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Re: new triplet for x32 psABI?

From: H.J. Lu
Subject: Re: new triplet for x32 psABI?
Date: Tue, 4 Oct 2011 12:53:23 -0700

On Mon, Oct 3, 2011 at 8:44 PM, Michael LIAO <address@hidden> wrote:
> On Mon, Oct 3, 2011 at 5:53 PM, H.J. Lu <address@hidden> wrote:
>> On Mon, Oct 3, 2011 at 4:47 PM, Michael LIAO <address@hidden> wrote:
>>> On Mon, Oct 3, 2011 at 4:03 PM, Mike Frysinger <address@hidden> 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.

X32 assembler/linker should handle it properly by zero-extending address
to 64bit.


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