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authorJohn Reiser <jreiser@bitwagon.com>2009-07-27 11:23:50 -0700
committerSteven Rostedt <rostedt@goodmis.org>2009-09-12 21:57:29 -0400
commit4b3b4c5e64ce26612646867ee354373620063534 (patch)
tree048ff75a616c83c5bd64372f4140d53c9f79f169 /include/asm-generic
parentb5130b1e7d3717d03ab1916b198bf0d49fa0a619 (diff)
ftrace: __start_mcount_loc should be .init.rodata
__start_mcount_loc[] is unused after init, yet occupies RAM forever as part of .rodata. 152kiB is typical on a 64-bit architecture. Instead, __start_mcount_loc should be in the interval [__init_begin, __init_end) so that the space is reclaimed after init. __start_mcount_loc[] is generated during the load portion of kernel build, and is used only by ftrace_init(). ftrace_init is declared '__init' and is in .init.text, which is freed after init. __start_mcount_loc is placed into .rodata by a call to MCOUNT_REC inside the RO_DATA macro of include/asm-generic/vmlinux.lds.h. The array *is* read-only, but more importantly it is not used after init. So the call to MCOUNT_REC should be moved from RO_DATA to INIT_DATA. This patch has been tested on x86_64 with CONFIG_DEBUG_PAGEALLOC=y which verifies that the address range never is accessed after init. Signed-off-by: John Reiser <jreiser@BitWagon.com> LKML-Reference: <4A6DF0B6.7080402@bitwagon.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'include/asm-generic')
-rw-r--r--include/asm-generic/vmlinux.lds.h5
1 files changed, 3 insertions, 2 deletions
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 6ad76bf5fb4..98b37cf3ac6 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -91,7 +91,8 @@
#endif
#ifdef CONFIG_FTRACE_MCOUNT_RECORD
-#define MCOUNT_REC() VMLINUX_SYMBOL(__start_mcount_loc) = .; \
+#define MCOUNT_REC() . = ALIGN(8); \
+ VMLINUX_SYMBOL(__start_mcount_loc) = .; \
*(__mcount_loc) \
VMLINUX_SYMBOL(__stop_mcount_loc) = .;
#else
@@ -331,7 +332,6 @@
/* __*init sections */ \
__init_rodata : AT(ADDR(__init_rodata) - LOAD_OFFSET) { \
*(.ref.rodata) \
- MCOUNT_REC() \
DEV_KEEP(init.rodata) \
DEV_KEEP(exit.rodata) \
CPU_KEEP(init.rodata) \
@@ -455,6 +455,7 @@
MEM_DISCARD(init.data) \
KERNEL_CTORS() \
*(.init.rodata) \
+ MCOUNT_REC() \
DEV_DISCARD(init.rodata) \
CPU_DISCARD(init.rodata) \
MEM_DISCARD(init.rodata)