| Message ID | 20240802031612.604-4-zhiwei_liu@linux.alibaba.com |
|---|---|
| State | New |
| Headers | show |
| Series | target/riscv: Remove redundant insn length check for zama16b | expand |
On 8/2/24 13:16, LIU Zhiwei wrote: > According to the risc-v specification: > "FLD and FSD are only guaranteed to execute atomically if the effective > address is naturally aligned and XLEN≥64." > > We currently implement fld as MO_ATOM_IFALIGN when XLEN < 64, which does > not violate the rules. But it will hide some problems. So relax it to > MO_ATOM_NONE. > > Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com> > --- > target/riscv/insn_trans/trans_rvd.c.inc | 26 ++++++++++++++++++------- > 1 file changed, 19 insertions(+), 7 deletions(-) > > diff --git a/target/riscv/insn_trans/trans_rvd.c.inc b/target/riscv/insn_trans/trans_rvd.c.inc > index dbe508c7e0..458d7db745 100644 > --- a/target/riscv/insn_trans/trans_rvd.c.inc > +++ b/target/riscv/insn_trans/trans_rvd.c.inc > @@ -48,12 +48,20 @@ static bool trans_fld(DisasContext *ctx, arg_fld *a) > REQUIRE_EXT(ctx, RVD); > > /* > - * Zama16b applies to loads and stores of no more than MXLEN bits defined > - * in the F, D, and Q extensions. Otherwise, it falls through to default > - * MO_ATOM_IFALIGN. > + * FLD and FSD are only guaranteed to execute atomically if the effective > + * address is naturally aligned and XLEN≥64. > */ > - if ((ctx->misa_mxl_max >= MXL_RV64) && ctx->cfg_ptr->ext_zama16b) { > - memop |= MO_ATOM_WITHIN16; > + if (ctx->misa_mxl_max >= MXL_RV64) { > + /* > + * Zama16b applies to loads and stores of no more than MXLEN bits > + * defined in the F, D, and Q extensions. Otherwise, it falls through > + * to default MO_ATOM_IFALIGN. > + */ > + if (ctx->cfg_ptr->ext_zama16b) { > + memop |= MO_ATOM_WITHIN16; > + } > + } else { > + memop |= MO_ATOM_NONE; > } Does this really have byte atomicity, not atomic on two aligned 32-bit loads (which would be MO_ATOM_IFALIGN_PAIR). It's probably clearer to fill out the if-tree completely, rather than explain about defaults. if (get_mxl(ctx) == MXL_RV32) { memop |= MO_ATOM_NONE; } else if (ctx->cfg_ptr->ext_zama16b) { memop |= MO_ATOM_WITHIN16; } else { memop |= MO_ATOM_IFALIGN; } r~
On 2024/8/2 13:52, Richard Henderson wrote: > On 8/2/24 13:16, LIU Zhiwei wrote: >> According to the risc-v specification: >> "FLD and FSD are only guaranteed to execute atomically if the effective >> address is naturally aligned and XLEN≥64." >> >> We currently implement fld as MO_ATOM_IFALIGN when XLEN < 64, which does >> not violate the rules. But it will hide some problems. So relax it to >> MO_ATOM_NONE. >> >> Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com> >> --- >> target/riscv/insn_trans/trans_rvd.c.inc | 26 ++++++++++++++++++------- >> 1 file changed, 19 insertions(+), 7 deletions(-) >> >> diff --git a/target/riscv/insn_trans/trans_rvd.c.inc >> b/target/riscv/insn_trans/trans_rvd.c.inc >> index dbe508c7e0..458d7db745 100644 >> --- a/target/riscv/insn_trans/trans_rvd.c.inc >> +++ b/target/riscv/insn_trans/trans_rvd.c.inc >> @@ -48,12 +48,20 @@ static bool trans_fld(DisasContext *ctx, arg_fld *a) >> REQUIRE_EXT(ctx, RVD); >> /* >> - * Zama16b applies to loads and stores of no more than MXLEN >> bits defined >> - * in the F, D, and Q extensions. Otherwise, it falls through to >> default >> - * MO_ATOM_IFALIGN. >> + * FLD