On Sun, 22 Dec 2002, Linus Torvalds wrote:
>
> I looked a bit at what it would take to have the TF bit handled by the
> sysenter path, and it might not be so horrible - certainly not as ugly as
> the register restore bits.
Hey, I tried it out, and it does indeed turn out to be fairly easy and
clean (in fact, it's mostly four pretty obvious "one-liners").
Let nobody say I won't change my mind - you were right Jamie (*). The
pushfl/popfl is unnessary, and does show up in microbenchmarks.
How does the attached patch work for people? I've verified that
single-stepping works, and I've also verified that it does improve
performance for simple system calls. Everything looks quite simple.
Linus
(*) In fact, people sometimes complain that I change my mind way too
often. Hey, sue me.
-=-=-=
===== arch/i386/kernel/signal.c 1.22 vs edited =====
--- 1.22/arch/i386/kernel/signal.c Fri Dec 6 09:43:43 2002
+++ edited/arch/i386/kernel/signal.c Sun Dec 22 20:31:38 2002
@@ -609,6 +609,11 @@
void do_notify_resume(struct pt_regs *regs, sigset_t *oldset,
__u32 thread_info_flags)
{
+ /* Pending single-step? */
+ if (thread_info_flags & _TIF_SINGLESTEP) {
+ regs->eflags |= TF_MASK;
+ clear_thread_flag(TIF_SINGLESTEP);
+ }
/* deal with pending signal delivery */
if (thread_info_flags & _TIF_SIGPENDING)
do_signal(regs,oldset);
===== arch/i386/kernel/sysenter.c 1.4 vs edited =====
--- 1.4/arch/i386/kernel/sysenter.c Sat Dec 21 16:02:02 2002
+++ edited/arch/i386/kernel/sysenter.c Sun Dec 22 20:17:28 2002
@@ -54,19 +54,18 @@
0xc3 /* ret */
};
static const char sysent[] = {
- 0x9c, /* pushf */
0x51, /* push %ecx */
0x52, /* push %edx */
0x55, /* push %ebp */
0x89, 0xe5, /* movl %esp,%ebp */
0x0f, 0x34, /* sysenter */
+ 0x00, /* align return point */
/* System call restart point is here! (SYSENTER_RETURN - 2) */
0xeb, 0xfa, /* jmp to "movl %esp,%ebp" */
/* System call normal return point is here! (SYSENTER_RETURN in entry.S) */
0x5d, /* pop %ebp */
0x5a, /* pop %edx */
0x59, /* pop %ecx */
- 0x9d, /* popf - restore TF */
0xc3 /* ret */
};
unsigned long page = get_zeroed_page(GFP_ATOMIC);
===== arch/i386/kernel/traps.c 1.36 vs edited =====
--- 1.36/arch/i386/kernel/traps.c Mon Nov 18 10:10:45 2002
+++ edited/arch/i386/kernel/traps.c Sun Dec 22 20:03:35 2002
@@ -605,7 +605,7 @@
* interface.
*/
if ((regs->xcs & 3) == 0)
- goto clear_TF;
+ goto clear_TF_reenable;
if ((tsk->ptrace & (PT_DTRACE|PT_PTRACED)) == PT_DTRACE)
goto clear_TF;
}
@@ -637,6 +637,8 @@
handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code, 1);
return;
+clear_TF_reenable:
+ set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
clear_TF:
regs->eflags &= ~TF_MASK;
return;
===== include/asm-i386/thread_info.h 1.8 vs edited =====
--- 1.8/include/asm-i386/thread_info.h Fri Dec 6 09:43:43 2002
+++ edited/include/asm-i386/thread_info.h Sun Dec 22 20:30:28 2002
@@ -109,6 +109,7 @@
#define TIF_NOTIFY_RESUME 1 /* resumption notification requested */
#define TIF_SIGPENDING 2 /* signal pending */
#define TIF_NEED_RESCHED 3 /* rescheduling necessary */
+#define TIF_SINGLESTEP 4 /* restore singlestep on return to user mode */
#define TIF_USEDFPU 16 /* FPU was used by this task this quantum (SMP) */
#define TIF_POLLING_NRFLAG 17 /* true if poll_idle() is polling TIF_NEED_RESCHED */
@@ -116,6 +117,7 @@
#define _TIF_NOTIFY_RESUME (1<<TIF_NOTIFY_RESUME)
#define _TIF_SIGPENDING (1<<TIF_SIGPENDING)
#define _TIF_NEED_RESCHED (1<<TIF_NEED_RESCHED)
+#define _TIF_SINGLESTEP (1<<TIF_SINGLESTEP)
#define _TIF_USEDFPU (1<<TIF_USEDFPU)
#define _TIF_POLLING_NRFLAG (1<<TIF_POLLING_NRFLAG)
-
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This archive was generated by hypermail 2b29 : Mon Dec 23 2002 - 22:00:31 EST