From 0d391dbcb808755a65fcc9a8a0ceaf3aa53d153f Mon Sep 17 00:00:00 2001
From: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Date: Mon, 19 Aug 2024 00:08:40 +0200
Subject: [PATCH] configure.ac: use AX_CHECK_LINK_FLAG() to test gcc flags

ledmon's configure.ac defines an AX_AM_CFLAGS_ADD() macro that allows
to test if a flag is supported by gcc, and if so add it to
AM_CFLAGS. In order to test if the flag works, it uses
AX_CHECK_COMPILE_FLAG(), which only does a *compile* test, but not
a *link* test. However, some flags such as -fstack-protector might
appear to work at compile time, but not link time. Therefore
-fstack-protector is considered functional:

checking whether C compiler accepts -fstack-protector-strong... yes

but the build later fails:

/home/buildroot/autobuild/instance-0/output-1/host/lib/gcc/m68k-buildroot-linux-uclibc/13.3.0/../../../../m68k-buildroot-linux-uclibc/bin/ld: cannot find -lssp_nonshared: No such file or directory
/home/buildroot/autobuild/instance-0/output-1/host/lib/gcc/m68k-buildroot-linux-uclibc/13.3.0/../../../../m68k-buildroot-linux-uclibc/bin/ld: cannot find -lssp: No such file or directory
collect2: error: ld returned 1 exit status

In order to fix this, we test all flags with AX_CHECK_LINK_FLAG()
which does a full *link* of the test program. This allows to make sure
that the flag is fully functional. In our test case,
-fstack-protector-strong will be determined as being non-functional,
and therefore won't be used.

Upstream: https://github.com/intel/ledmon/pull/244
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
---
 configure.ac | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index d3fada5..747b168 100644
--- a/configure.ac
+++ b/configure.ac
@@ -52,7 +52,7 @@ AC_CONFIG_HEADERS([config_ac.h])
 AM_CFLAGS='-Wall -I../config'
 AM_CPPFLAGS='-D_DEBUG -D_GNU_SOURCE -D_DEFAULT_SOURCE -DDMALLOC_DISABLE -DBUILD_LABEL=\""$(BUILD_LABEL)"\"'
 
-AC_DEFUN([AX_AM_CFLAGS_ADD],[AX_CHECK_COMPILE_FLAG($1, AM_CFLAGS="$AM_CFLAGS $1")])
+AC_DEFUN([AX_AM_CFLAGS_ADD],[AX_CHECK_LINK_FLAG($1, AM_CFLAGS="$AM_CFLAGS $1")])
 AX_AM_CFLAGS_ADD([-Wformat -Wformat-security])
 AX_AM_CFLAGS_ADD([-Wformat-overflow=2])
 AX_AM_CFLAGS_ADD([-Wno-strict-overflow])
-- 
2.46.0