* Re: ARMv7 Linux + Rust doesn't boot when compiling with only LLVM=1
[not found] <1286af8e-f908-45db-af7c-d9c5d592abfd@gmail.com>
@ 2025-12-14 6:06 ` Miguel Ojeda
2025-12-14 7:34 ` Rudraksha Gupta
0 siblings, 1 reply; 6+ messages in thread
From: Miguel Ojeda @ 2025-12-14 6:06 UTC (permalink / raw)
To: Rudraksha Gupta, Nathan Chancellor, Nicolas Schier
Cc: stable, regressions, rust-for-linux, Miguel Ojeda,
Björn Roy Baron, Alex Gaynor, Boqun Feng, Gary Guo,
Andreas Hindborg, Alice Ryhl, Danilo Krummrich, Trevor Gross,
Benno Lossin, Linux Kbuild mailing list
On Sun, Dec 14, 2025 at 12:54 AM Rudraksha Gupta <guptarud@gmail.com> wrote:
>
> - The kernel boots and outputs via UART when I build the kernel with the
> following:
>
> make LLVM=1 ARCH="$arm" CC="${CC:-gcc}"
>
> - The kernel doesn't boot and there is no output via UART when I build
> the kernel with the following:
>
> make LLVM=1 ARCH="$arm"
>
> The only difference being: CC="${CC:-gcc}". Is this expected?
It depends on what that resolves to, i.e. your environment etc., i.e.
that is resolved before Kbuild is called.
The normal way of calling would be the latter anyway -- with the
former you are setting a custom `CC` (either whatever you have there
or the `gcc` default). By default, `LLVM=1` means `CC=clang`.
So it could be that you are using a completely different compiler
(even Clang vs. GCC, or different versions, and so on). Hard to say.
And depending on that, you may end up with a very different kernel
image. Even substantial Kconfig options may get changed etc.
I would suggest comparing the kernel configuration of those two ways
(attaching them here could also be nice to see what compilers you are
using and so on).
Cc'ing Kbuild too so that they are in the loop.
I hope that helps.
Cheers,
Miguel
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: ARMv7 Linux + Rust doesn't boot when compiling with only LLVM=1
2025-12-14 6:06 ` ARMv7 Linux + Rust doesn't boot when compiling with only LLVM=1 Miguel Ojeda
@ 2025-12-14 7:34 ` Rudraksha Gupta
2025-12-15 11:19 ` Gary Guo
2025-12-15 12:17 ` Christian Schrefl
0 siblings, 2 replies; 6+ messages in thread
From: Rudraksha Gupta @ 2025-12-14 7:34 UTC (permalink / raw)
To: Miguel Ojeda, Nathan Chancellor, Nicolas Schier
Cc: stable, regressions, rust-for-linux, Miguel Ojeda,
Björn Roy Baron, Alex Gaynor, Boqun Feng, Gary Guo,
Andreas Hindborg, Alice Ryhl, Danilo Krummrich, Trevor Gross,
Benno Lossin, Linux Kbuild mailing list
On 12/13/25 22:06, Miguel Ojeda wrote:
> On Sun, Dec 14, 2025 at 12:54 AM Rudraksha Gupta <guptarud@gmail.com> wrote:
>> - The kernel boots and outputs via UART when I build the kernel with the
>> following:
>>
>> make LLVM=1 ARCH="$arm" CC="${CC:-gcc}"
>>
>> - The kernel doesn't boot and there is no output via UART when I build
>> the kernel with the following:
>>
>> make LLVM=1 ARCH="$arm"
>>
>> The only difference being: CC="${CC:-gcc}". Is this expected?
> It depends on what that resolves to, i.e. your environment etc., i.e.
> that is resolved before Kbuild is called.
Sorry about that, I should've specified in the original email. The CC
resolves to armv7-alpine-linux-musleabihf-gcc.
When both LLVM=1 and the CC=gcc are used, I can insmod the sample rust
modules just fine. However, if I only use LLVM=1, my phone doesn't
output anything over UART, and I assume that it fails to boot.
Interestingly enough, if I just specify LLVM=1 (with no CC=gcc), and
remove the rust related configs from the pmos.config fragment, then my
phone boots and I can see logs over UART.
