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GET /api/patches/2195795/?format=api
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{
    "id": 2195795,
    "url": "http://patchwork.ozlabs.org/api/patches/2195795/?format=api",
    "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260211221953.4099441-2-brian.cain@oss.qualcomm.com/",
    "project": {
        "id": 14,
        "url": "http://patchwork.ozlabs.org/api/projects/14/?format=api",
        "name": "QEMU Development",
        "link_name": "qemu-devel",
        "list_id": "qemu-devel.nongnu.org",
        "list_email": "qemu-devel@nongnu.org",
        "web_url": "",
        "scm_url": "",
        "webscm_url": "",
        "list_archive_url": "",
        "list_archive_url_format": "",
        "commit_url_format": ""
    },
    "msgid": "<20260211221953.4099441-2-brian.cain@oss.qualcomm.com>",
    "list_archive_url": null,
    "date": "2026-02-11T22:19:50",
    "name": "[v4,1/4] target/hexagon: Fix invalid duplex decoding",
    "commit_ref": null,
    "pull_url": null,
    "state": "new",
    "archived": false,
    "hash": "771f0bb7c5e12000390b4ab5f350c86d1d038af9",
    "submitter": {
        "id": 89839,
        "url": "http://patchwork.ozlabs.org/api/people/89839/?format=api",
        "name": "Brian Cain",
        "email": "brian.cain@oss.qualcomm.com"
    },
    "delegate": null,
    "mbox": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260211221953.4099441-2-brian.cain@oss.qualcomm.com/mbox/",
    "series": [
        {
            "id": 491915,
            "url": "http://patchwork.ozlabs.org/api/series/491915/?format=api",
            "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/list/?series=491915",
            "date": "2026-02-11T22:19:52",
            "name": "Handle some invalid encodings",
            "version": 4,
            "mbox": "http://patchwork.ozlabs.org/series/491915/mbox/"
        }
    ],
    "comments": "http://patchwork.ozlabs.org/api/patches/2195795/comments/",
    "check": "pending",
    "checks": "http://patchwork.ozlabs.org/api/patches/2195795/checks/",
    "tags": {},
    "related": [],
    "headers": {
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        ],
        "From": "Brian Cain <brian.cain@oss.qualcomm.com>",
        "To": "qemu-devel@nongnu.org",
        "Cc": "brian.cain@oss.qualcomm.com, ltaylorsimpson@gmail.com, alex@alexrp.com,\n Brian Cain <bcain@quicinc.com>,\n Pierrick Bouvier <pierrick.bouvier@linaro.org>",
        "Subject": "[PATCH v4 1/4] target/hexagon: Fix invalid duplex decoding",
        "Date": "Wed, 11 Feb 2026 14:19:50 -0800",
        "Message-Id": "<20260211221953.4099441-2-brian.cain@oss.qualcomm.com>",
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    },
    "content": "When decoding a duplex instruction, if the slot0 sub-instruction fails\nto decode after slot1 succeeds, QEMU was leaving the packet in a\npartially-decoded state. This allowed invalid duplex encodings (where\none sub-instruction doesn't match any valid pattern) to be executed\nincorrectly.\n\nFix by resetting the decoder state when slot0 fails, returning an empty\ninstruction that triggers an exception.\n\nAdd gen_exception_decode_fail() for raising exceptions when decode fails\nbefore ctx->next_PC is initialized. This keeps gen_exception_end_tb()\nsemantics unchanged (it continues to use ctx->next_PC for the exception\nPC after successful decode).