On Wed, 2009-10-21 at 17:14 +0400, Sergei Shtylyov wrote: > Hello. > > Steven Rostedt wrote: > > >>Need to check which registers is missing when saving/restoring for > >>_mcount: > > >>NESTED(ftrace_graph_caller, PT_SIZE, ra) > >> MCOUNT_SAVE_REGS > >> PTR_S v0, PT_R2(sp) > >> > >> MCOUNT_SET_ARGS > >> jal prepare_ftrace_return > >> nop > >> > >> /* overwrite the parent as &return_to_handler: v0 -> $1(at) */ > >> move $1, v0 > > > I'm confused here? I'm not exactly sure what the above is doing. Is $1 a > > register (AT)? > > Yes. Have replaced it by AT, thanks! > > > And how is this register used before calling mcount? > > >> PTR_L v0, PT_R2(sp) > >> MCOUNT_RESTORE_REGS > >> RETURN_BACK > >> END(ftrace_graph_caller) > > >> .align 2 > >> .globl return_to_handler > >>return_to_handler: > >> PTR_SUBU sp, PT_SIZE > >> PTR_S v0, PT_R2(sp) > > > BTW, is v0 the only return register? I know x86 can return two different > > registers depending on what it returns. What happens if a function > > returns a 64 bit value on a 32bit box? Does it use two registers for > > that? > > Yes, there's also v1 register. > Thanks, added. Regards, Wu Zhangjin
