new triplet for x32 psABI?

Michael LIAO michael.hliao@gmail.com
Tue Oct 4 03:44:00 GMT 2011


On Mon, Oct 3, 2011 at 5:53 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Oct 3, 2011 at 4:47 PM, Michael LIAO <michael.hliao@gmail.com> wrote:
>> On Mon, Oct 3, 2011 at 4:03 PM, Mike Frysinger <vapier@gentoo.org> wrote:
>>> On Monday, October 03, 2011 18:57:28 Michael LIAO wrote:
>>>
>>> please don't top post
>>>
>>
>> sorry, it's my first post on mailing.
>>
>>>> Most examples would be related to tools generating code.
>>>>
>>>> Suppose you have a software package with several hard-coded fully
>>>> optimized assembly file for different targets. Your build system need
>>>> to know the current target as well as target ABI to select the correct
>>>> assembly file to build it. It even desirable if it includes a simple
>>>> script to help generate assembly code (like the one in OpenSSL), you'd
>>>> better know the target ABI to prepare proper glue code without
>>>> breaking ABI.
>>>
>>> hjlu posted examples to the x32 site as to handle this.  the only difference
>>> between x86_64 and x32 is the size of the pointers.
>>>
>>
>> Besides the pointer size, there are other differences like indirect
>> branch which need different code sequence on x32 and x64. Indirect
>> branch would be used in assembly code (yeah, concrete example would
>> valuable here but indirect branch should be used potentially and
>> possibly in assembly code.) If the assembly code use indirect branch,
>> it needs to know the target ABI and generate/use difference code path.
>>
>
> In assembly codes, most, if not all, of x86-64 indirect branch work fine for x32
>

that may cause the target IP out of the first 4G range if assembly
code won't follow x32 abi, e.g. indirect target is stored in a memory
location and assembly direct use 64-bit near absolute indirect call
with m64 opernad since the branch target is 32 bits in memory but that
call will read 64-bit value and result in garbage on high 32 bits of
the final IP.

>
> --
> H.J.
>



More information about the Gcc mailing list