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Re: [PATCH 3/4] split-stack for powerpc64
- From: "Lynn A. Boger" <laboger at linux dot vnet dot ibm dot com>
- To: gcc-patches at gcc dot gnu dot org, David Edelsohn <dje dot gcc at gmail dot com>
- Date: Wed, 20 May 2015 07:13:24 -0500
- Subject: Re: [PATCH 3/4] split-stack for powerpc64
- Authentication-results: sourceware.org; auth=none
- References: <20150518025451 dot GW6140 at bubble dot grove dot modra dot org> <555B2F2F dot 8030909 at linux dot vnet dot ibm dot com> <20150520005220 dot GC6140 at bubble dot grove dot modra dot org>
On 05/19/2015 07:52 PM, Alan Modra wrote:
On Tue, May 19, 2015 at 07:40:15AM -0500, Lynn A. Boger wrote:
Questions on the use of the options for split stack:
- The way this is implemented, split stack is generated if the
target platform supports split stack, on ppc64/ppc64le as well
as on x86, and the use of -fno-split-stack doesn't seem to affect it
for any of these. Is that the way it should work? I would expect
-fno-split-stack to disable it completely.
Can you give a testcase to show what you mean? Picking one of the go
testsuite programs at random, I see
$ gcc/xgcc -Bgcc/ -S -I powerpc64le-linux/libgo /src/gcc-virgin/gcc/testsuite/go.test/test/args.go
$ grep morestack args.s
bl __morestack
bl __morestack
$ gcc/xgcc -Bgcc/ -fno-split-stack -S -I powerpc64le-linux/libgo /src/gcc-virgin/gcc/testsuite/go.test/test/args.go
$ grep morestack args.s
$
That shows -fno-split-stack being honoured.
You are correct. I made some mistake in my testing.
- The comments say that the gold linker is used for some
situations but I don't see any reference in the code to enabling
the gold linker for ppc64le, ppc64, or x86. Is the user expected
to add the option for the gold linker if needed?
At the moment I believe this is true.
I have been trying to use the gold linker with your patch and seems to
work fine. I added the following to
the STACK_SPLIT_SPEC in gcc/gcc.c to enable the gold linker if
-fsplit-stack is set, but that will cause problems
on systems where the gold linker (and the correct level of binutils
for Power) is not available. Is this an
absolute requirement to use split stack? Could the configure determine
if gold is available and
generate this one way or another?
--- gcc.c (revision 223217)
+++ gcc.c (working copy)
@@ -541,7 +541,8 @@ proper position among the other output files. */
libgcc. This is not yet a real spec, though it could become one;
it is currently just stuffed into LINK_SPEC. FIXME: This wrapping
only works with GNU ld and gold. */
-#define STACK_SPLIT_SPEC " %{fsplit-stack: --wrap=pthread_create}"
+#define STACK_SPLIT_SPEC \
+ " %{fsplit-stack: --wrap=pthread_create -fuse-ld=gold}"
#ifndef LIBASAN_SPEC
#define STATIC_LIBASAN_LIBS \