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@xxxxxxxxxx> --- 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 _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
