Missing builtins, attributes & atomics with clang on Alpine Linux on armv[78] and riscv64

[ac000]

          @ac000 thank you for patch! it allows to [build](https://gitlab.alpinelinux.org/alpine/aports/-/pipelines/178845) meantime exposed issues on armv7 and armv8 and riscv64

checking for GCC __builtin_expect() ... not found
checking for GCC __builtin_unreachable() ... not found
checking for GCC __builtin_prefetch() ... not found
checking for GCC __builtin_clz() ... not found
checking for GCC __builtin_popcount() ... not found
checking for GCC __attribute__ visibility ... not found
checking for GCC __attribute__ aligned ... not found
checking for GCC __attribute__ malloc ... not found
checking for GCC __attribute__ packed ... not found
checking for GCC __attribute__ unused ... not found
checking for GCC builtin atomic operations ... not found
checking for Solaris builtin atomic operations ... not found
checking for xlC builtin atomic operations ... not found
./configure: error: no atomic operations found.

maybe it's related to clang for this arches but at least "GCC" prefix for atomics is confusing when building with clang

Originally posted by @andypost in https://github.com/nginx/unit/issues/936#issuecomment-1708938752

[thresheek]

FWIW I can not reproduce with the same docker image as used on Alpine pipeline linked in https://github.com/nginx/unit/issues/936#issuecomment-1708938752 - running locally on Ubuntu 22.04 aarch64 host.

Output of build/autoconf.err will help.

[ac000]

@thresheek

Thanks for trying that. There is definitely something very broken in this case, from one of the failed builds

checking for endianness ... not found
checking for int size ... not found
checking for long size ... not found
checking for long long size ... not found
checking for void * size ... not found
checking for size_t size ... not found
checking for off_t size ... not found
checking for time_t size ... not found
checking for C99 variadic macro ... not found
checking for GCC variadic macro ... not found
checking for GCC __builtin_expect() ... not found
checking for GCC __builtin_unreachable() ... not found
checking for GCC __builtin_prefetch() ... not found
checking for GCC __builtin_clz() ... not found
checking for GCC __builtin_popcount() ... not found
checking for GCC __attribute__ visibility ... not found
checking for GCC __attribute__ aligned ... not found
checking for GCC __attribute__ malloc ... not found
checking for GCC __attribute__ packed ... not found
checking for GCC __attribute__ unused ... not found
checking for GCC builtin atomic operations ... not found
checking for Solaris builtin atomic operations ... not found
checking for xlC builtin atomic operations ... not found

Absolutely nothing worked!

@andypost as @thresheek says, if you could post the build/autoconf.err file from one of the failed builds, that may shed some light on the matter.

However it looks like clang is very broken on these systems.

[andypost]

@ac000 here's full log of build env https://gist.github.com/andypost/bfeb0f21637a0a2463c00151eb429e69

[ac000]

Thanks.

Heh. What's fix-clang.patch?

But it looks like all the tests are failing due to the unknown -fstack-clash-protection option.

checking for endianness
clang-16: error: argument unused during compilation: '-fstack-clash-protection' [-Werror,-Wunused-command-line-argument]

I don't know where that actually comes from. I can't see it set anywhere in Unit. There are other options like -Os which I can't see set in Unit.

As to fstack-clash-protection it looks like it is only implemented on some platforms currently

https://blog.llvm.org/posts/2021-01-05-stack-clash-protection/ https://reviews.llvm.org/D96007

So we need to find where this is coming from.

[ac000]

On Alpine Linux, this is the command I'm seeing run for these tests...

clang -pipe -fPIC -fvisibility=hidden -O -W -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -fstrict-aliasing -Wstrict-overflow=5 -Wmissing-prototypes -Werror -g -o build/autotest build/autotest.c

[andypost]

Probably builders/CI configured this way, I found other packages using it and now it pass https://gitlab.alpinelinux.org/alpine/aports/-/pipelines/178897

    case "$CARCH" in
    arm*|aarch64|riscv64)
        export CFLAGS="${CFLAGS/-fstack-clash-protection}"
        ;;
    esac

[ac000]

OK, cool. I'll go ahead and close this then.