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Re: PATCH: Add Linux/x32 sysdep.h

From: "H.J. Lu" <hjl dot tools at gmail dot com>
To: Roland McGrath <roland at hack dot frob dot com>
Cc: GNU C Library <libc-alpha at sourceware dot org>
Date: Wed, 16 May 2012 19:53:26 -0700
Subject: Re: PATCH: Add Linux/x32 sysdep.h
References: <20120516011540.GA29085@intel.com><20120516164949.6B8682C0B2@topped-with-meat.com><CAMe9rOoyZCKJVKxOy1Noa0TowBRMMd7G2N2wT8grEgumOMAMUw@mail.gmail.com><20120516183655.2A5692C0B8@topped-with-meat.com>

On Wed, May 16, 2012 at 11:36 AM, Roland McGrath <roland@hack.frob.com> wrote:
>> Leaving out SYSCALL_RETURN_INT64 makes is impossible to test
>> the change on Linux/x32.
>
> It only leaves lseek broken. ?Everything else will be fine.
> But if you prefer, we can do lseek first instead.
>
> It's really just more obfuscation to use syscall-template.S for that.
> What I'd do is just write it out:
>
> /* lseek system call stub for Linux/x32.
> ? Copyright ...
> */
>
> #include <sysdep-cancel.h>
>
> /* Comment about why this is needed at all. ?*/
>
> #undef ?SYSCALL_ERROR_LABEL
> #define SYSCALL_ERROR_LABEL 0f
> PSEUDO (__libc_lseek64, lseek, 3)
> ? ? ? ?ret
> 0:
>
> Then modify x86_64/sysdep.h so it defines a macro SYSCALL_SET_ERRNO
> that is just the part of SYSCALL_ERROR_HANDLER after the label and
> before setting %rax. ?Then it's:
>
> 0: ? ? ?SYSCALL_SET_ERRNO
> ? ? ? ?orq $-1, %rax ? /* Return -1LL in a full 64 bits. ?*/
> ? ? ? ?ret
>
> You can do the break-out of the SYSCALL_SET_ERRNO macro and the addition of
> x32/llseek.S in one change. ?Then you can make the existing sysdep.h macros
> uses R*_LP macros in a second change.
>

Here is what I implemented.  Since I need to refine SYSCALL_ERROR_HANDLER
anyway, I use it to define my own error handler.  Does it look OK?

I noticed that SYSCALL_ERROR_HANDLER has

  xorl %edx, %edx;				\
  subq %rax, %rdx;				\
  movl %edx, (%rcx);				\
  orq $-1, %rax;				\
  jmp L(pseudo_end);

Why not simply "neg %rax"?  Also why not just "ret" instead of jmp?

Thanks.

-- 
H.J.
---
2012-05-16  H.J. Lu  <hongjiu.lu@intel.com>

	* sysdeps/unix/sysv/linux/x86_64/sysdep.h (SYSCALL_SET_ERRNO):
	New macro.  Use R*LP on int and pointer.
	(SYSCALL_ERROR_HANDLER): Use SYSCALL_SET_ERRNO.
	* sysdeps/unix/sysv/linux/x86_64/x32/llseek.S: New file.
	* sysdeps/unix/sysv/linux/x86_64/x32/sysdep.h: Likewise.

diff --git a/sysdeps/unix/sysv/linux/x86_64/sysdep.h
b/sysdeps/unix/sysv/linux/x86_64/sysdep.h
index aae4cb0..dcb9218 100644
--- a/sysdeps/unix/sysv/linux/x86_64/sysdep.h
+++ b/sysdeps/unix/sysv/linux/x86_64/sysdep.h
@@ -112,30 +112,32 @@

