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: > > That leaves arm as the last remaining architecture with a non trivial > > ftrace_call_adjust function. There the least significant bit is removed > > from the address with an and operation. The comment says this is done > > for Thumb-2. This implies that for Thumb-1 the offset is 0 and for > > Thumb-2 the offset is -1, correct? > > ARM supports building the kernel using either the ARM instruction set or > the Thumb-2 instruction set. The kernel cannot be built with the > "Thumb-1" instruction set (btw usually referred to as just Thumb). > > 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. > 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? > 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? > > 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. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- 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
