Thanks for the answers.
I understood that, this hack makes more mess in codegen for arm,
but can you please clarify what did you mean by
>Only a single register can be used
> as the frame chain.
As far as I understood, GCC for arm with THUMB2 mode uses r7 register as
frame pointer register by default (with -fno-omit-frame-pointer flag),
GCC for arm with ARM mode uses r11, so I didn't really propose
to change the frame pointer register.
Thanks.
On 09/05/2018 06:32 PM, Wilco Dijkstra wrote:
Hi Denis,
Adding support for a frame chain would require an ABI change. It
would have to
> work across GCC, LLVM, Arm, Thumb-1 and Thumb-2 - not a trivial amount of
> effort.
Clang already works that way.
No, that's incorrect like Richard pointed out. Only a single register can be
used
as the frame chain.
If we change the size of the traces to 2, it could be something like this:
...
At the first example we lost the full context, from where the
control/data flow comes from.
If 2 is not sufficient, then try 3 or 4. It may also be feasible to only enable
deeper unwinding for particular libraries so you only pay an extra cost for
leaks you are interested in.
The stack layout like this enables only with compile time flag
(-mthumb-fp and works only together with -mthumb and
-fno-omit-frame-pointer). It does not affect other codegen.
But any code built like that will *always* run slower even if you don't use
the sanitizer.
Wilco
