Messages in this thread | | | Date | Wed, 24 Feb 2010 01:12:53 +0530 | From | Rabin Vincent <> | Subject | Re: [PATCH 02/10] ARM: ftrace: document mcount formats |
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On Mon, Feb 22, 2010 at 08:20:09PM +0100, Uwe Kleine-König wrote: > On Mon, Feb 22, 2010 at 11:36:24PM +0530, Rabin Vincent wrote: > > On Sat, Feb 13, 2010 at 09:37:48PM +0100, Uwe Kleine-König wrote: > > > On Sun, Feb 14, 2010 at 01:18:30AM +0530, Rabin Vincent wrote: > > > > + * With both the mcount types, we need to restore the original lr before > > > > + * returning. In the __gnu_mcount_nc, version we're allowed to clobber ip. > > > > + * No other registers should be clobbered. > > > > + */ > > > Very nice. > > > > > > Maybe make the last two sentences: > > > > > > In the __gnu_mcount_nc case the ip register is clobbered which is OK as > > > the calling convention for ARM allow clobbering this value for > > > subroutines and it doesn't contain parameters. > > > > Won't quoting calling conventions here be misleading? The mcounts don't > > following normal convention for the other bits (we can't clobber even > > the registers that are normally caller-saved, we need to restore lr, > > etc.) > actually mcount is a function in the middle of a function call. So it > must be transparent for both the caller and the callee. As the called > function needs to know the return address, mcount must not clobber it. > And as ip is don't care and can be clobbered mcount can use it as it > likes.
OK. How about this for the last paragraph:
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.)
Rabin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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