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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: torvalds@linux-foundation.org, tglx@linutronix.de, hpa@zytor.com,
	julien.thierry@arm.com, will.deacon@arm.com, luto@amacapital.net,
	mingo@kernel.org, catalin.marinas@arm.com, james.morse@arm.com,
	valentin.schneider@arm.com, brgerst@gmail.com, luto@kernel.org,
	bp@alien8.de, dvlasenk@redhat.com, linux-kernel@vger.kernel.org,
	dvyukov@google.com, rostedt@goodmis.org
Subject: Re: [PATCH 00/20] objtool: UACCESS validation v3
Date: Thu, 7 Mar 2019 11:48:02 -0600
Message-ID: <20190307174802.46fmpysxyo35hh43@treble> (raw)
In-Reply-To: <20190307174322.GK32477@hirez.programming.kicks-ass.net>

On Thu, Mar 07, 2019 at 06:43:22PM +0100, Peter Zijlstra wrote:
> On Thu, Mar 07, 2019 at 10:47:05AM -0600, Josh Poimboeuf wrote:
> 
> > This "fixes" it, and also seems to help -Os make much code:
> > 
> > diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> > index 445348facea9..8de63db58fdd 100644
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -67,7 +67,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> >  				.line = __LINE__,			\
> >  			};						\
> >  		______r = !!(cond);					\
> > -		______f.miss_hit[______r]++;					\
> > +		if (______r) ______f.miss_hit[1]++; else ______f.miss_hit[0]++; \
> >  		______r;						\
> >  	}))
> >  #endif /* CONFIG_PROFILE_ALL_BRANCHES */
> 
> Excellen; let me put the kids to bed and then I'll have a poke.

Here's a proper patch.

From: Josh Poimboeuf <jpoimboe@redhat.com>
Subject: [PATCH] tracing: Improve "if" macro code generation

With CONFIG_PROFILE_ALL_BRANCHES, the "if" macro converts the
conditional to an array index.  This can cause GCC to create horrible
code.  When there are nested ifs, the generated code uses register
values to encode branching decisions.

Make it easier for GCC to optimize by keeping the conditional as a
conditional rather than converting it to an integer.  This shrinks the
generated code quite a bit, and also makes the code sane enough for
objtool to understand.

Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 include/linux/compiler.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 445348facea9..d58aa0db05f9 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -67,7 +67,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
 				.line = __LINE__,			\
 			};						\
 		______r = !!(cond);					\
-		______f.miss_hit[______r]++;					\
+		______r ? ______f.miss_hit[1]++ : ______f.miss_hit[0]++;\
 		______r;						\
 	}))
 #endif /* CONFIG_PROFILE_ALL_BRANCHES */
-- 
2.17.2


