On Wed, 2008-12-24 at 16:08 +0800, Shaohua Li wrote: > On Wed, Dec 24, 2008 at 09:00:24AM +0800, Steven Rostedt wrote: > > > > On Wed, 2008-12-24 at 08:54 +0800, Shaohua Li wrote: > > > > > > > > > > +static unsigned char *ftrace_nop_replace(void) > > > > > +{ > > > > > + return ftrace_nop_code; > > > > > +} > > > > > + > > > > > +/* In IA64, each function will be added below two bundles with -pg option */ > > > > > +static unsigned char __attribute__((aligned(8))) > > > > > +ftrace_call_code[MCOUNT_INSN_SIZE] = { > > > > > + 0x02, 0x40, 0x31, 0x10, 0x80, 0x05, /* alloc r40=ar.pfs,12,8,0 */ > > > > > + 0xb0, 0x02, 0x00, 0x00, 0x42, 0x40, /* mov r43=r0;; */ > > > > > + 0x05, 0x00, 0xc4, 0x00, /* mov r42=b0 */ > > > > > + 0x11, 0x48, 0x01, 0x02, 0x00, 0x21, /* mov r41=r1 */ > > > > > + 0x00, 0x00, 0x00, 0x02, 0x00, 0x00, /* nop.i 0x0 */ > > > > > > > > If you made your own PLT stub, could you just change the one line to > > > > jump to that stub? > > > A simple jump to PLT stub doesn't work in IA64, as a lot of registers > > > should be saved. I'll do more investigation. > > > > So the registers are different depending on what function is called? > > That is, you would have to change more than one of these lines if you > > were to change it from calling _mcount to calling ftrace_stub? > Yes, module has different gp register against kernel. Before jump to > kernel, the register must be saved. > We need insert trampoline code in each module. The code should do the > register save and jump to ftrace_caller. Add a weak function in module.h > seems ok for the trampoline code, but I don't know how to find the > function address. Yes I understand that the module and kernel code is set up differently, PPC is pretty much the same in this aspect. I'm asking if it is easy to change a call from the module to kernel core to another function in kernel core? I must apologize that I'm pretty ignorant to how ia64 works. So there very well can be something that I do not understand that will prevent this. Question: if I have a call from the module to _mcount, how much has to change in the set up of the registers to make it call ftrace_call instead? Perhaps we could link in a call to ftrace_call via the tricks in recordmcount.pl to get the info needed to make that change? -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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