build: Fix warnings in x86_64 assembly check #1749

1. 
   hebasto commented at 9:59 pm on September 17, 2025: member

   On the master branch @ 10dab907e73ba984deb813e20f6e3fc9ec359a17, the x86_64 assembly check in both the Autotools and CMake build systems can fail depending on externally provided flags. For example:

   0$ env CFLAGS="-Wall -Werror" ./configure --with-asm=x86_64
   1<snip>
   2checking for x86_64 assembly availability... no
   3configure: error: x86_64 assembly requested but not available
   

   or

   0$ env CFLAGS="-Wall -Werror" cmake -B build -DSECP256K1_ASM=x86_64
   1<snip>
   2-- Performing Test HAVE_X86_64_ASM
   3-- Performing Test HAVE_X86_64_ASM - Failed
   4CMake Error at CMakeLists.txt:111 (message):
   5  x86_64 assembly requested but not available.
   6
   7
   8-- Configuring incomplete, errors occurred!
   

   The same issue occurs in CI jobs that build on Windows using clang-cl.

   This PR fixes both build systems.

2. hebasto renamed this:
   build: Fix `-Wuninitialized` warning in x86_64 assembly check code
   build: Fix `-Wuninitialized` warning in x86_64 assembly check
   on Sep 17, 2025
3. hebasto force-pushed on Sep 17, 2025
4. hebasto renamed this:
   build: Fix `-Wuninitialized` warning in x86_64 assembly check
   build: Fix warnings in x86_64 assembly check
   on Sep 17, 2025
5. in cmake/CheckX86_64Assembly.cmake:7 in 8b75fa0807 outdated

   5@@ -6,8 +6,9 @@ function(check_x86_64_assembly)
   6 
   7     int main()
   

   ---

   ---

   

   real-or-random commented at 1:53 pm on September 18, 2025:

   While we’re at it…

   0    int main(void)
   

   ---

   

   hebasto commented at 1:57 pm on September 18, 2025:

   Thanks! Fixed.
6. 
   real-or-random commented at 1:53 pm on September 18, 2025: contributor

   ACK mod nit
7. real-or-random added the label build on Sep 18, 2025
8. real-or-random added the label tweak/refactor on Sep 18, 2025
9. build: Fix warnings in x86_64 assembly check

   This change fixes:
   - `-Wuninitialized` in both Autotools and CMake;
   - `-Wreturn-type` in CMake only.

   ab560078aa
10. hebasto force-pushed on Sep 18, 2025
11. real-or-random approved
12. 
    real-or-random commented at 1:58 pm on September 18, 2025: contributor

    utACK ab560078aa9c7e977fade4ceae4a20ef8e5be025
13. 
    furszy commented at 7:53 pm on September 18, 2025: member

    ACK ab560078aa9c7e977fade4ceae4a20ef8e5be025
14. real-or-random merged this on Sep 19, 2025
15. real-or-random closed this on Sep 19, 2025

    ---

16. hebasto deleted the branch on Sep 19, 2025

Contributors
hebasto real-or-random furszy

Labels
build tweak/refactor