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Subject[PATCH 04/10] ARM: ftrace: allow building without frame pointers
Date
With a new enough GCC, ARM function tracing can be supported without the
need for frame pointers. This is essential for Thumb-2 support, since
frame pointers aren't available then.

Signed-off-by: Rabin Vincent <rabin@rab.in>
---
v2: #error if incompatible GCC.
arch/arm/Kconfig.debug | 5 +++++
arch/arm/kernel/armksyms.c | 2 ++
arch/arm/kernel/entry-common.S | 14 ++++++++++++++
kernel/trace/Kconfig | 2 +-
4 files changed, 22 insertions(+), 1 deletions(-)
diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index 91344af..4dbce53 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -27,6 +27,11 @@ config ARM_UNWIND
the performance is not affected. Currently, this feature
only works with EABI compilers. If unsure say Y.

+config OLD_MCOUNT
+ bool
+ depends on FUNCTION_TRACER && FRAME_POINTER
+ default y
+
config DEBUG_USER
bool "Verbose user fault messages"
help
diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c
index 8214bfe..e5e1e53 100644
--- a/arch/arm/kernel/armksyms.c
+++ b/arch/arm/kernel/armksyms.c
@@ -165,6 +165,8 @@ EXPORT_SYMBOL(_find_next_bit_be);
#endif

#ifdef CONFIG_FUNCTION_TRACER
+#ifdef CONFIG_OLD_MCOUNT
EXPORT_SYMBOL(mcount);
+#endif
EXPORT_SYMBOL(__gnu_mcount_nc);
#endif
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index f05a35a..6805a72 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -128,6 +128,13 @@ ENDPROC(ret_from_fork)
* allows it to be clobbered in subroutines and doesn't use it to hold
* parameters.)
*/
+
+#ifndef CONFIG_OLD_MCOUNT
+#if (__GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 4))
+#error Ftrace requires CONFIG_FRAME_POINTER=y with GCC older than 4.4.0.
+#endif
+#endif
+
#ifdef CONFIG_DYNAMIC_FTRACE
ENTRY(mcount)
stmdb sp!, {r0-r3, lr}
@@ -173,6 +180,12 @@ gnu_trace:
ldmia sp!, {r0-r3, ip, lr}
mov pc, ip

+#ifdef CONFIG_OLD_MCOUNT
+/*
+ * This is under an ifdef in order to force link-time errors for people trying
+ * to build with !FRAME_POINTER with a GCC which doesn't use the new-style
+ * mcount.
+ */
ENTRY(mcount)
stmdb sp!, {r0-r3, lr}
ldr r0, =ftrace_trace_function
@@ -191,6 +204,7 @@ trace:
mov pc, r2
ldr lr, [fp, #-4] @ restore lr
ldmia sp!, {r0-r3, pc}
+#endif

#endif /* CONFIG_DYNAMIC_FTRACE */

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 13e13d4..e10519f 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -124,7 +124,7 @@ if FTRACE
config FUNCTION_TRACER
bool "Kernel Function Tracer"
depends on HAVE_FUNCTION_TRACER
- select FRAME_POINTER
+ select FRAME_POINTER if (!ARM_UNWIND)
select KALLSYMS
select GENERIC_TRACER
select CONTEXT_SWITCH_TRACER
--
1.7.0


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