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Message-ID: <20081117121444.GA13427@poweredge.glommer> Date: Mon, 17 Nov 2008 10:14:44 -0200 From: Glauber Costa <glommer@...hat.com> To: Alexander van Heukelum <heukelum@...tmail.fm> Cc: Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>, Andi Kleen <andi@...stfloor.org>, Alexander van Heukelum <heukelum@...i.uni-sb.de>, Glauber Costa <gcosta@...hat.com> Subject: Re: [RFC] x86: save_args out of line On Sun, Nov 16, 2008 at 03:29:01PM +0100, Alexander van Heukelum wrote: > From: Alexander van Heukelum <heukelum@...ipnir.lusi.uni-sb.de> > > The macro "interrupt" in entry_64.S generates a lot of code. This > patch moves most of its contents into an external function. It > saves anywhere between 500 and 2500 bytes of text depending on the > configuration. > > The function returns with an altered stackpointer. > > Dwarf2-annotations are most probably wrong or missing. > > There is a comment in the original code about saving rbp twice, but > I don't understand what the code tries to do. First of all, the > second copy of rbp is written below the stack. This is not for the stack, but to keep the registers as the pt_regs struct expects them. We'll be casting this structure later, and not doing that can lead to bogus code, whenever we cast regs->bp. > Second, if the current > stack is already the irqstack, this second copy is overwritten. Third, > as far as I can tell, ebp should not be saved in pt_regs at all at > this stage as it is 'preserved' due to the C calling conventions. So > I left this second copy out and everything seems to work fine. If it > wouldn't, all exceptions and NMIs would be dangerous anyhow, as far > as I can see. Try testing with a kernel with CONFIG_FRAME_POINTER turned on. > > Signed-off-by: Alexander van Heukelum <heukelum@...tmail.fm> > Cc: Glauber Costa <gcosta@...hat.com> > > --- > arch/x86/kernel/entry_64.S | 123 ++++++++++++++++++++++++++------------------ > 1 files changed, 73 insertions(+), 50 deletions(-) > > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S > index a3a7fb2..eb57c23 100644 > --- a/arch/x86/kernel/entry_64.S > +++ b/arch/x86/kernel/entry_64.S > @@ -247,6 +247,78 @@ ENTRY(native_usergs_sysret64) > CFI_REL_OFFSET rsp,RSP > /*CFI_REL_OFFSET ss,SS*/ > .endm > + > +/* > + * initial frame state for interrupts and exceptions > + */ > + .macro _frame ref > + CFI_STARTPROC simple > + CFI_SIGNAL_FRAME > + CFI_DEF_CFA rsp,SS+8-\ref > + /*CFI_REL_OFFSET ss,SS-\ref*/ > + CFI_REL_OFFSET rsp,RSP-\ref > + /*CFI_REL_OFFSET rflags,EFLAGS-\ref*/ > + /*CFI_REL_OFFSET cs,CS-\ref*/ > + CFI_REL_OFFSET rip,RIP-\ref > + .endm > + > +/* initial frame state for interrupts (and exceptions without error code) */ > +#define INTR_FRAME _frame RIP > +/* initial frame state for exceptions with error code (and interrupts with > + vector already pushed) */ > +#define XCPT_FRAME _frame ORIG_RAX > + > +/* save_args changes the stack */ > +ENTRY(save_args) > + XCPT_FRAME > + cld > + subq $9*8, %rsp > + CFI_ADJUST_CFA_OFFSET 9*8 > + push 9*8(%rsp) /* copy return address */ > + CFI_ADJUST_CFA_OFFSET 8 > + movq %rdi, 8*8+16(%rsp) > + CFI_REL_OFFSET rdi, 8*8+16 > + movq %rsi, 7*8+16(%rsp) > + CFI_REL_OFFSET rsi, 7*8+16 > + movq %rdx, 6*8+16(%rsp) > + CFI_REL_OFFSET rdx, 6*8+16 > + movq %rcx, 