and FSD are only guaranteed to execute atomically if the >> effective >> + * address is naturally aligned and XLEN≥64. >> */ >> - if ((ctx->misa_mxl_max >= MXL_RV64) && ctx->cfg_ptr->ext_zama16b) { >> - memop |= MO_ATOM_WITHIN16; >> + if (ctx->misa_mxl_max >= MXL_RV64) { >> + /* >> + * Zama16b applies to loads and stores of no more than MXLEN >> bits >> + * defined in the F, D, and Q extensions. Otherwise, it >> falls through >> + * to default MO_ATOM_IFALIGN. >> + */ >> + if (ctx->cfg_ptr->ext_zama16b) { >> + memop |= MO_ATOM_WITHIN16; >> + } >> + } else { >> + memop |= MO_ATOM_NONE; >> } > > Does this really have byte atomicity, not atomic on two aligned 32-bit > loads (which would be MO_ATOM_IFALIGN_PAIR). The specification doesn't rule it. I think we can choose either way. The byte atomicity may expose more problems on alignment. > > It's probably clearer to fill out the if-tree completely, > rather than explain about defaults. > > if (get_mxl(ctx) == MXL_RV32) { > memop |= MO_ATOM_NONE; > } else if (ctx->cfg_ptr->ext_zama16b) { > memop |= MO_ATOM_WITHIN16; > } else { > memop |= MO_ATOM_IFALIGN; > } OK. Thanks, Zhiwei > > > r~
On 8/2/24 16:27, LIU Zhiwei wrote: >> Does this really have byte atomicity, not atomic on two aligned 32-bit loads (which >> would be MO_ATOM_IFALIGN_PAIR). > The specification doesn't rule it. I think we can choose either way. The byte atomicity > may expose more problems on alignment. Ok. r~
diff --git a/target/riscv/insn_trans/trans_rvd.c.inc b/target/riscv/insn_trans/trans_rvd.c.inc index dbe508c7e0..458d7db745 100644 --- a/target/riscv/insn_trans/trans_rvd.c.inc +++ b/target/riscv/insn_trans/trans_rvd.c.inc @@ -48,12 +48,20 @@ static bool trans_fld(DisasContext *ctx, arg_fld *a) REQUIRE_EXT(ctx, RVD); /* - * Zama16b applies to loads and stores of no more than MXLEN bits defined - * in the F, D, and Q extensions. Otherwise, it falls through to default - * MO_ATOM_IFALIGN. + * FLD and FSD are only guaranteed to execute atomically if the effective + * address is naturally aligned and XLEN≥64. */ - if ((ctx->misa_mxl_max >= MXL_RV64) && ctx->cfg_ptr->ext_zama16b) { - memop |= MO_ATOM_WITHIN16; + if (ctx->misa_mxl_max >= MXL_RV64) { + /* + * Zama16b applies to loads and stores of no more than MXLEN bits + * defined in the F, D, and Q extensions. Otherwise, it falls through + * to default MO_ATOM_IFALIGN. + */ + if (ctx->cfg_ptr->ext_zama16b) { + memop |= MO_ATOM_WITHIN16; + } + } else { + memop |= MO_ATOM_NONE; } decode_save_opc(ctx); @@ -72,8 +80,12 @@ static bool trans_fsd(DisasContext *ctx, arg_fsd *a) REQUIRE_FPU; REQUIRE_EXT(ctx, RVD); - if ((ctx->misa_mxl_max >= MXL_RV64) && ctx->cfg_ptr->ext_zama16b) { - memop |= MO_ATOM_WITHIN16; + if (ctx->misa_mxl_max >= MXL_RV64) { + if (ctx->cfg_ptr->ext_zama16b) { + memop |= MO_ATOM_WITHIN16; + } + } else { + memop |= MO_ATOM_NONE; } decode_save_opc(ctx);
According to the risc-v specification: "FLD and FSD are only guaranteed to execute atomically if the effective address is naturally aligned and XLEN≥64." We currently implement fld as MO_ATOM_IFALIGN when XLEN < 64, which does not violate the rules. But it will hide some problems. So relax it to MO_ATOM_NONE. Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com> --- target/riscv/insn_trans/trans_rvd.c.inc | 26 ++++++++++++++++++------- 1 file changed, 19 insertions(+), 7 deletions(-)