On Thu, May 01, 2025 at 06:34:57PM -0700, Linus Torvalds wrote:
On Thu, 1 May 2025 at 18:24, Nathan Chancellor nathan@kernel.org wrote:
but '= {0}' appears to work: https://godbolt.org/z/x7eae5vex
If using that instead upsets sparse still, then I can just abandon this change and update the other patch to disable -Wdefault-const-init-unsafe altogether (
The "= { 0 }" form makes sparse unhappy for a different reason:
void *a = { 0 };makes sparse (correctly) complain about the use of '0' for 'NULL'.
warning: Using plain integer as NULL pointerand gcc has also finally adopted that warning for braindamage:
warning: zero as null pointer constant [-Wzero-as-null-pointer-constant]
although it's not on by default (and apparently we've never enabled it for the kernel - although we really should).
sparse has complained about this since day one, because I personally find the "plain 0 as NULL" to be a complete BS mistake in the language (that came from avoiding a keyword, not from some "design" reason), and while it took C++ people three decades to figure that out, in the end they did indeed figure it out.
Yeah, that is all entirely reasonable. It does not really seem like there is a clean way to deal with this with our matrix (aside from something like a local __diag_push() sequence, which I understand you do not like), so I will abandon this and just turn off the warning entirely (unless folks have other ideas). I am not really sure we will miss it because clang will still warn if the variable is used uninitialized since -Wuninitialized is enabled in -Wall.
$ cat test.c int main(void) { const int a, b; return a; }
$ clang -fsyntax-only test.c test.c:3:15: warning: default initialization of an object of type 'const int' leaves the object uninitialized and is incompatible with C++ [-Wdefault-const-init-var-unsafe] 3 | const int a, b; | ^ test.c:3:18: warning: default initialization of an object of type 'const int' leaves the object uninitialized and is incompatible with C++ [-Wdefault-const-init-var-unsafe] 3 | const int a, b; | ^ 2 warnings generated.
$ clang -fsyntax-only -Wuninitialized test.c test.c:3:15: warning: default initialization of an object of type 'const int' leaves the object uninitialized and is incompatible with C++ [-Wdefault-const-init-var-unsafe] 3 | const int a, b; | ^ test.c:3:18: warning: default initialization of an object of type 'const int' leaves the object uninitialized and is incompatible with C++ [-Wdefault-const-init-var-unsafe] 3 | const int a, b; | ^ test.c:4:12: warning: variable 'a' is uninitialized when used here [-Wuninitialized] 4 | return a; | ^ test.c:3:16: note: initialize the variable 'a' to silence this warning 3 | const int a, b; | ^ | = 0 3 warnings generated.
Cheers, Nathan