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Date: Wed, 6 Feb 2019 00:10:48 +0000 From: Dmitry Safonov <dima@...sta.com> To: linux-kernel@...r.kernel.org Cc: Dmitry Safonov <dima@...sta.com>, Adrian Reber <adrian@...as.de>, Andrei Vagin <avagin@...nvz.org>, Andrei Vagin <avagin@...il.com>, Andy Lutomirski <luto@...nel.org>, Andy Tucker <agtucker@...gle.com>, Arnd Bergmann <arnd@...db.de>, Christian Brauner <christian.brauner@...ntu.com>, Cyrill Gorcunov <gorcunov@...nvz.org>, Dmitry Safonov <0x7f454c46@...il.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, Jeff Dike <jdike@...toit.com>, Oleg Nesterov <oleg@...hat.com>, Pavel Emelyanov <xemul@...tuozzo.com>, Shuah Khan <shuah@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, containers@...ts.linux-foundation.org, criu@...nvz.org, linux-api@...r.kernel.org, x86@...nel.org Subject: [PATCH 14/32] x86/VDSO: Build VDSO with -ffunction-sections As it has been discussed on timens RFC, adding a new conditional branch `if (inside_time_ns)` on VDSO for all processes is undesirable. It will add a penalty for everybody as branch predictor may mispredict the jump. Also there are instruction cache lines wasted on cmp/jmp. Those effects of introducing time namespace are very much unwanted having in mind how much work have been spent on micro-optimisation vdso code. Addressing those problems, there are two versions of VDSO's .so: for host tasks (without any penalty) and for processes inside of time namespace with clk_to_ns() that subtracts offsets from host's time. Unfortunately, to allow changing VDSO VMA on a running process, the entry points to VDSO should have the same offsets (addresses). That's needed as i.e. application that calls setns() may have already resolved VDSO symbols in GOT/PLT. Compile VDSO images with -ffunction-sections so that VDSO entries can be aligned on the same addresses with linker script magic. Put ia32 functions those are written in assembly into corresponding sections. Signed-off-by: Dmitry Safonov <dima@...sta.com> --- arch/x86/entry/vdso/Makefile | 2 +- arch/x86/entry/vdso/vdso32/sigreturn.S | 2 ++ arch/x86/entry/vdso/vdso32/system_call.S | 2 +- 3 files changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile index 2433ed9342fd..55ba81d4415c 100644 --- a/arch/x86/entry/vdso/Makefile +++ b/arch/x86/entry/vdso/Makefile @@ -3,7 +3,7 @@ # Building vDSO images for x86. # -KBUILD_CFLAGS += $(DISABLE_LTO) +KBUILD_CFLAGS += $(DISABLE_LTO) -ffunction-sections KASAN_SANITIZE := n UBSAN_SANITIZE := n OBJECT_FILES_NON_STANDARD := y diff --git a/arch/x86/entry/vdso/vdso32/sigreturn.S b/arch/x86/entry/vdso/vdso32/sigreturn.S index c3233ee98a6b..b641ccf8d664 100644 --- a/arch/x86/entry/vdso/vdso32/sigreturn.S +++ b/arch/x86/entry/vdso/vdso32/sigreturn.S @@ -11,6 +11,7 @@ .globl __kernel_sigreturn .type __kernel_sigreturn,@function nop /* this guy is needed for .LSTARTFDEDLSI1 below (watch for HACK) */ + .section .text.__kernel_sigreturn, "ax" ALIGN __kernel_sigreturn: .LSTART_sigreturn: @@ -21,6 +22,7 @@ __kernel_sigreturn: nop .size __kernel_sigreturn,.-.LSTART_sigreturn + .section .text.__kernel_rt_sigreturn, "ax" .globl __kernel_rt_sigreturn .type __kernel_rt_sigreturn,@function ALIGN diff --git a/arch/x86/entry/vdso/vdso32/system_call.S b/arch/x86/entry/vdso/vdso32/system_call.S index 263d7433dea8..13ec05287f63 100644 --- a/arch/x86/entry/vdso/vdso32/system_call.S +++ b/arch/x86/entry/vdso/vdso32/system_call.S @@ -8,7 +8,7 @@ #include <asm/cpufeatures.h> #include <asm/alternative-asm.h> - .text + .section .text.__kernel_vsyscall, "ax" .globl __kernel_vsyscall .type __kernel_vsyscall,@function ALIGN -- 2.20.1
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