Messages in this thread | | | Subject | Re: [PATCH] mips: function tracer: Fix broken function tracing | From | Steven Rostedt <> | Date | Tue, 15 Jan 2013 16:07:29 -0500 |
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On Tue, 2013-01-15 at 09:55 -0800, David Daney wrote:
> > There's nothing that states what the ftrace caller must be. We can have > > it do a proper stack update. That is, only at boot up do we need to > > handle the defined mcount. After that, those instructions are just place > > holders for our own algorithms. If the addiu was needed for the defined > > mcount, there's no reason to keep it for our own ftrace_caller. > > > > Would that work? > > ... either do as you suggest and dynamically change the ABI of the > target function.
We already change the ABI. We have it call ftrace_caller instead of mcount.
BTW, I've just compiled with gcc 4.6.3 against mips, and I don't see the issue. I have:
0000000000000000 <account_kernel_stack>: 0: 03e0082d move at,ra 4: 0c000000 jal 0 <account_kernel_stack> 4: R_MIPS_26 _mcount 4: R_MIPS_NONE *ABS* 4: R_MIPS_NONE *ABS* 8: 0000602d move t0,zero c: 2402000d li v0,13 10: 3c030000 lui v1,0x0 10: R_MIPS_HI16 mem_section 10: R_MIPS_NONE *ABS* 10: R_MIPS_NONE *ABS* 14: 000216fc dsll32 v0,v0,0x1b 18: 64630000 daddiu v1,v1,0
Is it dependent on the config?
> > Or add support to GCC for a better tracing ABI (as I already said we did > for mips64).
I wouldn't waste time changing gcc for this. If you're going to change gcc than please implement the -mfentry option. Look at x86_64 to understand this more.
-- Steve
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