From f5e6a9753ac2965564a14e6285a06f44043ed9c8 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Mon, 5 Oct 2015 17:48:24 -0700 Subject: [PATCH] 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 Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Link: http://lkml.kernel.org/r/0f773a894ab15c589ac794c2d34ca6ba9b5335c9.1444091585.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/entry/common.c | 50 ++++++++++++++++++++++++----------------- 1 file changed, 29 insertions(+), 21 deletions(-) diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index 66ccbd664d4c..b53e04d301a3 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -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 /* -- 2.34.1