On Thu, May 12, 2011 at 07:00:13PM +0530, Rabin Vincent wrote: > On Thu, May 12, 2011 at 14:54, Martin Schwidefsky > <schwidefsky@xxxxxxxxxx> wrote: > > On Wed, 11 May 2011 22:53:55 +0530 Rabin Vincent <rabin@xxxxxx> wrote: > >> On Tue, May 10, 2011 at 13:40, Martin Schwidefsky <schwidefsky@xxxxxxxxxx> wrote: > >> Thumb-2 via recordmcount.pl needs the clearing of the lsb because the > >> relocation (R_ARM_ABS32) that gets used for the assembly file > >> that recordmcount.pl generates and assembles dictates that the lsb be > >> set if the target symbol is Thumb/Thumb-2 function. mcount_adjust would > >> not help here since the ORing is done later, when the relocation is > >> applied. > > > > Hmm, from what I can make out the C version of recordmcount uses R_ARM_ABS32 > > as well. > > Right. It worked when I initially implemented ARM support there because > recordmcount.c always found the STT_SECTION symbol as a base and not a > STT_FUNC symbol. However, I noticed yesterday that this does not happen > in some cases, so I sent a patch to avoid STT_FUNC symbol as bases on > ARM, not because of this relocation, but because of a slightly different > oddity of Thumb symbols: > > http://lkml.org/lkml/2011/5/11/304 > > (The relocation problem alone could be solved by using R_ARM_ABS32_NOI > instead.) > > > > >> Thumb-2 via recordmcount.c does not need the clearing of the lsb in > >> ftrace_call_adjust. > > > > So the clearing of the lsb is only required if the recordmcount.pl script > > is used? > > Yes. > > >> Building with the ARM instruction set also does not need the clearing > >> of the lsb. > > > > Who does the ORing? I can't find anything in recordmount.pl/recordmcount.c > > which looks like doing an OR, does the assembler do that based on the > > symbol type? > > The lsb is set to 1 by the linker, when it applies the relocations as it > links vmlinux. > > > > >> > Thumb-2 the offset is -1, correct? If there is a way to distinguish > >> > the two targets in recordmcount at compile time we could convert arm > >> > as well. Which would allow us to remove the ftrace_call_adjust function. > >> > >> To remove ftrace_call_adjust, we could either deprecate the > >> recordmcount.pl usage for ARM (you already have to edit the Kconfig to > >> use it) or modify it to generate specific relocations explicitly instead > >> of using the assembler data directives. > > > > Hmm, it would be a desirable property if the C version and the pearl > > version of recordmcount would do the same. Or we could remove the arm > > support from the pearl script, the C version is faster anyway. > > I'm OK with removing the ARM support from recordmcount.pl; it doesn't > seem needed to make significant modifications to it for ARM when we > don't use it anyway. Is there any reason why the recordmcount.pl would ever be used now that the C implementation exists? I notice that arch/arm/Kconfig has: config ARM ... select HAVE_C_RECORDMCOUNT so deprecating ARM support from recordmcount.pl seems unlikely to hurt anyone. The C implementation seems to have worked fine when I was testing dynamic ftrace with Thumb-2 recently. Cheers ---Dave -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
