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Sun, 15 Mar 2026 19:50:55 -0700 (PDT) From: Lucas Amaral To: qemu-devel@nongnu.org Cc: qemu-arm@nongnu.org, agraf@csgraf.de, peter.maydell@linaro.org, mohamed@unpredictable.fr, Lucas Amaral Subject: [PATCH v4 5/6] target/arm/emulate: add atomic, compare-and-swap, and PAC load Date: Sun, 15 Mar 2026 23:50:33 -0300 Message-ID: <20260316025034.85611-6-lucaaamaral@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260316025034.85611-1-lucaaamaral@gmail.com> References: <20260315034123.41921-1-lucaaamaral@gmail.com> <20260316025034.85611-1-lucaaamaral@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=2607:f8b0:4864:20::1335; envelope-from=lucaaamaral@gmail.com; helo=mail-dy1-x1335.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, FSL_HELO_BARE_IP_2=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZohoMail-DKIM: pass (identity @gmail.com) X-ZM-MESSAGEID: 1773629510275154100 Add emulation for remaining ISV=3D0 load/store instruction classes. Atomic memory operations (DDI 0487 C3.3.2): - LDADD, LDCLR, LDEOR, LDSET: arithmetic/logic atomics - LDSMAX, LDSMIN, LDUMAX, LDUMIN: signed/unsigned min/max - SWP: atomic swap Non-atomic read-modify-write, sufficient for MMIO where concurrent access is not a concern. Acquire/release semantics are ignored. Compare-and-swap (DDI 0487 C3.3.1): - CAS/CASA/CASAL/CASL: single-register compare-and-swap - CASP/CASPA/CASPAL/CASPL: register-pair compare-and-swap CASP validates even register pairs; odd or r31 returns UNHANDLED. Load with PAC (DDI 0487 C6.2.121): - LDRAA/LDRAB: pointer-authenticated load, offset/pre-indexed Pointer authentication is not emulated (equivalent to auth always succeeding), which is correct for MMIO since PAC is a software security mechanism, not a memory access semantic. CASP uses two explicit decode patterns for the 32/64-bit size variants. LDRA's offset immediate is stored raw in the decode; the handler scales by << 3. Signed-off-by: Lucas Amaral --- target/arm/emulate/a64-ldst.decode | 45 ++++++ target/arm/emulate/arm_emulate.c | 233 +++++++++++++++++++++++++++++ 2 files changed, 278 insertions(+) diff --git a/target/arm/emulate/a64-ldst.decode b/target/arm/emulate/a64-ld= st.decode index fadf6fd2..9292bfdf 100644 --- a/target/arm/emulate/a64-ldst.decode +++ b/target/arm/emulate/a64-ldst.decode @@ -16,6 +16,16 @@ # Load/store pair (GPR and SIMD/FP) &ldstpair rt2 rt rn imm sz sign w p =20 +# Atomic memory operations +&atomic rs rn rt a r sz + +# Compare-and-swap +&cas rs rn rt sz a r + +# Load with PAC (LDRAA/LDRAB, FEAT_PAuth) +%ldra_imm 22:s1 12:9 +&ldra rt rn imm m w + # Load/store register offset &ldst rm rn rt sign ext sz opt s =20 @@ -36,6 +46,15 @@ # Load/store pair: imm7 is signed, scaled by element size in handler @ldstpair .. ... . ... . imm:s7 rt2:5 rn:5 rt:5 &ldstpair =20 +# Atomics +@atomic sz:2 ... . .. a:1 r:1 . rs:5 . ... .. rn:5 rt:5 &atomic + +# Compare-and-swap: sz extracted by pattern (CAS) or set constant (CASP) +@cas .. ...... . a:1 . rs:5 r:1 ..... rn:5 rt:5 &cas + +# Load with PAC +@ldra .. ... . .. m:1 . . ......... w:1 . rn:5 rt:5 &ldra im= m=3D%ldra_imm + # Load/store register offset @ldst .. ... . .. .. . rm:5 opt:3 s:1 .. rn:5 rt:5 &ldst =20 @@ -241,6 +260,32 @@ STR_v 00 111 1 00 10 1 ..... ... . 10 ..... = ..... @ldst sign=3D0 ext=3D LDR_v sz:2 111 1 00 01 1 ..... ... . 10 ..... ..... @ldst sign= =3D0 ext=3D0 LDR_v 00 111 1 00 11 1 ..... ... . 10 ..... ..... @ldst sign= =3D0 ext=3D0 sz=3D4 =20 +### Compare-and-swap + +# CAS / CASA / CASAL / CASL +CAS sz:2 001000 1 . 1 ..... . 