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>

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index bf9afadbb99e8f3eec711cf08097b72d6de0a6f4..9988c4b2de330c13a93f3ff7581e31dbf8b1a9e1 100644 (file)
--- 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