scripts/gen-btf.sh: fix shebang for NixOS

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

Posted by Gary Guo 3 weeks ago

From: Gary Guo <gary@garyguo.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@garyguo.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
-- 
2.51.2

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

Posted by Ihor Solodrai 3 weeks ago

On 1/20/26 10:20 AM, Gary Guo wrote:
> From: Gary Guo <gary@garyguo.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@garyguo.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).

But I wonder if all of these need the same change then:

$ git log --oneline -n1
24d479d26b25 (HEAD, tag: v6.19-rc6) Linux 6.19-rc6
$ grep -r '#!/bin/bash' ./scripts/
./scripts/check-uapi.sh:#!/bin/bash
./scripts/decodecode:#!/bin/bash
./scripts/extract-fwblobs:#!/bin/bash
./scripts/gfp-translate:#!/bin/bash
./scripts/git-resolve.sh:#!/bin/bash
./scripts/mkuboot.sh:#!/bin/bash
./scripts/objdiff:#!/bin/bash
./scripts/objdump-func:#!/bin/bash
./scripts/prune-kernel:#!/bin/bash
./scripts/tags.sh:#!/bin/bash
./scripts/tracing/ftrace-bisect.sh:#!/bin/bash
./scripts/livepatch/klp-build:#!/bin/bash

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

Posted by Gary Guo 3 weeks ago

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@garyguo.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@garyguo.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.

Best,
Gary

>
> But I wonder if all of these need the same change then:
>
> $ git log --oneline -n1
> 24d479d26b25 (HEAD, tag: v6.19-rc6) Linux 6.19-rc6
> $ grep -r '#!/bin/bash' ./scripts/
> ./scripts/check-uapi.sh:#!/bin/bash
> ./scripts/decodecode:#!/bin/bash
> ./scripts/extract-fwblobs:#!/bin/bash
> ./scripts/gfp-translate:#!/bin/bash
> ./scripts/git-resolve.sh:#!/bin/bash
> ./scripts/mkuboot.sh:#!/bin/bash
> ./scripts/objdiff:#!/bin/bash
> ./scripts/objdump-func:#!/bin/bash
> ./scripts/prune-kernel:#!/bin/bash
> ./scripts/tags.sh:#!/bin/bash
> ./scripts/tracing/ftrace-bisect.sh:#!/bin/bash
> ./scripts/livepatch/klp-build:#!/bin/bash

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

Posted by Thomas Weißschuh 3 weeks ago

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@garyguo.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@garyguo.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.


Thomas

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

Posted by Ihor Solodrai 3 weeks ago

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@garyguo.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@garyguo.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

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

Posted by Gary Guo 3 weeks ago

On Tue Jan 20, 2026 at 7:53 PM GMT, Ihor Solodrai wrote:
> 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@garyguo.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@garyguo.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?

Documentation/kbuild/makefiles.rst says:

Make rules may invoke scripts to build the kernel. The rules shall
always provide the appropriate interpreter to execute the script. They
shall not rely on the execute bits being set, and shall not invoke the
script directly. For the convenience of manual script invocation, such
as invoking ./scripts/checkpatch.pl, it is recommended to set execute
bits on the scripts nonetheless.

Kbuild provides variables $(CONFIG_SHELL), $(AWK), $(PERL),
and $(PYTHON3) to refer to interpreters for the respective
scripts.

So I suppose it would need to migate to POSIX shell...

Best,
Gary

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

Posted by Ihor Solodrai 3 weeks ago


On 1/20/26 3:54 PM, Gary Guo wrote:
>> [...]
>>
>> So it's trivial to put $(CONFIG_SHELL) in front of it. But then it
>> must be migrated to #!/bin/sh, right?
> 
> Documentation/kbuild/makefiles.rst says:
> 
> Make rules may invoke scripts to build the kernel. The rules shall
> always provide the appropriate interpreter to execute the script. They
> shall not rely on the execute bits being set, and shall not invoke the
> script directly. For the convenience of manual script invocation, such
> as invoking ./scripts/checkpatch.pl, it is recommended to set execute
> bits on the scripts nonetheless.
> 
> Kbuild provides variables $(CONFIG_SHELL), $(AWK), $(PERL),
> and $(PYTHON3) to refer to interpreters for the respective
> scripts.
> 
> So I suppose it would need to migate to POSIX shell...

That's my blunder then.

