Re: x86 double alignment (was egcs-1.1 release schedule)

[Marc Lehmann <pcg@goof.com>]

On Tue, Jun 23, 1998 at 07:47:24AM -0700, H.J. Lu wrote:
> 
> I believe Marc's patch doesn't change ABI by default. But you can

Sorry for me first sending the patch and then reading the list ;) I actually
have a backlog of >600 messages on egcs and just found this thread when
Bernd asked me about the double-alignment patch.

> turn on some optimizations by hand which will change ABI. But if

The original patch turned on -mstack-align-double, which I thought is safe,
but it isn't. I got a report from a windows user that it breaks most windows
function semantics, as these functions deallocate the stack themselves. In
this case, -mstack-align-double will break the program.

If we had -mstack-align-double in egcs, maybe glibc could compile _some_ functions
(like qsort or __libc_start) with it, so the problem of combine breaking code
is solved, so we can either

- document that -mno-stack-align-double should be used when linking against third-party-libs
- not making it on by default.

there are also speed issues, i.e. in integer-only programs, -mstack-align-double
slows down code (a bit), so it should probably be disabled anyway.

-marg-align-double never worked, due to limitations in calls.c (FUNCTION_ARG_BOUNDARY
is effectively ignored on calls, but not within the called function), and
breaks the abi, and was thus always optional. (it would align doubles in the
argument area, this _severely_ breaks the abi, of course)

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      ---==---(_)__  __ ____  __       Marc Lehmann       +--
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