> The normal way of calling would be the latter anyway -- with the
> former you are setting a custom `CC` (either whatever you have there
> or the `gcc` default). By default, `LLVM=1` means `CC=clang`.
>
> So it could be that you are using a completely different compiler
> (even Clang vs. GCC, or different versions, and so on). Hard to say.
> And depending on that, you may end up with a very different kernel
> image. Even substantial Kconfig options may get changed etc.
>
> I would suggest comparing the kernel configuration of those two ways
> (attaching them here could also be nice to see what compilers you are
> using and so on).
postmarketOS uses kernel config fragments and tracks the latest linux-next:
-
https://gitlab.postmarketos.org/postmarketOS/pmaports/-/blob/master/device/testing/linux-next/devices.config
-
https://gitlab.postmarketos.org/postmarketOS/pmaports/-/blob/master/device/testing/linux-next/pmos.config
- build recipe:
https://gitlab.postmarketos.org/postmarketOS/pmaports/-/blob/master/device/testing/linux-next/APKBUILD
The only thing that changed was whether CC=gcc was specified or not:
https://gitlab.postmarketos.org/postmarketOS/pmaports/-/commit/b9102ac5718b8d18acb6801a62e1cd4cc7edc0cb
> Cc'ing Kbuild too so that they are in the loop.
>
> I hope that helps.
Thanks for your help! Always appreciate your presence. :)
> Cheers,
> Miguel
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: ARMv7 Linux + Rust doesn't boot when compiling with only LLVM=1
2025-12-14 7:34 ` Rudraksha Gupta
@ 2025-12-15 11:19 ` Gary Guo
2025-12-17 10:01 ` Rudraksha Gupta
2025-12-15 12:17 ` Christian Schrefl
1 sibling, 1 reply; 6+ messages in thread
From: Gary Guo @ 2025-12-15 11:19 UTC (permalink / raw)
To: Rudraksha Gupta
Cc: Miguel Ojeda, Nathan Chancellor, Nicolas Schier, stable,
regressions, rust-for-linux, Miguel Ojeda, Björn Roy Baron,
Alex Gaynor, Boqun Feng, Andreas Hindborg, Alice Ryhl,
Danilo Krummrich, Trevor Gross, Benno Lossin,
Linux Kbuild mailing list
On Sat, 13 Dec 2025 23:34:31 -0800
Rudraksha Gupta <guptarud@gmail.com> wrote:
> On 12/13/25 22:06, Miguel Ojeda wrote:
> > On Sun, Dec 14, 2025 at 12:54 AM Rudraksha Gupta <guptarud@gmail.com> wrote:
> >> - The kernel boots and outputs via UART when I build the kernel with the
> >> following:
> >>
> >> make LLVM=1 ARCH="$arm" CC="${CC:-gcc}"
> >>
> >> - The kernel doesn't boot and there is no output via UART when I build
> >> the kernel with the following:
> >>
> >> make LLVM=1 ARCH="$arm"
> >>
> >> The only difference being: CC="${CC:-gcc}". Is this expected?
> > It depends on what that resolves to, i.e. your environment etc., i.e.
> > that is resolved before Kbuild is called.
>
> Sorry about that, I should've specified in the original email. The CC
> resolves to armv7-alpine-linux-musleabihf-gcc.
>
> When both LLVM=1 and the CC=gcc are used, I can insmod the sample rust
> modules just fine. However, if I only use LLVM=1, my phone doesn't
> output anything over UART, and I assume that it fails to boot.
> Interestingly enough, if I just specify LLVM=1 (with no CC=gcc), and
> remove the rust related configs from the pmos.config fragment, then my
> phone boots and I can see logs over UART.
Which drivers have you enabled that use Rust? Just having core Rust
infrastructure enabled shouldn't cause issues on its own, apart from
slightly bigger kernel image.
If just enabling Rust but none of Rust drivers cause issue, I would start
looking at
1) if there're any symbols somehow being overwritten by the Rust object
files.
2) if the size of kernel is pushed above a certain threshold that your
bootloader/firmware is unhappy.