I'll send a patch tomorrow to make gen-btf.sh runnable with /bin/sh

> 
> Best,
> Gary

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

Posted by Alexei Starovoitov 3 weeks ago

On Tue, Jan 20, 2026 at 8:50 PM Ihor Solodrai <ihor.solodrai@linux.dev> wrote:
>
>
>
> On 1/20/26 3:54 PM, Gary Guo wrote:
> >> [...]
> >>
> >> So it's trivial to put $(CONFIG_SHELL) in front of it. But then it
> >> must be migrated to #!/bin/sh, right?
> >
> > Documentation/kbuild/makefiles.rst says:
> >
> > Make rules may invoke scripts to build the kernel. The rules shall
> > always provide the appropriate interpreter to execute the script. They
> > shall not rely on the execute bits being set, and shall not invoke the
> > script directly. For the convenience of manual script invocation, such
> > as invoking ./scripts/checkpatch.pl, it is recommended to set execute
> > bits on the scripts nonetheless.
> >
> > Kbuild provides variables $(CONFIG_SHELL), $(AWK), $(PERL),
> > and $(PYTHON3) to refer to interpreters for the respective
> > scripts.
> >
> > So I suppose it would need to migate to POSIX shell...
>
> That's my blunder then.
>
> I'll send a patch tomorrow to make gen-btf.sh runnable with /bin/sh

Isn't the current patch enough?
-#!/bin/bash
+#!/usr/bin/env bash

I don't think all kernel build scripts are pure 'sh'.

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

Posted by Ihor Solodrai 3 weeks ago


On 1/20/26 8:52 PM, Alexei Starovoitov wrote:
> On Tue, Jan 20, 2026 at 8:50 PM Ihor Solodrai <ihor.solodrai@linux.dev> wrote:
>>
>>
>>
>> On 1/20/26 3:54 PM, Gary Guo wrote:
>>>> [...]
>>>>
>>>> So it's trivial to put $(CONFIG_SHELL) in front of it. But then it
>>>> must be migrated to #!/bin/sh, right?
>>>
>>> Documentation/kbuild/makefiles.rst says:
>>>
>>> Make rules may invoke scripts to build the kernel. The rules shall
>>> always provide the appropriate interpreter to execute the script. They
>>> shall not rely on the execute bits being set, and shall not invoke the
>>> script directly. For the convenience of manual script invocation, such
>>> as invoking ./scripts/checkpatch.pl, it is recommended to set execute
>>> bits on the scripts nonetheless.
>>>
>>> Kbuild provides variables $(CONFIG_SHELL), $(AWK), $(PERL),
>>> and $(PYTHON3) to refer to interpreters for the respective
>>> scripts.
>>>
>>> So I suppose it would need to migate to POSIX shell...
>>
>> That's my blunder then.
>>
>> I'll send a patch tomorrow to make gen-btf.sh runnable with /bin/sh
> 
> Isn't the current patch enough?
> -#!/bin/bash
> +#!/usr/bin/env bash
> 
> I don't think all kernel build scripts are pure 'sh'.

Well, if we want to follow the makefiles.rst (and Thomas')
recommendation, which is executing the script via $(CONFIG_SHELL),
then we have to migrate to #!/bin/sh, because that's the default.

This concerns only scripts in the kernel build pipeline AFAIU.

But you may be right that this is not a strict rule, idk.
It did come up quite late on the list.

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

Posted by Alexei Starovoitov 2 weeks, 6 days ago

On Tue, Jan 20, 2026 at 9:04 PM Ihor Solodrai <ihor.solodrai@linux.dev> wrote:
>
>
>
> On 1/20/26 8:52 PM, Alexei Starovoitov wrote:
> > On Tue, Jan 20, 2026 at 8:50 PM Ihor Solodrai <ihor.solodrai@linux.dev> wrote:
> >>
> >>
> >>
> >> On 1/20/26 3:54 PM, Gary Guo wrote:
> >>>> [...]
> >>>>
> >>>> So it's trivial to put $(CONFIG_SHELL) in front of it. But then it
> >>>> must be migrated to #!/bin/sh, right?
> >>>
> >>> Documentation/kbuild/makefiles.rst says:
> >>>
> >>> Make rules may invoke scripts to build the kernel. The rules shall
> >>> always provide the appropriate interpreter to execute the script. They
> >>> shall not rely on the execute bits being set, and shall not invoke the
> >>> script directly. For the convenience of manual script invocation, such
> >>> as invoking ./scripts/checkpatch.pl, it is recommended to set execute
> >>> bits on the scripts nonetheless.
> >>>
> >>> Kbuild provides variables $(CONFIG_SHELL), $(AWK), $(PERL),
> >>> and $(PYTHON3) to refer to interpreters for the respective
> >>> scripts.
> >>>
> >>> So I suppose it would need to migate to POSIX shell...
> >>
> >> That's my blunder then.
> >>
> >> I'll send a patch tomorrow to make gen-btf.sh runnable with /bin/sh
> >
> > Isn't the current patch enough?
> > -#!/bin/bash
> > +#!/usr/bin/env bash
> >
> > I don't think all kernel build scripts are pure 'sh'.
>
> Well, if we want to follow the makefiles.rst (and Thomas')
> recommendation, which is executing the script via $(CONFIG_SHELL),
> then we have to migrate to #!/bin/sh, because that's the default.
>
> This concerns only scripts in the kernel build pipeline AFAIU.
>
> But you may be right that this is not a strict rule, idk.
> It did come up quite late on the list.

git grep CONFIG_SHELL|wc -l
68

ok, let's convert to pure sh then.