This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: [x86-64-psABI] RFC: Add R_X86_64_RELAX_PC32 and R_X86_64_RELAX_PLT32


Hi,

On Mon, 11 May 2015, H.J. Lu wrote:

> To remove one direct branch to PLT for external function calls:
> 
> https://gcc.gnu.org/ml/gcc-patches/2015-05/msg00001.html
> 
> I am proposing to add 2 new relocations, R_X86_64_RELAX_PC32
> and R_X86_64_RELAX_PLT32:
> 
> 1. They can only be used on 32-bit PC relative call/jmp instructions.
> 2. call/jmp instructions must have a 0x48 prefix.
> 3. Linker can treat them as R_X86_64_PC32 and R_X86_64_PLT32,
> respectively.
> 4. Optionally, linker can convert
> 
> 0x48 call/jmp foo[@PLT]
> 
> to
> 
> call/jmp *foo@GOTPCREL(%rip)

Perhaps it should be clarified that the intention here is, that the 
respective GOT slot will be relocated with the PLT slot address+6, not 
with the final address of symbol foo (that will be done when actually 
jumping/calling through that got slot); at least when RELAX_PLT32 is used.


Ciao,
Michael.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]