Improve detection of -fzero-call-used-regs=all support

GCC doesn't tell us whether this option is supported unless it runs into
the situation where it would need to emit corresponding code.

diff --git a/m4/openssh.m4 b/m4/openssh.m4
index 4f9c3792dc171448c309c48ccabbf72166b6368f..8c33c701b8b42ee7eef99cdcbaf0c695591fe0b8 100644 (file)
--- a/m4/openssh.m4
+++ b/m4/openssh.m4
@@ -14,6 +14,8 @@ AC_DEFUN([OSSH_CHECK_CFLAG_COMPILE], [{
        AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
 #include <stdlib.h>
 #include <stdio.h>
+/* Trivial function to help test for -fzero-call-used-regs */
+void f(int n) {}
 int main(int argc, char **argv) {
        (void)argv;
        /* Some math to catch -ftrapv problems in the toolchain */
@@ -21,6 +23,7 @@ int main(int argc, char **argv) {
        float l = i * 2.1;
        double m = l / 0.5;
        long long int n = argc * 12345LL, o = 12345LL * (long long int)argc;
+       f(0);
        printf("%d %d %d %f %f %lld %lld\n", i, j, k, l, m, n, o);
        /*
         * Test fallthrough behaviour.  clang 10's -Wimplicit-fallthrough does