Commit 146b2b09 authored Mar 25, 2015 by Denys Vlasenko Committed by Ingo Molnar Mar 27, 2015

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@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1427303896-24023-1-git-send-email-dvlasenk@redhat.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 06ab9c1b

arch/x86/kernel/entry_64.S

+6 −7

Original line number	Diff line number	Diff line
		@@ -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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