V4 [PATCH] Add a C wrapper for prctl [BZ #25896]

["H.J. Lu" <hjl.tools@gmail.com>]

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On Thu, Apr 30, 2020 at 10:24 AM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 30/04/2020 13:51, Florian Weimer wrote:
> > * H. J. Lu via Libc-alpha:
> >
> >> On Thu, Apr 30, 2020 at 9:06 AM Adhemerval Zanella via Libc-alpha
> >> <libc-alpha@sourceware.org> wrote:
> >>>
> >>>
> >>>
> >>> On 30/04/2020 10:03, H.J. Lu via Libc-alpha wrote:
> >>>
> >>>> Here is the updated patch.  I added the assembly version for x86.  Other
> >>>> arches can do
> >>>>
> >>>> #include <sysdeps/unix/sysv/linux/x86/prctl.S>
> >>>
> >>> Do we really an assembly optimization for this? I hardly think this
> >>> a hotstop symbol.
> >>
> >> I have no strong opinion on this.
> >
> > Me neither.
> >
> I would prefer to push for an assembly optimization for symbol that
> performance is paramount and usually might appear as a hotspot.
> My understanding is usually prctl is used scarcely and I think
> it would be better to use the C generic.

This is the patch I am checking in.

-- 
H.J.

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From bd66a4111db106249d6f16fba7c55bd6cec1d779 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Wed, 29 Apr 2020 07:38:49 -0700
Subject: [PATCH] Add a C wrapper for prctl [BZ #25896]

Add a C wrapper to pass arguments in

/* Control process execution.  */
extern int prctl (int __option, ...) __THROW;

to prctl syscall:

extern int prctl (int, unsigned long int, unsigned long int,
		  unsigned long int, unsigned long int);
---
 include/sys/prctl.h                   |  1 +
 sysdeps/unix/sysv/linux/Makefile      |  2 +-
 sysdeps/unix/sysv/linux/prctl.c       | 42 +++++++++++++++++++++++++++
 sysdeps/unix/sysv/linux/syscalls.list |  1 -
 4 files changed, 44 insertions(+), 2 deletions(-)
 create mode 100644 sysdeps/unix/sysv/linux/prctl.c

diff --git a/include/sys/prctl.h b/include/sys/prctl.h
index 0920ed642b..d33f3a290e 100644
--- a/include/sys/prctl.h
+++ b/include/sys/prctl.h
@@ -4,6 +4,7 @@
 # ifndef _ISOMAC
 
 extern int __prctl (int __option, ...);
+libc_hidden_proto (__prctl)
 
 # endif /* !_ISOMAC */
 #endif
diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index db78eeadd1..0326f92c40 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -59,7 +59,7 @@ sysdep_routines += adjtimex clone umount umount2 readahead sysctl \
 		   eventfd eventfd_read eventfd_write prlimit \
 		   personality epoll_wait tee vmsplice splice \
 		   open_by_handle_at mlock2 pkey_mprotect pkey_set pkey_get \
-		   timerfd_gettime timerfd_settime \
+		   timerfd_gettime timerfd_settime prctl \
 		   process_vm_readv process_vm_writev
 
 CFLAGS-gethostid.c = -fexceptions
diff --git a/sysdeps/unix/sysv/linux/prctl.c b/sysdeps/unix/sysv/linux/prctl.c
new file mode 100644
index 0000000000..d5725f14cf
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/prctl.c
@@ -0,0 +1,42 @@
+/* prctl - Linux specific syscall.
+   Copyright (C) 2020 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 <sysdep.h>
+#include <stdarg.h>
+#include <sys/prctl.h>
+
+/* Unconditionally read all potential arguments.  This may pass
+   garbage values to the kernel, but avoids the need for teaching
+   glibc the argument counts of individual options (including ones
+   that are added to the kernel in the future).  */
+
+int
+__prctl (int option, ...)
+{
+  va_list arg;
+  va_start (arg, option);
+  unsigned long int arg2 = va_arg (arg, unsigned long int);
+  unsigned long int arg3 = va_arg (arg, unsigned long int);
+  unsigned long int arg4 = va_arg (arg, unsigned long int);
+  unsigned long int arg5 = va_arg (arg, unsigned long int);
+  va_end (arg);
+  return INLINE_SYSCALL_CALL (prctl, option, arg2, arg3, arg4, arg5);
+}
+
+libc_hidden_def (__prctl)
+weak_alias (__prctl, prctl)
diff --git a/sysdeps/unix/sysv/linux/syscalls.list b/sysdeps/unix/sysv/linux/syscalls.list
index ced77d49fa..1d8893d1b8 100644
--- a/sysdeps/unix/sysv/linux/syscalls.list
+++ b/sysdeps/unix/sysv/linux/syscalls.list
@@ -43,7 +43,6 @@ nfsservctl	EXTRA	nfsservctl	i:ipp	__compat_nfsservctl	nfsservctl@GLIBC_2.0:GLIBC
 pipe		-	pipe		i:f	__pipe		pipe
 pipe2		-	pipe2		i:fi	__pipe2		pipe2
 pivot_root	EXTRA	pivot_root	i:ss	pivot_root
-prctl		EXTRA	prctl		i:iiiii	__prctl		prctl
 query_module	EXTRA	query_module	i:sipip	__compat_query_module	query_module@GLIBC_2.0:GLIBC_2.23
 quotactl	EXTRA	quotactl	i:isip	quotactl
 remap_file_pages -	remap_file_pages i:pUiUi	__remap_file_pages remap_file_pages
-- 
2.26.2