Re: [Buildroot] [PATCH v1, next] package/llvm-project/compiler-rt: fix build with Ninja

["Yann E. MORIN" <yann.morin.1998@free.fr>]

Thomas D., All,

On 2023-08-08 13:22 +0200, Thomas Devoogdt spake thusly:
> > Not sure to understand: the default backend for CMake is still
> > makefiles, and compiler-rt was not switched to using ninja. So?
> 
> No, ninja is not yet the default.
> Yann did some tests to find out if it makes sense to make ninja the default.
> If only a few packages break on it, then we can force them to use make.
> But if there are too many of them, then we can just keep make as the default.
> 
> Either way, see this mail:
> https://lore.kernel.org/buildroot/20230806205447.GW421096@scaer/,
> where Yann told me that compiler-rt fails on ninja, so that's the
> reason for the patch.

Yes, but as Thomas P. explains, we only need to fix compiler-rt with
ninja if it is actually switched over to using ninja, which your patch
does not do.

Presumably, the build of compiler-rt succeeds now, so if it ain't
broken, so why would we need to fix it by building out-of-source?

But if you had tested, you'd have noticed that the build *is* already
broken even with makefiles. But make is (insanely) forgiving about
circular dependencies, and just arbitrarily drops a circular dependency:

    >>> compiler-rt 15.0.3 Building
    PATH="..." /home/ymorin/dev/buildroot/O/next/per-package/compiler-rt/host/bin/cmake --build /home/ymorin/dev/buildroot/O/next/build/compiler-rt-15.0.3/ -j9 -- 
    make[4]: Circular include/sanitizer/allocator_interface.h <- include/sanitizer/allocator_interface.h dependency dropped.
    make[4]: Circular include/sanitizer/asan_interface.h <- include/sanitizer/asan_interface.h dependency dropped.
    make[4]: Circular include/sanitizer/common_interface_defs.h <- include/sanitizer/common_interface_defs.h dependency dropped.
    make[4]: Circular include/sanitizer/coverage_interface.h <- include/sanitizer/coverage_interface.h dependency dropped.
    make[4]: Circular include/sanitizer/dfsan_interface.h <- include/sanitizer/dfsan_interface.h dependency dropped.
    make[4]: Circular include/sanitizer/hwasan_interface.h <- include/sanitizer/hwasan_interface.h dependency dropped.
    make[4]: Circular include/sanitizer/linux_syscall_hooks.h <- include/sanitizer/linux_syscall_hooks.h dependency dropped.
    make[4]: Circular include/sanitizer/lsan_interface.h <- include/sanitizer/lsan_interface.h dependency dropped.
    make[4]: Circular include/sanitizer/msan_interface.h <- include/sanitizer/msan_interface.h dependency dropped.
    make[4]: Circular include/sanitizer/netbsd_syscall_hooks.h <- include/sanitizer/netbsd_syscall_hooks.h dependency dropped.
    make[4]: Circular include/sanitizer/scudo_interface.h <- include/sanitizer/scudo_interface.h dependency dropped.
    make[4]: Circular include/sanitizer/tsan_interface.h <- include/sanitizer/tsan_interface.h dependency dropped.
    make[4]: Circular include/sanitizer/tsan_interface_atomic.h <- include/sanitizer/tsan_interface_atomic.h dependency dropped.
    make[4]: Circular include/sanitizer/ubsan_interface.h <- include/sanitizer/ubsan_interface.h dependency dropped.
    make[4]: Circular include/fuzzer/FuzzedDataProvider.h <- include/fuzzer/FuzzedDataProvider.h dependency dropped.
    make[4]: Circular include/sanitizer/memprof_interface.h <- include/sanitizer/memprof_interface.h dependency dropped.
    make[4]: Circular include/profile/MemProfData.inc <- include/profile/MemProfData.inc dependency dropped.
    make[4]: Circular include/xray/xray_interface.h <- include/xray/xray_interface.h dependency dropped.
    make[4]: Circular include/xray/xray_log_interface.h <- include/xray/xray_log_interface.h dependency dropped.
    make[4]: Circular include/xray/xray_records.h <- include/xray/xray_records.h dependency dropped.
    make[4]: Circular include/orc/c_api.h <- include/orc/c_api.h dependency dropped.
    make[4]: Circular include/profile/InstrProfData.inc <- include/profile/InstrProfData.inc dependency dropped.

In this case, this is OK because the file depends on itself, so breaking
the circular dependency actually removes the spurious dependency.

However, this is not correct, and thus we do need to build compiler-rt
with out-of-source, even with makefile, because it *is* broken.

So, the rationale is wrong: it is not broken because of ninja. It is
broken despite ninja, but ninja exposes the breakage.

Really, when we have a patch that fixes something, what is broken and
why it is broken, is of the utmost most importance; the explanations for
the technical fix is important too, but it only comes second, with the
code actually being the less interesting thing.

Can you please resubmit the patch, but with a corrected commit log that
summarises the above explanations, please?

Regards,
Yann E. MORIN.

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