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x86/asm/entry/32: Shorten __audit_syscall_entry() args preparation

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We use three MOVs to swap edx and ecx. We can use one XCHG
instead.

Expand the comments. It's difficult to keep track which arg#
every register corresponds to, so spell it out.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
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: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1433876051-26604-3-git-send-email-dvlasenk@redhat.com
[ Expanded the comments some more. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Denys Vlasenko 2015-06-09 20:54:09 +02:00 committed by Ingo Molnar
parent 1536bb46fa
commit a92fde2523
1 changed files with 19 additions and 10 deletions
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29
arch/x86/entry/entry_64_compat.S
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@ -178,17 +178,26 @@ sysexit_from_sys_call:
#ifdef CONFIG_AUDITSYSCALL
.macro auditsys_entry_common
movl %esi, %r8d /* 5th arg: 4th syscall arg */
movl %ecx, %r9d /* swap with edx */
movl %edx, %ecx /* 4th arg: 3rd syscall arg */
movl %r9d, %edx /* 3rd arg: 2nd syscall arg */
movl %ebx, %esi /* 2nd arg: 1st syscall arg */
movl %eax, %edi /* 1st arg: syscall number */
call __audit_syscall_entry
/*
* We are going to jump back to syscall dispatch.
* Prepare syscall args as required by 64-bit C ABI.
* Clobbered registers are loaded from pt_regs on stack.
* At this point, registers hold syscall args in the 32-bit syscall ABI:
* EAX is syscall number, the 6 args are in EBX,ECX,EDX,ESI,EDI,EBP.
*
* We want to pass them to __audit_syscall_entry(), which is a 64-bit
* C function with 5 parameters, so shuffle them to match what
* the function expects: RDI,RSI,RDX,RCX,R8.
*/
movl %esi, %r8d /* arg5 (R8 ) <= 4th syscall arg (ESI) */
xchg %ecx, %edx /* arg4 (RCX) <= 3rd syscall arg (EDX) */
/* arg3 (RDX) <= 2nd syscall arg (ECX) */
movl %ebx, %esi /* arg2 (RSI) <= 1st syscall arg (EBX) */
movl %eax, %edi /* arg1 (RDI) <= syscall number (EAX) */
call __audit_syscall_entry
/*
* We are going to jump back to the syscall dispatch code.
* Prepare syscall args as required by the 64-bit C ABI.
* Registers clobbered by __audit_syscall_entry() are
* loaded from pt_regs on stack:
*/
movl ORIG_RAX(%rsp), %eax /* syscall number */
movl %ebx, %edi /* arg1 */