Re: Unaligned accesses when loading modules

[Sami Tolvanen]

Hi Mikulas,

On Tue, Jan 14, 2025 at 6:07 PM Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
>
> Hi
>
> On PA-RISC, with the kernel 6.12.9, I get unaligned pointer warnings when
> a module is loaded. The warnings are caused by the fact that the
> .gnu.linkonce.this_module section is not aligned to the appropriate
> boundary. If I dump the module content with "objdump -h configs.ko", I get
> this. Note that the .gnu.linkonce.this_module has "File off 000042d2" and
> "Algn 2**4".
>
> On x86-64, the same misalignment can be seen, but it doesn't cause
> warnings because unaligned pointers are handled in hardware.
>
> This seems to be a bug in the linker, because when I compile an old kernel
> with a new linker, I also get the misalignment. Do you have an idea how to
> work around this bug?

Does explicitly specifying section alignment in the module linker
script fix this by any chance?

> kernel-6.12.9, binutils from Debian ports:
> [...]
> kernel 6.10, older binutils:

Which exact versions of binutils were used here? I don't see the
alignment issue with binutils 2.42 on either x86_64 or parisc64, so I
assume you're testing with something newer?

$ hppa64-linux-gnu-ld.bfd --version
GNU ld (GNU Binutils for Debian) 2.42.50.20240625

$ hppa64-linux-gnu-objdump -h configs.ko | grep -E '(format|this_module)'
configs.ko:     file format elf64-hppa-linux
 17 .gnu.linkonce.this_module 00000300  0000000000000000
0000000000000000  00005c50  2**4

Sami