daurnimator
commented
5 years ago This looks like a bug with GCC. Could you report it there?
Closed pspacek closed 5 years ago
daurnimator
commented
5 years ago This looks like a bug with GCC. Could you report it there?
daurnimator
commented
5 years ago Minimal reproduction: https://godbolt.org/z/LIfUzV
/*
* C O M P I L E R A N N O T A T I O N S
*
* GCC with -Wextra, and clang by default, complain about overrides in
* initializer lists. Overriding previous member initializers is well
* defined behavior in C. We rely on this behavior to define default,
* overrideable member values when instantiating configuration objects.
*
* quietinit() guards a compound literal expression with pragmas to
* silence these shrill warnings. This alleviates the burden of requiring
* third-party projects to adjust their compiler flags.
*
* NOTE: If you take the address of the compound literal, take the address
* of the transformed expression, otherwise the compound literal lifetime is
* tied to the scope of the GCC statement expression.
*
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
#if defined __clang__
#define PRAGMA_PUSH _Pragma("clang diagnostic push")
#define PRAGMA_QUIET _Pragma("clang diagnostic ignored \"-Winitializer-overrides\"")
#define PRAGMA_POP _Pragma("clang diagnostic pop")
#define quietinit(...) \
PRAGMA_PUSH PRAGMA_QUIET __VA_ARGS__ PRAGMA_POP
#elif (__GNUC__ == 4 && __GNUC_MINOR__ >= 6) || __GNUC__ > 4
#define PRAGMA_PUSH _Pragma("GCC diagnostic push")
#define PRAGMA_QUIET _Pragma("GCC diagnostic ignored \"-Woverride-init\"")
#define PRAGMA_POP _Pragma("GCC diagnostic pop")
/* GCC parses the _Pragma operator less elegantly than clang. */
#define quietinit(...) \
__extension__ ({ PRAGMA_PUSH PRAGMA_QUIET __VA_ARGS__; PRAGMA_POP })
#else
#define PRAGMA_PUSH
#define PRAGMA_QUIET
#define PRAGMA_POP
#define quietinit(...) __VA_ARGS__
#endif
struct bar {
int a;
};
int main() {
void *x = &quietinit((struct bar){ 0, .a = 0 });
}<source>: In function 'main':
<source>:46:15: error: lvalue required as unary '&' operand
46 | void *x = &quietinit((struct bar){ 0, .a = 0 });
| ^
Compiler returned: 1
vcunat
commented
5 years ago @daurnimator: at a quick look, this seems intentional. It's not about overriding the parameters at all. The quiteinit() macro starts a block scope, and you're trying to take address outside of it. See the the first C language issue for details.
daurnimator
commented
5 years ago If this is an intentional change by GCC, what should the code be instead so that -Woverride-init can be ignored for a specific initializer?
vcunat
commented
5 years ago I can't see such a nice way ATM. Anyway, I think this issue would better be discussed with gcc devs, for a number of reasons.
daurnimator
commented
5 years ago 
pspacek
commented
5 years ago daurnimator
commented
5 years ago @wahern please drop in here :)
nicki-krizek
commented
5 years ago This patch makes it possible to compile with GCC 9 on Fedora, altough it might cause some issues with clang
vcunat
commented
5 years ago Note: GCC 9 was released today, so the problem should soon start affecting more people.
Hello,
it turns out that latest version of cqueues does not build using GCC 9.
Example: https://kojipkgs.fedoraproject.org//work/tasks/3269/32433269/build.log
or similarly
This is going to break the package in Fedora 30 which is moving to GCC 9 right now: https://fedoraproject.org/wiki/Changes/GCC9