11111 ..... ..... @cas + +# CASP / CASPA / CASPAL / CASPL (pair: Rt,Rt+1 and Rs,Rs+1) +CASP 00 001000 0 . 1 ..... . 11111 ..... ..... @cas sz=3D2 +CASP 01 001000 0 . 1 ..... . 11111 ..... ..... @cas sz=3D3 + +### Atomic memory operations + +LDADD .. 111 0 00 . . 1 ..... 0000 00 ..... ..... @atomic +LDCLR .. 111 0 00 . . 1 ..... 0001 00 ..... ..... @atomic +LDEOR .. 111 0 00 . . 1 ..... 0010 00 ..... ..... @atomic +LDSET .. 111 0 00 . . 1 ..... 0011 00 ..... ..... @atomic +LDSMAX .. 111 0 00 . . 1 ..... 0100 00 ..... ..... @atomic +LDSMIN .. 111 0 00 . . 1 ..... 0101 00 ..... ..... @atomic +LDUMAX .. 111 0 00 . . 1 ..... 0110 00 ..... ..... @atomic +LDUMIN .. 111 0 00 . . 1 ..... 0111 00 ..... ..... @atomic +SWP .. 111 0 00 . . 1 ..... 1000 00 ..... ..... @atomic + +### Load with PAC (FEAT_PAuth) + +# LDRAA (M=3D0) / LDRAB (M=3D1), offset (W=3D0) / pre-indexed (W=3D1) +LDRA 11 111 0 00 . . 1 ......... . 1 ..... ..... @ldra + ### System instructions =E2=80=94 DC cache maintenance =20 # SYS with CRn=3DC7 covers all data cache operations (DC CIVAC, CVAC, etc.= ). diff --git a/target/arm/emulate/arm_emulate.c b/target/arm/emulate/arm_emul= ate.c index 52e41703..44a559ad 100644 --- a/target/arm/emulate/arm_emulate.c +++ b/target/arm/emulate/arm_emulate.c @@ -499,6 +499,239 @@ static bool trans_LDXP(DisasContext *ctx, arg_stxr *a) return true; } =20 +/* + * Atomic memory operations (DDI 0487 C3.3.2) + * + * Non-atomic read-modify-write; sufficient for MMIO. + * Acquire/release semantics ignored (sequentially consistent by design). + */ + +typedef uint64_t (*atomic_op_fn)(uint64_t old, uint64_t operand, int bits); + +static uint64_t atomic_add(uint64_t old, uint64_t op, int bits) +{ + (void)bits; + return old + op; +} + +static uint64_t atomic_clr(uint64_t old, uint64_t op, int bits) +{ + (void)bits; + return old & ~op; +} + +static uint64_t atomic_eor(uint64_t old, uint64_t op, int bits) +{ + (void)bits; + return old ^ op; +} + +static uint64_t atomic_set(uint64_t old, uint64_t op, int bits) +{ + (void)bits; + return old | op; +} + +static uint64_t atomic_smax(uint64_t old, uint64_t op, int bits) +{ + int64_t a =3D sign_extend(old, bits); + int64_t b =3D sign_extend(op, bits); + return (a >=3D b) ? old : op; +} + +static uint64_t atomic_smin(uint64_t old, uint64_t op, int bits) +{ + int64_t a =3D sign_extend(old, bits); + int64_t b =3D sign_extend(op, bits); + return (a <=3D b) ? old : op; +} + +static uint64_t atomic_umax(uint64_t old, uint64_t op, int bits) +{ + uint64_t mask =3D (bits =3D=3D 64) ? UINT64_MAX : (1ULL << bits) - 1; + return ((old & mask) >=3D (op & mask)) ? old : op; +} + +static uint64_t atomic_umin(uint64_t old, uint64_t op, int bits) +{ + uint64_t mask =3D (bits =3D=3D 64) ? UINT64_MAX : (1ULL << bits) - 1; + return ((old & mask) <=3D (op & mask)) ? old : op; +} + +static bool do_atomic(DisasContext *ctx, arg_atomic *a, atomic_op_fn fn) +{ + int esize =3D 1 << a->sz; + int bits =3D 8 * esize; + uint64_t va =3D base_read(ctx, a->rn); + uint64_t old =3D 0; + + if (mem_read(ctx, va, &old, esize) !=3D 0) { + return true; + } + + uint64_t operand =3D gpr_read(ctx, a->rs); + uint64_t result =3D fn(old, operand, bits); + + if (mem_write(ctx, va, &result, esize) !