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dcce50e6cc
When building with Clang and CONFIG_TRACE_BRANCH_PROFILING, there are a lot of unreachable warnings, like: arch/x86/kernel/traps.o: warning: objtool: handle_xfd_event()+0x134: unreachable instruction Without an input to the inline asm, 'volatile' is ignored for some reason and Clang feels free to move the reachable() annotation away from its intended location. Fix that by re-adding the counter value to the inputs. Fixes:f1069a8756("compiler.h: Avoid using inline asm operand modifiers") Fixes:c199f64ff9("instrumentation.h: Avoid using inline asm operand modifiers") Reported-by: kernel test robot <lkp@intel.com> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Link: https://lore.kernel.org/r/0417e96909b97a406323409210de7bf13df0b170.1636410380.git.jpoimboe@redhat.com Cc: Peter Zijlstra <peterz@infradead.org> Cc: x86@kernel.org Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Miroslav Benes <mbenes@suse.cz>
61 lines
1.9 KiB
C
61 lines
1.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __LINUX_INSTRUMENTATION_H
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#define __LINUX_INSTRUMENTATION_H
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#if defined(CONFIG_DEBUG_ENTRY) && defined(CONFIG_STACK_VALIDATION)
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#include <linux/stringify.h>
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/* Begin/end of an instrumentation safe region */
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#define __instrumentation_begin(c) ({ \
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asm volatile(__stringify(c) ": nop\n\t" \
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".pushsection .discard.instr_begin\n\t" \
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".long " __stringify(c) "b - .\n\t" \
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".popsection\n\t" : : "i" (c)); \
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})
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#define instrumentation_begin() __instrumentation_begin(__COUNTER__)
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/*
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* Because instrumentation_{begin,end}() can nest, objtool validation considers
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* _begin() a +1 and _end() a -1 and computes a sum over the instructions.
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* When the value is greater than 0, we consider instrumentation allowed.
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*
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* There is a problem with code like:
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*
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* noinstr void foo()
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* {
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* instrumentation_begin();
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* ...
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* if (cond) {
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* instrumentation_begin();
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* ...
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* instrumentation_end();
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* }
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* bar();
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* instrumentation_end();
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* }
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*
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* If instrumentation_end() would be an empty label, like all the other
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* annotations, the inner _end(), which is at the end of a conditional block,
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* would land on the instruction after the block.
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*
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* If we then consider the sum of the !cond path, we'll see that the call to
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* bar() is with a 0-value, even though, we meant it to happen with a positive
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* value.
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*
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* To avoid this, have _end() be a NOP instruction, this ensures it will be
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* part of the condition block and does not escape.
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*/
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#define __instrumentation_end(c) ({ \
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asm volatile(__stringify(c) ": nop\n\t" \
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".pushsection .discard.instr_end\n\t" \
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".long " __stringify(c) "b - .\n\t" \
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".popsection\n\t" : : "i" (c)); \
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})
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#define instrumentation_end() __instrumentation_end(__COUNTER__)
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#else
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# define instrumentation_begin() do { } while(0)
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# define instrumentation_end() do { } while(0)
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#endif
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#endif /* __LINUX_INSTRUMENTATION_H */
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