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[PATCH, go] Passing Complex64 and Complex128 values via reflect.Call (using libffi) introduces ABI mismatch

From: Uros Bizjak <ubizjak at gmail dot com>
To: Ian Lance Taylor <iant at google dot com>
Cc: gcc-patches <gcc-patches at gcc dot gnu dot org>, gofrontend-dev at googlegroups dot com
Date: Fri, 1 Mar 2013 13:57:19 +0100
Subject: [PATCH, go] Passing Complex64 and Complex128 values via reflect.Call (using libffi) introduces ABI mismatch

Hello!

Due to the fact that libFFI does not handle C99 _Complex arguments
correctly [1], libgo passes Complex64 and Complex128 arguments via a
temporary structure. However, passing parts of complex number in a
structure is not the same as passing true C99 _Complex value, so this
workaround introduces ABI mismatch between caller and callee. This
mismatch results in wrong passed values of complex types.

Fortunately all x86 ABIs tolerate this mismatch, but other targets
(i.e. alpha) don't have this privilege.

Attached patch disables passing of C99 _Complex arguments via FFI on
all targets, other than x86 (to be on the safe side w.r.t. other
targets). Hopefully, someday libffi will be extended to handle
_Complex arguments in correct way.

Patch was tested on x86_64-pc-linux-gnu {,-m32} and alphaev68-pc-linux-gnu.

[1] http://sourceware.org/ml/libffi-discuss/2007/msg00010.html

Uros.

Attachment: g.diff.txt
Description: Text document

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  - From: Ian Lance Taylor

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