Hi Will,
On 25 June 2014 11:01, Will Deacon will.deacon@arm.com wrote:
On Fri, Jun 20, 2014 at 09:10:35AM +0100, Jean Pihet wrote:
Hi Will,
Hi Jean,
On 18 June 2014 14:53, Will Deacon will.deacon@arm.com wrote:
On Tue, Jun 17, 2014 at 06:11:05PM +0100, Jean Pihet wrote:
Tested with perf record and tracepoints filtering (-e <tracepoint>), with unwinding using fp (--call-graph fp) and dwarf info (--call-graph dwarf).
Whilst the old ACPS unwinding only needs PC, FP and SP, is this definitely true for exidx and DWARF-based unwinding? Given that libunwind ends up running a state machine for the latter, can we guarantee that we won't hit instructions that require access to other general purpose registers?
Yes. dwarf unwinding does not need anything extra. Once seeded all the rest is extracted from the dwarf trace info.
Ok, but what if the LR isn't saved on the stack, for example? What if the code you're trying to unwind is hand-written assembly annotated with CFI directives?
Then in that case the unwinding is not possible unless the hand-crafted asm is compatible with the requested unwinding method (fp, dwarf etc.). Do you expect problems there, if so can you give more details?
Will
Jean