Re: [PATCH dwarves 1/2] dwarf_loader: Trust the entry value register over the first location entry

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Sat, Sep 26, 2026 at 10:49 PM Yonghong Song <yonghong.song@linux.dev> wrote:
> Maybe we need to poke into locations to get precise parameter register.
> For example, for argument 'b', we have
> 	[0x0000000000000000, 0x0000000000000000): DW_OP_reg4 RSI
> 	...
> 	[0x0000000000000008, 0x0000000000000015): DW_OP_entry_value(DW_OP_reg5 RDI), DW_OP_stack_value)
> RSI has location starts from 0x0, RDI starts from 0x8 although it has DW_OP_entry_value.
>
> But this makes things complicated, and there is no garantee across different compilers due to
> code gen.

I don't think it has to be complicated.
In your gcc 14 dump the first entry of 'b' starts at low_pc and it's RSI.
In scx_bpf_task_set_lazy_resched() low_pc is ...d70 and the first entry
of 'lazy' starts at ...d8b. RBP there says nothing about the register
'lazy' was passed in.
parameter__decode_location() already has 'start' of every entry.
Can it take the register of the first entry only when that entry
starts at low_pc and use the entry value otherwise?

There is no guarantee, right, but when the guess is wrong the function
is dropped. It's not encoded with a wrong signature.

> One possible workaround is change 'lazy' type from 'bool' to say 'int'.
> As Alexei mentioned in the above, clang didn't handle 'bool' well
> in debug info.

That works for this kfunc and for pahole that is already released,
but every other function with a bool arg is still dropped.
Can clang be fixed to keep the entry range?