The following code w/ ToT LLVM (clang-15) produces the following warnings:

void*x(void) {return (char*)0+42;}void*y(void) {return (void*)0+42;}

<source>:2:21: warning: arithmetic on a null pointer treated as a cast from integer to pointer is a GNU extension [-Wnull-pointer-arithmetic]    return (char*)0 + 42;           ~~~~~~~~ ^<source>:6:21: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]    return (void*)0 + 42;           ~~~~~~~~ ^

for the Linux kernel, we're using-std=gnu11 -Wno-gnu, so we should not be observing ANY warnings that we're using GNU C extensions.

I suspect that these two checks should be split into two different named command line flags, such that the one pertaining to GNU C extensions is placed within the-Wgnu flag group, such that-Wno-gnu implicitly disables it.

cc@AaronBallman@andykaylor

(link#4440)

As reported inthis thread.