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Re: [PATCH 1/3][GCC] Add new target hook asm_post_cfi_startproc

From: Jason Merrill <jason at redhat dot com>
To: Sam Tebbs <Sam dot Tebbs at arm dot com>, Richard Biener <rguenther at suse dot de>
Cc: "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, Richard Earnshaw <Richard dot Earnshaw at arm dot com>, "jakub at redhat dot com" <jakub at redhat dot com>, nd <nd at arm dot com>, "law at redhat dot com" <law at redhat dot com>, "ccoutant at gmail dot com" <ccoutant at gmail dot com>
Date: Thu, 13 Dec 2018 14:03:58 -0500
Subject: Re: [PATCH 1/3][GCC] Add new target hook asm_post_cfi_startproc
References: <1615d64d-7f42-a261-8041-281914712941@arm.com> <043bdf88-6e4b-33df-4772-2cc4ddffae98@arm.com> <alpine.LSU.2.20.1811050853030.1827@zhemvz.fhfr.qr> <8f32de8a-4248-98dd-44b2-5e9cfd69f856@arm.com>

On 11/5/18 5:18 AM, Sam Tebbs wrote:



On 11/05/2018 07:54 AM, Richard Biener wrote:

On Fri, 2 Nov 2018, Sam Tebbs wrote:

On 11/02/2018 05:28 PM, Sam Tebbs wrote:

Hi all,

This patch adds a new target hook called "asm_post_cfi_startproc". This hook is
intended to be used by the aarch64 backend to emit a directive that enables
support for unwinding frames signed with the pointer authentication B-key. This
hook is triggered after the ".cfi_startproc" directive is emitted in
gcc/dwarf2out.c.

Bootstrapped on aarch64-none-linux-gnu and tested on aarch64-none-elf with no regressions.

Ok for trunk?

Can you explain why existing prologue/cfi emission points are not
enough?


I couldn't find any target hooks that were triggered at the
assembly-printing level at the correct point in time (after
.cfi_startproc is emitted), please do point me to one if that is not the
case.

An alternative could have been to implement a new reg_note but that
would have meant adding target-specific code to target-agnostic files
and wouldn't have been as flexible.

And this seems consistent with the other stuff indwarf2out_do_cfi_startproc. You might amend the documentation tomention that the expected use is to add more .cfi_* directives. OK withthat change.


Jason

Follow-Ups:
- Re: [PATCH 1/3][GCC] Add new target hook asm_post_cfi_startproc
  - From: Sam Tebbs

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