linux-kernel - Re: [PATCH] scripts/decode_stacktrace.sh: optionally use LLVM utilities

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Message-ID: <ZYDu_ulZkxKg0I4x@google.com>
Date: Tue, 19 Dec 2023 01:16:46 +0000
From: Carlos Llamas <cmllamas@...gle.com>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
	kernel-team@...roid.com, Will Deacon <will@...nel.org>,
	John Stultz <jstultz@...gle.com>,
	Masahiro Yamada <masahiroy@...nel.org>
Subject: Re: [PATCH] scripts/decode_stacktrace.sh: optionally use LLVM
 utilities

On Tue, Dec 19, 2023 at 12:23:18AM +0000, Justin Stitt wrote:
> Hi,
> 
> On Fri, Sep 29, 2023 at 03:48:17AM +0000, Carlos Llamas wrote:
> > GNU's addr2line can have problems parsing a vmlinux built with LLVM,
> > particularly when LTO was used. In order to decode the traces correctly
> > this patch adds the ability to switch to LLVM's utilities readelf and
> > addr2line. The same approach is followed by Will in [1].
> >
> > Before:
> >   $ scripts/decode_stacktrace.sh vmlinux < kernel.log
> >   [17716.240635] Call trace:
> >   [17716.240646] skb_cow_data (??:?)
> >   [17716.240654] esp6_input (ld-temp.o:?)
> >   [17716.240666] xfrm_input (ld-temp.o:?)
> >   [17716.240674] xfrm6_rcv (??:?)
> >   [...]
> 
> Perhaps it is due to where I am dumping the stack, but I am getting good
> stack traces on mainline (with a LLVM-built kernel) without this patch.

Maybe you have set CROSS_COMPILE=llvm- in your environment? This is an
alternative workaround. I write more about this in the commit log.

> 
> With that being said, applying this patch still has good stack traces
> and it makes sense if it helps others.
> 
> >
> > After:
> >   $ LLVM=1 scripts/decode_stacktrace.sh vmlinux < kernel.log
> >   [17716.240635] Call trace:
> >   [17716.240646] skb_cow_data (include/linux/skbuff.h:2172 net/core/skbuff.c:4503)
> >   [17716.240654] esp6_input (net/ipv6/esp6.c:977)
> >   [17716.240666] xfrm_input (net/xfrm/xfrm_input.c:659)
> >   [17716.240674] xfrm6_rcv (net/ipv6/xfrm6_input.c:172)
> >   [...]
> >
> > Note that one could set CROSS_COMPILE=llvm- instead to hack around this
> > issue. However, doing so can break the decodecode routine as it will
> > force the selection of other LLVM utilities down the line e.g. llvm-as.
> >
> > [1] https://lore.kernel.org/all/20230914131225.13415-3-will@kernel.org/
> >
> > Cc: Will Deacon <will@...nel.org>
> > Cc: John Stultz <jstultz@...gle.com>
> > Cc: Masahiro Yamada <masahiroy@...nel.org>
> > Signed-off-by: Carlos Llamas <cmllamas@...gle.com>
> 
> Tested-by: Justin Stitt <justinstitt@...gle.com>
> 
> Note that this patch is similar: https://lore.kernel.org/all/20231215-llvm-decode-stacktrace-v1-1-201cb86f4879@quicinc.com/

Ha, I see. Elliot's patch help revive this thread. Cool!

--
Thanks,
Carlos Llamas