Re: [RFC][PATCH 2/3] x86_64: Allow breakpoints to emulate call functions

[Steven Rostedt]

On Tue, 7 May 2019 14:14:12 -0500
Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:

> On Tue, May 07, 2019 at 03:01:53PM -0400, Steven Rostedt wrote:
> > How's this?
> > 
> > -- Steve
> > 
> > From d29dc2e9e0275c9857932b80cebc01551b669efb Mon Sep 17 00:00:00 2001
> > From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Date: Wed, 1 May 2019 15:11:17 +0200
> > Subject: [PATCH] x86_64: Allow breakpoints to emulate call functions
> > 
> > In order to allow breakpoints to emulate call functions, they need to push
> > the return address onto the stack. But because the breakpoint exception
> > frame is added to the stack when the breakpoint is hit, there's no room to
> > add the address onto the stack and return to the address of the emulated
> > called funtion.  
> 
> The 2nd sentence can probably be removed since it's technically no
> longer true, thanks to the previous patch.
> 
> > This helper functions are added:  
> 
> "These"

New version:

    x86_64: Allow breakpoints to emulate call functions
    
    In order to allow breakpoints to emulate call functions, they need to push
    the return address onto the stack. The x86_64 int3 handler adds a small gap
    to allow the stack to grow some. Use this gap to add the return address to
    be able to emulate a call instruction at the breakpoint location.
    
    These helper functions are added:
    
      int3_emulate_jmp(): changes the location of the regs->ip to return there.
    
     (The next two are only for x86_64)
      int3_emulate_push(): to push the address onto the gap in the stack
      int3_emulate_call(): push the return address and change regs->ip

-- Steve