Re: [PATCH v2 02/37] target/ppc: Migrate atomic loads to decodetree

[Amit Machhiwal <amachhiw@linux.ibm.com>]

On 2026/08/26 10:38 AM, Chinmay Rath wrote:
> From: Nikhil Kumar Singh <nikhilks@linux.ibm.com>
> 
> Migrate load-and-reserve instructions (lbarx, lharx, lwarx, ldarx,
> lqarx) to decodetree using the X-form layout.
> 
> A shared helper (do_load_locked) is introduced for standard-width
> variants, while LQARX is handled separately due to its 128-bit
> semantics and register pairing constraints.
> 
> The implementation preserves legacy behavior, including:
>   - Reservation granularity and overwrite semantics
>   - Alignment requirements
>   - Invalid instruction cases for LQARX
> 
> Testing:
>   - Verified TCG equivalence with legacy implementation
> 
> Signed-off-by: Nikhil Kumar Singh <nikhilks@linux.ibm.com>
> Reviewed-by: Glenn Miles <milesg@linux.ibm.com>
> Signed-off-by: Chinmay Rath <rathc@linux.ibm.com>
> ---
>  target/ppc/insn32.decode |   7 +++
>  target/ppc/translate.c   | 124 +++++++++++++++++++--------------------
>  2 files changed, 69 insertions(+), 62 deletions(-)
> 
> diff --git a/target/ppc/insn32.decode b/target/ppc/insn32.decode
> index 342e65dadf..26948e08a7 100644
> --- a/target/ppc/insn32.decode
> +++ b/target/ppc/insn32.decode
> @@ -1309,6 +1309,13 @@ XVF64GERNN      111011 ... -- .... 0 ..... 11111010 ..-  @XX3_at xa=%xx_xa_pair
>  ##Extend Sign Word and Shift Left Immediate XS-form
>  EXTSWSLI         011111 ..... ..... ..... 110111101 . .         @XS
>  
> +## Load and Reserve Instructions
> +LBARX           011111 ..... ..... ..... 0000110100 .   @X_rc
> +LHARX           011111 ..... ..... ..... 0001110100 .   @X_rc
> +LWARX           011111 ..... ..... ..... 0000010100 .   @X_rc
> +LDARX           011111 ..... ..... ..... 0001010100 .   @X_rc
> +LQARX           011111 ..... ..... ..... 0100010100 .   @X_rc
> +
>  ## Vector Division Instructions
>  
>  VDIVSW          000100 ..... ..... ..... 00110001011    @VX
> diff --git a/target/ppc/translate.c b/target/ppc/translate.c
> index e627f48f9e..cc9287dcc5 100644
> --- a/target/ppc/translate.c
> +++ b/target/ppc/translate.c
> @@ -2947,30 +2947,6 @@ static void gen_isync(DisasContext *ctx)
>      ctx->base.is_jmp = DISAS_EXIT_UPDATE;
>  }
>  
> -static void gen_load_locked(DisasContext *ctx, MemOp memop)
> -{
> -    TCGv gpr = cpu_gpr[rD(ctx->opcode)];
> -    TCGv t0 = tcg_temp_new();
> -
> -    gen_set_access_type(ctx, ACCESS_RES);
> -    gen_addr_reg_index(ctx, t0);
> -    tcg_gen_qemu_ld_tl(gpr, t0, ctx->mem_idx, DEF_MEMOP(memop) | MO_ALIGN);
> -    tcg_gen_mov_tl(cpu_reserve, t0);
> -    tcg_gen_movi_tl(cpu_reserve_length, memop_size(memop));
> -    tcg_gen_mov_tl(cpu_reserve_val, gpr);
