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-rw-r--r--arch/arm/kernel/entry-common.S124
1 files changed, 80 insertions, 44 deletions
diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S
index 2c1db77..f05a35a 100644
--- a/arch/arm/kernel/entry-common.S
+++ b/arch/arm/kernel/entry-common.S
@@ -92,75 +92,111 @@ ENDPROC(ret_from_fork)
#define CALL(x) .long x
#ifdef CONFIG_FUNCTION_TRACER
+/*
+ * When compiling with -pg, gcc inserts a call to the mcount routine at the
+ * start of every function. In mcount, apart from the function's address (in
+ * lr), we need to get hold of the function's caller's address.
+ *
+ * Older GCCs (pre-4.4) inserted a call to a routine called mcount like this:
+ *
+ * bl mcount
+ *
+ * These versions have the limitation that in order for the mcount routine to
+ * be able to determine the function's caller's address, an APCS-style frame
+ * pointer (which is set up with something like the code below) is required.
+ *
+ * mov ip, sp
+ * push {fp, ip, lr, pc}
+ * sub fp, ip, #4
+ *
+ * With EABI, these frame pointers are not available unless -mapcs-frame is
+ * specified, and if building as Thumb-2, not even then.
+ *
+ * Newer GCCs (4.4+) solve this problem by introducing a new version of mcount,
+ * with call sites like:
+ *
+ * push {lr}
+ * bl __gnu_mcount_nc
+ *
+ * With these compilers, frame pointers are not necessary.
+ *
+ * mcount can be thought of as a function called in the middle of a subroutine
+ * call. As such, it needs to be transparent for both the caller and the
+ * callee: the original lr needs to be restored when leaving mcount, and no
+ * registers should be clobbered. (In the __gnu_mcount_nc implementation, we
+ * clobber the ip register. This is OK because the ARM calling convention
+ * allows it to be clobbered in subroutines and doesn't use it to hold
+ * parameters.)
+ */
#ifdef CONFIG_DYNAMIC_FTRACE
ENTRY(mcount)
- stmdb sp!, {r0-r3, lr}
- mov r0, lr
- sub r0, r0, #MCOUNT_INSN_SIZE
+ stmdb sp!, {r0-r3, lr}
+ mov r0, lr
+ sub r0, r0, #MCOUNT_INSN_SIZE
.globl mcount_call
mcount_call:
- bl ftrace_stub
- ldr lr, [fp, #-4] @ restore lr
- ldmia sp!, {r0-r3, pc}
+ bl ftrace_stub
+ ldr lr, [fp, #-4] @ restore lr
+ ldmia sp!, {r0-r3, pc}
ENTRY(ftrace_caller)
- stmdb sp!, {r0-r3, lr}
- ldr r1, [fp, #-4]
- mov r0, lr
- sub r0, r0, #MCOUNT_INSN_SIZE
+ stmdb sp!, {r0-r3, lr}
+ ldr r1, [fp, #-4]
+ mov r0, lr
+ sub r0, r0, #MCOUNT_INSN_SIZE
.globl ftrace_call
ftrace_call:
- bl ftrace_stub
- ldr lr, [fp, #-4] @ restore lr
- ldmia sp!, {r0-r3, pc}
+ bl ftrace_stub
+ ldr lr, [fp, #-4] @ restore lr
+ ldmia sp!, {r0-r3, pc}
#else
ENTRY(__gnu_mcount_nc)
- stmdb sp!, {r0-r3, lr}
- ldr r0, =ftrace_trace_function
- ldr r2, [r0]
- adr r0, ftrace_stub
- cmp r0, r2
- bne gnu_trace
- ldmia sp!, {r0-r3, ip, lr}
- mov pc, ip
+ stmdb sp!, {r0-r3, lr}
+ ldr r0, =ftrace_trace_function
+ ldr r2, [r0]
+ adr r0, ftrace_stub
+ cmp r0, r2
+ bne gnu_trace
+ ldmia sp!, {r0-r3, ip, lr}
+ mov pc, ip
gnu_trace:
- ldr r1, [sp, #20] @ lr of instrumented routine
- mov r0, lr
- sub r0, r0, #MCOUNT_INSN_SIZE
- mov lr, pc
- mov pc, r2
- ldmia sp!, {r0-r3, ip, lr}
- mov pc, ip
+ ldr r1, [sp, #20] @ lr of instrumented routine
+ mov r0, lr
+ sub r0, r0, #MCOUNT_INSN_SIZE
+ mov lr, pc
+ mov pc, r2
+ ldmia sp!, {r0-r3, ip, lr}
+ mov pc, ip
ENTRY(mcount)
- stmdb sp!, {r0-r3, lr}
- ldr r0, =ftrace_trace_function
- ldr r2, [r0]
- adr r0, ftrace_stub
- cmp r0, r2
- bne trace
- ldr lr, [fp, #-4] @ restore lr
- ldmia sp!, {r0-r3, pc}
+ stmdb sp!, {r0-r3, lr}
+ ldr r0, =ftrace_trace_function
+ ldr r2, [r0]
+ adr r0, ftrace_stub
+ cmp r0, r2
+ bne trace
+ ldr lr, [fp, #-4] @ restore lr
+ ldmia sp!, {r0-r3, pc}
trace:
- ldr r1, [fp, #-4] @ lr of instrumented routine
- mov r0, lr
- sub r0, r0, #MCOUNT_INSN_SIZE
- mov lr, pc
- mov pc, r2
- ldr lr, [fp, #-4] @ restore lr
- ldmia sp!, {r0-r3, pc}
+ ldr r1, [fp, #-4] @ lr of instrumented routine
+ mov r0, lr
+ sub r0, r0, #MCOUNT_INSN_SIZE
+ mov lr, pc
+ mov pc, r2
+ ldr lr, [fp, #-4] @ restore lr
+ ldmia sp!, {r0-r3, pc}
#endif /* CONFIG_DYNAMIC_FTRACE */
.globl ftrace_stub
ftrace_stub:
- mov pc, lr
+ mov pc, lr
#endif /* CONFIG_FUNCTION_TRACER */
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