Best,
Gary
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: ARMv7 Linux + Rust doesn't boot when compiling with only LLVM=1
2025-12-14 7:34 ` Rudraksha Gupta
2025-12-15 11:19 ` Gary Guo
@ 2025-12-15 12:17 ` Christian Schrefl
2025-12-17 10:10 ` Rudraksha Gupta
1 sibling, 1 reply; 6+ messages in thread
From: Christian Schrefl @ 2025-12-15 12:17 UTC (permalink / raw)
To: Rudraksha Gupta, Miguel Ojeda, Nathan Chancellor, Nicolas Schier
Cc: stable, regressions, rust-for-linux, Miguel Ojeda,
Björn Roy Baron, Alex Gaynor, Boqun Feng, Gary Guo,
Andreas Hindborg, Alice Ryhl, Danilo Krummrich, Trevor Gross,
Benno Lossin, Linux Kbuild mailing list
On 12/14/25 8:34 AM, Rudraksha Gupta wrote:
> On 12/13/25 22:06, Miguel Ojeda wrote:
>> On Sun, Dec 14, 2025 at 12:54 AM Rudraksha Gupta <guptarud@gmail.com> wrote:
>>> - The kernel boots and outputs via UART when I build the kernel with the
>>> following:
>>>
>>> make LLVM=1 ARCH="$arm" CC="${CC:-gcc}"
>>>
>>> - The kernel doesn't boot and there is no output via UART when I build
>>> the kernel with the following:
>>>
>>> make LLVM=1 ARCH="$arm"
>>>
>>> The only difference being: CC="${CC:-gcc}". Is this expected?
>> It depends on what that resolves to, i.e. your environment etc., i.e.
>> that is resolved before Kbuild is called.
>
> Sorry about that, I should've specified in the original email. The CC resolves to armv7-alpine-linux-musleabihf-gcc.
>
> When both LLVM=1 and the CC=gcc are used, I can insmod the sample rust modules just fine. However, if I only use LLVM=1, my phone doesn't output anything over UART, and I assume that it fails to boot. Interestingly enough, if I just specify LLVM=1 (with no CC=gcc), and remove the rust related configs from the pmos.config fragment, then my phone boots and I can see logs over UART.
Did you try other architectures / devices as well (especially can you reproduce it on qemu-arm)?
Did you try a LLVM=1 build without rust enabled?
>
>> The normal way of calling would be the latter anyway -- with the
>> former you are setting a custom `CC` (either whatever you have there
>> or the `gcc` default). By default, `LLVM=1` means `CC=clang`.
>>
>> So it could be that you are using a completely different compiler
>> (even Clang vs. GCC, or different versions, and so on). Hard to say.
>> And depending on that, you may end up with a very different kernel
>> image. Even substantial Kconfig options may get changed etc.
>>
>> I would suggest comparing the kernel configuration of those two ways
>> (attaching them here could also be nice to see what compilers you are
>> using and so on).
>
> postmarketOS uses kernel config fragments and tracks the latest linux-next:
>
> - https://gitlab.postmarketos.org/postmarketOS/pmaports/-/blob/master/device/testing/linux-next/devices.config
>
> - https://gitlab.postmarketos.org/postmarketOS/pmaports/-/blob/master/device/testing/linux-next/pmos.config
>
> - build recipe: https://gitlab.postmarketos.org/postmarketOS/pmaports/-/blob/master/device/testing/linux-next/APKBUILD
>
>
> The only thing that changed was whether CC=gcc was specified or not:
>
> https://gitlab.postmarketos.org/postmarketOS/pmaports/-/commit/b9102ac5718b8d18acb6801a62e1cd4cc7edc0cb
>
I'm not familiar with pmbootstrap, what is required to reproduce this?
Do I just need to use the edge channel with linux-next or is something special required?
I might habe time to look into trying to reproduce it this week, but I'm not sure.
I have a armv7 based asus-flo device to try it out. Its not very well supported, but
It should be sufficient for this.
