On Tue, Feb 09, 2021 at 12:09:31PM -0800, Nick Desaulniers wrote: > On Tue, Feb 9, 2021 at 11:06 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote: > > > > On Tue, Feb 09, 2021 at 05:13:42PM +0100, Jiri Olsa wrote: > > > On Tue, Feb 09, 2021 at 04:09:36PM +0100, Jiri Olsa wrote: > > > > > > SNIP > > > > > > > > > > > DW_AT_prototyped (true) > > > > > > > > DW_AT_type (0x01cfdfe4 "long int") > > > > > > > > DW_AT_external (true) > > > > > > > > > > > > > > > > > > > > > > Ok, the problem appears to be not in DWARF, but in mcount_loc data. > > > > > > > vfs_truncate's address is not recorded as ftrace-attachable, and thus > > > > > > > pahole ignores it. I don't know why this happens and it's quite > > > > > > > strange, given vfs_truncate is just a normal global function. > > > > > > > > > > right, I can't see it in mcount adresses.. but it begins with instructions > > > > > that appears to be nops, which would suggest it's traceable > > > > > > > > > > ffff80001031f430 <vfs_truncate>: > > > > > ffff80001031f430: 5f 24 03 d5 hint #34 > > > > > ffff80001031f434: 1f 20 03 d5 nop > > > > > ffff80001031f438: 1f 20 03 d5 nop > > > > > ffff80001031f43c: 3f 23 03 d5 hint #25 > > > > > > > > > > > > > > > > > > > I'd like to understand this issue before we try to fix it, but there > > > > > > > is at least one improvement we can make: pahole should check ftrace > > > > > > > addresses only for static functions, not the global ones (global ones > > > > > > > should be always attachable, unless they are special, e.g., notrace > > > > > > > and stuff). We can easily check that by looking at the corresponding > > > > > > > symbol. But I'd like to verify that vfs_truncate is ftrace-attachable > > > > > > > > I'm still trying to build the kernel.. however ;-) > > > > > > I finally reproduced.. however arm's not using mcount_loc > > > but some other special section.. so it's new mess for me > > > > so ftrace data actualy has vfs_truncate address but with extra 4 bytes: > > > > ffff80001031f434 > > > > real vfs_truncate address: > > > > ffff80001031f430 g F .text 0000000000000168 vfs_truncate > > > > vfs_truncate disasm: > > > > ffff80001031f430 <vfs_truncate>: > > ffff80001031f430: 5f 24 03 d5 hint #34 > > ffff80001031f434: 1f 20 03 d5 nop > > ffff80001031f438: 1f 20 03 d5 nop > > ffff80001031f43c: 3f 23 03 d5 hint #25 > > > > thats why we don't match it in pahole.. I checked few other functions > > and some have the same problem and some match the function boundary > > > > those that match don't have that first hint instrucion, like: > > > > ffff800010321e40 <do_faccessat>: > > ffff800010321e40: 1f 20 03 d5 nop > > ffff800010321e44: 1f 20 03 d5 nop > > ffff800010321e48: 3f 23 03 d5 hint #25 > > > > any hints about hint instructions? ;-) > > aarch64 makes *some* newer instructions reuse the "hint" ie "nop" > encoding space to make software backwards compatible on older hardware > that doesn't support such instructions. Is this BTI, perhaps? (The > function is perhaps the destination of an indirect call?) It seems like it. The issue is not reproducible when CONFIG_ARM64_BTI_KERNEL is not set. Cheers, Nathan
