On Sun, 2009-10-25 at 14:37 +0100, Patrik Kluba wrote: > On Sun, Oct 25, 2009 at 11:48 AM, Wu Zhangjin <wuzhangjin@xxxxxxxxx> wrote: > > > > do you mean if enabling PROFILE_BEFORE_PROLOGUE, there will be some > > problems with module support using -mlong-calls? > > > > No, there are no problems. I've tested it on friday, and function > graph tracing was working correctly. > I meant to say that 4.2.1 we use does not generate correct profile > calls from kernel modules. Maybe this issue was fixed in newer > releases, I did not check. I've applied a patch (don't remember where > have I found that, maybe it was created by you) to our toolchain > several months ago. I have never sent a patch to gcc before :-) but perhaps somebody have fixed it for us. so, the left job is hoping somebody enable PROFILE_BEFORE_PROLOGUE for MIPS in the next version of gcc if there is no side effect, and then we can hijack the return address of non-leaf & leaf function directly in the same way in _mcount. > > I was thinking about dynamic tracing, and I think a toolchain patch > can be avoided completely. We only need to make difference between > "jal _mcount" and "jalr v1"-style mcount calls when replacing them > with "nop" instructions in the code-patching function called by > ftrace_convert_nops(). This can be done in 2 ways: > 1) keeping old instructions - takes extra memory, not an option > 2) using 2 separate instructions to replace with. One of them could be > the normal NOP instruction, which expands to "sll r0, r0, 0". For the > other we could use "sll r0, r0, 1" but as it has already special > meaning (SSNOP) a better candidate could be something like "sll r1, > r1, 0". This way we can decide which instruction to patch in when > tracing is enabled for a function, eg. when the code patcher > encounters a "sll r0, r0, 0" it emits a function call using JAL and > when it encounters "sll r1, r1, 0" it emits a function call using > "JALR v1". If only thinking about dynamic tracing, no patch for gcc needed, -mlong-calls is enough, I have done it via a "stupid" trick, will send the patchset out asap :-) Regards, Wu Zhangjin