Cheers,
Christian
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: ARMv7 Linux + Rust doesn't boot when compiling with only LLVM=1
2025-12-15 11:19 ` Gary Guo
@ 2025-12-17 10:01 ` Rudraksha Gupta
0 siblings, 0 replies; 6+ messages in thread
From: Rudraksha Gupta @ 2025-12-17 10:01 UTC (permalink / raw)
To: Gary Guo
Cc: Miguel Ojeda, Nathan Chancellor, Nicolas Schier, stable,
regressions, rust-for-linux, Miguel Ojeda, Björn Roy Baron,
Alex Gaynor, Boqun Feng, Andreas Hindborg, Alice Ryhl,
Danilo Krummrich, Trevor Gross, Benno Lossin,
Linux Kbuild mailing list
On 12/15/25 03:19, Gary Guo wrote:
> On Sat, 13 Dec 2025 23:34:31 -0800
> Rudraksha Gupta <guptarud@gmail.com> wrote:
>
>> On 12/13/25 22:06, Miguel Ojeda wrote:
>>> On Sun, Dec 14, 2025 at 12:54 AM Rudraksha Gupta <guptarud@gmail.com> wrote:
>>>> - The kernel boots and outputs via UART when I build the kernel with the
>>>> following:
>>>>
>>>> make LLVM=1 ARCH="$arm" CC="${CC:-gcc}"
>>>>
>>>> - The kernel doesn't boot and there is no output via UART when I build
>>>> the kernel with the following:
>>>>
>>>> make LLVM=1 ARCH="$arm"
>>>>
>>>> The only difference being: CC="${CC:-gcc}". Is this expected?
>>> It depends on what that resolves to, i.e. your environment etc., i.e.
>>> that is resolved before Kbuild is called.
>> Sorry about that, I should've specified in the original email. The CC
>> resolves to armv7-alpine-linux-musleabihf-gcc.
>>
>> When both LLVM=1 and the CC=gcc are used, I can insmod the sample rust
>> modules just fine. However, if I only use LLVM=1, my phone doesn't
>> output anything over UART, and I assume that it fails to boot.
>> Interestingly enough, if I just specify LLVM=1 (with no CC=gcc), and
>> remove the rust related configs from the pmos.config fragment, then my
>> phone boots and I can see logs over UART.
> Which drivers have you enabled that use Rust? Just having core Rust
> infrastructure enabled shouldn't cause issues on its own, apart from
> slightly bigger kernel image.
Just these ones:
https://gitlab.postmarketos.org/postmarketOS/pmaports/-/blob/master/device/testing/linux-next/pmos.config#L264
I'm starting to think this might be an clang issue. Ran this on qemu-arm
and encountering similar issues:
https://gitlab.postmarketos.org/postmarketOS/pmbootstrap/-/issues/2635#note_521740
> If just enabling Rust but none of Rust drivers cause issue, I would start
> looking at
>
> 1) if there're any symbols somehow being overwritten by the Rust object
> files.
If I suspect it to be a clang issue now, is this still the best way to
go about looking into the problem? This is a little bit out of my
domain, but happy to learn.
> 2) if the size of kernel is pushed above a certain threshold that your
> bootloader/firmware is unhappy.
I believe lk2nd (fastboot bootloader) would complain if this were the
case. I'm currently flashing lk2nd into the boot partition (to override
the proprietary bootloader's defaults) and then flashing posmarketOS
kernel and rootfs in data and system partitions.
>
> Best,
> Gary
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: ARMv7 Linux + Rust doesn't boot when compiling with only LLVM=1
2025-12-15 12:17 ` Christian Schrefl
@ 2025-12-17 10:10 ` Rudraksha Gupta
0 siblings, 0 replies; 6+ messages in thread
From: Rudraksha Gupta @ 2025-12-17 10:10 UTC (permalink / raw)
To: Christian Schrefl, Miguel Ojeda, Nathan Chancellor,
Nicolas Schier
Cc: stable, regressions, rust-for-linux, Miguel Ojeda,
Björn Roy Baron, Alex Gaynor, Boqun Feng, Gary Guo,
Andreas Hindborg, Alice Ryhl, Danilo Krummrich, Trevor Gross,
Benno Lossin, Linux Kbuild mailing list
On 12/15/25 04:17, Christian Schrefl wrote:
> On 12/14/25 8:34 AM, Rudraksha Gupta wrote:
>> On 12/13/25 22:06, Miguel Ojeda wrote:
>>> On Sun, Dec 14, 2025 at 12:54 AM Rudraksha Gupta <guptarud@gmail.com> wrote:
>>>> - The kernel boots and outputs via UART when I build the kernel with the
>>>> following:
>>>>
>>>> make LLVM=1 ARCH="$arm" CC="${CC:-gcc}"
>>>>
>>>> - The kernel doesn't boot and there is no output via UART when I build
>>>> the kernel with the following:
>>>>
>>>> make LLVM=1 ARCH="$arm"
>>>>
>>>> The only difference being: CC="${CC:-gcc}". Is this expected?
