linux: Add execveat system call wrapper

It operates similar to execve and it is is already used to implement
fexecve without requiring /proc to be mounted.  However, different
than fexecve, if the syscall is not supported by the kernel an error
is returned instead of trying a fallback.

Checked on x86_64-linux-gnu and powerpc64le-linux-gnu.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1 files changed, 32 insertions, 0 deletions

diff --git a/sysdeps/unix/sysv/linux/execveat.c b/sysdeps/unix/sysv/linux/execveat.c
new file mode 100644
index 0000000000..29ab81a464
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/execveat.c
@@ -0,0 +1,32 @@
+/* Execute program relative to a directory file descriptor.
+   Copyright (C) 2021 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <fd_to_filename.h>
+#include <sysdep.h>
+#include <unistd.h>
+
+/* Execute the file FD refers to, overlaying the running program image.
+   ARGV and ENVP are passed to the new program, as for 'execve'.  */
+int
+execveat (int dirfd, const char *path, char *const argv[], char *const envp[],
+          int flags)
+{
+  /* Avoid implicit array coercion in syscall macros.  */
+  return INLINE_SYSCALL_CALL (execveat, dirfd, path, &argv[0], &envp[0],
+			      flags);
+}