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Thu, 11 Jun 2020 16:45:05 -0700 (PDT) Subject: Re: [PATCH 2/5] gcc-plugins/stackleak: Use asm instrumentation to avoid useless register saving To: Kees Cook Cc: Emese Revfy , Miguel Ojeda , Masahiro Yamada , Michal Marek , Andrew Morton , Masahiro Yamada , Thiago Jung Bauermann , Luis Chamberlain , Jessica Yu , Sven Schnelle , Iurii Zaikin , Catalin Marinas , Will Deacon , Vincenzo Frascino , Thomas Gleixner , Peter Collingbourne , Naohiro Aota , Alexander Monakov , Mathias Krause , PaX Team , Brad Spengler , Laura Abbott , Florian Weimer , kernel-hardening@lists.openwall.com, linux-kbuild@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, gcc@gcc.gnu.org, notify@kernel.org References: <20200604134957.505389-1-alex.popov@linux.com> <20200604134957.505389-3-alex.popov@linux.com> <202006091143.AD1A662@keescook> <757cbafb-1e13-8989-e30d-33c557d33cc4@linux.com> <202006101302.AC218FA1@keescook> From: Alexander Popov Autocrypt: addr=alex.popov@linux.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <202006101302.AC218FA1@keescook> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 10.06.2020 23:03, Kees Cook wrote: > On Wed, Jun 10, 2020 at 06:47:14PM +0300, Alexander Popov wrote: >> On 09.06.2020 21:46, Kees Cook wrote: >> The inline asm statement that is used for instrumentation is arch-specific. >> Trying to add >> asm volatile("call stackleak_track_stack") >> in gcc plugin on aarch64 makes gcc break spectacularly. > > Ah! Thank you, that eluded my eyes. :) > >> I pass the target arch name to the plugin and check it explicitly to avoid that. >> >> Moreover, I'm going to create a gcc enhancement request for supporting >> no_caller_saved_registers attribute on aarch64. > > For arm64 right now it looks like the plugin will just remain > "inefficient" in these cleanup, as before, yes? Yes, for arm64 the instrumentation didn't change in this patch series. I checked the disasm and see the similar issue with useless register saving. I'm going to add asm instrumentation for arm64 when (I hope) the no_caller_saved_registers attribute becomes available for that platform. Best regards, Alexander