linux-kernel - [tip:x86/asm] x86/asm/entry/64: Use better label name, fix comments

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Date:	Fri, 27 Mar 2015 04:46:44 -0700
From:	tip-bot for Denys Vlasenko <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	luto@...capital.net, fweisbec@...il.com,
	linux-kernel@...r.kernel.org, ast@...mgrid.com,
	dvlasenk@...hat.com, bp@...en8.de, mingo@...nel.org,
	wad@...omium.org, oleg@...hat.com, rostedt@...dmis.org,
	torvalds@...ux-foundation.org, hpa@...or.com,
	keescook@...omium.org, tglx@...utronix.de
Subject: [tip:x86/asm] x86/asm/entry/64: Use better label name,
  fix comments

Commit-ID:  146b2b097d7a322b64b88a927fc5d870fc79a60b
Gitweb:     http://git.kernel.org/tip/146b2b097d7a322b64b88a927fc5d870fc79a60b
Author:     Denys Vlasenko <dvlasenk@...hat.com>
AuthorDate: Wed, 25 Mar 2015 18:18:13 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 27 Mar 2015 09:57:05 +0100

x86/asm/entry/64: Use better label name, fix comments

A named label "ret_from_sys_call" implies that there are jumps
to this location from elsewhere, as happens with many other
labels in this file.

But this label is used only by the JMP a few insns above.
To make that obvious, use local numeric label instead.

Improve comments:

"and return regs->ax" isn't too informative. We always return
regs->ax.

The comment suggesting that it'd be cool to use rip relative
addressing for CALL is deleted. It's unclear why that would be
an improvement - we aren't striving to use position-independent
code here. PIC code here would require something like LEA
sys_call_table(%rip),reg + CALL *(reg,%rax*8)...

"iret frame is also incomplete" is no longer true, fix that too.

Also fix typo in comment.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Alexei Starovoitov <ast@...mgrid.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Will Drewry <wad@...omium.org>
Link: http://lkml.kernel.org/r/1427303896-24023-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/entry_64.S | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index bf9afad..9988c4b 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -258,16 +258,15 @@ system_call_fastpath:
 	andl $__SYSCALL_MASK,%eax
 	cmpl $__NR_syscall_max,%eax
 #endif
-	ja ret_from_sys_call  /* and return regs->ax */
+	ja	1f	/* return -ENOSYS (already in pt_regs->ax) */
 	movq %r10,%rcx
-	call *sys_call_table(,%rax,8)  # XXX:	 rip relative
+	call *sys_call_table(,%rax,8)
 	movq %rax,RAX(%rsp)
+1:
 /*
- * Syscall return path ending with SYSRET (fast path)
- * Has incompletely filled pt_regs, iret frame is also incomplete.
+ * Syscall return path ending with SYSRET (fast path).
+ * Has incompletely filled pt_regs.
  */
-ret_from_sys_call:
-
 	LOCKDEP_SYS_EXIT
 	DISABLE_INTERRUPTS(CLBR_NONE)
 	TRACE_IRQS_OFF
@@ -1407,7 +1406,7 @@ ENTRY(nmi)
 	 * NMI.
 	 */
 
-	/* Use %rdx as out temp variable throughout */
+	/* Use %rdx as our temp variable throughout */
 	pushq_cfi %rdx
 	CFI_REL_OFFSET rdx, 0
 
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