GCC 16 and busybox-w32

[rmyorston]

I've just done my first prerelease build of busybox-w32 with x86_64-w64-mingw32-gcc (version 16.0.1) on Fedora 44. The 32-bit binaries were fine, but the two x86_64 binaries were about 20KB larger than the last build on Fedora 43. The increase was entirely in the text section.

Looking at the sizes of the object files, most were about the same size as before but ~7% of them were a lot bigger. For example, the text section of libbb/trim.o went from 136 to 592 bytes. The assembly code seemed to indicate that the difference was a call to memmove being expanded into inline assembler. Apparently this is a thing.

OK, we can fix that: add -fno-builtin-memmove to the compiler flags at line 160 of Makefile.flags. And the size of the binaries goes back to normal.

I've tried the same thing with w64devkit's GCC 16.1.1 with the same effect.

Before:

 $ x86_64-w64-mingw32-size.exe busybox.exe
   text    data     bss     dec     hex filename
 744588    1168    5616  751372   b770c busybox.exe

After:

$ x86_64-w64-mingw32-size busybox.exe
   text    data     bss     dec     hex filename
 724520    1168    5616  731304   b28a8 busybox.exe

Just thought you'd like to know.

[Peter0x44]

Thanks for sharing, that's unfortunate. I think I'll try reporting this to GCC.