Here's an interesting bug I just ran into, a bug in commit
c12d3362a74b ("int128: move __uint128_t compiler test to Kconfig")
My x86-64 kernel build is lacking CC_HAS_INT128 and therefore
CONFIG_ARCH_SUPPORTS_INT128, even through it supports
__int128 just fine.
The reason is that the actuall call which tests for compiler support is
execve("/usr/bin/gcc", ["gcc", "-Werror", "-D__SIZEOF_INT128__=0", "-S", "-x", "c", "/dev/null", "-o", "/dev/null"], 0x5818d390 /* 122 vars */) = 0
and it doesn't detect the redefined symbol.
$ gcc -Werror -D__SIZEOF_INT128__=0 -S -x c /dev/null -o /dev/null
$ echo $?
0
But on my machine, gcc defaults to the 32-bit compiler. The kernel
is compiled with -m64, and with that on the command line, things
fail as expected:
$ gcc -m64 -Werror -D__SIZEOF_INT128__=0 -S -x c /dev/null -o /dev/null
<command-line>: error: "__SIZEOF_INT128__" redefined [-Werror]
<built-in>: note: this is the location of the previous definition
cc1: all warnings being treated as errors
$
I haven't figured out how to fix this, but hopefully someone more familiar
with the innards of Kconfig can.