=3D 0) { + return true; + } + + /* Rt receives the old value (before modification) */ + gpr_write(ctx, a->rt, old); + return true; +} + +static bool trans_LDADD(DisasContext *ctx, arg_atomic *a) +{ + return do_atomic(ctx, a, atomic_add); +} + +static bool trans_LDCLR(DisasContext *ctx, arg_atomic *a) +{ + return do_atomic(ctx, a, atomic_clr); +} + +static bool trans_LDEOR(DisasContext *ctx, arg_atomic *a) +{ + return do_atomic(ctx, a, atomic_eor); +} + +static bool trans_LDSET(DisasContext *ctx, arg_atomic *a) +{ + return do_atomic(ctx, a, atomic_set); +} + +static bool trans_LDSMAX(DisasContext *ctx, arg_atomic *a) +{ + return do_atomic(ctx, a, atomic_smax); +} + +static bool trans_LDSMIN(DisasContext *ctx, arg_atomic *a) +{ + return do_atomic(ctx, a, atomic_smin); +} + +static bool trans_LDUMAX(DisasContext *ctx, arg_atomic *a) +{ + return do_atomic(ctx, a, atomic_umax); +} + +static bool trans_LDUMIN(DisasContext *ctx, arg_atomic *a) +{ + return do_atomic(ctx, a, atomic_umin); +} + +static bool trans_SWP(DisasContext *ctx, arg_atomic *a) +{ + int esize =3D 1 << a->sz; + uint64_t va =3D base_read(ctx, a->rn); + uint64_t old =3D 0; + + if (mem_read(ctx, va, &old, esize) !=3D 0) { + return true; + } + + uint64_t newval =3D gpr_read(ctx, a->rs); + if (mem_write(ctx, va, &newval, esize) !=3D 0) { + return true; + } + + gpr_write(ctx, a->rt, old); + return true; +} + +/* Compare-and-swap: CAS, CASP (DDI 0487 C3.3.1) */ + +static bool trans_CAS(DisasContext *ctx, arg_cas *a) +{ + int esize =3D 1 << a->sz; + uint64_t va =3D base_read(ctx, a->rn); + uint64_t current =3D 0; + + if (mem_read(ctx, va, ¤t, esize) !=3D 0) { + return true; + } + + uint64_t mask =3D (esize =3D=3D 8) ? UINT64_MAX : (1ULL << (8 * esize)= ) - 1; + uint64_t compare =3D gpr_read(ctx, a->rs) & mask; + + if ((current & mask) =3D=3D compare) { + uint64_t newval =3D gpr_read(ctx, a->rt) & mask; + if (mem_write(ctx, va, &newval, esize) !=3D 0) { + return true; + } + } + + /* Rs receives the old memory value (whether or not swap occurred) */ + gpr_write(ctx, a->rs, current); + return true; +} + +/* CASP: compare-and-swap pair (Rs,Rs+1 compared; Rt,Rt+1 stored) */ +static bool trans_CASP(DisasContext *ctx, arg_cas *a) +{ + /* CASP requires even register pairs; odd or r31 is UNPREDICTABLE */ + if ((a->rs & 1) || a->rs >=3D 31 || (a->rt & 1) || a->rt >=3D 31) { + return false; + } + + int esize =3D 1 << a->sz; /* per-register size */ + uint64_t va =3D base_read(ctx, a->rn); + uint8_t buf[16]; + uint64_t cur1 =3D 0, cur2 =3D 0; + + if (mem_read(ctx, va, buf, 2 * esize) !=3D 0) { + return true; + } + memcpy(&cur1, buf, esize); + memcpy(&cur2, buf + esize, esize); + + uint64_t mask =3D (esize =3D=3D 8) ? UINT64_MAX : (1ULL << (8 * esize)= ) - 1; + uint64_t cmp1 =3D gpr_read(ctx, a->rs) & mask; + uint64_t cmp2 =3D gpr_read(ctx, a->rs + 1) & mask; + + if ((cur1 & mask) =3D=3D cmp1 && (cur2 & mask) =3D=3D cmp2) { + uint64_t new1 =3D gpr_read(ctx, a->rt) & mask; + uint64_t new2 =3D gpr_read(ctx, a->rt + 1) & mask; + memcpy(buf, &new1, esize); + memcpy(buf + esize, &new2, esize); + if (mem_write(ctx, va, buf, 2 * esize) !=3D 0) { + return true; + } + } + + gpr_write(ctx, a->rs, cur1); + gpr_write(ctx, a->rs + 1, cur2); + return true; +} + +/* + * Load with PAC: LDRAA / LDRAB (FEAT_PAuth) + * (DDI 0487 C6.2.121) + * + * Pointer authentication is not emulated -- the base register is used + * directly (equivalent to auth always succeeding). + */ + +static bool trans_LDRA(DisasContext *ctx, arg_ldra *a) +{ + int64_t offset =3D (int64_t)a->imm << 3; /* S:imm9, scaled by 8 */ + uint64_t base =3D base_read(ctx, a->rn); + uint64_t va =3D base + offset; /* auth not emulated */ + uint64_t val =3D 0; + + if (mem_read(ctx, va, &val, 8) !=3D 0) { + return true; + } + + gpr_write(ctx, a->rt, val); + + if (a->w) { + base_write(ctx, a->rn, va); + } + return true; +} + /* PRFM, DC cache maintenance -- treated as NOP */ static bool trans_NOP(DisasContext *ctx, arg_NOP *a) { --=20 2.52.0