Messages in this thread | | | Subject | Re: [PATCH] clear the frame pointer in copy_thread | From | Yanmin Zhang <> | Date | Wed, 20 Jun 2012 09:28:15 +0800 |
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On Tue, 2012-06-19 at 06:57 -0700, H. Peter Anvin wrote: > It isn't clear to me this is the right thing to do this in the kernel. A frame pointer isn't obligatory and doing this in user space seems more appropriate. Peter,
Thanks for the kind comments. You are right.
Yanmin
> > "Su, Xuemin" <xuemin.su@intel.com> wrote: > > >From: xueminsu <xuemin.su@intel.com> > > > >When creating a userspace thread, kernel copies all parent > >thread’s registers to the child thread, including bp register > >which is used to create stack frame. At this point, the bp > >register is pointing to the parent thread’s last stack frame. > > > >So, after the child thread is created, its bp register points > >to the parent thread’s stack area, and the value would be pushed > >to its own stack to form its first stack frame when it calls its > >first function. > > > >This would not be a problem if the child thread and the parent > >thread do not share the VM or if they share the VM and have the > >same stack. But if they share the VM and have different stacks, > >this would cause an issue: when we try to print the child thread’s > >stack trace, we would eventually walk into the parent thread’s > >stack area, and sometimes we will occasionally prints out the > >parent thread’s stack trace. > > > >Currently some version of libc clears the frame pointer just after > >the thread is created, but this is not guaranteed. > > > >Signed-off-by: xueminsu <xuemin.su@intel.com> > >--- > > arch/x86/kernel/process_32.c | 9 +++++++++ > > arch/x86/kernel/process_64.c | 9 +++++++++ > > 2 files changed, 18 insertions(+), 0 deletions(-) > > > >diff --git a/arch/x86/kernel/process_32.c > >b/arch/x86/kernel/process_32.c > >index 516fa18..b1b6d42 100644 > >--- a/arch/x86/kernel/process_32.c > >+++ b/arch/x86/kernel/process_32.c > >@@ -139,6 +139,15 @@ int copy_thread(unsigned long clone_flags, > >unsigned long sp, > > childregs->ax = 0; > > childregs->sp = sp; > > > >+ /* > >+ * If the child thread and the parent thread share the VM > >+ * but have different stack, the child thread's bp register > >+ * should be set to null, preventing it from pointing to > >+ * the parent thread's stack area. > >+ */ > >+ if ((sp != regs->sp) && (clone_flags & CLONE_VM)) > >+ childregs->bp = 0; > >+ > > p->thread.sp = (unsigned long) childregs; > > p->thread.sp0 = (unsigned long) (childregs+1); > > > >diff --git a/arch/x86/kernel/process_64.c > >b/arch/x86/kernel/process_64.c > >index 61cdf7f..5acff83 100644 > >--- a/arch/x86/kernel/process_64.c > >+++ b/arch/x86/kernel/process_64.c > >@@ -163,6 +163,15 @@ int copy_thread(unsigned long clone_flags, > >unsigned long sp, > > else > > childregs->sp = (unsigned long)childregs; > > > >+ /* > >+ * If the child thread and the parent thread share the VM > >+ * but have different stack, the child thread's bp register > >+ * should be set to null, preventing it from pointing to > >+ * the parent thread's stack area. > >+ */ > >+ if ((sp != regs->sp) && (clone_flags & CLONE_VM)) > >+ childregs->bp = 0; > >+ > > p->thread.sp = (unsigned long) childregs; > > p->thread.sp0 = (unsigned long) (childregs+1); > > p->thread.usersp = me->thread.usersp; > >-- > >1.7.6 >
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