git: 64584008139f - main - csu: C standard requires errno on main() entry

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=64584008139f73b07fa7c7979c41780be458b8cc

commit 64584008139f73b07fa7c7979c41780be458b8cc
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2025-06-23 23:46:43 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2025-06-24 01:11:17 +0000

    csu: C standard requires errno on main() entry
    
    Reported by:    Greg Becker <greg.becker@klarasystems.com>
    Reviewed by:    emaste, kevans, markj
    Sponsored by:   The FreeBSD Foundation
    MFC after:      1 week
    Also see:       https://reviews.freebsd.org/D50998
    Differential revision:  https://reviews.freebsd.org/D50997
---
 lib/libc/csu/libc_start1.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lib/libc/csu/libc_start1.c b/lib/libc/csu/libc_start1.c
index 045ea1e68141..5b08ba03ba8c 100644
--- a/lib/libc/csu/libc_start1.c
+++ b/lib/libc/csu/libc_start1.c
@@ -28,6 +28,7 @@
 #include <sys/param.h>
 #include <sys/elf.h>
 #include <sys/elf_common.h>
+#include <errno.h>
 #include <stdlib.h>
 #include "libc_private.h"
 
@@ -169,6 +170,13 @@ __libc_start1(int argc, char *argv[], char *env[], void (*cleanup)(void),
 	}
 
 	handle_static_init(argc, argv, env);
+
+	/*
+	 * C17 4.3 paragraph 3:
+	 * The value of errno in the initial thread is zero at program
+	 * startup.
+	 */
+	errno = 0;
 	exit(mainX(argc, argv, env));
 }
 
@@ -194,5 +202,6 @@ __libc_start1_gcrt(int argc, char *argv[], char *env[],
 	monstartup(eprolp, etextp);
 
 	handle_static_init(argc, argv, env);
+	errno = 0;
 	exit(mainX(argc, argv, env));
 }