From c61b8d63121a906e20216bee927c6e3a48f5c6b7 Mon Sep 17 00:00:00 2001
From: Matthieu Baerts <matthieu.baerts@tessares.net>
Date: Thu, 12 May 2022 18:57:38 +0200
Subject: [PATCH] api: force setting _GNU_SOURCE

Without that, a warning is emitted when compiling libyaml with musl
libc:

  api.c: In function 'yaml_strdup':
  api.c:66:27: warning: implicit declaration of function 'strdup'; did you mean 'strcmp'? [-Wimplicit-function-declaration]
       return (yaml_char_t *)strdup((char *)str);
                             ^~~~~~
                             strcmp

If the warning is ignored, a program using libyaml starts but crashes
because strdup() is returning garbage:

  (gdb) b parser.c:1365
  Breakpoint 11 at 0x43ecf4: file parser.c, line 1365.
  (gdb) run
  (...)
  Breakpoint 1, yaml_parser_append_tag_directive (
      parser=parser@entry=0x7ffffff5f0, value=...,
      allow_duplicates=allow_duplicates@entry=1, mark=...) at parser.c:1365
  1365    in parser.c
  (gdb) p copy
  $1 = {
    handle = 0xffffffffb8000fe0 <error: Cannot access memory at address 0xffffffffb8000fe0>,
    prefix = 0xffffffffb7f76fe0 <error: Cannot access memory at address 0xffffffffb7f76fe0>}

The solution is to follow strdup()'s manpage and define _GNU_SOURCE
before including string.h.

I guess when using other libc, it fallbacks to another version or maybe
_GNU_SOURCE is set by default.

Fixes: 625fcfe ("Refactor internal and external API.")
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Change-Id: Ida011378a9d4da24735c4d4fdfdfb9d5f80ec970
---
 src/api.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/api.c b/src/api.c
index 16f88bd7..8f531ab8 100644
--- a/src/api.c
+++ b/src/api.c
@@ -1,3 +1,5 @@
+#define _GNU_SOURCE
+#include <string.h>
 
 #include "yaml_private.h"