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author | Ingo Molnar <mingo@kernel.org> | 2020-07-24 13:50:25 +0200 |
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committer | Ingo Molnar <mingo@kernel.org> | 2020-07-24 13:56:23 +0200 |
commit | d19e789f068b3d633cbac430764962f404198022 (patch) | |
tree | a28ff85a1c35d05b9712d43a53cc879a705ba2fb /include/linux/instrumentation.h | |
parent | Merge tag 's390-5.8-6' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux into master (diff) | |
download | wireguard-linux-d19e789f068b3d633cbac430764962f404198022.tar.xz wireguard-linux-d19e789f068b3d633cbac430764962f404198022.zip |
compiler.h: Move instrumentation_begin()/end() to new <linux/instrumentation.h> header
Linus pointed out that compiler.h - which is a key header that gets included in every
single one of the 28,000+ kernel files during a kernel build - was bloated in:
655389666643: ("vmlinux.lds.h: Create section for protection against instrumentation")
Linus noted:
> I have pulled this, but do we really want to add this to a header file
> that is _so_ core that it gets included for basically every single
> file built?
>
> I don't even see those instrumentation_begin/end() things used
> anywhere right now.
>
> It seems excessive. That 53 lines is maybe not a lot, but it pushed
> that header file to over 12kB, and while it's mostly comments, it's
> extra IO and parsing basically for _every_ single file compiled in the
> kernel.
>
> For what appears to be absolutely zero upside right now, and I really
> don't see why this should be in such a core header file!
Move these primitives into a new header: <linux/instrumentation.h>, and include that
header in the headers that make use of it.
Unfortunately one of these headers is asm-generic/bug.h, which does get included
in a lot of places, similarly to compiler.h. So the de-bloating effect isn't as
good as we'd like it to be - but at least the interfaces are defined separately.
No change to functionality intended.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200604071921.GA1361070@gmail.com
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Diffstat (limited to 'include/linux/instrumentation.h')
-rw-r--r-- | include/linux/instrumentation.h | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/include/linux/instrumentation.h b/include/linux/instrumentation.h new file mode 100644 index 000000000000..93e2ad67fc10 --- /dev/null +++ b/include/linux/instrumentation.h @@ -0,0 +1,57 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __LINUX_INSTRUMENTATION_H +#define __LINUX_INSTRUMENTATION_H + +#if defined(CONFIG_DEBUG_ENTRY) && defined(CONFIG_STACK_VALIDATION) + +/* Begin/end of an instrumentation safe region */ +#define instrumentation_begin() ({ \ + asm volatile("%c0: nop\n\t" \ + ".pushsection .discard.instr_begin\n\t" \ + ".long %c0b - .\n\t" \ + ".popsection\n\t" : : "i" (__COUNTER__)); \ +}) + +/* + * Because instrumentation_{begin,end}() can nest, objtool validation considers + * _begin() a +1 and _end() a -1 and computes a sum over the instructions. + * When the value is greater than 0, we consider instrumentation allowed. + * + * There is a problem with code like: + * + * noinstr void foo() + * { + * instrumentation_begin(); + * ... + * if (cond) { + * instrumentation_begin(); + * ... + * instrumentation_end(); + * } + * bar(); + * instrumentation_end(); + * } + * + * If instrumentation_end() would be an empty label, like all the other + * annotations, the inner _end(), which is at the end of a conditional block, + * would land on the instruction after the block. + * + * If we then consider the sum of the !cond path, we'll see that the call to + * bar() is with a 0-value, even though, we meant it to happen with a positive + * value. + * + * To avoid this, have _end() be a NOP instruction, this ensures it will be + * part of the condition block and does not escape. + */ +#define instrumentation_end() ({ \ + asm volatile("%c0: nop\n\t" \ + ".pushsection .discard.instr_end\n\t" \ + ".long %c0b - .\n\t" \ + ".popsection\n\t" : : "i" (__COUNTER__)); \ +}) +#else +# define instrumentation_begin() do { } while(0) +# define instrumentation_end() do { } while(0) +#endif + +#endif /* __LINUX_INSTRUMENTATION_H */ |