[PATCH v1 0/5] LoongArch tls le model linker relaxation support.

[Jinyang He]

On 2023-12-01 17:07, changjiachen wrote:

> This is the v1 version of patches to support loongarch linker tls le model relax.
>
> This support does three main things:
>
> 1. Modify LoongArch tls le model assembly instruction sequence.
>
> This change is mainly implemented in gcc. Due to the characteristics
> of st.w instruction in Loongarch and the unique addressing mode of
> tls le model, in order to implement tls le model linker relax, it is
> decided to change the tls le model instruction sequence.
>
> The specific changes are as follows:
>
> example: __thread int a = 1;
>
> old insn sequence:
>
> lu12i.w $r12,%le_hi20_r(a)
> ori     $r12,$r12,%le_lo12_r(a)
> add.d   $r12,$r12,$r2,%le_add_r(a)
> li.w	$r13,$r0,1
> stptr.w $r13,$r12,0

Hi,


It's more complex than I thought as you said it is mainly implemented
in gcc. Now I compile it, in archlinux, by gcc 13.2.1, and insn sequence
like follows,

lu12i.w $r12,%le_hi20(a)
ori     $r12,$r12,%le_lo12(a)
addi.w  $r13,$r0,1
stx.w   $r13,$r12,$r2

It use `stx.w` rather than `st.w` or `stptr.w`. Will the gcc implementation
change this sequence?


>
> new insn sequence:
>
> lu12i.w $r12,%le_hi20_r(a)
> add.d   $r12,$r12,$r2,%le_add_r(a)
> li.w    $r13,$r0,1
> st.w    $r13,$r12,%le_lo12_r(a)

In old sequence, $r12 is the real address of "a". In new sequence, $r12 is
not the real address of "a". How about we use $r12 after this sequence?


> 2. Added LoongArch three relocations related to tls le model relax.
>
> In order to ensure forward compatibility of binutils versions and
> implement tls le model relax, it was decided to add three relocation items.
>
> The relocation items are as follows:
>
> R_LARCH_TLS_LE_HI20_R
> R_LARCH_TLS_LE_LO12_R
> R_LARCH_TLS_LE_ADD_R
>
> 3. Implement Loongarch tls le model relax in ld.
>
> This change will add a loongarch_relax_tls_le function to relax tls le model.
>
> The instructions before and after relax change as follows:
>
> example: __thread int a = 1;
>
> before relax insn:
>
> lu12i.w	 $t0, 0
> add.d	 $t0, $t0, $tp
> li.w	 $t1, 1
> st.w	 $t1, $t0, 0
>
> after relax insn:
>
> li.w     $t1, 1
> st.w     $t1, $tp, 0
>
> changjiachen (5):
>    LoongArch: bfd: Add support for tls le relax.
>    LoongArch: include: Add support for tls le relax.
>    LoongArch: opcodes: Add support for tls le relax.
>    LoongArch: gas: Add support for tls le relax.
>    LoongArch: ld: Add support for tls le relax.
>
>   bfd/bfd-in2.h                                 |   4 +
>   bfd/elfnn-loongarch.c                         |  74 +++++++++
>   bfd/elfxx-loongarch.c                         |  50 ++++++
>   bfd/libbfd.h                                  |   3 +
>   bfd/reloc.c                                   |   6 +
>   gas/config/tc-loongarch.c                     |  12 +-
>   gas/testsuite/gas/loongarch/reloc.d           |  18 +++
>   gas/testsuite/gas/loongarch/reloc.s           |  11 ++
>   include/elf/loongarch.h                       |  13 ++
>   ld/testsuite/ld-loongarch-elf/old-tls-le.s    |  19 +++
>   .../relax-bound-check-tls-le.s                |  48 ++++++
>   .../ld-loongarch-elf/relax-check-tls-le.s     |  43 ++++++
>   ld/testsuite/ld-loongarch-elf/relax-tls-le.s  |  17 ++
>   ld/testsuite/ld-loongarch-elf/relax.exp       | 146 +++++++++++++++++-
>   .../tls-relax-compatible-check-old.s          |  39 +++++
>   opcodes/loongarch-opc.c                       |   1 +
>   16 files changed, 501 insertions(+), 3 deletions(-)
>   create mode 100644 ld/testsuite/ld-loongarch-elf/old-tls-le.s
>   create mode 100644 ld/testsuite/ld-loongarch-elf/relax-bound-check-tls-le.s
>   create mode 100644 ld/testsuite/ld-loongarch-elf/relax-check-tls-le.s
>   create mode 100644 ld/testsuite/ld-loongarch-elf/relax-tls-le.s
>   create mode 100644 ld/testsuite/ld-loongarch-elf/tls-relax-compatible-check-old.s
>