Weisbecker <fweisbec@xxxxxxxxx>,Stanislav Kinsburskiy <skinsbursky@xxxxxxxxxxxxx>,Ingo Molnar <mingo@xxxxxxxxxx>,Paolo Bonzini <pbonzini@xxxxxxxxxx>,Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>,Borislav Petkov <bp@xxxxxxxxx>,Josh Poimboeuf <jpoimboe@xxxxxxxxxx>,Brian Gerst <brgerst@xxxxxxxxx>,Jan Beulich <JBeulich@xxxxxxxx>,Christian Borntraeger <borntraeger@xxxxxxxxxx>,Fenghua Yu <fenghua.yu@xxxxxxxxx>,He Chen <he.chen@xxxxxxxxxxxxxxx>,Russell King <linux@xxxxxxxxxxxxxxx>,Vladimir Murzin <vladimir.murzin@xxxxxxx>,Will Deacon <will.deacon@xxxxxxx>,Catalin Marinas <catalin.marinas@xxxxxxx>,Mark Rutland <mark.rutland@xxxxxxx>,James Morse <james.morse@xxxxxxx>,"David A . Long" <dave.long@xxxxxxxxxx>,Pratyush Anand <panand@xxxxxxxxxx>,Laura Abbott <labbott@xxxxxxxxxx>,Andre Przywara <andre.przywara@xxxxxxx>,Chris Metcalf <cmetcalf@xxxxxxxxxxxx>,linux-s390 <linux-s390@xxxxxxxxxxxxxxx>,LKML <linux-kernel@xxxxxxxxxxxxxxx>,Linux API <linux-api@xxxxxxxxxxxxxxx>,the arch/x86 maintainers <x86@xxxxxxxxxx>,"linux-arm-kernel@xxxxxxxxxxxxxxxxxxx" <linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>,Kernel Hardening <kernel-hardening@xxxxxxxxxxxxxxxxxx> From: hpa@xxxxxxxxx Message-ID: <E0C934E7-6789-4598-AF55-468C84B8568B@xxxxxxxxx> On March 22, 2017 2:11:12 PM PDT, Thomas Garnier <thgarnie@xxxxxxxxxx> wrote: >On Wed, Mar 22, 2017 at 1:49 PM, H. Peter Anvin <hpa@xxxxxxxxx> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
