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Commit c7b0d173 authored by Steven Rostedt's avatar Steven Rostedt Committed by Ingo Molnar
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powerpc: ftrace, do nothing in mcount call for dyn ftrace 



Impact: quicken mcount calls that are not replaced by dyn ftrace

Dynamic ftrace no longer does on the fly recording of mcount locations.
The mcount locations are now found at compile time. The mcount
function no longer needs to store registers and call a stub function.
It can now just simply return.

Since there are some functions that do not get converted to a nop
(.init sections and other code that may disappear), this patch should
help speed up that code.

Also, the stub for mcount on PowerPC 32 can not be a simple branch
link register like it is on PowerPC 64. According to the ABI specification:

"The _mcount routine is required to restore the link register from
 the stack so that the profiling code can be inserted transparently,
 whether or not the profiled function saves the link register itself."

This means that we must restore the link register that was used
to make the call to mcount.  The minimal mcount function for PPC32
ends up being:

 mcount:
        mflr    r0
        mtctr   r0
        lwz     r0, 4(r1)
        mtlr    r0
        bctr

Where we move the link register used to call mcount into the
ctr register, and then restore the link register from the stack.
Then we use the ctr register to jump back to the mcount caller.
The r0 register is free for us to use.

Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 813b8520

arch/powerpc/kernel/entry_32.S

+9 −31
Original line number Original line Diff line number Diff line
@@ -1162,39 +1162,17 @@ machine_check_in_rtas: 
#ifdef CONFIG_DYNAMIC_FTRACE

#ifdef CONFIG_DYNAMIC_FTRACE

_GLOBAL(mcount)

_GLOBAL(mcount)

_GLOBAL(_mcount)

_GLOBAL(_mcount)

	stwu	r1,-48(r1)

	/*

	stw	r3, 12(r1)

	 * It is required that _mcount on PPC32 must preserve the

	stw	r4, 16(r1)

	 * link register. But we have r0 to play with. We use r0

	stw	r5, 20(r1)

	 * to push the return address back to the caller of mcount

	stw	r6, 24(r1)

	 * into the ctr register, restore the link register and

	mflr	r3

	 * then jump back using the ctr register.

	stw	r7, 28(r1)

	 */

	mfcr	r5

	mflr	r0

	stw	r8, 32(r1)

	stw	r9, 36(r1)

	stw	r10,40(r1)

	stw	r3, 44(r1)

	stw	r5, 8(r1)

	subi	r3, r3, MCOUNT_INSN_SIZE

	.globl mcount_call

mcount_call:

	bl	ftrace_stub

	nop

	lwz	r6, 8(r1)

	lwz	r0, 44(r1)

	lwz	r3, 12(r1)

	mtctr	r0

	mtctr	r0

	lwz	r4, 16(r1)

	lwz	r0, 4(r1)

	mtcr	r6

	lwz	r5, 20(r1)

	lwz	r6, 24(r1)

	lwz	r0, 52(r1)

	lwz	r7, 28(r1)

	lwz	r8, 32(r1)

	mtlr	r0

	mtlr	r0

	lwz	r9, 36(r1)

	lwz	r10,40(r1)

	addi	r1, r1, 48

	bctr

	bctr





_GLOBAL(ftrace_caller)

_GLOBAL(ftrace_caller)

arch/powerpc/kernel/entry_64.S

+0 −12
Original line number Original line Diff line number Diff line
@@ -888,18 +888,6 @@ _GLOBAL(enter_prom) 
#ifdef CONFIG_DYNAMIC_FTRACE

#ifdef CONFIG_DYNAMIC_FTRACE

_GLOBAL(mcount)

_GLOBAL(mcount)

_GLOBAL(_mcount)

_GLOBAL(_mcount)

	/* Taken from output of objdump from lib64/glibc */

	mflr	r3

	stdu	r1, -112(r1)

	std	r3, 128(r1)

	subi	r3, r3, MCOUNT_INSN_SIZE

	.globl mcount_call

mcount_call:

	bl	ftrace_stub

	nop

	ld	r0, 128(r1)

	mtlr	r0

	addi	r1, r1, 112

	blr

	blr





_GLOBAL(ftrace_caller)

_GLOBAL(ftrace_caller)