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Date:   Mon, 5 Mar 2018 11:09:01 -0600
From:   Segher Boessenkool <segher@kernel.crashing.org>
To:     Torsten Duwe <duwe@lst.de>
Cc:     Michael Ellerman <mpe@ellerman.id.au>,
        Jiri Kosina <jkosina@suse.cz>, linux-kernel@vger.kernel.org,
        Nicholas Piggin <npiggin@gmail.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        live-patching@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2] On ppc64le we HAVE_RELIABLE_STACKTRACE
Message-ID: <20180305170901.GS21977@gate.crashing.org>
References: <20180305164928.GA17953@lst.de>
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On Mon, Mar 05, 2018 at 05:49:28PM +0100, 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.
> 
>  – In instances where a function’s 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.)
> [...]
>  – The function shall save the link register that contains its return
>    address in the LR save doubleword of its caller’s stack frame before
>    calling another function.

All of this is also true for the other PowerPC ABIs, fwiw (both 32-bit
and 64-bit; the offset of the LR save slot isn't the same in all ABIs).


Segher