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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. Thanks Sri > > -- > H.J.
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convert_indirect_call_patch.txt
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