On Tue, Feb 09, 2021 at 05:13:38PM +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 > > however I tried the same build without LLVM=1 and it passed, > so my guess is that clang is doing something unexpected > > jirka > Additionally, if I remove the btfid generation section in scripts/link-vmlinux.sh to bypass that and get a working Image.gz, vfs_truncate is in the list of available functions: / # grep vfs_truncate /sys/kernel/debug/tracing/available_filter_functions vfs_truncate / # cat /proc/version Linux version 5.11.0-rc7-dirty (nathan@ubuntu-m3-large-x86) (ClangBuiltLinux clang version 13.0.0 (https://github.com/llvm/llvm-project 8f130f108fedfcf6cb80ef594560a87341028a37), LLD 13.0.0 (https://github.com/llvm/llvm-project 8f130f108fedfcf6cb80ef594560a87341028a37)) #1 SMP PREEMPT Tue Feb 9 09:25:36 MST 2021 / # zcat /proc/config.gz | grep "DEBUG_INFO_BTF\|FTRACE\|BPF" # CONFIG_CGROUP_BPF is not set CONFIG_BPF=y # CONFIG_BPF_LSM is not set CONFIG_BPF_SYSCALL=y CONFIG_ARCH_WANT_DEFAULT_BPF_JIT=y # CONFIG_BPF_JIT_ALWAYS_ON is not set CONFIG_BPF_JIT_DEFAULT_ON=y # CONFIG_BPF_PRELOAD is not set # CONFIG_NETFILTER_XT_MATCH_BPF is not set # CONFIG_BPFILTER is not set # CONFIG_NET_CLS_BPF is not set # CONFIG_NET_ACT_BPF is not set CONFIG_BPF_JIT=y CONFIG_HAVE_EBPF_JIT=y # CONFIG_PSTORE_FTRACE is not set CONFIG_DEBUG_INFO_BTF=y CONFIG_DEBUG_INFO_BTF_MODULES=y CONFIG_HAVE_DYNAMIC_FTRACE=y CONFIG_HAVE_DYNAMIC_FTRACE_WITH_REGS=y CONFIG_HAVE_FTRACE_MCOUNT_RECORD=y CONFIG_FTRACE=y CONFIG_DYNAMIC_FTRACE=y CONFIG_DYNAMIC_FTRACE_WITH_REGS=y # CONFIG_FTRACE_SYSCALLS is not set CONFIG_BPF_EVENTS=y CONFIG_FTRACE_MCOUNT_RECORD=y # CONFIG_FTRACE_RECORD_RECURSION is not set # CONFIG_FTRACE_STARTUP_TEST is not set # CONFIG_TEST_BPF is not set Cheers, Nathan
