Singlestep through a syscall using vsyscall-sysenter had two bugs:
1. Setting TIF_SINGLESTEP is not enough to force
do_notify_resume() to be run on return to user;
TIF_IRET must also be set.
2. do_notify_resume() was being passed masked copies
of task_thread_flags, so TIF_SINGLESTEP was never
seen as set when it was called. This was changed
to use the 'test' instruction instead of 'and';
a duplicated piece of code was removed instead
of fixing that part too.
Also changed some misleading 'jne' to 'jnz' to make it
clearer what is happening.
Signed-off-by: Chuck Ebbert <[email protected]>
---
arch/i386/kernel/entry.S | 17 +++++------------
arch/i386/kernel/traps.c | 1 +
2 files changed, 6 insertions(+), 12 deletions(-)
--- 2.6.16-rc3-nb.orig/arch/i386/kernel/entry.S
+++ 2.6.16-rc3-nb/arch/i386/kernel/entry.S
@@ -152,9 +152,9 @@ ENTRY(resume_userspace)
# setting need_resched or sigpending
# between sampling and the iret
movl TI_flags(%ebp), %ecx
- andl $_TIF_WORK_MASK, %ecx # is there any work to be done on
+ testl $_TIF_WORK_MASK, %ecx # is there any work to be done on
# int/exception return?
- jne work_pending
+ jnz work_pending
jmp restore_all
#ifdef CONFIG_PREEMPT
@@ -301,21 +301,14 @@ work_pending:
jz work_notifysig
work_resched:
call schedule
- cli # make sure we don't miss an interrupt
- # setting need_resched or sigpending
- # between sampling and the iret
- movl TI_flags(%ebp), %ecx
- andl $_TIF_WORK_MASK, %ecx # is there any work to be done other
- # than syscall tracing?
- jz restore_all
- testb $_TIF_NEED_RESCHED, %cl
- jnz work_resched
+ jmp resume_userspace
+ ALIGN
work_notifysig: # deal with pending signals and
# notify-resume requests
testl $VM_MASK, EFLAGS(%esp)
movl %esp, %eax
- jne work_notifysig_v86 # returning to kernel-space or
+ jnz work_notifysig_v86 # returning to kernel-space or
# vm86-space
xorl %edx, %edx
call do_notify_resume
--- 2.6.16-rc3-nb.orig/arch/i386/kernel/traps.c
+++ 2.6.16-rc3-nb/arch/i386/kernel/traps.c
@@ -795,6 +795,7 @@ debug_vm86:
clear_TF_reenable:
set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
+ set_tsk_thread_flag(tsk, TIF_IRET);
regs->eflags &= ~TF_MASK;
return;
}
--
Chuck
"Equations are the Devil's sentences." --Stephen Colbert
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