> -}
> -
> -#define LARX(name, memop)                  \
> -static void gen_##name(DisasContext *ctx)  \
> -{                                          \
> -    gen_load_locked(ctx, memop);           \
> -}
> -
> -/* lwarx */
> -LARX(lbarx, MO_UB)
> -LARX(lharx, MO_UW)
> -LARX(lwarx, MO_UL)
> -
>  static void gen_fetch_inc_conditional(DisasContext *ctx, MemOp memop,
>                                        TCGv EA, TCGCond cond, int addend)
>  {
> @@ -3219,42 +3195,9 @@ STCX(sthcx_, MO_UW)
>  STCX(stwcx_, MO_UL)
>  
>  #if defined(TARGET_PPC64)
> -/* ldarx */
> -LARX(ldarx, MO_UQ)
>  /* stdcx. */
>  STCX(stdcx_, MO_UQ)
>  
> -/* lqarx */
> -static void gen_lqarx(DisasContext *ctx)
> -{
> -    int rd = rD(ctx->opcode);
> -    TCGv EA, hi, lo;
> -    TCGv_i128 t16;
> -
> -    if (unlikely((rd & 1) || (rd == rA(ctx->opcode)) ||
> -                 (rd == rB(ctx->opcode)))) {
> -        gen_inval_exception(ctx, POWERPC_EXCP_INVAL_INVAL);
> -        return;
> -    }
> -
> -    gen_set_access_type(ctx, ACCESS_RES);
> -    EA = tcg_temp_new();
> -    gen_addr_reg_index(ctx, EA);
> -
> -    /* Note that the low part is always in RD+1, even in LE mode.  */
> -    lo = cpu_gpr[rd + 1];
> -    hi = cpu_gpr[rd];
> -
> -    t16 = tcg_temp_new_i128();
> -    tcg_gen_qemu_ld_i128(t16, EA, ctx->mem_idx, DEF_MEMOP(MO_128 | MO_ALIGN));
> -    tcg_gen_extr_i128_i64(lo, hi, t16);
> -
> -    tcg_gen_mov_tl(cpu_reserve, EA);
> -    tcg_gen_movi_tl(cpu_reserve_length, 16);
> -    tcg_gen_st_tl(hi, tcg_env, offsetof(CPUPPCState, reserve_val));
> -    tcg_gen_st_tl(lo, tcg_env, offsetof(CPUPPCState, reserve_val2));
> -}
> -
>  /* stqcx. */
>  static void gen_stqcx_(DisasContext *ctx)
>  {
> @@ -5741,6 +5684,68 @@ static bool trans_EXTSWSLI(DisasContext *ctx, arg_XS *a)
>      return true;
>  }
>  
> +/*
> + * Load-and-reserve core
> + */
> +static bool do_load_locked(DisasContext *ctx, arg_X_rc *a, MemOp memop)
> +{
> +    TCGv EA = do_ea_calc(ctx, a->ra, cpu_gpr[a->rb]);
> +    TCGv gpr = cpu_gpr[a->rt];
> +
> +    gen_set_access_type(ctx, ACCESS_RES);
> +
> +    tcg_gen_qemu_ld_tl(gpr, EA, ctx->mem_idx, memop | MO_ALIGN);
> +
> +    tcg_gen_mov_tl(cpu_reserve, EA);
> +    tcg_gen_movi_tl(cpu_reserve_length, memop_size(memop));
> +
> +    tcg_gen_mov_tl(cpu_reserve_val, gpr);
> +
> +    return true;
> +}
> +
> +TRANS_FLAGS2(ATOMIC_ISA206, LBARX, do_load_locked, DEF_MEMOP(MO_UB))
> +TRANS_FLAGS2(ATOMIC_ISA206, LHARX, do_load_locked, DEF_MEMOP(MO_UW))
> +TRANS(LWARX, do_load_locked, DEF_MEMOP(MO_UL))
> +TRANS64(LDARX, do_load_locked, DEF_MEMOP(MO_UQ))
> +
> +static bool trans_LQARX(DisasContext *ctx, arg_LQARX *a)
> +{
> +    REQUIRE_64BIT(ctx);
> +    REQUIRE_INSNS_FLAGS2(ctx, ISA207S);

