From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Vasily Gorbik <gor@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@suse.de>,
Miroslav Benes <mbenes@suse.cz>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] compiler.h: Avoid using inline asm operand modifiers
Date: Fri, 5 Nov 2021 09:54:18 -0700 [thread overview]
Message-ID: <20211105165418.ucsrpk53dv5kgu6k@treble> (raw)
In-Reply-To: <patch-1.thread-1a26be.git-930d1b44844a.your-ad-here.call-01621428935-ext-2104@work.hours>
On Wed, May 19, 2021 at 03:03:08PM +0200, Vasily Gorbik wrote:
> The expansion of annotate_reachable/annotate_unreachable on s390 will
> result in a compiler error if the __COUNTER__ value is high enough.
> For example with "i" (154) the "%c0" operand of annotate_reachable
> will be expanded to -102:
>
> -102:
> .pushsection .discard.reachable
> .long -102b - .
> .popsection
>
> This is a quirk of the gcc backend for s390, it interprets the %c0
> as a signed byte value. Avoid using operand modifiers in this case
> by simply converting __COUNTER__ to string, with the same result,
> but in an arch assembler independent way.
>
> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Hi Vasily,
This patch causes these macros to break with Clang and
CONFIG_TRACE_BRANCH_PROFILING.
I get a lot of warnings like
arch/x86/kernel/traps.o: warning: objtool: handle_xfd_event()+0x134: unreachable instruction
Without an asm input, 'volatile' is ignored for some reason and Clang
feels free to move the reachable() annotation away from its intended
location.
I wonder if we could go back to the original approach of providing
__COUNTER__ as an input to the asm, but then mask it to < 128.
Does this work on s390?
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 3d5af56337bd..42935500a712 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -115,24 +115,18 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
* The __COUNTER__ based labels are a hack to make each instance of the macros
* unique, to convince GCC not to merge duplicate inline asm statements.
*/
-#define __stringify_label(n) #n
-
-#define __annotate_reachable(c) ({ \
- asm volatile(__stringify_label(c) ":\n\t" \
+#define annotate_reachable() ({ \
+ asm volatile("%c0:\n\t" \
".pushsection .discard.reachable\n\t" \
- ".long " __stringify_label(c) "b - .\n\t" \
- ".popsection\n\t"); \
+ ".long %c0b - .\n\t" \
+ ".popsection\n\t" : : "i" (__COUNTER__ & 0x7f)); \
})
-#define annotate_reachable() __annotate_reachable(__COUNTER__)
-
-#define __annotate_unreachable(c) ({ \
- asm volatile(__stringify_label(c) ":\n\t" \
+#define annotate_unreachable() ({ \
+ asm volatile("%c0:\n\t" \
".pushsection .discard.unreachable\n\t" \
- ".long " __stringify_label(c) "b - .\n\t" \
- ".popsection\n\t"); \
+ ".long %c0b - .\n\t" \
+ ".popsection\n\t" : : "i" (__COUNTER__ & 0x7f)); \
})
-#define annotate_unreachable() __annotate_unreachable(__COUNTER__)
-
#define ASM_UNREACHABLE \
"999:\n\t" \
".pushsection .discard.unreachable\n\t" \
next prev parent reply other threads:[~2021-11-05 16:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-19 13:03 [PATCH 0/2] objtool annotations: Avoid using inline asm operand modifiers Vasily Gorbik
2021-05-19 13:03 ` [PATCH 1/2] compiler.h: " Vasily Gorbik
2021-11-05 16:54 ` Josh Poimboeuf [this message]
2021-11-08 15:40 ` Vasily Gorbik
2021-11-08 16:50 ` Josh Poimboeuf
2021-11-10 10:39 ` David Laight
2021-05-19 13:03 ` [PATCH 2/2] instrumentation.h: " Vasily Gorbik
2021-05-19 20:52 ` [PATCH 0/2] objtool annotations: " Josh Poimboeuf
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