On Mon, May 18, 2015 at 6:13 AM, Michael Matz <m...@suse.de> wrote: > Hi, > > On Mon, 18 May 2015, H.J. Lu wrote: > >> To avoid indirect branch to internal functions, I am proposing to add a >> new relocation, R_X86_64_RELAX_GOTPCREL, to x86-64 psABI: >> >> 1. When branching to an external function, foo, compiler may generate >> call/jmp *foo@GOTRELAX(%rip) >> which generates R_X86_64_RELAX_GOTPCREL relocation, instead of >> call/jmp foo[@PLT] >> 2. When function foo is locally defined, linker converts >> call/jmp *foo@GOTRELAX(%rip) >> to >> nop call/jmp foo > > For the jmp case the nop can also be added after it, to not even disturb
Yes, we should convert it to nop call foo/jmp foo nop I implemented it on users/hjl/relax branch in binutils git repo. > the insn decoder. For calls as well of course, but there it might be > better to have it before the call. > I think a nop prefix is better on call. We won't mandate "nop call foo" in psABI and linker is free to use either a nop prefix or a nop suffix. Should we move forward with it? Thanks. -- H.J.
