Fix execl(3) sentinel undefined behaviour.

execl(3) and its variants use a sentinel to terminate the variadic
argument list, in the form of a null pointer constant of type pointer to
char. POSIX mandates that NULL is a null pointer constant of type
pointer to void, which is not of an equivalent type to that required by
execl(3) and its variants, resulting in undefined behaviour.

This commit casts all such instances of NULL to pointer to char type.
For consistency, it also adds const-qualification to any such instances
which had already been casted, and were not const-qualified.

dispd/client/session.c

@@ -91,13 +91,13 @@ bool dispd_session_setup_game_rgba(struct dispd_session* session)
 		const char* chvideomode = "chvideomode";
 #if 1
 		// TODO chvideomode currently launches --bpp 32 as a program...
-		execlp(chvideomode, chvideomode, NULL);
+		execlp(chvideomode, chvideomode, (const char*) NULL);
 #else
 		execlp(chvideomode, chvideomode,
 		       "--bpp", "32",
 		       "--show-graphics", "true",
 		       "--show-text", "false",
-		       NULL);
+		       (const char*) NULL);
 #endif
 		perror(chvideomode);
 		exit(127);

init/init.c

@@ -395,7 +395,7 @@ static void set_kblayout(void)
 		return warning("unable to set keyboard layout: fork: %m");
 	if ( !child_pid )
 	{
-		execlp("chkblayout", "chkblayout", "--", kblayout, (char*) NULL);
+		execlp("chkblayout", "chkblayout", "--", kblayout, (const char*) NULL);
 		warning("setting keyboard layout: chkblayout: %m");
 		_exit(127);
 	}

libc/stdio/popen.c

@@ -131,7 +131,7 @@ FILE* popen(const char* command, const char* type)
         close(pipefds[unused_end]) )
 		_exit(127);
 
-	execlp("sh", "sh", "-c", command, NULL);
+	execlp("sh", "sh", "-c", command, (const char*) NULL);
 	_exit(127);
 
 cleanup_pipes:

libc/stdlib/system.c

@@ -39,6 +39,6 @@ int system(const char* command)
 			return ret_error;
 		return status;
 	}
-	execlp("sh", "sh", "-c", command, NULL);
+	execlp("sh", "sh", "-c", command, (const char*) NULL);
 	_exit(exit_error);
 }

sh/proper-sh.c

@@ -46,7 +46,7 @@ bool is_existing_shell(const char* candidate)
 		open("/dev/null", O_RDONLY);
 		open("/dev/null", O_WRONLY);
 		open("/dev/null", O_WRONLY);
-		execlp("which", "which", "--", candidate, (char*) NULL);
+		execlp("which", "which", "--", candidate, (const char*) NULL);
 		exit(127);
 	}
 	int status;

sh/sh.c

@@ -1299,7 +1299,7 @@ struct execute_result execute(char** tokens,
 	if ( interactive && errno == ENOENT )
 	{
 		int errno_saved = errno;
-		execlp("command-not-found", "command-not-found", argv[0], NULL);
+		execlp("command-not-found", "command-not-found", argv[0], (const char*) NULL);
 		errno = errno_saved;
 	}
 

trianglix/trianglix.cpp

@@ -193,7 +193,7 @@ static void ExecuteFile(const char* path, int curdirfd)
 	if ( ForkAndWait() )
 	{
 		fchdir(curdirfd);
-		execl(path, path, (char*) NULL);
+		execl(path, path, (const char*) NULL);
 		_exit(127);
 	}
 }
@@ -204,7 +204,7 @@ static void DisplayFile(const char* path, int curdirfd)
 	if ( ForkAndWait() )
 	{
 		fchdir(curdirfd);
-		execlp("editor", "editor", path, (char*) NULL);
+		execlp("editor", "editor", path, (const char*) NULL);
 		_exit(127);
 	}
 }
@@ -215,7 +215,7 @@ static void ExecutePath(const char* path, int curdirfd)
 	if ( ForkAndWait() )
 	{
 		fchdir(curdirfd);
-		execlp(path, path, (char*) NULL);
+		execlp(path, path, (const char*) NULL);
 		_exit(127);
 	}
 }
@@ -229,7 +229,7 @@ void ExecuteShellCommand(const char* command, int curdirfd)
 	if ( ForkAndWait() )
 	{
 		fchdir(curdirfd);
-		execlp("sh", "sh", "-c", command, (char*) NULL);
+		execlp("sh", "sh", "-c", command, (const char*) NULL);
 		error(127, errno, "`%s'", "sh");
 	}
 	unsigned int cur_termmode;
@@ -505,7 +505,7 @@ private:
 
 void exec_program::invoke()
 {
-	execlp(program, program, (char*) NULL);
+	execlp(program, program, (const char*) NULL);
 }
 
 class development : public object

utils/help.c

@@ -52,8 +52,8 @@ int main(void)
 			dup2(pipe_fds[0], 0);
 			close(pipe_fds[0]);
 			close(pipe_fds[1]);
-			execlp("column", "column", NULL);
-			execlp("cat", "cat", NULL);
+			execlp("column", "column", (const char*) NULL);
+			execlp("cat", "cat", (const char*) NULL);
 			int ic;
 			while ( (ic = fgetc(stdin)) != EOF )
 				fputc(ic, stdout);