[Bug target/38496] Gcc misaligns arrays when stack is forced follow the x8632 ABI

[joseph at codesourcery dot com]

------- Comment #7 from joseph at codesourcery dot com  2008-12-12 00:01 -------
Subject: Re:   New: Gcc misaligns arrays when stack is
 forced follow the x8632 ABI

On Thu, 11 Dec 2008, whaley at cs dot utsa dot edu wrote:

> I notice that gcc does not follow the 32-bit ABI for the x86, in that it forces
> the stack alignment to 16 bytes rather than the ABI-required 4 bytes.  This is
> a problem when interacting with compilers that are ABI-compliant.

I suppose that by "32-bit ABI for the x86" you mean a document with 
1990-1996 SCO copyrights.

This document should be considered of only marginal relevant to current 
systems; it may have described an ABI for some particular system that is 
now obsolete, but is not an accurate description of (for example) the ABI 
used on IA32 GNU/Linux, which is a de facto ABI with no written document 
corresponding precisely.  
<http://groups.google.com/group/ia32-abi/browse_thread/thread/4f9b3e5069943bf1> 
(and the messages linked from it) is a description of this area of the de 
facto ABI.

In principle GCC's documentation should for all target systems give a 
description of the ABI it is intended to implement for those systems with 
links to relevant documents and descriptions of how the ABI deviates from 
those documents.  In practice, it does not, but it is still the case that 
just because there exists a document claiming to be a psABI for a 
particular processor does not mean that GCC follows it or that it would be 
correct for GCC to follow it.  The older the document, the less likely it 
is relevant; some ABIs such as x86-64 are actively maintained (meaning 
that defects in the ABI document may be fixed - a disagreement between 
implementations and documents may be concluded to be a defect on either or 
both sides) while others are not.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38496