linux-kernel - Re: [PATCH] scripts/gen-btf.sh: fix shebang for NixOS

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Message-ID: <5364d5ec-f30c-40d6-9a99-c251fec3868c@linux.dev>
Date: Tue, 20 Jan 2026 11:53:42 -0800
From: Ihor Solodrai <ihor.solodrai@...ux.dev>
To: Thomas Weißschuh <linux@...ssschuh.net>,
 Gary Guo <gary@...yguo.net>
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>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scripts/gen-btf.sh: fix shebang for NixOS

On 1/20/26 11:38 AM, Thomas Weißschuh wrote:
> On 2026-01-20 19:15:11+0000, Gary Guo wrote:
>> On Tue Jan 20, 2026 at 6:59 PM GMT, Ihor Solodrai wrote:
>>> On 1/20/26 10:20 AM, Gary Guo wrote:
>>>> From: Gary Guo <gary@...yguo.net>
>>>>
>>>> NixOS only puts /usr/bin/env and /bin/sh at the standard location as
>>>> required by POSIX, but not other shells. Other program that kernel build
>>>> depends on is supplied via PATH, so shebang needs to use /usr/bin/env to
>>>> find them.
>>>>
>>>> This has been done to a few other scripts already, e.g.
>>>> gen_test_kallsyms.sh or decode_stacktrace.sh.
>>>>
>>>> Fixes: 522397d05e7d ("resolve_btfids: Change in-place update with raw binary output")
>>>> Signed-off-by: Gary Guo <gary@...yguo.net>
>>>> ---
>>>>  scripts/gen-btf.sh | 2 +-
>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/scripts/gen-btf.sh b/scripts/gen-btf.sh
>>>> index be21ccee3487..4cd3159f2ddb 100755
>>>> --- a/scripts/gen-btf.sh
>>>> +++ b/scripts/gen-btf.sh
>>>> @@ -1,4 +1,4 @@
>>>> -#!/bin/bash
>>>> +#!/usr/bin/env bash
>>>>  # SPDX-License-Identifier: GPL-2.0
>>>>  # Copyright (c) 2025 Meta Platforms, Inc. and affiliates.
>>>>  #
>>>>
>>>> base-commit: 053966c344dbd346e71305f530e91ea77916189f
>>>
>>> Hi Gary, thanks for the patch.
>>>
>>> I'm guessing this came up because gen-btf.sh is part of the vmlinux
>>> build, and link-vmlinux.sh has #!/bin/sh (not bash).
>>
>> My typical experience is that when I see an error about /bin/bash not found, I
>> just use "bash <script path>" instead without putting much think into it.
>>
>> gen-btf.sh is part of build so I don't get to invoke the script directly, hence
>> the patch.
> 
> For the build we have $(CONFIG_SHELL) to stick before the script.
> It is only 'sh', but it is the well-known variable users know to
> override. IMO all script invocations should use this mechanism.

There are two places where gen-btf.sh is invoked.

In link-vmlinux.sh:

	if ! ${srctree}/scripts/gen-btf.sh .tmp_vmlinux1; then
		echo >&2 "Failed to generate BTF for vmlinux"
		echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
		exit 1
	fi

And in Makefile.modfinal:

quiet_cmd_btf_ko = BTF [M] $@
      cmd_btf_ko = 							\
	if [ ! -f $(objtree)/vmlinux ]; then				\
		printf "Skipping BTF generation for %s due to unavailability of vmlinux\n" $@ 1>&2; \
	else	\
		$(srctree)/scripts/gen-btf.sh --btf_base $(objtree)/vmlinux $@; \
	fi;

So it's trivial to put $(CONFIG_SHELL) in front of it. But then it
must be migrated to #!/bin/sh, right?


> 
> 
> Thomas