Messages in this thread | | | Date | Tue, 15 Jan 2013 13:34:48 -0800 | From | David Daney <> | Subject | Re: [PATCH] mips: function tracer: Fix broken function tracing |
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On 01/15/2013 01:07 PM, Steven Rostedt wrote: > 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?
Yes.
You need to select a 32-bit kernel (which in turn may require selecting a board type that also supports it).
The ABI is different for 32-bit and 64-bit _mcount.
David Daney
> >> >> 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.
A good point. But I don't really plan on doing any work related to 32-bit mips things at this point, so any such change would have to be done by someone else.
David Daney
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