[PATCH] fw_base.S: Fix assembler error with clang 16+

[Anup Patel]

On Thu, Aug 3, 2023 at 10:31 PM Mitchell Horne <mhorne at freebsd.org> wrote:
>
>
> Attempting to build OpenSBI with clang 16 and the following command:
>
>    $ make LLVM=1 PLATFORM=generic
>
> Results in the following error:
>
>     AS        platform/generic/firmware/fw_dynamic.o
>    /tmp/fw_dynamic-d000a6.s:429:9: error: symbol '_fw_start' can not be undefined in a subtraction expression
>     .dword _fw_rw_start - _fw_start
>
> Work around this issue by eliminating the __fw_rw_offset variable and
> performing the offset calculation at run-time instead. This takes
> advantage of the fact that the a4 register contains the value of
> _fw_start.
>
> Signed-off-by: Mitchell Horne <mhorne at FreeBSD.org>

Looks good to me.

Reviewed-by: Anup Patel <anup at brainfault.org>

Applied this patch to the riscv/opensbi repo.

Thanks,
Anup

> ---
>   firmware/fw_base.S | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/firmware/fw_base.S b/firmware/fw_base.S
> index b947423..ca34b4c 100644
> --- a/firmware/fw_base.S
> +++ b/firmware/fw_base.S
> @@ -309,8 +309,8 @@ _scratch_init:
>         REG_S   a5, SBI_SCRATCH_FW_SIZE_OFFSET(tp)
>         /* Store R/W section's offset in scratch space */
> -       lla     a4, __fw_rw_offset
> -       REG_L   a5, 0(a4)
> +       lla     a5, _fw_rw_start
> +       sub     a5, a5, a4
>         REG_S   a5, SBI_SCRATCH_FW_RW_OFFSET(tp)
>         /* Store fw_heap_offset and fw_heap_size in scratch space */
> @@ -536,8 +536,6 @@ _link_start:
>         RISCV_PTR       FW_TEXT_START
>   _link_end:
>         RISCV_PTR       _fw_reloc_end
> -__fw_rw_offset:
> -       RISCV_PTR       _fw_rw_start - _fw_start
>         .section .entry, "ax", %progbits
>         .align 3
> --
> 2.41.0
>
>
>
> --
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