Re: [PATCH, x86_64] Remove R_X86_64_PC32_BND and R_X86_64_PLT32_BND

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Fri, Nov 14, 2014 at 6:46 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Fri, Nov 14, 2014 at 6:34 AM, Zamyatin, Igor <igor.zamyatin@intel.com> wrote:
>> Hi!
>>
>> It is appeared that for Intel MPX R_X86_64_*_BND relocations are not enough in case of indirect calls like eg in the following example:
>>
>> foo:
>>          movq    fp@GOTPCREL(%rip), %rax
>>          bnd jmp     *(%rax)
>>          .globl  fp
>>          .section        .data.rel,"aw",@progbits
>>          .align 8
>>          .type   fp, @object
>>          .size   fp, 8
>>  fp:
>>          .quad   memcpy
>>
>> There will be no R_X86_64_*_BND relocation but anyway linker needs to
>> generate extended PLT entry for memcpy.
>>
>> The given patch contains changes that create separate linker option (-z bndplt) which forces
>> linker to create extended PLT entry for any call (this option will be passed to linker when compilation is in MPX mode).
>> Thus we can omit R_X86_64_*_BND relocations completely. (They left in the code just for backward compatibility).
>>
>> MPX ABI changed accordingly (https://github.com/hjl-tools/x86-64-psABI/tree/hjl/mpx/master).
>>
>> Thanks,
>> Igor
>>
>> Changelogs:
>>
>> bfd/ChangeLog
>>
>> 2014-11-14  Igor Zamyatin  <igor.zamyatin@intel.com>
>>
>>         * elf64-x86-64.c (elf_x86_64_check_relocs): MPX PLT is now supported
>>         for R_X86_64_PC32, R_X86_64_PLT32, R_X86_64_32 and R_X86_64_64 when
>>         bndplt option is specified.
>>
>>
>> include/ChangeLog
>>
>> 2014-11-14  Igor Zamyatin  <igor.zamyatin@intel.com>
>>
>>         * bfdlink.h (struct bfd_link_info): New field bndplt.
>>
>> ld/ChangeLog
>>
>> 2014-11-14  Igor Zamyatin  <igor.zamyatin@intel.com>
>>
>>         * emulparams/elf_x86_64.sh: Set BNDPLT for x86_64.
>>         * emultempl/elf32.em: Handle bndplt option and add description for it.
>>         * ld.texinfo: Add description for bndplt.
>>         * testsuite/ld-x86-64/bnd-ifunc-1.d: Add bndplt option.
>>         * testsuite/ld-x86-64/bnd-ifunc-2.d: Ditto.
>>         * testsuite/ld-x86-64/bnd-plt-1.d: Ditto. Update dissassembly
>>         sections.
>>         * testsuite/ld-x86-64/mpx.exp: Handle mpx3 and mpx4 tests.
>>         * testsuite/ld-x86-64/mpx3.dd: New file.
>>         * testsuite/ld-x86-64/mpx3a.s: New file.
>>         * testsuite/ld-x86-64/mpx3b.s: New file.
>>         * testsuite/ld-x86-64/mpx4.dd: New file.
>>         * testsuite/ld-x86-64/mpx4a.s: New file.
>>         * testsuite/ld-x86-64/mpx4b.s: New file.
>>
>
> Looks good.
>
>> diff --git a/ld/ld.texinfo b/ld/ld.texinfo
>> index 5762dc6..eaa925d 100644
>> --- a/ld/ld.texinfo
>> +++ b/ld/ld.texinfo
>> @@ -1104,6 +1104,10 @@ Specify a stack size for in an ELF @code{PT_GNU_STACK} segment.
>>  Specifying zero will override any default non-zero sized
>>  @code{PT_GNU_STACK} segment creation.
>>
>> +@item bndplt
>> +Always generate BND prefix in PLT entries.
>> +Enabled for Linux/x86_64.
>
> Please use
>
> Always generate BND prefix in PLT entries.  Supported for Linux/x86-64.
>
>>  @end table
>>
>
> Please add your ChangeLog entries to ChangeLog files and use
>
> # git format-patch origin/master
>
> to regenerate the patch and post it so that I can do
>
> # git am
> # git rebase
>
> to apply it.
>

One more thing.  Please update gas not to generate _BND
relocations.

-- 
H.J.