The old GEN_HANDLER_E used PPC2_LSQ_ISA207, but the new code uses
PPC2_ISA207S . In the current QEMU CPU model set this makes no practical
difference — every CPU that sets PPC2_ISA207S also sets PPC2_LSQ_ISA207.
However, PPC2_LSQ_ISA207 is the precise flag for this feature and keeps
lqarx symmetric with its companion stqcx_ (line 5870) which correctly
continues to use PPC2_LSQ_ISA207. Please use REQUIRE_INSNS_FLAGS2(ctx,
LSQ_ISA207) for consistency and to guard against future CPU models that
may set these flags independently

> +#if defined(TARGET_PPC64)
> +    TCGv EA;
> +    TCGv_i128 t16;
> +    /* Must use even register and avoid overlap */
> +    if (unlikely((a->rt & 1) || (a->rt == a->ra) || (a->rt == a->rb))) {
> +        gen_inval_exception(ctx, POWERPC_EXCP_INVAL_INVAL);
> +        return true;
> +    }
> +
> +    gen_set_access_type(ctx, ACCESS_RES);
> +    EA = do_ea_calc(ctx, a->ra, cpu_gpr[a->rb]);
> +    t16 = tcg_temp_new_i128();
> +
> +    tcg_gen_qemu_ld_i128(t16, EA, ctx->mem_idx,
> +                         DEF_MEMOP(MO_128 | MO_ALIGN));
> +
> +    tcg_gen_extr_i128_i64(cpu_gpr[a->rt + 1],
> +                         cpu_gpr[a->rt],
> +                         t16);
> +
> +    tcg_gen_mov_tl(cpu_reserve, EA);
> +    tcg_gen_movi_tl(cpu_reserve_length, 16);
> +
> +    tcg_gen_st_i64(cpu_gpr[a->rt],
> +                   tcg_env, offsetof(CPUPPCState, reserve_val));

All these multi-line calls can be collapsed to single lines — they are
within 80 characters respectively and fit within the 80-column limit.
The only exception is tcg_gen_st_i64(..., reserve_val2) at 85 chars,
which legitimately needs wrapping. The unnecessary line splits add
visual noise without any readability benefit.

> +    tcg_gen_st_i64(cpu_gpr[a->rt + 1],
> +                   tcg_env, offsetof(CPUPPCState, reserve_val2));
> +#else
> +    qemu_build_not_reached();
> +#endif
> +    return true;
> +}
> +
>  #include "translate/fixedpoint-impl.c.inc"
>  
>  #include "translate/fp-impl.c.inc"
> @@ -5853,9 +5858,6 @@ GEN_HANDLER(lswx, 0x1F, 0x15, 0x10, 0x00000001, PPC_STRING),
>  GEN_HANDLER(stswi, 0x1F, 0x15, 0x16, 0x00000001, PPC_STRING),
>  GEN_HANDLER(stswx, 0x1F, 0x15, 0x14, 0x00000001, PPC_STRING),
>  GEN_HANDLER(isync, 0x13, 0x16, 0x04, 0x03FFF801, PPC_MEM),
> -GEN_HANDLER_E(lbarx, 0x1F, 0x14, 0x01, 0, PPC_NONE, PPC2_ATOMIC_ISA206),
> -GEN_HANDLER_E(lharx, 0x1F, 0x14, 0x03, 0, PPC_NONE, PPC2_ATOMIC_ISA206),
> -GEN_HANDLER(lwarx, 0x1F, 0x14, 0x00, 0x00000000, PPC_RES),
>  GEN_HANDLER_E(lwat, 0x1F, 0x06, 0x12, 0x00000001, PPC_NONE, PPC2_ISA300),
>  GEN_HANDLER_E(stwat, 0x1F, 0x06, 0x16, 0x00000001, PPC_NONE, PPC2_ISA300),
>  GEN_HANDLER_E(stbcx_, 0x1F, 0x16, 0x15, 0, PPC_NONE, PPC2_ATOMIC_ISA206),
> @@ -5864,8 +5866,6 @@ GEN_HANDLER2(stwcx_, "stwcx.", 0x1F, 0x16, 0x04, 0x00000000, PPC_RES),
>  #if defined(TARGET_PPC64)
>  GEN_HANDLER_E(ldat, 0x1F, 0x06, 0x13, 0x00000001, PPC_NONE, PPC2_ISA300),
>  GEN_HANDLER_E(stdat, 0x1F, 0x06, 0x17, 0x00000001, PPC_NONE, PPC2_ISA300),
> -GEN_HANDLER(ldarx, 0x1F, 0x14, 0x02, 0x00000000, PPC_64B),
> -GEN_HANDLER_E(lqarx, 0x1F, 0x14, 0x08, 0, PPC_NONE, PPC2_LSQ_ISA207),
>  GEN_HANDLER2(stdcx_, "stdcx.", 0x1F, 0x16, 0x06, 0x00000000, PPC_64B),
>  GEN_HANDLER_E(stqcx_, 0x1F, 0x16, 0x05, 0, PPC_NONE, PPC2_LSQ_ISA207),
>  #endif
> -- 
> 2.55.0
>