Weisbecker <fweis...@gmail.com>,Stanislav Kinsburskiy <skinsbur...@virtuozzo.com>,Ingo Molnar <mi...@redhat.com>,Paolo Bonzini <pbonz...@redhat.com>,Dmitry Safonov <dsafo...@virtuozzo.com>,Borislav Petkov <b...@alien8.de>,Josh Poimboeuf <jpoim...@redhat.com>,Brian Gerst <brge...@gmail.com>,Jan Beulich <jbeul...@suse.com>,Christian Borntraeger <borntrae...@de.ibm.com>,Fenghua Yu <fenghua...@intel.com>,He Chen <he.c...@linux.intel.com>,Russell King <li...@armlinux.org.uk>,Vladimir Murzin <vladimir.mur...@arm.com>,Will Deacon <will.dea...@arm.com>,Catalin Marinas <catalin.mari...@arm.com>,Mark Rutland <mark.rutl...@arm.com>,James Morse <james.mo...@arm.com>,"David A . Long" <dave.l...@linaro.org>,Pratyush Anand <pan...@redhat.com>,Laura Abbott <labb...@redhat.com>,Andre Przywara <andre.przyw...@arm.com>,Chris Metcalf <cmetc...@mellanox.com>,linux-s390 <linux-s...@vger.kernel.org>,LKML <linux-kernel@vger.kernel.org>,Linux API <linux-...@vger.kernel.org>,the arch/x86 maintainers <x...@kernel.org>,"linux-arm-ker...@lists.infradead.org" <linux-arm-ker...@lists.infradead.org>,Kernel Hardening <kernel-harden...@lists.openwall.com> From: h...@zytor.com Message-ID: <e0c934e7-6789-4598-af55-468c84b85...@zytor.com>
On March 22, 2017 2:11:12 PM PDT, Thomas Garnier <thgar...@google.com> wrote: >On Wed, Mar 22, 2017 at 1:49 PM, H. Peter Anvin <h...@zytor.com> wrote: >> On 03/22/17 13:41, Thomas Garnier wrote: >>>>> with the change below for additional feedback. >>>> >>>> Can you specify what that means? >>> >>> If I set inline by default, the compiler chose not to inline it on >>> x86. If I force inline the size impact was actually bigger (without >>> the architecture specific code). >>> >> >> That's utterly bizarre. Something strange is going on there. I >suspect >> the right thing to do is to out-of-line the error case only, but even >> that seems strange. It should be something like four instructions >inline. >> > >The compiler seemed to often inline other functions called by the >syscall handlers. I assume the growth was due to changes in code >optimization because the function is much larger at the end. > >>>> >>>> On x86, where there is only one caller of this, it really seems >like it >>>> ought to reduce the overhead to almost zero (since it most likely >is >>>> hidden in the pipeline.) >>>> >>>> I would like to suggest defining it inline if >>>> CONFIG_ARCH_NO_SYSCALL_VERIFY_PRE_USERMODE_STATE is set; I really >don't >>>> care about an architecture which doesn't have it. >>> >>> But if there is only one caller, does the compiler is not suppose to >>> inline the function based on options? >> >> If it is marked static in the same file, yes, but you have it in a >> different file from what I can tell. > >If we do global optimization, it should. Having it as a static inline >make it easier on all types of builds. > >> >>> The assembly will call it too, so I would need an inline and a >>> non-inline based on the caller. >> >> Where? I don't see that anywhere, at least for x86. > >After the latest changes on x86, yes. On arm/arm64, we call it with >the CHECK_DATA_CORRUPTION config. > >> >> -hpa >> If we do global optimization, yes, but global optimization (generally called link-time optimization, LTO, on Linux) is very much the exception and not the rule for the Linux kernel at this time. -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
