01-test.c

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

static void
handler(int s)
{
        printf("x %d\n", s);

        void *array[10];
        size_t size = backtrace (array, 10);
        printf ("Backtrace %zd stack frames.\n", size);
        backtrace_symbols_fd (array, size, 2);
}

__attribute__ ((noinline)) 
int 
run(void) {
        for (;;)
                continue;
}

int
main(int argc, char **argv)
{
        signal(SIGINT, handler);
        run();
        return 0;
}

02-fix.patch

===================================================================
RCS file: /cvsroot/src/lib/libc/arch/x86_64/sys/__sigtramp2.S,v
retrieving revision 1.8
diff -u -r1.8 __sigtramp2.S
--- arch/x86_64/sys/__sigtramp2.S       12 Oct 2020 17:55:54 -0000      1.8
+++ arch/x86_64/sys/__sigtramp2.S       18 Oct 2020 15:51:51 -0000
@@ -58,7 +58,7 @@
        .cfi_offset rsi, UC_GREGS_RSI
        .cfi_offset rdi, UC_GREGS_RDI
        .cfi_offset rbp, UC_GREGS_RBP
-       /* The unwinder will use the CFA to restore RSP. */
+       .cfi_offset rsp, UC_GREGS_RSP
        .cfi_offset r8,  UC_GREGS_R8
        .cfi_offset r9,  UC_GREGS_R9
        .cfi_offset r10, UC_GREGS_R10