linux-kernel - Re: [PATCH] [alpha] Add minimal support for software performance events.

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Message-ID: <4AE6AAD3.3000102@orcon.net.nz>
Date:	Tue, 27 Oct 2009 21:09:55 +1300
From:	Michael Cree <mcree@...on.net.nz>
To:	Ingo Molnar <mingo@...e.hu>
CC:	linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org,
	Richard Henderson <rth@...ddle.net>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] [alpha] Add minimal support for software performance
 events.

Ingo Molnar wrote:
> * Michael Cree <mcree@...on.net.nz> wrote:
>   
>> In the kernel the patch enables configuration of the perf event 
>> option, adds the perf_event_open syscall, and includes a minimal 
>> architecture specific asm/perf_event.h header file.
>>
>> For the perf tool the patch implements an Alpha specific section
>> in the perf.h header file and adjusts options used in the
>> Makefile to allow compilation on Alpha.  The -Wcast-align gives
>> a "cast increases required alignment of target type" warning for
>> the list_for_each_entry() macro. The -fstack-protector-all
>> option generates a "not supported for this target" warning which
>> with -Werror causes the compiler to abort.
>>
>> Signed-off-by: Michael Cree <mcree@...on.net.nz>
>> ---
>>  arch/alpha/Kconfig                  |    1 +
>>  arch/alpha/include/asm/perf_event.h |    9 +++++++++
>>  arch/alpha/include/asm/unistd.h     |    3 ++-
>>  arch/alpha/kernel/systbls.S         |    1 +
>>  tools/perf/Makefile                 |    5 ++---
>>  tools/perf/perf.h                   |    6 ++++++
>>  6 files changed, 21 insertions(+), 4 deletions(-)
>>  create mode 100644 arch/alpha/include/asm/perf_event.h
>>     
>
> Nice!
>
> I've picked up the perf.h bit in an independent commit. Is there a tree 
> for Alpha bits?
>   

Not that I know of.  Note also that this patch is on top of the patch 
"alpha: Wire up missing/new syscalls" recently posted by Daniele Calore 
(http://lkml.org/lkml/2009/10/21/99).  Hopefully this and prior patches 
get picked up by the Alpha maintainers.

> This portion:
>   
>> --- a/tools/perf/Makefile
>> +++ b/tools/perf/Makefile
>> @@ -201,7 +200,7 @@ EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wold-style-definition
>>  EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wstrict-prototypes
>>  EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wdeclaration-after-statement
>>  
>> -CFLAGS = $(MBITS) -ggdb3 -Wall -Wextra -std=gnu99 -Werror -O6 -fstack-protector-all -D_FORTIFY_SOURCE=2 $(EXTRA_WARNINGS)
>> +CFLAGS = $(MBITS) -ggdb3 -Wall -Wextra -std=gnu99 -Werror -O6 -D_FORTIFY_SOURCE=2 $(EXTRA_WARNINGS)
>>  LDFLAGS = -lpthread -lrt -lelf -lm
>>  ALL_CFLAGS = $(CFLAGS)
>>  ALL_LDFLAGS = $(LDFLAGS)
>>     
>
> Should be done not by removing the stack-protector build unconditionally 
> - but by auto-testing whether stackprotector is supported by GCC and 
> using it if yes.
>   

Revised patch attached.  It includes a test that the compiler doesn't 
bomb out with -fstack-protector-all and only adds the option to CFLAGS 
if ok.  But I have had to put the test below the definition of the macro 
CC.  This has the side effect of separating the addition of 
-fstack-protector-all from the main definitions of CFLAGS and 
ALL_CFLAGS, and is not ideal in my opinion.  The patch also removes 
-Wcast-align (I forgot to say that in the commit message of the patch).

Michael.



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