\n\nResolves: https://gitlab.com/qemu-project/qemu/-/issues/3291\nSigned-off-by: Brian Cain <bcain@quicinc.com>\nReviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>\nReviewed-by: Taylor Simpson <ltaylorsimpson@gmail.com>\n---\n linux-user/hexagon/cpu_loop.c        |  4 ++\n target/hexagon/decode.c              | 13 ++++-\n target/hexagon/translate.c           | 18 ++++++-\n tests/tcg/hexagon/Makefile.target    |  1 +\n tests/tcg/hexagon/invalid-encoding.c | 81 ++++++++++++++++++++++++++++\n 5 files changed, 113 insertions(+), 4 deletions(-)\n create mode 100644 tests/tcg/hexagon/invalid-encoding.c",
    "diff": "diff --git a/linux-user/hexagon/cpu_loop.c b/linux-user/hexagon/cpu_loop.c\nindex 1941f4c9c1..c0e1098e3f 100644\n--- a/linux-user/hexagon/cpu_loop.c\n+++ b/linux-user/hexagon/cpu_loop.c\n@@ -64,6 +64,10 @@ void cpu_loop(CPUHexagonState *env)\n             force_sig_fault(TARGET_SIGBUS, TARGET_BUS_ADRALN,\n                             env->gpr[HEX_REG_R31]);\n             break;\n+        case HEX_CAUSE_INVALID_PACKET:\n+            force_sig_fault(TARGET_SIGILL, TARGET_ILL_ILLOPC,\n+                            env->gpr[HEX_REG_PC]);\n+            break;\n         case EXCP_ATOMIC:\n             cpu_exec_step_atomic(cs);\n             break;\ndiff --git a/target/hexagon/decode.c b/target/hexagon/decode.c\nindex b5ece60450..69ba1ec96c 100644\n--- a/target/hexagon/decode.c\n+++ b/target/hexagon/decode.c\n@@ -509,8 +509,14 @@ decode_insns(DisasContext *ctx, Insn *insn, uint32_t encoding)\n                 insn->iclass = iclass_bits(encoding);\n                 return 2;\n             }\n+            /*\n+             * Slot0 decode failed after slot1 succeeded. This is an invalid\n+             * duplex encoding (both sub-instructions must be valid).\n+             */\n+            ctx->insn = --insn;\n         }\n-        g_assert_not_reached();\n+        /* Invalid duplex encoding - return 0 to signal failure */\n+        return 0;\n     }\n }\n \n@@ -674,7 +680,10 @@ int decode_packet(DisasContext *ctx, int max_words, const uint32_t *words,\n         encoding32 = words[words_read];\n         end_of_packet = is_packet_end(encoding32);\n         new_insns = decode_insns(ctx, insn, encoding32);\n-        g_assert(new_insns > 0);\n+        if (new_insns == 0) {\n+            /* Invalid instruction encoding */\n+            return 0;\n+        }\n         /*\n          * If we saw an extender, mark next word extended so immediate\n          * decode works\ndiff --git a/target/hexagon/translate.c b/target/hexagon/translate.c\nindex e88e19cc1a..7fe8b35351 100644\n--- a/target/hexagon/translate.c\n+++ b/target/hexagon/translate.c\n@@ -195,7 +195,21 @@ static void gen_exception_end_tb(DisasContext *ctx, int excp)\n     tcg_gen_movi_tl(hex_gpr[HEX_REG_PC], ctx->next_PC);\n     gen_exception_raw(excp);\n     ctx->base.is_jmp = DISAS_NORETURN;\n+}\n \n+/*\n+ * Generate exception for decode failures. Unlike gen_exception_end_tb,\n+ * this is used when decode fails before ctx->next_PC is initialized.\n+ */\n+static void gen_exception_decode_fail(DisasContext *ctx, int nwords, int excp)\n+{\n+    target_ulong fail_pc = ctx->base.pc_next + nwords * sizeof(uint32_t);\n+\n+    gen_exec_counters(ctx);\n+    tcg_gen_movi_tl(hex_gpr[HEX_REG_PC], fail_pc);\n+    gen_exception_raw(excp);\n+    ctx->base.is_jmp = DISAS_NORETURN;\n+    ctx->base.pc_next = fail_pc;\n }\n \n static int read_packet_words(CPUHexagonState *env, DisasContext *ctx,\n@@ -935,7 +949,7 @@ static void decode_and_translate_packet(CPUHexagonState *env, DisasContext *ctx)\n \n     nwords = read_packet_words(env, ctx, words);\n     if (!nwords) {\n-        gen_exception_end_tb(ctx, HEX_CAUSE_INVALID_PACKET);\n+        gen_exception_decode_fail(ctx, 0, HEX_CAUSE_INVALID_PACKET);\n         return;\n     }\n \n@@ -950,7 +964,7 @@ static void decode_and_translate_packet(CPUHexagonState *env, DisasContext *ctx)\n         gen_commit_packet(ctx);\n         ctx->base.pc_next += pkt.encod_pkt_size_in_bytes;\n     } else {\n-        gen_exception_end_tb(ctx, HEX_CAUSE_INVALID_PACKET);\n+        gen_exception_decode_fail(ctx, nwords, HEX_CAUSE_INVALID_PACKET);\n     }\n }\n \ndiff --git a/tests/tcg/hexagon/Makefile.target b/tests/tcg/hexagon/Makefile.target\nindex e5182c01d8..16669e04a8 100644\n--- a/tests/tcg/hexagon/Makefile.target\n+++ b/tests/tcg/hexagon/Makefile.target\n@@ -51,6 +51,7 @@ HEX_TESTS += scatter_gather\n HEX_TESTS += hvx_misc\n HEX_TESTS += hvx_histogram\n HEX_TESTS += invalid-slots\n+HEX_TESTS += invalid-encoding\n HEX_TESTS += unaligned_pc\n \n run-and-check-exception = $(call run-test,$2,$3 2>$2.stderr; \\\ndiff --git a/tests/tcg/hexagon/invalid-encoding.c b/tests/tcg/hexagon/invalid-encoding.c\nnew file mode 100644\nindex 0000000000..010a5eb741\n--- /dev/null\n+++ b/tests/tcg/hexagon/invalid-encoding.c\n@@ -0,0 +1,81 @@\n+/*\n+ * Test that invalid instruction encodings are properly rejected.\n+ *\n+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.\n+ * SPDX-License-Identifier: GPL-2.0-or-later\n+ */\n+\n+#include <assert.h>\n+#include <signal.h>\n+#include <stdio.h>\n+#include <stdlib.h>\n+#include <string.h>\n+#include <unistd.h>\n+\n+static void *resume_pc;\n+\n+static void handle_sigill(int sig, siginfo_t *info, void *puc)\n+{\n+    ucontext_t *uc = (ucontext_t *)puc;\n+\n+    if (sig != SIGILL) {\n+        _exit(EXIT_FAILURE);\n+    }\n+\n+    uc->uc_mcontext.r0 = SIGILL;\n+    uc->uc_mcontext.pc = (unsigned long)resume_pc;\n+}\n+\n+/*\n+ * Each test function:\n+ *   - Sets r0 to something other than SIGILL\n+ *   - Stores the resume address into resume_pc\n+ *   - Executes the invalid encoding\n+ *   - The handler sets r0 = SIGILL and resumes after the faulting packet\n+ *   - Returns the value in r0\n+ */\n+\n+/*\n+ * Invalid duplex encoding (issue #3291):\n+ * - Word 0: 0x0fff6fff = immext(#0xfffbffc0), parse bits = 01\n+ * - Word 1: 0x600237b0 = duplex with:\n+ *     - slot0 = 0x17b0 (invalid S2 subinstruction encoding)\n+ *     - slot1 = 0x0002 (valid SA1_addi)\n+ *     - duplex iclass = 7 (S2 for slot0, A for slot1)\n+ *\n+ * Since slot0 doesn't decode to any valid S2 subinstruction, this packet\n+ * should be rejected and raise SIGILL.\n+ */\n+static int test_invalid_duplex(void)\n+{\n+    int sig;\n+\n+    asm volatile(\n+        \"r0 = #0\\n\"\n+        \"r1 = ##1f\\n\"\n+        \"memw(%1) = r1\\n\"\n+        \".word 0x0fff6fff\\n\"  /* immext(#0xfffbffc0), parse=01 */\n+        \".word 0x600237b0\\n\"  /* duplex: slot0=0x17b0 (invalid) */\n+        \"1:\\n\"\n+        \"%0 = r0\\n\"\n+        : \"=r\"(sig)\n+        : \"r\"(&resume_pc)\n+        : \"r0\", \"r1\", \"memory\");\n+\n+    return sig;\n+}\n+\n+int main()\n+{\n+    struct sigaction act;\n+\n+    memset(&act, 0, sizeof(act));\n+    act.sa_sigaction = handle_sigill;\n+    act.sa_flags = SA_SIGINFO;\n+    assert(sigaction(SIGILL, &act, NULL) == 0);\n+\n+    assert(test_invalid_duplex() == SIGILL);\n+\n+    puts(\"PASS\");\n+    return EXIT_SUCCESS;\n+}\n",
    "prefixes": [
        "v4",
        "1/4"
    ]
}