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On Tue, May 31, 2016 at 11:02 AM, Sriraman Tallam <tmsriram@google.com> wrote: > On Sat, May 28, 2016 at 10:44 AM, H.J. Lu <hjl.tools@gmail.com> wrote: >> On Fri, May 27, 2016 at 3:14 PM, Sriraman Tallam <tmsriram@google.com> wrote: >>> On Fri, May 20, 2016 at 1:32 PM, H.J. Lu <hjl.tools@gmail.com> wrote: >>>> On Fri, May 20, 2016 at 1:27 PM, Sriraman Tallam <tmsriram@google.com> wrote: >>>>> Hi, >>>>> >>>>> GCC has option -fno-plt which converts all extern calls to indirect >>>>> calls via GOT to prevent the linker for generating any PLT stubs. >>>>> However, if the function ends up defined in the executable this patch >>>>> will convert those indirect calls/jumps to direct. Since the indirect >>>>> calls are one byte longer, an extra nop is needed at the beginning. >>>>> >>>>> Here is a simple example: >>>>> >>>>> main.c >>>>> --------- >>>>> extern int foo(); >>>>> int main() { >>>>> return foo(); >>>>> } >>>>> >>>>> deffoo.c >>>>> ----------- >>>>> int foo() { >>>>> return 0; >>>>> } >>>>> >>>>> $ gcc -fno-plt main.c deffoo.c >>>>> $objdump -d a.out >>>>> >>>>> 0000000000400626 <main>: >>>>> ... >>>>> 40062a: ff 15 28 14 00 00 callq *0x1428(%rip) # >>>>> 401a58 <_DYNAMIC+0x1d8> >>>>> >>>>> The call is indirect even though foo is defined in the executable. >>>>> >>>>> With this patch, >>>>> 0000000000400606 <main>: >>>>> .... >>>>> 40060a: 90 nop >>>>> 40060b: e8 03 00 00 00 callq 400613 <foo> >>>>> >>>>> The call is now direct with an extra nop. >>>>> >>>>> >>>> >>>> Please try ld, which uses 0x67 prefix (addr32) instead of nop. >>>> Also for >>>> >>>> jmp *foo#GOTPCREL(%rip) >>>> >>>> ld converts it to >>>> >>>> jmp foo >>>> nop >>> >>> I have modified the patch to keep it consistent with what ld produces. >>> >>> Please take another look. >>> >>> * x86_64.cc (can_convert_callq_to_direct): New function. >>> Target_x86_64<size>::Scan::global: Check if an indirect call via >>> GOT can be converted to direct. >>> Target_x86_64<size>::Relocate::relocate: Change any indirect call >>> via GOT that can be converted. >>> * testsuite/Makefile.am (x86_64_indirect_call_to_direct.sh): New test. >>> * testsuite/Makefile.in: Regenerate. >>> * testsuite/x86_64_indirect_call_to_direct1.s: New file. >>> * testsuite/x86_64_indirect_jump_to_direct1.s: New file. >>> >> >> Do you need to check R_X86_64_REX_GOTPCRELX for branch? > > Ok, patch changed to not check for this and refactored a bit. Ping, Is this patch ok now? * x86_64.cc (can_convert_callq_to_direct): New function. Target_x86_64<size>::Scan::global: Check if an indirect call via GOT can be converted to direct. Target_x86_64<size>::Relocate::relocate: Change any indirect call via GOT that can be converted. * testsuite/Makefile.am (x86_64_indirect_call_to_direct.sh): New test. * testsuite/Makefile.in: Regenerate. * testsuite/x86_64_indirect_call_to_direct1.s: New file. * testsuite/x86_64_indirect_jump_to_direct1.s: New file. Patch attached. Thanks Sri > > Thanks > Sri > >> >> -- >> H.J.
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convert_indirect_call_patch.txt
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