCAL_STORAGE_AREA #undef BASE -#if DL_RUNIME_RESOLVE_REALIGN_STACK +#if DL_RUNTIME_RESOLVE_REALIGN_STACK # define REGISTER_SAVE_AREA (REGISTER_SAVE_AREA_RAW + 8) /* Local stack area before jumping to function address: RBX. */ # define LOCAL_STORAGE_AREA 8 @@ -57,7 +57,7 @@ cfi_startproc _dl_runtime_resolve: cfi_adjust_cfa_offset(16) # Incorporate PLT -#if DL_RUNIME_RESOLVE_REALIGN_STACK +#if DL_RUNTIME_RESOLVE_REALIGN_STACK # if LOCAL_STORAGE_AREA != 8 # error LOCAL_STORAGE_AREA must be 8 # endif @@ -146,7 +146,7 @@ _dl_runtime_resolve: VMOV (REGISTER_SAVE_VEC_OFF + VEC_SIZE * 5)(%rsp), %VEC(5) VMOV (REGISTER_SAVE_VEC_OFF + VEC_SIZE * 6)(%rsp), %VEC(6) VMOV (REGISTER_SAVE_VEC_OFF + VEC_SIZE * 7)(%rsp), %VEC(7) -#if DL_RUNIME_RESOLVE_REALIGN_STACK +#if DL_RUNTIME_RESOLVE_REALIGN_STACK mov %RBX_LP, %RSP_LP cfi_def_cfa_register(%rsp) movq (%rsp), %rbx -- 2.5.0