Re: [PATCH] x86/insn_decoder_test: allow longer symbol-names

Richard W.M. Jones
2024-11-29T15:40:40Z

[Sorry for possible mail threading errors, I don't have the original
email in my archive.]

We're hitting the bug mentioned in this old patch:

[https://lore.kernel.org/lkml/Y9ES4UKl%2F+DtvAVS@gmail.com/T/]

> Increase the allowed line-length of the insn-decoder-test to 4k to allow
> for symbol-names longer than 256 characters.
>
> The insn-decoder-test takes objdump output as input, which may contain
> symbol-names as instruction arguments. With rust-code entering the
> kernel, those symbol-names will include mangled-symbols which might
> exceed the current line-length-limit of the tool.
>
> By bumping the line-length-limit of the tool to 4k, we get a reasonable
> buffer for all objdump outputs I have seen so far. Unfortunately, ELF
> symbol-names are not restricted in length, so technically this might
> still end up failing if we encounter longer names in the future.
>
> My compile-failure looks like this:
>
> arch/x86/tools/insn_decoder_test: error: malformed line 1152000:
> tBb_+0xf2>
>
> ..which overflowed by 10 characters reading this line:
>
> ffffffff81458193: 74 3d je ffffffff814581d2 <_RNvXse_NtNtNtCshGpAVYOtgW1_4core4iter8adapters7flattenINtB5_13FlattenCompatINtNtB7_3map3MapNtNtNtBb_3str4iter5CharsNtB1v_17CharEscapeDefaultENtNtBb_4char13EscapeDefaultENtNtBb_3fmt5Debug3fmtBb_+0xf2>

in Fedora:

https://bugzilla.redhat.com/show_bug.cgi?id=2329496

I notice that BUFSIZE is still set to 256. Setting it to 512 fixed
the problem for me, although I understand that this is just a hack.

Was there any further effort to get this patch upstream?

Unfortunately I don't know what exact symbol is overflowing in the
Fedora case, but we do have a very full-featured kernel, including
Rust enabled (if that is relevant).

Rich.

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