Commit 4b3b4c5e authored Jul 27, 2009 by John Reiser Committed by Steven Rostedt Sep 12, 2009

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>

parent b5130b1e

include/asm-generic/vmlinux.lds.h

+3 −2

Original line number	Diff line number	Diff line
		@@ -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)