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Fri, 05 Sep 2025 00:53:26 -0700 (PDT) From: Nicholas Piggin To: qemu-riscv@nongnu.org Cc: Nicholas Piggin , Laurent Vivier , Palmer Dabbelt , Alistair Francis , Weiwei Li , Daniel Henrique Barboza , Liu Zhiwei , qemu-devel@nongnu.org, Nicholas Joaquin , Ganesh Valliappan Subject: [PATCH v2 1/3] target/riscv: Fix IALIGN check in misa write Date: Fri, 5 Sep 2025 17:49:56 +1000 Message-ID: <20250905074959.426911-2-npiggin@gmail.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20250905074959.426911-1-npiggin@gmail.com> References: <20250905074959.426911-1-npiggin@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::102e; envelope-from=npiggin@gmail.com; helo=mail-pj1-x102e.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, 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: 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: 1757058874582116600 The instruction alignment check for the C extension was inverted. The new value should be checked for C bit clear (thus increasing IALIGN). If IALIGN is incompatible, then the write to misa should be suppressed, not just ignoring the update to the C bit. From the ISA: Writing misa may increase IALIGN, e.g., by disabling the "C" extension. If an instruction that would write misa increases IALIGN, and the subsequent instruction=E2=80=99s address is not IALIGN-bit aligne= d, the write to misa is suppressed, leaving misa unchanged. This was found with a verification test generator based on RiESCUE. Reported-by: Nicholas Joaquin Reported-by: Ganesh Valliappan Signed-off-by: Nicholas Piggin --- target/riscv/csr.c | 16 ++++- tests/tcg/riscv64/Makefile.softmmu-target | 5 ++ tests/tcg/riscv64/misa-ialign.S | 88 +++++++++++++++++++++++ 3 files changed, 106 insertions(+), 3 deletions(-) create mode 100644 tests/tcg/riscv64/misa-ialign.S diff --git a/target/riscv/csr.c b/target/riscv/csr.c index 8842e07a73..64b55b7add 100644 --- a/target/riscv/csr.c +++ b/target/riscv/csr.c @@ -2140,9 +2140,19 @@ static RISCVException write_misa(CPURISCVState *env,= int csrno, /* Mask extensions that are not supported by this hart */ val &=3D env->misa_ext_mask; =20 - /* Suppress 'C' if next instruction is not aligned. */ - if ((val & RVC) && (get_next_pc(env, ra) & 3) !=3D 0) { - val &=3D ~RVC; + /* + * misa writes that increase IALIGN beyond alignment of the next + * instruction cause the write to misa to be suppressed. Clearing + * "C" extension increases IALIGN. + */ + if (!(val & RVC) && (get_next_pc(env, ra) & 3) !=3D 0) { + /* + * If the next instruction is unaligned mod 4 then "C" must be + * set or this instruction could not be executing, so we know + * this is is clearing "C" (and not just keeping it clear). + */ + g_assert(env->misa_ext & RVC); + return RISCV_EXCP_NONE; } =20 /* Disable RVG if any of its dependencies are disabled */ diff --git a/tests/tcg/riscv64/Makefile.softmmu-target b/tests/tcg/riscv64/= Makefile.softmmu-target index 3ca595335d..6e470a028f 100644 --- a/tests/tcg/riscv64/Makefile.softmmu-target +++ b/tests/tcg/riscv64/Makefile.softmmu-target @@ -24,5 +24,10 @@ EXTRA_RUNS +=3D run-test-mepc-masking run-test-mepc-masking: test-mepc-masking $(call run-test, $<, $(QEMU) $(QEMU_OPTS)$<) =20 +EXTRA_RUNS +=3D run-misa-ialign +run-misa-ialign: QEMU_OPTS :=3D -cpu rv64,c=3Dtrue,v=3Dtrue,x-misa-w=3Don = $(QEMU_OPTS) +run-misa-ialign: misa-ialign + $(call run-test, $<, $(QEMU) $(QEMU_OPTS)$<) + # We don't currently support the multiarch system tests undefine MULTIARCH_TESTS diff --git a/tests/tcg/riscv64/misa-ialign.S b/tests/tcg/riscv64/misa-ialig= n.S new file mode 100644 index 0000000000..7f1eb30023 --- /dev/null +++ b/tests/tcg/riscv64/misa-ialign.S @@ -0,0 +1,88 @@ +/* + * Test for MISA changing C and related IALIGN alignment cases + * + * This test verifies that the "C" extension can be cleared and set in MIS= A, + * that a branch to 2-byte aligned instructions can be executed when "C" is + * enabled, and that a write to MISA which would increase IALIGN and cause + * the next instruction to be unaligned is ignored. + * + * SPDX-License-Identifier: GPL-2.0-or-later + */ + +#define RVC (1 << ('C'-'A')) +#define RVV (1 << ('V'-'A')) + +.option norvc + .text + .global _start +_start: + lla t0, trap + csrw mtvec, t0 + + csrr t0, misa + li t1, RVC + not t1, t1 + and t0, t0, t1 + csrw misa, t0 + csrr t1, misa + li a0, 2 # fail code + bne t0, t1, _exit # Could not clear RVC in MISA + + li t1, RVC + or t0, t0, t1 + csrw misa, t0 + csrr t1, misa + li a0, 3 # fail code + bne t0, t1, _exit # Could not set RVC in MISA + + j unalign +. =3D . + 2 +unalign: + + li t1, RVC + not t1, t1 + and t0, t0, t1 + csrw misa, t0 + csrr t1, misa + li a0, 4 # fail code + beq t0, t1, _exit # Was able to clear RVC in MISA + + li t0, (RVC|RVV) + not t0, t0 + and t0, t0, t1 + csrw misa, t0 + csrr t0, misa + li a0, 5 # fail code + bne t0, t1, _exit # MISA write was not ignored (RVV was cleared) + + j realign +. =3D . + 2 +realign: + + # Success! + li a0, 0 + j _exit + +trap: + # Any trap is a fail code 1 + li a0, 1 + +# Exit code in a0 +_exit: + lla a1, semiargs + li t0, 0x20026 # ADP_Stopped_ApplicationExit + sd t0, 0(a1) + sd a0, 8(a1) + li a0, 0x20 # TARGET_SYS_EXIT_EXTENDED + + # Semihosting call sequence + .balign 16 + slli zero, zero, 0x1f + ebreak + srai zero, zero, 0x7 + j . + + .data + .balign 16 +semiargs: + .space 16 --=20 2.51.0