llvm dev - Dec 2019 - Issue combining SanitizerCoverage with LTO

An issue was reported to me that involved using
"-fsanitize-coverage=trace-pc-guard -flto=thin".

Currently, what seems to happen is that the sancov instrumentation gets inserted
at compile-time, then at LTO-time some instrumented functions get erased.  The
associated sancov globals don't get erased, though.  The end result is that
some sancov globals have null MD_associated metadata, and the linker prints an
error like "incompatible section flags for __sancov_guards".  This
seems to happen for any program where a function is erased at link time.  For
example, the following program:

void testfn(){}
__attribute((visibility("hidden"))) void testfn2(){}

I'm not sure how __sancov_guards is supposed to work in this context.  Is
LTO misbehaving, or is SanitizerCoverage making bad assumptions?

-Eli
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20191203/167714fa/attachment.html>

I believe i have reported a related issue in
https://bugs.llvm.org/show_bug.cgi?id=41734
"-fsanitize-coverage=inline-8bit-counters + ThinLTO = lld crash"

On Wed, Dec 4, 2019 at 12:56 AM Eli Friedman via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> An issue was reported to me that involved using
“-fsanitize-coverage=trace-pc-guard -flto=thin”.
>
>
>
> Currently, what seems to happen is that the sancov instrumentation gets
inserted at compile-time, then at LTO-time some instrumented functions get
erased.  The associated sancov globals don’t get erased, though.  The end result
is that some sancov globals have null MD_associated metadata, and the linker
prints an error like “incompatible section flags for __sancov_guards”.  This
seems to happen for any program where a function is erased at link time.  For
example, the following program:
>
>
>
> void testfn(){}
>
> __attribute((visibility("hidden"))) void testfn2(){}
>
>
>
> I’m not sure how __sancov_guards is supposed to work in this context.  Is
LTO misbehaving, or is SanitizerCoverage making bad assumptions?
>
>
>
> -Eli
Roman
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev