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([2a01:cb14:499:3d00:cd47:f651:9d80:157a]) by smtp.gmail.com with ESMTPSA id u6sm16367526wrn.95.2020.08.03.05.13.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Aug 2020 05:13:16 -0700 (PDT) Subject: Re: [PATCH v2 9/9] objtool: Abstract unwind hint reading To: Josh Poimboeuf Cc: linux-kernel@vger.kernel.org, peterz@infradead.org, mbenes@suse.cz, raphael.gault@arm.com, benh@kernel.crashing.org References: <20200730094652.28297-1-jthierry@redhat.com> <20200730094652.28297-10-jthierry@redhat.com> <20200730150341.udqnykbw7yfsjvin@treble> <1a078563-001d-c666-d2f5-9291f0efd35a@redhat.com> <20200731140441.cpzr4lrlkcrmoz2c@treble> From: Julien Thierry Message-ID: <6a314dba-4086-717b-d226-6c292240a3e9@redhat.com> Date: Mon, 3 Aug 2020 13:13:14 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20200731140441.cpzr4lrlkcrmoz2c@treble> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/31/20 3:04 PM, Josh Poimboeuf wrote: > On Fri, Jul 31, 2020 at 08:00:58AM +0100, Julien Thierry wrote: >>>> + cfa->offset = hint->sp_offset; >>>> + insn->cfi.hint_type = hint->type; >>>> + insn->cfi.end = hint->end; >>>> + >>>> + insn->cfi.sp_only = hint->type == ORC_TYPE_REGS || hint->type == ORC_TYPE_REGS_IRET; >>> >>> What does "sp" mean here in sp_only? >>> >> >> Stack pointer, like in CFI_SP. When objtool encounters one of these hints, >> it starts to only track the stack frame with the stack pointer (no BP, no >> drap register, no move to temporary registers). Just trying to make some >> sense of this corner case. > > I think that's not quite right, because ORC_TYPE_CALL could also be > "sp_only" in some cases, by that definition. > But in that case the code will still track when/if the CFI becomes pointed to by BP. > The call to update_cfi_state_regs() is really regs-specific, not > sp-specific. > I must admit I don't really understand what "regs" is and why exactly such an exception in stack state tracking is made where only operations to SP are taken into account. -- Julien Thierry