Signal number to name?

glib 2.32 (released on 2020-08-05) introduced the function sigabbrev_np(int). Since that version you cannot use sys_siglist[] anymore too.

From man strsignal:

The sigabbrev_np() function returns the abbreviated name of the signal, sig. For example, given the value SIGINT, it returns the string "INT".
[...]
sigdescr_np() and sigdabbrev_np() first appeared in glibc 2.32. Starting with version 2.32, the sys_siglist symbol is no longer exported by glibc.

And from the release notes:

The functions sigabbrev_np and sigdescr_np have been added. The sigabbrev_np returns the abbreviated signal name (e.g. "HUP" for SIGHUP) [...] both functions return NULL for an invalid signal number.

They should be used instead of sys_siglist or sys_sigabbrev and they are both thread and async-signal safe. These functions are GNU extensions.

My strsignal(3) man page says you can get the names directly from the sys_signame array. Here's a simple example program I wrote to test it:

#include <signal.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

void upcase(char *s)
{
    while (*s)
    {
        *s = toupper(*s);
        s++;        
    }
}

int main(void)
{    
    for (int sig = 1; sig < NSIG; sig++)
    {
        char *str = strdup(sys_signame[sig]);
        if (!str)
            return -1;

        upcase(str);
        printf("%2d -> SIG%s\n", sig, str);

        free(str);
    }

    return 0;
}

I think this program produces the output you're looking for:

$ ./example 
 1 -> SIGHUP
 2 -> SIGINT
 3 -> SIGQUIT
 4 -> SIGILL
 5 -> SIGTRAP
 6 -> SIGABRT
 7 -> SIGEMT
 8 -> SIGFPE
 9 -> SIGKILL
10 -> SIGBUS
11 -> SIGSEGV
12 -> SIGSYS
13 -> SIGPIPE
14 -> SIGALRM
15 -> SIGTERM
16 -> SIGURG
17 -> SIGSTOP
18 -> SIGTSTP
19 -> SIGCONT
20 -> SIGCHLD
21 -> SIGTTIN
22 -> SIGTTOU
23 -> SIGIO
24 -> SIGXCPU
25 -> SIGXFSZ
26 -> SIGVTALRM
27 -> SIGPROF
28 -> SIGWINCH
29 -> SIGINFO
30 -> SIGUSR1
31 -> SIGUSR2