Re: [PATCH 2/2] ftrace: support for PowerPC
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From: Scott Wood <hidden>
Date: 2008-05-15 16:49:37
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On Wed, May 14, 2008 at 10:28:57PM -0700, David Miller wrote:
From: Steven Rostedt <rostedt@goodmis.org> Date: Wed, 14 May 2008 23:49:44 -0400quoted
+#ifdef CONFIG_FTRACE +#ifdef CONFIG_DYNAMIC_FTRACE +_GLOBAL(mcount) +_GLOBAL(_mcount) + stwu r1,-48(r1) + stw r3, 12(r1) + stw r4, 16(r1) + stw r5, 20(r1) + stw r6, 24(r1) + mflr r3 + stw r7, 28(r1) + mfcr r5 + stw r8, 32(r1) + stw r9, 36(r1) + stw r10,40(r1) + stw r3, 44(r1) + stw r5, 8(r1)Yikes, that's really expensive. Can't you do a tail call and let the function you end up calling do all the callee-saved register pops onto the stack?
The PPC32 ABI seems to (unfortunately) suggest that, with mcount, all
registers are callee-saved (except for the modifiable-during-function-linkage
registers like r0, r11, and r12) -- so mcount has to save the registers that
the callee won't (because they're normally volatile).
-Scott