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RE: [x86-64 PATCH] PR target/26223: x86-64 ABI vs -mno-80387
- From: Roger Sayle <roger at eyesopen dot com>
- To: "Menezes, Evandro" <evandro dot menezes at amd dot com>
- Cc: Jan Hubicka <jh at suse dot cz>, <gcc-patches at gcc dot gnu dot org>
- Date: Wed, 7 Jun 2006 15:48:42 -0600 (MDT)
- Subject: RE: [x86-64 PATCH] PR target/26223: x86-64 ABI vs -mno-80387
On Wed, 7 Jun 2006, Menezes, Evandro wrote:
> FWIW, x87 is a required processor feature for x86-64 psABI compliance.
> Therefore, does it make sense at all to have -mno-80387 for x86-64?
I believe the issue is the same as the reason the x86_64 also allows
the "-mno-sse" command line option; to (i) prevent the compiler from
introducing FP instructions in code that doesn't preserve the state
of the FP units and (ii) error if the developer inadvertantly introduces
code that demands that the use of an FP unit. This is particularly
useful when building operating system kernels.
For a relevent thread see:
http://gcc.gnu.org/ml/gcc/2005-01/msg00313.html
http://gcc.gnu.org/ml/gcc/2005-01/msg00366.html
http://gcc.gnu.org/ml/gcc/2005-01/msg00381.html
As pointed out this doesn't make much sense in user code, but the
potential utility to kernel developers makes issuing these errors
much more useful than generally ignoring or disabling -mno-80387.
Roger
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