Re: [PATCH] target/hppa: Allow, but diagnose, LDCW aligned only mod 4

[Philippe Mathieu-Daudé]

On Fri, Jan 17, 2020 at 2:53 AM Richard Henderson
<address@hidden> wrote:
>
> The PA-RISC 1.1 specification says that LDCW must be aligned mod 16
> or the operation is undefined.  However, real hardware only generates
> an unaligned access trap for unaligned mod 4.

This Linux kernel commit seems relevant:

https://github.com/torvalds/linux/commit/14e256c107304#diff-e85862c7227599cb24e36494f75948d5R159-R164

  /* From: "Jim Hull" <jim.hull of hp.com>
  I've attached a summary of the change, but basically, for PA 2.0, as
  long as the ",CO" (coherent operation) completer is specified, then the
  16-byte alignment requirement for ldcw and ldcd is relaxed, and instead
  they only require "natural" alignment (4-byte for ldcw, 8-byte for
  ldcd). */

(I couldn't find the original post on
http://lists.parisc-linux.org/pipermail/parisc-linux/)

Maybe you can point to it in the description.

> Match real hardware, but diagnose with GUEST_ERROR a violation of the
> specification.
>
> Reported-by: Helge Deller <address@hidden>
> Suggested-by: John David Anglin <address@hidden>
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>
> Helge, can you please test this against your failing kernel?
> You will of course want to add -D logfile -d guest_errors to
> you qemu command-line.
>
>
> r~
>
> ---
>  target/hppa/helper.h    | 2 ++
>  target/hppa/op_helper.c | 9 +++++++++
>  target/hppa/translate.c | 6 +++++-
>  3 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/target/hppa/helper.h b/target/hppa/helper.h
> index 38d834ef6b..2d483aab58 100644
> --- a/target/hppa/helper.h
> +++ b/target/hppa/helper.h
> @@ -17,6 +17,8 @@ DEF_HELPER_FLAGS_3(stby_b_parallel, TCG_CALL_NO_WG, void, 
> env, tl, tr)
>  DEF_HELPER_FLAGS_3(stby_e, TCG_CALL_NO_WG, void, env, tl, tr)
>  DEF_HELPER_FLAGS_3(stby_e_parallel, TCG_CALL_NO_WG, void, env, tl, tr)
>
> +DEF_HELPER_FLAGS_1(ldc_check, TCG_CALL_NO_RWG, void, tl)
> +
>  DEF_HELPER_FLAGS_4(probe, TCG_CALL_NO_WG, tr, env, tl, i32, i32)
>
>  DEF_HELPER_FLAGS_1(loaded_fr0, TCG_CALL_NO_RWG, void, env)
> diff --git a/target/hppa/op_helper.c b/target/hppa/op_helper.c
> index f0516e81f1..345cef2c08 100644
> --- a/target/hppa/op_helper.c
> +++ b/target/hppa/op_helper.c
> @@ -153,6 +153,15 @@ void HELPER(stby_e_parallel)(CPUHPPAState *env, 
> target_ulong addr,
>      do_stby_e(env, addr, val, true, GETPC());
>  }
>
> +void HELPER(ldc_check)(target_ulong addr)
> +{
> +    if (unlikely(addr & 0xf)) {
> +        qemu_log_mask(LOG_GUEST_ERROR,
> +                      "Undefined ldc to address unaligned mod 16: "
> +                      TARGET_FMT_lx "\n", addr);
> +    }
> +}
> +
>  target_ureg HELPER(probe)(CPUHPPAState *env, target_ulong addr,
>                            uint32_t level, uint32_t want)
>  {
> diff --git a/target/hppa/translate.c b/target/hppa/translate.c
> index 2f8d407a82..669381dc1d 100644
> --- a/target/hppa/translate.c
> +++ b/target/hppa/translate.c
> @@ -2942,7 +2942,7 @@ static bool trans_st(DisasContext *ctx, arg_ldst *a)
>
>  static bool trans_ldc(DisasContext *ctx, arg_ldst *a)
>  {
> -    MemOp mop = MO_TEUL | MO_ALIGN_16 | a->size;
> +    MemOp mop = MO_TE | MO_ALIGN | a->size;
>      TCGv_reg zero, dest, ofs;
>      TCGv_tl addr;
>
> @@ -2958,8 +2958,12 @@ static bool trans_ldc(DisasContext *ctx, arg_ldst *a)
>
>      form_gva(ctx, &addr, &ofs, a->b, a->x, a->scale ? a->size : 0,
>               a->disp, a->sp, a->m, ctx->mmu_idx == MMU_PHYS_IDX);
> +
> +    gen_helper_ldc_check(addr);
>      zero = tcg_const_reg(0);
>      tcg_gen_atomic_xchg_reg(dest, addr, zero, ctx->mmu_idx, mop);
> +    tcg_temp_free(zero);
> +
>      if (a->m) {
>          save_gpr(ctx, a->b, ofs);
>      }
> --
> 2.20.1
>
>