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. Provide two linker scripts: - *-timens.lds for building VDSO for processes inside time namespace (it has bigger functions and needs to build firstly) - *.lds for host processes VDSO (it has smaller functions and entry addresses should be adjusted with the linker script magic to fit with entries from timens) Signed-off-by: Dmitry Safonov <dima@xxxxxxxxxx> --- arch/x86/entry/vdso/.gitignore | 1 + arch/x86/entry/vdso/Makefile | 18 ++++++++++++++---- arch/x86/entry/vdso/vdso-timens.lds.S | 7 +++++++ arch/x86/entry/vdso/vdso32/.gitignore | 1 + arch/x86/entry/vdso/vdso32/vdso32-timens.lds.S | 8 ++++++++ 5 files changed, 31 insertions(+), 4 deletions(-) create mode 100644 arch/x86/entry/vdso/vdso-timens.lds.S create mode 100644 arch/x86/entry/vdso/vdso32/vdso32-timens.lds.S diff --git a/arch/x86/entry/vdso/.gitignore b/arch/x86/entry/vdso/.gitignore index 9ab4fa4c7e7b..aaddf8f2171c 100644 --- a/arch/x86/entry/vdso/.gitignore +++ b/arch/x86/entry/vdso/.gitignore @@ -1,4 +1,5 @@ vdso.lds +vdso-timens.lds vdsox32.lds vdso32-syscall-syms.lds vdso32-sysenter-syms.lds diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile index ccb572831ea1..4e1659619e7e 100644 --- a/arch/x86/entry/vdso/Makefile +++ b/arch/x86/entry/vdso/Makefile @@ -44,11 +44,14 @@ vobjs := $(foreach F,$(vobjs-y),$(obj)/$F) vobjs32 := $(foreach F,$(vobjs32-y),$(obj)/$F) vobjs-timens := $(foreach F,$(vobjs-timens-y),$(obj)/$F) vobjs32-timens := $(foreach F,$(vobjs32-timens-y),$(obj)/$F) +dep-vdso.lds-$(CONFIG_TIME_NS) += $(obj)/vdso-image-64-timens.c +dep-vdso32.lds-$(CONFIG_TIME_NS) += $(obj)/vdso-image-32-timens.c $(obj)/vdso.o: $(obj)/vdso.so targets += vdso.lds $(vobjs-y) $(vobjs-timens-y) vdso64.entries targets += vdso32/vdso32.lds $(vobjs32-y) $(vobjs32-timens-y) vdso32.entries +targets += vdso-timens.lds vdso32/vdso32-timens.lds # Build the vDSO image C files and link them in. vdso_img_objs := $(vdso_img-y:%=vdso-image-%.o) @@ -59,11 +62,13 @@ targets += $(vdso_img_cfiles) targets += $(vdso_img_sodbg) $(vdso_img-y:%=vdso%.so) CPPFLAGS_vdso.lds += -P -C +CPPFLAGS_vdso-timens.lds := $(CPPFLAGS_vdso.lds) VDSO_LDFLAGS_vdso.lds = -m elf_x86_64 -soname linux-vdso.so.1 --no-undefined \ -z max-page-size=4096 +VDSO_LDFLAGS_vdso-timens.lds := $(VDSO_LDFLAGS_vdso.lds) -$(obj)/vdso64-timens.so.dbg: $(obj)/vdso.lds $(vobjs-timens) FORCE +$(obj)/vdso64-timens.so.dbg: $(obj)/vdso-timens.lds $(vobjs-timens) FORCE $(call if_changed,vdso) $(obj)/vdso64.so.dbg: $(obj)/vdso.lds $(vobjs) FORCE @@ -79,6 +84,9 @@ quiet_cmd_vdso2c = VDSO2C $@ $(obj)/vdso-image-%.c: $(obj)/vdso%.so.dbg $(obj)/vdso%.so $(obj)/vdso2c FORCE $(call if_changed,vdso2c) +$(obj)/vdso.lds: $(dep-vdso.lds-y) $(obj)/vdso2c FORCE +$(obj)/vdso32/vdso32.lds: $(dep-vdso32.lds-y) $(obj)/vdso2c FORCE + # # Don't omit frame pointers for ease of userspace debugging, but do # optimize sibling calls. @@ -142,8 +150,10 @@ $(obj)/%.so: $(obj)/%.so.dbg $(obj)/vdsox32.so.dbg: $(obj)/vdsox32.lds $(vobjx32s) FORCE $(call if_changed,vdso) -CPPFLAGS_vdso32.lds = $(CPPFLAGS_vdso.lds) -VDSO_LDFLAGS_vdso32.lds = -m elf_i386 -soname linux-gate.so.1 +CPPFLAGS_vdso32.lds := $(CPPFLAGS_vdso.lds) +CPPFLAGS_vdso32-timens.lds := $(CPPFLAGS_vdso32.lds) +VDSO_LDFLAGS_vdso32.lds := -m elf_i386 -soname linux-gate.so.1 +VDSO_LDFLAGS_vdso32-timens.lds := $(VDSO_LDFLAGS_vdso32.lds) KBUILD_AFLAGS_32 := $(filter-out -m64,$(KBUILD_AFLAGS)) -DBUILD_VDSO $(obj)/vdso32.so.dbg: KBUILD_AFLAGS = $(KBUILD_AFLAGS_32) @@ -172,7 +182,7 @@ endif $(obj)/vdso32.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32) $(obj)/vdso32-timens.so.dbg: KBUILD_CFLAGS = $(KBUILD_CFLAGS_32) -$(obj)/vdso32-timens.so.dbg: $(obj)/vdso32/vdso32.lds $(vobjs32-timens) FORCE +$(obj)/vdso32-timens.so.dbg: $(obj)/vdso32/vdso32-timens.lds $(vobjs32-timens) FORCE $(call if_changed,vdso) $(obj)/vdso32.so.dbg: $(obj)/vdso32/vdso32.lds $(vobjs32) FORCE diff --git a/arch/x86/entry/vdso/vdso-timens.lds.S b/arch/x86/entry/vdso/vdso-timens.lds.S new file mode 100644 index 000000000000..687aba3bc5f0 --- /dev/null +++ b/arch/x86/entry/vdso/vdso-timens.lds.S @@ -0,0 +1,7 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Linker script for 64-bit timens vDSO. + */ + +#define UNALIGNED_ENTRIES +#include "vdso.lds.S" diff --git a/arch/x86/entry/vdso/vdso32/.gitignore b/arch/x86/entry/vdso/vdso32/.gitignore index e45fba9d0ced..ce4afb6ffb62 100644 --- a/arch/x86/entry/vdso/vdso32/.gitignore +++ b/arch/x86/entry/vdso/vdso32/.gitignore @@ -1 +1,2 @@ vdso32.lds +vdso32-timens.lds diff --git a/arch/x86/entry/vdso/vdso32/vdso32-timens.lds.S b/arch/x86/entry/vdso/vdso32/vdso32-timens.lds.S new file mode 100644 index 000000000000..1a3b3b1f0517 --- /dev/null +++ b/arch/x86/entry/vdso/vdso32/vdso32-timens.lds.S @@ -0,0 +1,8 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Linker script for 32-bit timens vDSO. + */ + +#define UNALIGNED_ENTRIES + +#include "vdso32.lds.S" -- 2.20.1
