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

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Message-ID: <r242oj55chpgo4j5i5ofqwgv5bm7ujruldhf22hnrji7iktogc@5xvd6kkn2tom>
Date: Tue, 24 Dec 2024 09:24:22 -0600
From: Andrew Halaney <ajhalaney@...il.com>
To: "Richard W.M. Jones" <rjones@...hat.com>
Cc: David Rheinsberg <david@...dahead.eu>, linux-kernel@...r.kernel.org, 
	"H. Peter Anvin" <hpa@...or.com>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>, 
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/insn_decoder_test: allow longer symbol-names

On Fri, Nov 29, 2024 at 03:40:31PM +0000, Richard W.M. Jones wrote:
> [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).
> 

For what its worth I hit this as well building linux-next
(next-20240923) with the fedora config (attached) updated. The
hack mentioned works around the issue for now for me.

Thanks,
Andrew

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