[PATCH 2/2] osdep: protect qemu/osdep.h with extern "C"

[Paolo Bonzini <pbonzini@redhat.com>]

System headers may include templates if compiled with a C++ compiler,
which cause the compiler to complain if qemu/osdep.h is included
within a C++ source file's 'extern "C"' block.  Add
an 'extern "C"' block directly to qemu/osdep.h, so that
system headers can be kept out of it.

There is a stray declaration early in qemu/osdep.h, which needs
to be special cased.  Add a definition in qemu/compiler.h to
make it look nice.

config-host.h, CONFIG_TARGET, exec/poison.h and qemu/compiler.h
are included outside the 'extern "C"' block; that is not
an issue because they consist entirely of preprocessor directives.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 disas/nanomips.cpp      |  2 +-
 include/qemu/compiler.h |  6 ++++++
 include/qemu/osdep.h    | 10 +++++++++-
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/disas/nanomips.cpp b/disas/nanomips.cpp
index 2b09655271..8ddef897f0 100644
--- a/disas/nanomips.cpp
+++ b/disas/nanomips.cpp
@@ -27,8 +27,8 @@
  *      Reference Manual", Revision 01.01, April 27, 2018
  */
 
-extern "C" {
 #include "qemu/osdep.h"
+extern "C" {
 #include "disas/dis-asm.h"
 }
 
diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index cf28bb2bcd..091c45248b 100644
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -11,6 +11,12 @@
 #define QEMU_STATIC_ANALYSIS 1
 #endif
 
+#ifdef __cplusplus
+#define QEMU_EXTERN_C extern "C"
+#else
+#define QEMU_EXTERN_C extern
+#endif
+
 #define QEMU_NORETURN __attribute__ ((__noreturn__))
 
 #define QEMU_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index b67b0a1e8c..3f8785a471 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -57,7 +57,7 @@
 #define daemon qemu_fake_daemon_function
 #include <stdlib.h>
 #undef daemon
-extern int daemon(int, int);
+QEMU_EXTERN_C int daemon(int, int);
 #endif
 
 #ifdef _WIN32
@@ -113,6 +113,10 @@ extern int daemon(int, int);
 
 #include "glib-compat.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 #ifdef _WIN32
 #include "sysemu/os-win32.h"
 #endif
@@ -723,4 +727,8 @@ static inline int platform_does_not_support_system(const char *command)
 }
 #endif /* !HAVE_SYSTEM_FUNCTION */
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif
-- 
2.30.1