Issue

Example of usage:

void closefrom (int lowfd);

int main()
{
    // expected warning
    closefrom(-1);
    return 0;
}

Specifically: I should implement diagnostics (compiler warning) for function calls. Function located in glibc: void closefrom (int lowfd);

If lowfd is negative compiler should issue a warning.

Here is some information about closefrom:

https://sourceware.org/pipermail/libc-alpha/2021-August/129718.html

Maybe attribute of the function will somehow help in this?

Solution

want to issue warning only if compiler is able to calculate the value (by optimizations, or if the value is constant). Otherwise just use function without warnin

In short, with GNU extensions:

void foo (int lowfd);

#if defined(__GNUC__) && defined(__OPTIMIZE__)
#define curb(expr, msg) \
     __extension__({ \
          if (__builtin_constant_p(expr)) { \
              if (!(expr)) { \
                    __attribute__((__noinline__, \
                    __warning__(msg))) void warnit() {__asm__("");}; warnit(); \
              } \
           } \
     })
#else
#define curb(expr, msg)  (void)0
#endif

#define foo(x)  (curb(x >= 0, "x is lower than 0"), foo(x))

int main()
{
    // expected warning
    foo(-1);
    return 0;
}

I have this https://gitlab.com/Kamcuk/kamillibc/-/blob/master/libs/curb/src/curb.h#L46 in my tree about the idea of issuing a warning or error if the expression is known at compile time, and if it isn't, failing at runtime or not. The && defined(__OPTIMIZE__) seems not to be needed in this case.

Answered By - KamilCuk

Answer Checked By - Senaida (WPSolving Volunteer)

Friday, June 3, 2022

[SOLVED] How can I add warning feature to the GCC?

Issue

Solution