  reply index

Thread overview: 100+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-07 11:45 Peter Zijlstra
2019-03-07 11:45 ` [PATCH 01/20] x86/ia32: Fix ia32_restore_sigcontext AC leak Peter Zijlstra
2019-03-07 11:45 ` [PATCH 02/20] i915,uaccess: Fix redundant CLAC Peter Zijlstra
2019-03-07 11:45 ` [PATCH 03/20] x86/uaccess: Move copy_user_handle_tail into asm Peter Zijlstra
2019-03-08 18:53   ` Josh Poimboeuf
2019-03-08 19:48     ` Peter Zijlstra
2019-03-08 19:53       ` Josh Poimboeuf
2019-03-10 13:22         ` Peter Zijlstra
2019-03-07 11:45 ` [PATCH 04/20] x86/uaccess: Fix up the fixup Peter Zijlstra
2019-03-07 11:45 ` [PATCH 05/20] x86/uaccess/xen: Suppress SMAP warnings Peter Zijlstra
2019-03-07 12:22   ` Juergen Gross
2019-03-07 12:32     ` Peter Zijlstra
2019-03-07 12:36       ` Juergen Gross
2019-03-08 19:00   ` Josh Poimboeuf
2019-03-08 19:03     ` Josh Poimboeuf
2019-03-10 13:19       ` Peter Zijlstra
2019-03-11 17:59         ` Josh Poimboeuf
2019-03-08 19:50     ` Peter Zijlstra
2019-03-07 11:45 ` [PATCH 06/20] x86/uaccess: Always inline user_access_begin() Peter Zijlstra
2019-03-07 11:45 ` [PATCH 07/20] x86/uaccess: Always inline force_valid_ss() Peter Zijlstra
2019-03-07 13:50   ` Peter Zijlstra
2019-03-07 18:05   ` Andy Lutomirski
2019-03-07 18:59     ` Peter Zijlstra
2019-03-07 19:06       ` Andy Lutomirski
2019-03-07 11:45 ` [PATCH 08/20] x86/uaccess: Introduce user_access_{save,restore}() Peter Zijlstra
2019-03-07 11:45 ` [PATCH 09/20] x86/uaccess,kasan: Fix KASAN vs SMAP Peter Zijlstra
2019-03-07 11:45 ` [PATCH 10/20] x86/uaccess,ubsan: Fix UBSAN " Peter Zijlstra
2019-03-07 11:45 ` [PATCH 11/20] x86/uaccess,ftrace: Fix ftrace_likely_update() " Peter Zijlstra
2019-03-07 11:45 ` [PATCH 12/20] objtool: Set insn->func for alternatives Peter Zijlstra
2019-03-08 19:16   ` Josh Poimboeuf
2019-03-08 19:51     ` Peter Zijlstra
2019-03-07 11:45 ` [PATCH 13/20] objtool: Hande function aliases Peter Zijlstra
2019-03-08 19:23   ` Josh Poimboeuf
2019-03-08 19:52     ` Peter Zijlstra
2019-03-08 20:00       ` Josh Poimboeuf
2019-03-07 11:45 ` [PATCH 14/20] objtool: Rewrite add_ignores() Peter Zijlstra
2019-03-08 19:29   ` Josh Poimboeuf
2019-03-07 11:45 ` [PATCH 15/20] objtool: Add --backtrace support Peter Zijlstra
2019-03-08 19:33   ` Josh Poimboeuf
2019-03-07 11:45 ` [PATCH 16/20] objtool: Rewrite alt->skip_orig Peter Zijlstra
2019-03-08 20:15   ` Josh Poimboeuf
2019-03-08 21:34     ` Peter Zijlstra
2019-03-08 22:27       ` Josh Poimboeuf
2019-03-07 11:45 ` [PATCH 17/20] objtool: Fix sibling call detection Peter Zijlstra
2019-03-08 20:22   ` Josh Poimboeuf
2019-03-07 11:45 ` [PATCH 18/20] objtool: Add UACCESS validation Peter Zijlstra
2019-03-07 16:33   ` Linus Torvalds
2019-03-07 17:10     ` hpa
2019-03-07 17:41     ` Peter Zijlstra
2019-03-07 17:54       ` Linus Torvalds
2019-03-07 18:48         ` Peter Zijlstra
2019-03-07 18:51           ` hpa
2019-03-07 19:03           ` Peter Zijlstra
2019-03-08 15:01             ` Josh Poimboeuf
2019-03-08 15:07               ` Peter Zijlstra
2019-03-07 20:23           ` Peter Zijlstra
2019-03-07 20:40             ` Peter Zijlstra
2019-03-08 15:07               ` Josh Poimboeuf
2019-03-08 15:23                 ` Peter Zijlstra
2019-03-07 20:15       ` Andrey Ryabinin
2019-03-07 20:33         ` Peter Zijlstra
2019-03-07 20:40           ` Andrey Ryabinin
2019-03-07 20:42           ` Peter Zijlstra
2019-03-08 21:02   ` Josh Poimboeuf
2019-03-08 21:31     ` Peter Zijlstra
2019-03-08 21:54       ` Josh Poimboeuf
2019-03-10 13:10     ` Peter Zijlstra
2019-03-11 18:01       ` Josh Poimboeuf
2019-03-07 11:45 ` [PATCH 19/20] objtool: uaccess PUSHF/POPF support Peter Zijlstra
2019-03-08 21:11   ` Josh Poimboeuf
2019-03-10 13:12     ` Peter Zijlstra
2019-03-07 11:45 ` [PATCH 20/20] objtool: Add Direction Flag validation Peter Zijlstra
2019-03-08 21:16   ` Josh Poimboeuf
2019-03-08 21:33     ` Peter Zijlstra
2019-03-08 21:56       ` Josh Poimboeuf
2019-03-10 13:13         ` Peter Zijlstra
2019-03-11 18:00           ` Josh Poimboeuf
2019-03-07 12:03 ` [PATCH 00/20] objtool: UACCESS validation v3 Peter Zijlstra
2019-03-07 12:55   ` Peter Zijlstra
2019-03-07 13:13     ` Peter Zijlstra
2019-03-07 16:47       ` Josh Poimboeuf
2019-03-07 16:50         ` Josh Poimboeuf
2019-03-07 17:00         ` Linus Torvalds
2019-03-07 17:17           ` Josh Poimboeuf
2019-03-07 17:38             ` Peter Zijlstra
2019-03-07 17:45               ` Linus Torvalds
2019-03-07 18:18                 ` Steven Rostedt
2019-03-10 13:16                   ` Peter Zijlstra
2019-04-19 10:08                     ` [PATCH] compiler.h, tracing: Remove CONFIG_PROFILE_ALL_BRANCHES Ingo Molnar
2019-04-19 13:04                       ` Steven Rostedt
2019-03-07 17:04         ` [PATCH 00/20] objtool: UACCESS validation v3 hpa
2019-03-07 17:18           ` Josh Poimboeuf
2019-03-07 17:29             ` hpa
2019-03-07 17:45               ` Josh Poimboeuf
2019-03-07 17:48                 ` Linus Torvalds
2019-03-07 17:43         ` Peter Zijlstra
2019-03-07 17:48           ` Josh Poimboeuf [this message]
2019-04-03  8:21             ` [tip:core/objtool] tracing: Improve "if" macro code generation tip-bot for Josh Poimboeuf
2019-03-07 16:31   ` [PATCH 00/20] objtool: UACCESS validation v3 Linus Torvalds
2019-03-07 17:14 ` hpa

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