Re: [PATCH 3/7] objtool: Add support for intra-function calls

[Julien Thierry]

On 4/3/20 1:41 PM, Peter Zijlstra wrote:
> On Fri, Apr 03, 2020 at 09:01:38AM +0100, Julien Thierry wrote:
> > Last I found is in qcom_link_stack_sanitization() [2], but that's just a
> > workaround for a very specific hardware. In my local tree I just put the
> > function as STACK_FRAME_NON_STANDARD. But the code just saves the return
> > address, has 16 call instructions that just call the instruction after them,
> > restores the return address and lets the C-function return normally (and it
> > somehow fixes something for that hardware).
> That sounds very much like the RSB flushing we do.

Yes, the piece of code you posted reminded me of this. The difference is 
that the RSB part uses a loop and counter while the qcom thing has a 
fixed amount of call instructions (which can make things easier for 
static analysis, if we'd really want to go down that road).

--
Julien Thierry