when compiling c++ code with glibc, MINSIGSTKSZ gets incorrect value of -1

[andrewrk]

Zig Version

0.10.0-dev.445+d7deffee8

Steps to Reproduce

$ cat test.cpp
#include <csignal>
#include <iostream>

int main() {
      std::cout << "Hello World!" << MINSIGSTKSZ << "\n";
      return 0;
}
$ zig run -lc++ test.cpp -target native-native-musl
Hello World!2048
$ zig run -lc++ test.cpp -target native-native-gnu
Hello World!-1
$ cat test.c
#include <signal.h>
#include <stdio.h>
int main(int argc, char **argv) {
    printf("%d\n", MINSIGSTKSZ);
    return 0;
}
$ zig run -lc test.c -target native-native-gnu
2048

Expected Behavior

Expected the same result (2048) for musl and glibc, and expected the same result (2048) for C++ and C.

Actual Behavior

When compiling C++ code with glibc, MINSIGSTKSZ has incorrect value of -1.

[andrewrk]

Here's what I figured out so far:

When using -target with gnu as the C ABI, the default -std flag used by clang++ is -std=gnu++14. This sets the _GNU_SOURCE preprocessor definition. In turn, this causes:

/* If _GNU_SOURCE was defined by the user, turn on all the other features.  */
#ifdef _GNU_SOURCE
# undef  _ISOC95_SOURCE
# define _ISOC95_SOURCE	1
# undef  _ISOC99_SOURCE
# define _ISOC99_SOURCE	1
# undef  _ISOC11_SOURCE
# define _ISOC11_SOURCE	1
# undef  _ISOC2X_SOURCE
# define _ISOC2X_SOURCE	1
# undef  _POSIX_SOURCE
# define _POSIX_SOURCE	1
# undef  _POSIX_C_SOURCE
# define _POSIX_C_SOURCE	200809L
# undef  _XOPEN_SOURCE
# define _XOPEN_SOURCE	700
# undef  _XOPEN_SOURCE_EXTENDED
# define _XOPEN_SOURCE_EXTENDED	1
# undef	 _LARGEFILE64_SOURCE
# define _LARGEFILE64_SOURCE	1
# undef  _DEFAULT_SOURCE
# define _DEFAULT_SOURCE	1
# undef  _ATFILE_SOURCE
# define _ATFILE_SOURCE	1
# undef  _DYNAMIC_STACK_SIZE_SOURCE
# define _DYNAMIC_STACK_SIZE_SOURCE 1
#endif

Emphasis on _DYNAMIC_STACK_SIZE_SOURCE. This gets used like this:

#if defined __USE_DYNAMIC_STACK_SIZE && __USE_DYNAMIC_STACK_SIZE
# include <unistd.h>

/* Default stack size for a signal handler: sysconf (SC_SIGSTKSZ).  */
# undef SIGSTKSZ
# define SIGSTKSZ sysconf (_SC_SIGSTKSZ)

/* Minimum stack size for a signal handler: SIGSTKSZ.  */
# undef MINSIGSTKSZ
# define MINSIGSTKSZ SIGSTKSZ
#endif

So turns out MINSIGSTKSZ actually ends up being a call to sysconf which is apparently returning -1 (error) for some reason.

[andrewrk]

Patch sent upstream: https://patchwork.sourceware.org/project/glibc/patch/20220129023727.1496360-1-andrew@ziglang.org/