msgbuf: Ensure memmem() is correctly typed and visible where required

To ensure memmem() is visible _GNU_SOURCE needs to be defined early,
at least before any system headers are included. Define it in the build
flags as clang-tidy will re-order includes based on vibes rather than
dependencies. Finally, clean up the remaining compiler warnings by
dropping the unnecessary casts.

Note that _GNU_SOURCE implies _DEFAULT_SOURCE, so we drop the latter:

> Since glibc 2.19, defining _GNU_SOURCE also has the effect of
> implicitly defining _DEFAULT_SOURCE.  Before glibc 2.20, defining
> _GNU_SOURCE also had the effect of implicitly defining _BSD_SOURCE
> and _SVID_SOURCE.

https://www.man7.org/linux/man-pages/man7/feature_test_macros.7.html

Fixes: ibm-openbmc#12
Fixes: 1523778 ("msgbuf: Add pldm_msgbuf_span_string_utf16()")
Change-Id: I9206f7616740790a89366762cce11d3045471b97
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>

meson.build

@@ -17,7 +17,8 @@ if get_option('tests').allowed()
   add_languages('cpp')
 endif
 
-add_project_arguments('-D_DEFAULT_SOURCE', language: ['c'])
+# For memmem() in src/msgbuf.h
+add_project_arguments('-D_GNU_SOURCE', language: ['c'])
 
 compiler = meson.get_compiler('c')
 conf = configuration_data()

src/msgbuf.h

@@ -2,13 +2,6 @@
 #ifndef PLDM_MSGBUF_H
 #define PLDM_MSGBUF_H
 
-// NOLINTBEGIN(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
-#ifndef _GNU_SOURCE
-/* For memmem(3) */
-#define _GNU_SOURCE
-#endif
-// NOLINTEND(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
-
 /*
  * Historically, many of the structs exposed in libpldm's public headers are
  * defined with __attribute__((packed)). This is unfortunate: it gives the
@@ -1140,7 +1133,7 @@ pldm_msgbuf_span_string_utf16(struct pldm_msgbuf *ctx, void **cursor,
 	 * not form a UTF16 NUL _code-point_ due to alignment with respect to the
 	 * start of the string
 	 */
-	end = (char *)ctx->cursor;
+	end = ctx->cursor;
 	do {
 		if (end != ctx->cursor) {
 			/*
@@ -1150,8 +1143,8 @@ pldm_msgbuf_span_string_utf16(struct pldm_msgbuf *ctx, void **cursor,
 			end = (char *)end + 1;
 		}
 		measured = (char *)end - (char *)ctx->cursor;
-		end = (char *)memmem(end, ctx->remaining - measured, &term,
-				     sizeof(term));
+		end = memmem(end, ctx->remaining - measured, &term,
+			     sizeof(term));
 	} while (end && ((uintptr_t)end & 1) != ((uintptr_t)ctx->cursor & 1));
 
 	if (!end) {

src/requester/instance-id.c

@@ -1,6 +1,5 @@
 /* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later */
 // NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp)
-#define _GNU_SOURCE
 #include <libpldm/instance-id.h>
 #include <libpldm/pldm.h>
 

src/transport/test.c

@@ -1,6 +1,5 @@
 /* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later */
 /* NOLINTNEXTLINE(bugprone-reserved-identifier,cert-dcl37-c,cert-dcl51-cpp) */
-#define _GNU_SOURCE
 #include "array.h"
 #include "container-of.h"
 #include "transport.h"