On Fri, Nov 20, 2009 at 08:34:38PM +0800, Wu Zhangjin wrote: > That thread "MIPS: Add option to pass return address location to > _mcount" from "David Daney <ddaney@xxxxxxxxxxxxxxxxxx>" have added a new > option -mmcount-ra-address to gcc(4.5) for MIPS to transfer the location > of the return address to _mcount. > > Benefit from this new feature, function graph tracer on MIPS will be > easier and safer to hijack the return address of the kernel function, > which will save some overhead and make the whole thing more reliable. > > In this patch, at first, try to enable the option -mmcount-ra-address in > arch/mips/Makefile with cc-option, if gcc support it, it will be > enabled, otherwise, no side effect. > > and then, we need to support this new option of gcc 4.5 and also support > the old gcc versions. > > with _mcount in the old gcc versions, it's not easy to get the location > of return address(tracing: add function graph tracer support for MIPS), > so, we do it in a C function: ftrace_get_parent_addr(ftrace.c), but > with -mmcount-ra-address, only several instructions need to get what > we want, so, I put into asm(mcount.S). and also, as the $12(t0) is > used by -mmcount-ra-address for transferring the localtion of return > address to _mcount, we need to save it into the stack and restore it > when enabled dynamic function tracer, 'Cause we have called > "ftrace_call" before "ftrace_graph_caller", which may destroy > $12(t0). > > (Thanks to David for providing that -mcount-ra-address and giving the > idea of KBUILD_MCOUNT_RA_ADDRESS, both of them have made the whole > thing more beautiful!) > > Signed-off-by: Wu Zhangjin <wuzhangjin@xxxxxxxxx> Queued for 2.6.33 but due to patch 3/3 I won't propagate this series immediately to linux-next. Thanks! Ralf
