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x86/entry: Split and inline syscall_return_slowpath() 

GCC is unable to properly optimize functions that have a very
short likely case and a longer and register-heavier cold part --
it fails to sink all of the register saving and stack frame
setup code into the unlikely part.

Help it out with syscall_return_slowpath() by splitting it into
two parts and inline the hot part.

Saves 6 cycles for compat syscalls.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/0f773a894ab15c589ac794c2d34ca6ba9b5335c9.1444091585.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Andy Lutomirski 2015-10-05 17:48:24 -07:00 committed by Ingo Molnar
parent 39b48e575e
commit f5e6a9753a
1 changed files with 29 additions and 21 deletions
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50
arch/x86/entry/common.c
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@ -284,15 +284,40 @@ __visible inline void prepare_exit_to_usermode(struct pt_regs *regs)
user_enter();
}
#define SYSCALL_EXIT_WORK_FLAGS \
(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
_TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)
static void syscall_slow_exit_work(struct pt_regs *regs, u32 cached_flags)
{
bool step;
audit_syscall_exit(regs);
if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
trace_sys_exit(regs, regs->ax);
/*
* If TIF_SYSCALL_EMU is set, we only get here because of
* TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
* We already reported this syscall instruction in
* syscall_trace_enter().
*/
step = unlikely(
(cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
== _TIF_SINGLESTEP);
if (step || cached_flags & _TIF_SYSCALL_TRACE)
tracehook_report_syscall_exit(regs, step);
}
/*
* Called with IRQs on and fully valid regs. Returns with IRQs off in a
* state such that we can immediately switch to user mode.
*/
__visible void syscall_return_slowpath(struct pt_regs *regs)
__visible inline void syscall_return_slowpath(struct pt_regs *regs)
{
struct thread_info *ti = pt_regs_to_thread_info(regs);
u32 cached_flags = READ_ONCE(ti->flags);
bool step;
CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
@ -304,25 +329,8 @@ __visible void syscall_return_slowpath(struct pt_regs *regs)
* First do one-time work. If these work items are enabled, we
* want to run them exactly once per syscall exit with IRQs on.
*/
if (cached_flags & (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT |
_TIF_SINGLESTEP | _TIF_SYSCALL_TRACEPOINT)) {
audit_syscall_exit(regs);
if (cached_flags & _TIF_SYSCALL_TRACEPOINT)
trace_sys_exit(regs, regs->ax);
/*
* If TIF_SYSCALL_EMU is set, we only get here because of
* TIF_SINGLESTEP (i.e. this is PTRACE_SYSEMU_SINGLESTEP).
* We already reported this syscall instruction in
* syscall_trace_enter().
*/
step = unlikely(
(cached_flags & (_TIF_SINGLESTEP | _TIF_SYSCALL_EMU))
== _TIF_SINGLESTEP);
if (step || cached_flags & _TIF_SYSCALL_TRACE)
tracehook_report_syscall_exit(regs, step);
}
if (unlikely(cached_flags & SYSCALL_EXIT_WORK_FLAGS))
syscall_slow_exit_work(regs, cached_flags);
#ifdef CONFIG_COMPAT
/*