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Date: Sat, 27 Dec 2008 11:59:44 +0100 From: Ingo Molnar <mingo@...e.hu> To: Paul Mackerras <paulus@...ba.org> Cc: Sam Ravnborg <sam@...nborg.org>, Yinghai Lu <yinghai@...nel.org>, David Howells <dhowells@...hat.com>, Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>, Andrew Morton <akpm@...ux-foundation.org>, Stephen Rothwell <sfr@...b.auug.org.au>, linux-next@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, mel@....ul.ie Subject: Re: [PATCH] kbuild, sparseirq: work around GCC bug with __weak aliases * Paul Mackerras <paulus@...ba.org> wrote: > Ingo Molnar writes: > > > * Ingo Molnar <mingo@...e.hu> wrote: > > > > > > I recall David Howells had a similar issue with the bootparamter patch > > > > set. The workaround he used was to add a barrier(); call in the weak > > > > function to avoid the inline. > > > > > > could we add some extra attribute to __weak that would have a similar > > > effect? Something like __attribute__((noinline)), or something silly > > > like __attribute__((deprecated)) - just to keep gcc from screwing up > > > __weak functions? Perhaps adding a section attribute would have a > > > similar effect? (putting weak definitions into an extra section is > > > probably helpful anyway) > > > > I've applied the patch below to tip/irq/sparseirq - could someone with an > > affected GCC version please check whether this solves the crash? > > I recall from discussions earlier that noinline doesn't fix the problem, > and I just tested a similar case and verified that adding noinline > doesn't stop some versions of gcc from inlining them. The empty weak > functions in kernel/perf_counter.c were getting inlined by the cross-gcc > (gcc 4.1.1) I use for compiling powerpc kernels on my laptop, and adding > noinline doesn't help there. hm, does Yinghai's patch below do the trick? (also in perfcounters/core and tip/master) Ingo --------------------> >From 01ea1ccaa24dea3552e103be13b7897211607a8b Mon Sep 17 00:00:00 2001 From: Yinghai Lu <yinghai@...nel.org> Date: Fri, 26 Dec 2008 21:05:06 -0800 Subject: [PATCH] perf_counter: more barrier in blank weak function Impact: fix panic possible panic Some versions of GCC inline the weak global function if it's empty. Add a barrier() to work it around. Signed-off-by: Yinghai Lu <yinghai@...nel.org> Signed-off-by: Ingo Molnar <mingo@...e.hu> --- kernel/perf_counter.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c index d7a79f3..37f7716 100644 --- a/kernel/perf_counter.c +++ b/kernel/perf_counter.c @@ -45,8 +45,8 @@ hw_perf_counter_init(struct perf_counter *counter) } u64 __weak hw_perf_save_disable(void) { return 0; } -void __weak hw_perf_restore(u64 ctrl) { } -void __weak hw_perf_counter_setup(void) { } +void __weak hw_perf_restore(u64 ctrl) { barrier(); } +void __weak hw_perf_counter_setup(void) { barrier(); } static void list_add_counter(struct perf_counter *counter, struct perf_counter_context *ctx) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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