On 11/11/24 1:54 AM, Jiri Olsa wrote:
On Fri, Nov 08, 2024 at 10:05:24AM -0800, Yonghong Song wrote:
Song Liu reported that a kernel func (perf_event_read()) cannot be traced
in certain situations since the func is not in vmlinux bTF. This happens
in kernels 6.4, 6.9 and 6.11 and the kernel is built with pahole 1.27.
The perf_event_read() signature in kernel (kernel/events/core.c):
static int perf_event_read(struct perf_event *event, bool group)
Adding '-V' to pahole command line, and the following error msg can be found:
skipping addition of 'perf_event_read'(perf_event_read) due to unexpected register used for parameter
Eventually the error message is attributed to the setting
(parm->unexpected_reg = 1) in parameter__new() function.
The following is the dwarf representation for perf_event_read():
0x0334c034: DW_TAG_subprogram
DW_AT_low_pc (0xffffffff812c6110)
DW_AT_high_pc (0xffffffff812c640a)
DW_AT_frame_base (DW_OP_reg7 RSP)
DW_AT_GNU_all_call_sites (true)
DW_AT_name ("perf_event_read")
DW_AT_decl_file ("/rw/compile/kernel/events/core.c")
DW_AT_decl_line (4641)
DW_AT_prototyped (true)
DW_AT_type (0x03324f6a "int")
0x0334c04e: DW_TAG_formal_parameter
DW_AT_location (0x007de9fd:
[0xffffffff812c6115, 0xffffffff812c6141): DW_OP_reg5 RDI
[0xffffffff812c6141, 0xffffffff812c6323): DW_OP_reg14 R14
[0xffffffff812c6323, 0xffffffff812c63fe): DW_OP_GNU_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value
[0xffffffff812c63fe, 0xffffffff812c6405): DW_OP_reg14 R14
[0xffffffff812c6405, 0xffffffff812c640a): DW_OP_GNU_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value)
DW_AT_name ("event")
DW_AT_decl_file ("/rw/compile/kernel/events/core.c")
DW_AT_decl_line (4641)
DW_AT_type (0x0333aac2 "perf_event *")
0x0334c05e: DW_TAG_formal_parameter
DW_AT_location (0x007dea82:
[0xffffffff812c6137, 0xffffffff812c63f2): DW_OP_reg12 R12
[0xffffffff812c63f2, 0xffffffff812c63fe): DW_OP_GNU_entry_value(DW_OP_reg4 RSI), DW_OP_stack_value
[0xffffffff812c63fe, 0xffffffff812c640a): DW_OP_reg12 R12)
DW_AT_name ("group")
DW_AT_decl_file ("/rw/compile/kernel/events/core.c")
DW_AT_decl_line (4641)
DW_AT_type (0x03327059 "bool")
hi,
I don't see that on gcc compiled kernel, is that related to clang?
Yes, the case I tried to fix is from clang compiled kernel.
<1><318d475>: Abbrev Number: 74 (DW_TAG_subprogram)
<318d476> DW_AT_name : (indirect string, offset: 0xf5776): perf_event_read
<318d47a> DW_AT_decl_file : 1
<318d47a> DW_AT_decl_line : 4746
<318d47c> DW_AT_decl_column : 12
<318d47d> DW_AT_prototyped : 1
<318d47d> DW_AT_type : <0x3135e35>
<318d481> DW_AT_low_pc : 0xffffffff8135be90
<318d489> DW_AT_high_pc : 0x196
<318d491> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa)
<318d493> DW_AT_call_all_calls: 1
<318d493> DW_AT_sibling : <0x318d900>
<2><318d497>: Abbrev Number: 30 (DW_TAG_formal_parameter)
<318d498> DW_AT_name : (indirect string, offset: 0x491590): event
<318d49c> DW_AT_decl_file : 1
<318d49c> DW_AT_decl_line : 4746
<318d49e> DW_AT_decl_column : 47
<318d49f> DW_AT_type : <0x313a680>
<318d4a3> DW_AT_location : 0x70c118 (location list)
<318d4a7> DW_AT_GNU_locviews: 0x70c110
<2><318d4ab>: Abbrev Number: 30 (DW_TAG_formal_parameter)
<318d4ac> DW_AT_name : (indirect string, offset: 0x51a865): group
<318d4b0> DW_AT_decl_file : 1
<318d4b0> DW_AT_decl_line : 4746
<318d4b2> DW_AT_decl_column : 59
<318d4b3> DW_AT_type : <0x3136055>
<318d4b7> DW_AT_location : 0x70c144 (location list)
<318d4bb> DW_AT_GNU_locviews: 0x70c13e
locations:
0070c144 ffffffff8135be90 (base address)
0070c14d v000000000000000 v000000000000000 views at 0070c13e for:
ffffffff8135be90 ffffffff8135bed2 (DW_OP_reg4 (rsi))
0070c152 v000000000000000 v000000000000000 views at 0070c140 for:
ffffffff8135bed2 ffffffff8135bf17 (DW_OP_reg14 (r14))
0070c158 v000000000000000 v000000000000000 views at 0070c142 for:
ffffffff8135bf17 ffffffff8135c026 (DW_OP_entry_value: (DW_OP_reg4 (rsi)); DW_OP_stack_value)
0070c162 <End of list>
other than that lgtm and I like the change Eduard suggested
thanks,
jirka
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