linux-kernel - Re: [PATCH bpf-next] scripts/gen-btf.sh: Disable LTO when generating initial .o file

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Message-ID: <20260105234605.GB1276749@ax162>
Date: Mon, 5 Jan 2026 16:46:05 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Ihor Solodrai <ihor.solodrai@...ux.dev>
Cc: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Yonghong Song <yonghong.song@...ux.dev>, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH bpf-next] scripts/gen-btf.sh: Disable LTO when generating
 initial .o file

On Mon, Jan 05, 2026 at 02:01:36PM -0800, Ihor Solodrai wrote:
> Hi Nathan, thank you for the patch.
> 
> I'm starting to think it wasn't a good idea to do
> 
> 	echo "" | ${CC} ...
> 
> here, given the number of associated bugs.

Yeah, I was wondering if a lack of KBUILD_CPPFLAGS would also be a
problem since that contains the endianness flag for some targets. I
cannot imagine any more issues than that but I can understand wanting to
back out of it.

> Before gen-btf.sh was introduced, the .btf.o binary was generated with this [1]:
> 
> 	${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \
> 		--strip-all ${1} "${btf_data}" 2>/dev/null
> 
> I changed to ${CC} on the assumption it's a quicker operation than
> stripping entire vmlinux. But maybe it's not worth it and we should
> change back to --strip-all? wdyt?

That certainly seems more robust to me. I see the logic but with
'--only-section' and no glob, I would expect that to be a rather quick
operation but I am running out of time today to test and benchmark such
a change. I will try to do it tomorrow unless someone beats me to it.

Cheers,
Nathan