>>> It depends on what that resolves to, i.e. your environment etc., i.e.
>>> that is resolved before Kbuild is called.
>> Sorry about that, I should've specified in the original email. The CC resolves to armv7-alpine-linux-musleabihf-gcc.
>>
>> When both LLVM=1 and the CC=gcc are used, I can insmod the sample rust modules just fine. However, if I only use LLVM=1, my phone doesn't output anything over UART, and I assume that it fails to boot. Interestingly enough, if I just specify LLVM=1 (with no CC=gcc), and remove the rust related configs from the pmos.config fragment, then my phone boots and I can see logs over UART.
> Did you try other architectures / devices as well (especially can you reproduce it on qemu-arm)?
>
> Did you try a LLVM=1 build without rust enabled?
Seems like you've found the preliminary qemu-arm patches I posted, but
for completeness sake for others, this is reproducible on qemu-arm:
https://gitlab.postmarketos.org/postmarketOS/pmbootstrap/-/issues/2635#note_521740
As Christian mentioned, and I also now seem to conclude, it seems to be
a clang issue.
>>> The normal way of calling would be the latter anyway -- with the
>>> former you are setting a custom `CC` (either whatever you have there
>>> or the `gcc` default). By default, `LLVM=1` means `CC=clang`.
>>>
>>> So it could be that you are using a completely different compiler
>>> (even Clang vs. GCC, or different versions, and so on). Hard to say.
>>> And depending on that, you may end up with a very different kernel
>>> image. Even substantial Kconfig options may get changed etc.
>>>
>>> I would suggest comparing the kernel configuration of those two ways
>>> (attaching them here could also be nice to see what compilers you are
>>> using and so on).
>> postmarketOS uses kernel config fragments and tracks the latest linux-next:
>>
>> - https://gitlab.postmarketos.org/postmarketOS/pmaports/-/blob/master/device/testing/linux-next/devices.config
>>
>> - https://gitlab.postmarketos.org/postmarketOS/pmaports/-/blob/master/device/testing/linux-next/pmos.config
>>
>> - build recipe: https://gitlab.postmarketos.org/postmarketOS/pmaports/-/blob/master/device/testing/linux-next/APKBUILD
>>
>>
>> The only thing that changed was whether CC=gcc was specified or not:
>>
>> https://gitlab.postmarketos.org/postmarketOS/pmaports/-/commit/b9102ac5718b8d18acb6801a62e1cd4cc7edc0cb
>>
> I'm not familiar with pmbootstrap, what is required to reproduce this?
> Do I just need to use the edge channel with linux-next or is something special required?
>
> I might habe time to look into trying to reproduce it this week, but I'm not sure.
> I have a armv7 based asus-flo device to try it out. Its not very well supported, but
> It should be sufficient for this.
asus-flo would probably also encounter this. Currently it's a bit broken
in pmbootstrap, but I've provided a general guide here on how to go
about fixing it:
https://postmarketos.org/edge/2025/11/17/apq8064-kernel-removed/
Would love to help you setup the asus-flo, since it also seems that
upstream's IOMMU is broken and likely other things as well. If you'd
like to drop by in the Matrix chat, we'd love to help you there if needed.
^ permalink raw reply [flat|nested] 6+ messages in thread
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[not found] <1286af8e-f908-45db-af7c-d9c5d592abfd@gmail.com>
2025-12-14 6:06 ` ARMv7 Linux + Rust doesn't boot when compiling with only LLVM=1 Miguel Ojeda
2025-12-14 7:34 ` Rudraksha Gupta
2025-12-15 11:19 ` Gary Guo
2025-12-17 10:01 ` Rudraksha Gupta
2025-12-15 12:17 ` Christian Schrefl
2025-12-17 10:10 ` Rudraksha Gupta
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