nickdesaulniers added a comment.
In D141451#4258031 <https://reviews.llvm.org/D141451#4258031>, @aaron.ballman
wrote:
> Have you checked to see how the diagnostics work in practice on deep inlining
> stacks? If it's usually only 1-2 extra notes, that's probably not going to
> overwhelm anyone. But if it's significantly more, that could be distracting.
> Do we want any options to control when to emit the notes? e.g., do we want to
> give users a way to say "only emit the last N inlining decision notes"?
I don't have a good means of aggregating such data, but in my kernel experience
we only ever emit about 2-4 notes before we stop inlining. It is usually much
less than the inclusion chain of headers reported. Example (I've manually
added a bad memcmp to kernel sources):
In file included from drivers/nfc/nfcmrvl/fw_dnld.c:8:
In file included from ./include/linux/module.h:13:
In file included from ./include/linux/stat.h:19:
In file included from ./include/linux/time.h:60:
In file included from ./include/linux/time32.h:13:
In file included from ./include/linux/timex.h:67:
In file included from ./arch/x86/include/asm/timex.h:5:
In file included from ./arch/x86/include/asm/processor.h:23:
In file included from ./arch/x86/include/asm/msr.h:11:
In file included from ./arch/x86/include/asm/cpumask.h:5:
In file included from ./include/linux/cpumask.h:12:
In file included from ./include/linux/bitmap.h:11:
In file included from ./include/linux/string.h:254:
./include/linux/fortify-string.h:661:4: error: call to '__read_overflow2'
declared with 'error' attribute: detected read beyond size of object (2nd
parameter)
__read_overflow2();
^
note: In function 'fw_dnld_rx_work'
note: which inlined function 'process_state_reset'
note: which inlined function 'memcmp(void const*, void const*
pass_dynamic_object_size0, unsigned long pass_dynamic_object_size0)'
1 error generated.
Can you construct come "cuckoo-bananas" cases with this though? Yes:
https://godbolt.org/z/9eP8vjeb8
> Also, how does this work with LTO when it makes different inlining decisions?
The concern with LTO is less about a change in inlining decisions, and more so
about loss of fidelity with corresponding SourceLocations.
Testing the same kernel code same above, but with LTO enabled, we simply get a
backend diagnostic from LLD, since the sources and thus SourceLocations are not
retained:
ld.lld: error: call to __read_overflow2 marked "dontcall-error": detected
read beyond size of object (2nd parameter)
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