On Tue, Jul 16, 2019 at 10:08:18PM +0800, Changbin Du wrote: > On Mon, Jul 15, 2019 at 12:12:31PM +0200, Peter Zijlstra wrote:
> > Alternatively, we can have recordmcount (or objtool) mark all functions > > with a return value when the build has DEBUG_INFO on. The dwarves know > > the function signature. > > > We can extend the recordmcount tool to search 'subprogram' tag in the DIE > tree. > In below example, the 'DW_AT_type' is the type of function pidfd_create(). > > $ readelf -w kernel/pid.o > [...] > <1><1b914>: Abbrev Number: 232 (DW_TAG_subprogram) > <1b916> DW_AT_name : (indirect string, offset: 0x415e): > pidfd_create > <1b91a> DW_AT_decl_file : 1 > <1b91b> DW_AT_decl_line : 471 > <1b91d> DW_AT_decl_column : 12 > <1b91e> DW_AT_prototyped : 1 > <1b91e> DW_AT_type : <0xcc> > <1b922> DW_AT_low_pc : 0x450 > <1b92a> DW_AT_high_pc : 0x50 > <1b932> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa) > <1b934> DW_AT_GNU_all_call_sites: 1 > <1b934> DW_AT_sibling : <0x1b9d9> > [...] > > To that end, we need to introduce libdw library for recordmcount. I will have > a > try this week. Right; but only when this config option is set. > And probably, we can also record the parameters? The 'fun' part is where to store all this information in the kernel and how fast you can find it while tracing.
