Re: [PATCH v3 2/4] s390/jump_label: Implement ARCH_STATIC_BRANCH_JUMP_ASM and ARCH_STATIC_BRANCH_ASM macros

[Jan Polensky]

 On Wed, May 27, 2026 at 05:57:58AM +0000, Alice Ryhl wrote:
> On Thu, May 21, 2026 at 06:56:20PM +0200, Jan Polensky wrote:
> > Rust static branch support needs the s390 jump label instruction sequence
> > and __jump_table emission in a reusable form. The current implementation
> > embeds the sequence directly in the C asm goto blocks, which cannot be
> > shared with Rust.
> >
> > Introduce ARCH_STATIC_BRANCH_ASM and ARCH_STATIC_BRANCH_JUMP_ASM to
> > describe the brcl sequences for the likely-false and likely-true cases
> > and to emit the same __jump_table entries as before. Switch the existing
> > C helpers to use the new macros to avoid duplication without changing
> > the generated code.
> >
> > Signed-off-by: Jan Polensky <japo@xxxxxxxxxxxxx>
>
> This looks right.
>
> Reviewed-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
>
> Did you test it?
>
> Alice

Hi Alice,

yes, I tested it.

I used a small Rust sample module to exercise and validate the
behavior on s390. The patch is attached for reference. I did not
include the sample in this series.

It was not only rust I've used, my samples are not part of this series
(attached):

    ❯ readelf -SW samples/rust/rust_jump_label.ko | egrep '__jump_table|text|rela'
      [ 2] .rela__ksymtab    RELA            0000000000000000 06c298 000048 18   I 46   1  8
      [ 5] __jump_table      PROGBITS        0000000000000000 000060 000010 00  WA  0   0  8
      [ 6] .rela__jump_table RELA            0000000000000000 06c2e0 000048 18   I 46   5  8
      [ 7] .text             PROGBITS        0000000000000000 000070 0001bc 00  AX  0   0 16
      [ 8] .rela.text        RELA            0000000000000000 06c328 000228 18   I 46   7  8
      [ 9] .exit.text        PROGBITS        0000000000000000 000230 00003c 00  AX  0   0 16
      [10] .rela.exit.text   RELA            0000000000000000 06c550 000060 18   I 46   9  8
      [11] .init.text        PROGBITS        0000000000000000 000270 000026 00  AX  0   0 16
      [12] .rela.init.text   RELA            0000000000000000 06c5b0 000018 18   I 46  11  8
      [16] .rela.gnu.linkonce.this_module RELA            0000000000000000 06c5c8 000030 18   I 46  15  8
      [20] .rela.init.data   RELA            0000000000000000 06c5f8 000018 18   I 46  19  8
      [22] .rela.exit.data   RELA            0000000000000000 06c610 000018 18   I 46  21  8
      [32] .rela.debug_aranges RELA            0000000000000000 06c628 000108 18   I 46  31  8
      [34] .rela.debug_info  RELA            0000000000000000 06c730 0573f0 18   I 46  33  8
      [37] .rela.debug_line  RELA            0000000000000000 0c3b20 000048 18   I 46  36  8
      [39] .rela.debug_frame RELA            0000000000000000 0c3b68 000120 18   I 46  38  8
      [42] .rela.debug_loc   RELA            0000000000000000 0c3c88 000150 18   I 46  41  8
      [44] .rela.debug_ranges RELA            0000000000000000 0c3dd8 000300 18   I 46  43  8

Best regards,
Jan