Le 06/12/2022 à 15:38, Mathieu Desnoyers a écrit :
> On 2022-12-05 17:50, Michael Ellerman wrote:
>> Michael Jeanson <mjeanson@xxxxxxxxxxxx> writes:
>>> On 2022-12-05 15:11, Michael Jeanson wrote:
>>>>>>> Michael Jeanson <mjeanson@xxxxxxxxxxxx> writes:
>>>>>>>> In v5.7 the powerpc syscall entry/exit logic was rewritten in C, on
>>>>>>>> PPC64_ELF_ABI_V1 this resulted in the symbols in the syscall table
>>>>>>>> changing from their dot prefixed variant to the non-prefixed ones.
>>>>>>>>
>>>>>>>> Since ftrace prefixes a dot to the syscall names when matching
>>>>>>>> them to
>>>>>>>> build its syscall event list, this resulted in no syscall events
>>>>>>>> being
>>>>>>>> available.
>>>>>>>>
>>>>>>>> Remove the PPC64_ELF_ABI_V1 specific version of
>>>>>>>> arch_syscall_match_sym_name to have the same behavior across all
>>>>>>>> powerpc
>>>>>>>> variants.
>>>>>>>
>>>>>>> This doesn't seem to work for me.
>>>>>>>
>>>>>>> Event with it applied I still don't see anything in
>>>>>>> /sys/kernel/debug/tracing/events/syscalls
>>>>>>>
>>>>>>> Did we break it in some other way recently?
>>>>>>>
>>>>>>> cheers
>>>
>>> I did some further testing, my config also enabled KALLSYMS_ALL, when
>>> I remove
>>> it there is indeed no syscall events.
>>
>> Aha, OK that explains it I guess.
>>
>> I was using ppc64_guest_defconfig which has ABI_V1 and FTRACE_SYSCALLS,
>> but does not have KALLSYMS_ALL. So I guess there's some other bug
>> lurking in there.
>
> I don't have the setup handy to validate it, but I suspect it is caused
> by the way scripts/kallsyms.c:symbol_valid() checks whether a symbol
> entry needs to be integrated into the assembler output when
> --all-symbols is not specified. It only keeps symbols which addresses
> are in the text range. On PPC64_ELF_ABI_V1, this means only the
> dot-prefixed symbols will be kept (those point to the function begin),
> leaving out the non-dot-prefixed symbols (those point to the function
> descriptors).
>
> So I see two possible solutions there: either we ensure that
> FTRACE_SYSCALLS selects KALLSYMS_ALL on PPC64_ELF_ABI_V1, or we modify
> scripts/kallsyms.c:symbol_valid() to also include function descriptor
> symbols. This would mean accepting symbols pointing into the .opd ELF
> section.
>
> IMHO the second option would be better because it does not increase the
> kernel image size as much as KALLSYMS_ALL.
>
Yes, seems to be the best solution.
Maybe the only thing to do is to add a new range to text_ranges,
something like (untested):
diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 03fa07ad45d9..decf31c497f5 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -64,6 +64,7 @@ static unsigned long long relative_base;
static struct addr_range text_ranges[] = {
{ "_stext", "_etext" },
{ "_sinittext", "_einittext" },
+ { "__start_opd", "__end_opd" },
};
#define text_range_text (&text_ranges[0])
#define text_range_inittext (&text_ranges[1])
---
Christophe
