From: John Reiser Date: Mon, 27 Jul 2009 18:23:50 +0000 (-0700) Subject: ftrace: __start_mcount_loc should be .init.rodata X-Git-Tag: firefly_0821_release~12934^2~18 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=4b3b4c5e64ce26612646867ee354373620063534;p=firefly-linux-kernel-4.4.55.git 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 LKML-Reference: <4A6DF0B6.7080402@bitwagon.com> Signed-off-by: Steven Rostedt --- diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 6ad76bf5fb40..98b37cf3ac6d 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)