[PATCH v1 2/8] arm: Fix "file truncated" linker errors from empty built-in.a in SPL/TPL/VPL builds

[Yuslaimi, Alif Zakuan]

Hi Marek,

On 25/11/2025 8:23 pm, Marek Vasut wrote:
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> On 11/25/25 9:13 AM, alif.zakuan.yuslaimi at altera.com wrote:
>> From: Tien Fong Chee <tien.fong.chee at intel.com>
>>
>> When building 32-bit ARM SPL (e.g. Arria 10), linking may fail with:
>>
>>      arch/arm/cpu/built-in.a: file not recognized: File truncated
>>      cmd/built-in.a: file not recognized: File truncated
>>      dts/built-in.a: file not recognized: File truncated
>>
>> This happens when a directory (such as arch/arm/cpu/, cmd/, or dts/)
>> produces no object files under SPL. GNU `ar` still creates a zero-length
>> archive, which older ARM 32-bit linkers (arm-linux-gnueabihf-ld) treat as
>> invalid. The final link step then aborts with the "file truncated" error.
>>
>> By contrast, 64-bit SoCFPGA (Agilex 5) builds use aarch64 linkers that
>> tolerate empty thin archives, so the same condition does not cause an
>> error.
>>
>> To make XPL (SPL/TPL/VPL) builds consistent across architectures, this
>> patch ensures each affected directory always contributes at least one 
>> valid
>> object:
>>
>>    * `arch/arm/cpu/Makefile` — add a persistent `dummy.o`
>>    * `cmd/Makefile` — add `dummy.o` only when CONFIG_XPL_BUILD=y
>>    * `dts/Makefile` — add `dummy.o` only when CONFIG_XPL_BUILD=y
>>
>> These dummy objects define no functional code and do not affect runtime
>> behavior. They only guarantee a valid archive for the linker, preventing
>> false "file truncated" errors on strict toolchains.
>>
>> Signed-off-by: Tien Fong Chee <tien.fong.chee at altera.com>
>> Signed-off-by: Alif Zakuan Yuslaimi <alif.zakuan.yuslaimi at altera.com>
> Such generic fixes should not be buried in SoC specific series.
> 
> +CC Tom
> 
> Maybe you need a fix similar to
> 
> 37a777e1286e ("Makefile: Make sure all linker input objects exist")
> 
> ?

I already have the referenced commit in my test branch, and I can 
confirm that the same compilation error still appears on CycloneV when 
certain directories produce no SPL objects.

The existing fix ensures that built-in.o is always present, but it does 
not prevent ar from generating empty built-in.a archives, which older 
ARM 32-bit linkers (such as CycloneV toolchains) reject as “file truncated”.

This patch complements the earlier fix by ensuring that each SPL 
directory contributes at least one real object, so the resulting 
built-in.a archives are non-empty and accepted by all toolchains. It 
does not change runtime behavior—only ensures the archives remain valid.

Thanks,
Alif