Add the CONFIG_X86_PIE option which builds the kernel as a Position Independent Executable (PIE). The kernel is currently build with the mcmodel=kernel option which forces it to stay on the top 2G of the virtual address space. With PIE, the kernel will be able to move below the current limit. The --emit-relocs linker option was kept instead of using -pie to limit the impact on mapped sections. Any incompatible relocation will be catch by the arch/x86/tools/relocs binary at compile time. Performance/Size impact: Size of vmlinux (Default configuration): File size: - PIE disabled: +0.000031% - PIE enabled: -3.210% (less relocations) .text section: - PIE disabled: +0.000644% - PIE enabled: +0.837% Size of vmlinux (Ubuntu configuration): File size: - PIE disabled: -0.201% - PIE enabled: -0.082% .text section: - PIE disabled: same - PIE enabled: +1.319% Size of vmlinux (Default configuration + ORC): File size: - PIE enabled: -3.167% .text section: - PIE enabled: +0.814% Size of vmlinux (Ubuntu configuration + ORC): File size: - PIE enabled: -3.167% .text section: - PIE enabled: +1.26% The size increase is mainly due to not having access to the 32-bit signed relocation that can be used with mcmodel=kernel. A small part is due to reduced optimization for PIE code. This bug [1] was opened with gcc to provide a better code generation for kernel PIE. Hackbench (50% and 1600% on thread/process for pipe/sockets): - PIE disabled: no significant change (avg +0.1% on latest test). - PIE enabled: between -0.50% to +0.86% in average (default and Ubuntu config). slab_test (average of 10 runs): - PIE disabled: no significant change (-2% on latest run, likely noise). - PIE enabled: between -1% and +0.8% on latest runs. Kernbench (average of 10 Half and Optimal runs): Elapsed Time: - PIE disabled: no significant change (avg -0.239%) - PIE enabled: average +0.07% System Time: - PIE disabled: no significant change (avg -0.277%) - PIE enabled: average +0.7% [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82303 Signed-off-by: Thomas Garnier <thgarnie@xxxxxxxxxx> --- arch/x86/Kconfig | 8 ++++++++ arch/x86/Makefile | 1 + 2 files changed, 9 insertions(+) diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 1e4b399c64e5..b92f96923712 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2141,6 +2141,14 @@ config X86_GLOBAL_STACKPROTECTOR bool depends on CC_STACKPROTECTOR +config X86_PIE + bool + depends on X86_64 + select DEFAULT_HIDDEN + select DYNAMIC_MODULE_BASE + select MODULE_REL_CRCS if MODVERSIONS + select X86_GLOBAL_STACKPROTECTOR if CC_STACKPROTECTOR + config HOTPLUG_CPU bool "Support for hot-pluggable CPUs" depends on SMP diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 42774185a58a..c49855b4b1be 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -144,6 +144,7 @@ else KBUILD_CFLAGS += -mno-red-zone ifdef CONFIG_X86_PIE + KBUILD_CFLAGS += -fPIC KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/x86/kernel/module.lds else KBUILD_CFLAGS += -mcmodel=kernel -- 2.14.2.920.gcf0c67979c-goog _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
