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Re: PATCH: Add x32 arch_prctl support


On Tue, May 22, 2012 at 9:53 AM, Roland McGrath <roland@hack.frob.com> wrote:
>> I submitted a patch to remove x32 PTRACE_ARCH_PRCTL from
>> kernel. ?Here is a patch with only arch_prctl.c. OK to install?
>
> I'm certainly happy with the ptrace cleanup.
>
>> +/* Since x32 arch_prctl stores 32-bit base address of segment register %fs
>
> "the 32-bit ..."
> "segment registers"
>
>> + ? and %gs as unsigned 64-bit value via ARCH_GET_FS and ARCH_GET_GS, we
>
> "as an unsigned 64-bit value"
>
>> + ? use a local unsigned 64-bit variable to hold the base address and copy
>> + ? it to ADDR after arch_prctl return. ?*/
>
> "after the system call returns"
>
...
>> +weak_alias (__arch_prctl, arch_prctl)
>
> We usually don't have a blank line before a weak_alias like this.
>

Here is the updated patch.  The differences are

1. Old:

   0:	67 8d 97 fd ef ff ff 	lea    -0x1003(%edi),%edx
   7:	83 fa 01             	cmp    $0x1,%edx
   a:	77 08                	ja     14 <__arch_prctl+0x14>
   c:	41 89 f0             	mov    %esi,%r8d
   f:	67 8d 74 24 f8       	lea    -0x8(%esp),%esi
  14:	b8 9e 00 00 40       	mov    $0x4000009e,%eax
  19:	0f 05                	syscall

2. New

  0:	67 8d 97 fd ef ff ff 	lea    -0x1003(%edi),%edx
   7:	49 89 f0             	mov    %rsi,%r8
   a:	67 8d 74 24 f8       	lea    -0x8(%esp),%esi
   f:	b8 9e 00 00 40       	mov    $0x4000009e,%eax
  14:	83 fa 01             	cmp    $0x1,%edx
  17:	41 0f 47 f0          	cmova  %r8d,%esi
  1b:	0f 05                	syscall

There are no GCC warnings.  OK to install?

Thanks.

-- 
H.J.
----
	* sysdeps/unix/sysv/linux/x86_64/x32/Makefile (sysdep_routines):
	Add arch_prctl.
	* sysdeps/unix/sysv/linux/x86_64/x32/arch_prctl.c: New file.

diff --git a/sysdeps/unix/sysv/linux/x86_64/x32/Makefile
b/sysdeps/unix/sysv/linux/x86_64/x32/Makefile
index 5f77df7..aa78238 100644
--- a/sysdeps/unix/sysv/linux/x86_64/x32/Makefile
+++ b/sysdeps/unix/sysv/linux/x86_64/x32/Makefile
@@ -1,3 +1,7 @@
+ifeq ($(subdir),misc)
+sysdep_routines += arch_prctl
+endif
+
 ifeq ($(subdir),posix)
 sysdep_routines += getcpu sched_getcpu-static
 endif
diff --git a/sysdeps/unix/sysv/linux/x86_64/x32/arch_prctl.c
b/sysdeps/unix/sysv/linux/x86_64/x32/arch_prctl.c
new file mode 100644
index 0000000..6933306
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/x32/arch_prctl.c
@@ -0,0 +1,62 @@
+/* arch_prctl call for Linux/x32.
+   Copyright (C) 2012 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
+   <http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <sys/prctl.h>
+#include <sys/syscall.h>
+#include <sysdep.h>
+
+/* Since x32 arch_prctl stores 32-bit base address of segment registers
+   %fs and %gs as unsigned 64-bit value via ARCH_GET_FS and ARCH_GET_GS,
+   we use an unsigned 64-bit variable to hold the base address and copy
+   it to ADDR after the system call returns.  */
+
+int
+__arch_prctl (int code, uintptr_t *addr)
+{
+  int res;
+  uint64_t addr64;
+  void *prctl_arg = addr;
+
+  switch (code)
+    {
+    case ARCH_GET_FS:
+    case ARCH_GET_GS:
+      prctl_arg = &addr64;
+      break;
+    }
+
+  res = INLINE_SYSCALL (arch_prctl, 2, code, prctl_arg);
+  if (res == 0)
+    switch (code)
+      {
+      case ARCH_GET_FS:
+      case ARCH_GET_GS:
+	 /* Check for a large value that overflows.  */
+	if ((uintptr_t) addr64 != addr64)
+	  {
+	    __set_errno (EOVERFLOW);
+	    return -1;
+	  }
+	*addr = (uintptr_t) addr64;
+	break;
+      }
+
+  return res;
+}
+weak_alias (__arch_prctl, arch_prctl)


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