[PATCH 08/10] x86-64: select DYNAMIC_DEBUG_RELATIVE_POINTERS

Rasmus Villemoes
2019-04-09T21:26:29Z

This reduces the size of struct _ddebug from 56 to 40 bytes. There's
one such struct for each pr_debug(), netdev_debug() etc. in a
CONFIG_DYNAMIC_DEBUG kernel. An Ubuntu 4.15 kernel has about 2550
entries in the __verbose section of vmlinux, amounting to ~40K
saved. (Modules also become smaller, but it's harder to quantify how
much that yields at runtime.)

For comparison, the __bug_table section of that Ubuntu kernel is 75576
bytes, i.e. 6298 12-byte bug_entrys, so GENERIC_BUG_RELATIVE_POINTERS
saves ~50K.

Due to the build-time sanity checks in asm-generic/dynamic_debug.h, we
need to add another #undef to vclock_gettime.c.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
arch/x86/Kconfig | 1 +
arch/x86/entry/vdso/vdso32/vclock_gettime.c | 1 +
arch/x86/include/asm/Kbuild | 1 +
3 files changed, 3 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5ad92419be19..eb5488b4577d 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -30,6 +30,7 @@ config X86_64
select SWIOTLB
select X86_DEV_DMA_OPS
select ARCH_HAS_SYSCALL_WRAPPER
+ select DYNAMIC_DEBUG_RELATIVE_POINTERS

#
# Arch settings
diff --git a/arch/x86/entry/vdso/vdso32/vclock_gettime.c b/arch/x86/entry/vdso/vdso32/vclock_gettime.c
index 9242b28418d5..9acec4426206 100644
--- a/arch/x86/entry/vdso/vdso32/vclock_gettime.c
+++ b/arch/x86/entry/vdso/vdso32/vclock_gettime.c
@@ -17,6 +17,7 @@
#undef CONFIG_ILLEGAL_POINTER_VALUE
#undef CONFIG_SPARSEMEM_VMEMMAP
#undef CONFIG_NR_CPUS
+#undef CONFIG_DYNAMIC_DEBUG_RELATIVE_POINTERS

#define CONFIG_X86_32 1
#define CONFIG_PGTABLE_LEVELS 2
diff --git a/arch/x86/include/asm/Kbuild b/arch/x86/include/asm/Kbuild
index a0ab9ab61c75..793d2c6735b9 100644
--- a/arch/x86/include/asm/Kbuild
+++ b/arch/x86/include/asm/Kbuild
@@ -7,6 +7,7 @@ generated-y += unistd_64_x32.h
generated-y += xen-hypercalls.h

generic-y += dma-contiguous.h
+generic-y += dynamic_debug.h
generic-y += early_ioremap.h
generic-y += export.h
generic-y += mcs_spinlock.h
--
2.20.1