Hi,

is there an implicit maximum size (besides the size_t data type of
course) of the ss_size field in the sigaltstack struct when using
sigaltstack()? E.g., following example based on `man 2 sigaltstack`

---8<--------------------------------------------------------------------------
#include <sys/mman.h>

#include <signal.h>
#include <stdio.h>

#define R_USAGE 1

static struct sigaltstack sigstk;

int main(int argc, char *argv[])
{
        if ((sigstk.ss_sp = mmap(NULL, SIGSTKSIZE + R_USAGE, PROT_WRITE | 
PROT_READ,
                MAP_PRIVATE | MAP_ANON | MAP_STACK, -1, 0)) == MAP_FAILED) {
                perror("mmap");
        }
        sigstk.ss_size = SIGSTKSIZE + R_USAGE;
        sigstk.ss_flags = 0;
        if (sigaltstack(&sigstk, 0) == -1)
                perror("sigaltstack");
        return 0;
}
---8<--------------------------------------------------------------------------

works for R_USAGE == 0 but seems to fail for > 0 values (with "sigaltstack:
Invalid argument").

It is a pattern observed in math/R
(https://github.com/wch/r-source/blob/trunk/src/main/main.c#L641-L654) which
worked with malloc() but stopped working when switching to mmap() with
MAP_STACK.

Ideas? Comments?

Thank you.

Best regards,
Ingo

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