On Mon, 1 Jun 2026, at 10:37, Kevin Brodsky wrote:
> On 29/05/2026 16:47, Ard Biesheuvel wrote:
>>>>>> + /* fixmap BSS starts here - preceding data/BSS is omitted from
>>>>>> the linear map */
>>>>>> + .pgdir.bss (NOLOAD) : ALIGN(PAGE_SIZE) {
>>>>> Do we actually need the NOLOAD type here?
>>>> Yes, otherwise it is emitted as PROGBITS, resulting in all of BSS to be
>>>> emitted into Image.
>>> That's rather strange, aren't the .pgdir.bss input sections already
>>> NOBITS since __pgtbl_bss is only used on default-initialised globals?
>> Not sure why, but the section was PROGBITS not NOBITS before I added the
>> (NOLOAD)
>
> I've had a closer look into this. Similar sections in other
> architectures are all named .bss..<something>. If I rename this section
> to .bss..pgdir, then indeed the compiler does emit an object file with
> that section marked NOBITS:
>
> $ readelf -e out/arch/arm64/mm/fixmap.o | grep bss
> [ 4] .bss NOBITS 0000000000000000 0002ac 000000
> 00 WA 0 0 1
> [18] .bss..pgdir NOBITS 0000000000000000 000750 005000
> 00 WA 0 0 4096
>
> And then the linker does the right thing without having to use NOLOAD.
>
> I was concerned that .bss..pgdir might get caught by BSS_SECTION(), but
> it seems that the double dots are meant to prevent exactly that.
>
Thanks for this. As Sashiko appears to be making me do a v8 anyway, I'll
rename the section to .bss..pgdir too.