5*8+16(%rsp) > + CFI_REL_OFFSET rcx, 5*8+16 > + movq %rax, 4*8+16(%rsp) > + CFI_REL_OFFSET rax, 4*8+16 > + movq %r8, 3*8+16(%rsp) > + CFI_REL_OFFSET r8, 3*8+16 > + movq %r9, 2*8+16(%rsp) > + CFI_REL_OFFSET r9, 2*8+16 > + movq %r10, 1*8+16(%rsp) > + CFI_REL_OFFSET r10, 1*8+16 > + movq %r11, 0*8+16(%rsp) > + CFI_REL_OFFSET r11, 0*8+16 > + leaq -ARGOFFSET+16(%rsp),%rdi /* arg1 for handler */ > + movq %rbp, 8(%rsp) /* push %rbp */ > + leaq 8(%rsp), %rbp /* mov %rsp, %ebp */ > + testl $3, CS(%rdi) > + je 1f > + SWAPGS > + /* > + * irqcount is used to check if a CPU is already on an interrupt stack > + * or not. While this is essentially redundant with preempt_count it is > + * a little cheaper to use a separate counter in the PDA (short of > + * moving irq_enter into assembly, which would be too much work) > + */ > +1: incl %gs:pda_irqcount > + jne 2f > + pop %rax /* move return address... */ > + mov %gs:pda_irqstackptr,%rsp > + push %rax /* ... to the new stack */ > + /* > + * We entered an interrupt context - irqs are off: > + */ > +2: TRACE_IRQS_OFF > + ret > + CFI_ENDPROC > +END(save_args) > + > /* > * A newly forked process directly context switches into this. > */ > @@ -615,26 +687,6 @@ ENTRY(stub_rt_sigreturn) > END(stub_rt_sigreturn) > > /* > - * initial frame state for interrupts and exceptions > - */ > - .macro _frame ref > - CFI_STARTPROC simple > - CFI_SIGNAL_FRAME > - CFI_DEF_CFA rsp,SS+8-\ref > - /*CFI_REL_OFFSET ss,SS-\ref*/ > - CFI_REL_OFFSET rsp,RSP-\ref > - /*CFI_REL_OFFSET rflags,EFLAGS-\ref*/ > - /*CFI_REL_OFFSET cs,CS-\ref*/ > - CFI_REL_OFFSET rip,RIP-\ref > - .endm > - > -/* initial frame state for interrupts (and exceptions without error code) */ > -#define INTR_FRAME _frame RIP > -/* initial frame state for exceptions with error code (and interrupts with > - vector already pushed) */ > -#define XCPT_FRAME _frame ORIG_RAX > - > -/* > * Interrupt entry/exit. > * > * Interrupt entry points save only callee clobbered registers in fast path. > @@ -644,36 +696,7 @@ END(stub_rt_sigreturn) > > /* 0(%rsp): interrupt number */ > .macro interrupt func > - cld > - SAVE_ARGS > - leaq -ARGOFFSET(%rsp),%rdi # arg1 for handler > - pushq %rbp > - /* > - * Save rbp twice: One is for marking the stack frame, as usual, and the > - * other, to fill pt_regs properly. This is because bx comes right > - * before the last saved register in that structure, and not bp. If the > - * base pointer were in the place bx is today, this would not be needed. > - */ > - movq %rbp, -8(%rsp) > - CFI_ADJUST_CFA_OFFSET 8 > - CFI_REL_OFFSET rbp, 0 > - movq %rsp,%rbp > - CFI_DEF_CFA_REGISTER rbp > - testl $3,CS(%rdi) > - je 1f > - SWAPGS > - /* irqcount is used to check if a CPU is already on an interrupt > - stack or not. While this is essentially redundant with preempt_count > - it is a little cheaper to use a separate counter in the PDA > - (short of moving irq_enter into assembly, which would be too > - much work) */ > -1: incl %gs:pda_irqcount > - cmoveq %gs:pda_irqstackptr,%rsp > - push %rbp # backlink for old unwinder > - /* > - * We entered an interrupt context - irqs are off: > - */ > - TRACE_IRQS_OFF > + call save_args > call \func > .endm > > -- > 1.5.4.3 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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