Re: [PATCH v3] On ppc64le we HAVE_RELIABLE_STACKTRACE

[Josh Poimboeuf]

On Fri, May 04, 2018 at 02:38:34PM +0200, Torsten Duwe wrote:
> 
> The "Power Architecture 64-Bit ELF V2 ABI" says in section 2.3.2.3:
> 
> [...] There are several rules that must be adhered to in order to ensure
> reliable and consistent call chain backtracing:
> 
> * Before a function calls any other function, it shall establish its
>   own stack frame, whose size shall be a multiple of 16 bytes.
> 
>  â In instances where a functionâs prologue creates a stack frame, the
>    back-chain word of the stack frame shall be updated atomically with
>    the value of the stack pointer (r1) when a back chain is implemented.
>    (This must be supported as default by all ELF V2 ABI-compliant
>    environments.)
> [...]
>  â The function shall save the link register that contains its return
>    address in the LR save doubleword of its callerâs stack frame before
>    calling another function.
> 
> To me this sounds like the equivalent of HAVE_RELIABLE_STACKTRACE.
> This patch may be unneccessarily limited to ppc64le, but OTOH the only
> user of this flag so far is livepatching, which is only implemented on
> PPCs with 64-LE, a.k.a. ELF ABI v2.
> 
> Feel free to add other ppc variants, but so far only ppc64le got tested.
> 
> This change also implements save_stack_trace_tsk_reliable() for ppc64le
> that checks for the above conditions, where possible.
> 
> Signed-off-by: Torsten Duwe <duwe@xxxxxxx>
> Signed-off-by: Nicolai Stange <nstange@xxxxxxx>

The subject doesn't actively describe what the patch does, maybe change
it to something like:

  powerpc: Add support for HAVE_RELIABLE_STACKTRACE

or maybe

  powerpc: Add support for livepatch consistency model

Otherwise it looks great to me.

Acked-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

-- 
Josh