 # define ret_ERRVAL ret

-# ifndef PIC
-#  define SYSCALL_ERROR_HANDLER	/* Nothing here; code in sysdep.S is used.  */
-# elif RTLD_PRIVATE_ERRNO
-#  define SYSCALL_ERROR_HANDLER			\
-0:						\
-  leaq rtld_errno(%rip), %rcx;			\
+# if defined PIC && defined RTLD_PRIVATE_ERRNO
+#  define SYSCALL_SET_ERRNO			\
+  lea rtld_errno(%rip), %RCX_LP;		\
   xorl %edx, %edx;				\
-  subq %rax, %rdx;				\
-  movl %edx, (%rcx);				\
-  orq $-1, %rax;				\
-  jmp L(pseudo_end);
+  sub %RAX_LP, %RDX_LP;				\
+  movl %edx, (%rcx);
 # else
 #  ifndef NOT_IN_libc
 #   define SYSCALL_ERROR_ERRNO __libc_errno
 #  else
 #   define SYSCALL_ERROR_ERRNO errno
 #  endif
-#  define SYSCALL_ERROR_HANDLER			\
-0:						\
+#  define SYSCALL_SET_ERRNO			\
   movq SYSCALL_ERROR_ERRNO@GOTTPOFF(%rip), %rcx;\
   xorl %edx, %edx;				\
-  subq %rax, %rdx;				\
-  movl %edx, %fs:(%rcx);			\
-  orq $-1, %rax;				\
+  sub %RAX_LP, %RDX_LP;				\
+  movl %edx, %fs:(%rcx);
+# endif
+
+# ifndef PIC
+#  define SYSCALL_ERROR_HANDLER	/* Nothing here; code in sysdep.S is used.  */
+# else
+#  define SYSCALL_ERROR_HANDLER			\
+0:						\
+  SYSCALL_SET_ERRNO				\
+  or $-1, %RAX_LP;				\
   jmp L(pseudo_end);
 # endif	/* PIC */

diff --git a/sysdeps/unix/sysv/linux/x86_64/x32/llseek.S
b/sysdeps/unix/sysv/linux/x86_64/x32/llseek.S
new file mode 100644
index 0000000..85f4d70
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/x32/llseek.S
@@ -0,0 +1,43 @@
+/* The lseek system call with 64-bit offset.  Linux/x32 version.
+   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 <sysdep-cancel.h>
+
+/* Return -1LL in a full 64 bits.  */
+#undef SYSCALL_ERROR_HANDLER
+#define SYSCALL_ERROR_HANDLER	\
+0:				\
+	SYSCALL_SET_ERRNO	\
+	orq $-1, %rax;		\
+	ret;
+
+/* Always use our own error handler.  */
+#undef SYSCALL_ERROR_LABEL
+#define SYSCALL_ERROR_LABEL 0f
+
+PSEUDO (__libc_lseek64, lseek, 3)
+	ret
+PSEUDO_END (__libc_lseek64)
+
+weak_alias (__libc_lseek64, __lseek64)
+libc_hidden_weak (__lseek64)
+weak_alias (__libc_lseek64, lseek64)
+libc_hidden_weak (lseek64)
+weak_alias (__libc_lseek64, __lseek)
+libc_hidden_weak (__lseek)
+weak_alias (__libc_lseek64, lseek)
diff --git a/sysdeps/unix/sysv/linux/x86_64/x32/sysdep.h
b/sysdeps/unix/sysv/linux/x86_64/x32/sysdep.h
new file mode 100644
index 0000000..35e4c84
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/x86_64/x32/sysdep.h
@@ -0,0 +1,25 @@
+/* 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/>.  */
+
+#ifndef _LINUX_X32_SYSDEP_H
+#define _LINUX_X32_SYSDEP_H 1
+
+/* There is some commonality.  */
+#include <sysdeps/unix/sysv/linux/x86_64/sysdep.h>
+#include <sysdeps/x86_64/x32/sysdep.h>
+
+#endif /* linux/x86_64/x32/sysdep.h */

Follow-Ups:
- Re: PATCH: Add Linux/x32 sysdep.h
  - From: Roland McGrath

References:
- PATCH: Add Linux/x32 sysdep.h
  - From: H.J. Lu
- Re: PATCH: Add Linux/x32 sysdep.h
  - From: Roland McGrath
- Re: PATCH: Add Linux/x32 sysdep.h
  - From: H.J. Lu
- Re: PATCH: Add Linux/x32 sysdep.h
  - From: Roland McGrath

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