[#PCC-82] invalid assembly on amd64

pcc

invalid assembly on amd64

Created: 19/Aug/09 09:31 PM Updated: 03/Jun/10 09:57 PM

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Fix Version/s:

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Environment:

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[/usr/src/bin/cp] uname -msrvp
OpenBSD 4.6 GENERIC.MP#130 amd64 Intel(R) Core(TM)2 Duo CPU T7100 @ 1.80GHz

Description

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Compiling with -O2 on OpenBSD/amd64 produces the following error for some code

[/usr/src/bin/cp] pcc -O2 -c cp.c
/tmp/ctm.sE01ll: Assembler messages:
/tmp/ctm.sE01ll:488: Error: `(%eax,%r14d)' is not a valid 64 bit base/index expression

Leaving out the -O2 seems to work
[/usr/src/bin/cp] pcc -c cp.c
[/usr/src/bin/cp]

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Comments

Change History

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Jonathan Gray added a comment - 14/Sep/09 05:25 PM

pcc:

        leal (%eax,%ebx),%eax
        leal (%eax,%ecx),%ebx

gcc:

        leal (%rax,%rbx),%eax
        leal (%rax,%rcx),%ebx

perhaps this wasn't noticed during development as NetBSD supports -m32 on amd64?

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Jonathan Gray added a comment - 14/Sep/09 06:25 PM

It is worth pointing out that OpenBSD currently uses binutils 2.15, there have been several noteable amd64 changes since
such as:

Changes from binutils 2.16.91.0.2:
2. Support x86-64 medium model.
Changes from binutils 2.16.91.0.1:
4. Add x86-64 new relocations for medium model.

When specifying -mcmodel=medium to gcc it will generate code with leal instructions that looks like that of pcc.

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Jonathan Gray added a comment - 14/Sep/09 06:33 PM

I mistakenly used pcc in the last test not gcc, all leal instructions still use %r* registers with the different mcmodel it would seem.

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Anders Magnusson added a comment - 03/Jun/10 09:57 PM

This is a bug in the old gas used in OpenBSD, it do not accept constructs like "leal (%eax,%ebx),%ecx" which does not have anything to do with addresses but in fact is a 3-operand addition. pcc may emit it to avoid an extra movl instruction.

It must be fixed in OpenBSD, it's not a compiler problem. Newer gas supports this.