On Wed, Jun 25, 2014 at 03:54:14PM +0100, Jean Pihet wrote: > Hi Will, Hello,
> On 25 June 2014 11:01, Will Deacon <will.dea...@arm.com> wrote: > > On Fri, Jun 20, 2014 at 09:10:35AM +0100, Jean Pihet wrote: > >> On 18 June 2014 14:53, Will Deacon <will.dea...@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? To use a readily available AArch64 example, take a look at __kernel_gettimeofday in arch/arm64/kernel/vdso/gettimeofday.S It starts by moving the link register into x2, so that it can later call __do_get_tspec without clobbering it. Furthermore, it doesn't make use of the stack at all. How can you unwind that using your current code? Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/