Message ID | 20200922003011.GB5452@bubble.grove.modra.org |
---|---|
State | New |
Headers | show |
Series | [RS6000] Power10 libffi fixes | expand |
Hi! On Tue, Sep 22, 2020 at 10:00:11AM +0930, Alan Modra wrote: > Power10 pc-relative code doesn't use or preserve r2 as a TOC pointer. > That means calling between pc-relative and TOC using code can't be > done without intervening linker stubs, and a call from TOC code to > pc-relative code must have a nop after the bl in order to restore r2. > > Now the PowerPC libffi assembly code doesn't use r2 except for the > implicit use when making calls back to C, ffi_closure_helper_LINUX64 > and ffi_prep_args64. So changing the assembly to interoperate with > pc-relative code without stubs is easily done. Controlling that is a > new built-in macro. > > Upstream libffi currently has a different patch applied to work around > the power10 build failure. I'll post a delta for upstream. > Bootstrapped and regression tested on power8, built for power10. > > gcc/ > * config/rs6000/rs6000-c.c (rs6000_target_modify_macros): > Conditionally define __PCREL__. Please do that as a separate (earlier) patch (because it *is*, and to simplify backports, etc). > libffi/ > * src/powerpc/linux64.S (ffi_call_LINUX64): Don't emit global > entry when __PCREL__. Call using @notoc. > (ffi_closure_LINUX64, ffi_go_closure_linux64): Likewise. This is okay for trunk, and for backports (possibly expedited, talk with Peter for what is wanted/needed for AT). Thanks! Segher
On Tue, Sep 22, 2020 at 07:16:57PM -0500, Segher Boessenkool wrote: > Hi! > > On Tue, Sep 22, 2020 at 10:00:11AM +0930, Alan Modra wrote: > > gcc/ > > * config/rs6000/rs6000-c.c (rs6000_target_modify_macros): > > Conditionally define __PCREL__. > > Please do that as a separate (earlier) patch (because it *is*, and to > simplify backports, etc). Done. > > libffi/ > > * src/powerpc/linux64.S (ffi_call_LINUX64): Don't emit global > > entry when __PCREL__. Call using @notoc. > > (ffi_closure_LINUX64, ffi_go_closure_linux64): Likewise. > > This is okay for trunk, and for backports (possibly expedited, talk > with Peter for what is wanted/needed for AT). I've fixed the changelog, a comment, and added a nop after bl for the old calls without @notoc. While there really isn't a need for the nops in libffi.so since the callee is hidden visibility, there is a miniscule chance that a static libffi.a user has a very large TOC and somehow manages to have ffi_call_LINUX64 and ffi_prep_args64 using different TOC pointers. In that case the linker would arrange the call to go via a toc-adjusting stub and want to replace the nop with a toc restore.
On Thu, Sep 24, 2020 at 01:11:02PM +0930, Alan Modra wrote: > I've fixed the changelog, a comment, and added a nop after bl for the > old calls without @notoc. While there really isn't a need for the > nops in libffi.so since the callee is hidden visibility, there is a > miniscule chance that a static libffi.a user has a very large TOC and > somehow manages to have ffi_call_LINUX64 and ffi_prep_args64 using > different TOC pointers. In that case the linker would arrange the > call to go via a toc-adjusting stub and want to replace the nop with a > toc restore. Adding those nops broke libffi, and I pushed the patch before bootstrap finished.. So this one committed as obvious to fix the breakage. * src/powerpc/linux64_closure.S (ffi_closure_LINUX64): Correct location of .Lret. diff --git a/libffi/src/powerpc/linux64_closure.S b/libffi/src/powerpc/linux64_closure.S index 3e30db36190..5663bb40223 100644 --- a/libffi/src/powerpc/linux64_closure.S +++ b/libffi/src/powerpc/linux64_closure.S @@ -159,15 +159,17 @@ ffi_closure_LINUX64: # if defined _CALL_LINUX || _CALL_ELF == 2 # ifdef __PCREL__ bl ffi_closure_helper_LINUX64@notoc +.Lret: # else bl ffi_closure_helper_LINUX64 +.Lret: nop # endif # else bl .ffi_closure_helper_LINUX64 +.Lret: nop # endif -.Lret: # now r3 contains the return type # so use it to look up in a table
diff --git a/gcc/config/rs6000/rs6000-c.c b/gcc/config/rs6000/rs6000-c.c index f5982907e90..cc1e997524e 100644 --- a/gcc/config/rs6000/rs6000-c.c +++ b/gcc/config/rs6000/rs6000-c.c @@ -597,6 +597,9 @@ rs6000_target_modify_macros (bool define_p, HOST_WIDE_INT flags, /* Tell the user if we support the MMA instructions. */ if ((flags & OPTION_MASK_MMA) != 0) rs6000_define_or_undefine_macro (define_p, "__MMA__"); + /* Whether pc-relative code is being generated. */ + if ((flags & OPTION_MASK_PCREL) != 0) + rs6000_define_or_undefine_macro (define_p, "__PCREL__"); } void diff --git a/libffi/src/powerpc/linux64.S b/libffi/src/powerpc/linux64.S index b2ae60ead6e..bfb4d2957ae 100644 --- a/libffi/src/powerpc/linux64.S +++ b/libffi/src/powerpc/linux64.S @@ -36,8 +36,10 @@ .cfi_startproc # if _CALL_ELF == 2 ffi_call_LINUX64: +# ifndef __PCREL__ addis %r2, %r12, .TOC.-ffi_call_LINUX64@ha addi %r2, %r2, .TOC.-ffi_call_LINUX64@l +# endif .localentry ffi_call_LINUX64, . - ffi_call_LINUX64 # else .section ".opd","aw" @@ -89,7 +91,11 @@ ffi_call_LINUX64: /* Call ffi_prep_args64. */ mr %r4, %r1 # if defined _CALL_LINUX || _CALL_ELF == 2 +# ifdef __PCREL__ + bl ffi_prep_args64@notoc +# else bl ffi_prep_args64 +# endif # else bl .ffi_prep_args64 # endif diff --git a/libffi/src/powerpc/linux64_closure.S b/libffi/src/powerpc/linux64_closure.S index 6487d2a2970..938e86034f1 100644 --- a/libffi/src/powerpc/linux64_closure.S +++ b/libffi/src/powerpc/linux64_closure.S @@ -37,8 +37,10 @@ .cfi_startproc # if _CALL_ELF == 2 ffi_closure_LINUX64: +# ifndef __PCREL__ addis %r2, %r12, .TOC.-ffi_closure_LINUX64@ha addi %r2, %r2, .TOC.-ffi_closure_LINUX64@l +# endif .localentry ffi_closure_LINUX64, . - ffi_closure_LINUX64 # else .section ".opd","aw" @@ -155,7 +157,11 @@ ffi_closure_LINUX64: # make the call # if defined _CALL_LINUX || _CALL_ELF == 2 +# ifdef __PCREL__ + bl ffi_closure_helper_LINUX64@notoc +# else bl ffi_closure_helper_LINUX64 +# endif # else bl .ffi_closure_helper_LINUX64 # endif @@ -396,8 +402,10 @@ ffi_closure_LINUX64: .cfi_startproc # if _CALL_ELF == 2 ffi_go_closure_linux64: +# ifndef __PCREL__ addis %r2, %r12, .TOC.-ffi_go_closure_linux64@ha addi %r2, %r2, .TOC.-ffi_go_closure_linux64@l +# endif .localentry ffi_go_closure_linux64, . - ffi_go_closure_linux64 # else .section ".opd","aw"