system/ulib/hypervisor/include/hypervisor/decode.h

// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#pragma once

#include <zircon/types.h>

// clang-format off

#define X86_FLAGS_STATUS    ((1u << 11 /* OF */) |                  \
                             (1u << 7 /* SF */) |                   \
                             (1u << 6 /* ZF */) |                   \
                             (1u << 2 /* PF */) |                   \
                             (1u << 1 /* Reserved (must be 1) */) | \
                             (1u << 0 /* CF */))

#define INST_MOV_READ       0u
#define INST_MOV_WRITE      1u
#define INST_TEST           2u

// clang-format on

__BEGIN_CDECLS

typedef struct zx_vcpu_state zx_vcpu_state_t;

/* Stores info from a decoded instruction. */
typedef struct instruction {
    uint8_t type;
    uint8_t mem;
    uint32_t imm;
    uint64_t* reg;
    uint32_t* flags;
} instruction_t;

zx_status_t inst_decode(const uint8_t* inst_buf, uint32_t inst_len, zx_vcpu_state_t* vcpu_state,
                        instruction_t* inst);

#define DEFINE_INST_VAL(size)                                                \
    static inline uint##size##_t inst_val##size(const instruction_t* inst) { \
        return (uint##size##_t)(inst->reg != NULL ? *inst->reg : inst->imm); \
    }
DEFINE_INST_VAL(32);
DEFINE_INST_VAL(16);
DEFINE_INST_VAL(8);
#undef DEFINE_INST_VAL

#define DEFINE_INST_READ(size)                                                                   \
    static inline zx_status_t inst_read##size(const instruction_t* inst, uint##size##_t value) { \
        if (inst->type != INST_MOV_READ || inst->mem != (size / 8))                              \
            return ZX_ERR_NOT_SUPPORTED;                                                         \
        *inst->reg = value;                                                                      \
        return ZX_OK;                                                                            \
    }
DEFINE_INST_READ(32);
DEFINE_INST_READ(16);
DEFINE_INST_READ(8);
#undef DEFINE_INST_READ

#define DEFINE_INST_WRITE(size)                                                                    \
    static inline zx_status_t inst_write##size(const instruction_t* inst, uint##size##_t* value) { \
        if (inst->type != INST_MOV_WRITE || inst->mem != (size / 8))                               \
            return ZX_ERR_NOT_SUPPORTED;                                                           \
        *value = inst_val##size(inst);                                                             \
        return ZX_OK;                                                                              \
    }
DEFINE_INST_WRITE(32);
DEFINE_INST_WRITE(16);
#undef DEFINE_INST_WRITE

#define DEFINE_INST_RW(size)                                                                    \
    static inline zx_status_t inst_rw##size(const instruction_t* inst, uint##size##_t* value) { \
        if (inst->type == INST_MOV_READ) {                                                      \
            return inst_read##size(inst, *value);                                               \
        } else if (inst->type == INST_MOV_WRITE) {                                              \
            return inst_write##size(inst, value);                                               \
        } else {                                                                                \
            return ZX_ERR_NOT_SUPPORTED;                                                        \
        }                                                                                       \
    }
DEFINE_INST_RW(32);
DEFINE_INST_RW(16);
#undef DEFINE_INST_RW

#if defined(__x86_64__)
// Returns the flags that are assigned to the x86 flags register by an
// 8-bit TEST instruction for the given two operand values.
static inline uint16_t x86_flags_for_test8(uint8_t value1, uint8_t value2) {
    // TEST cannot set the overflow flag (bit 11).
    uint16_t ax_reg;
    __asm__ volatile(
        "testb %[i1], %[i2];"
        "lahf" // Copies flags into the %ah register
        : "=a"(ax_reg)
        : [i1] "r"(value1), [i2] "r"(value2)
        : "cc");
    // Extract the value of the %ah register from the %ax register.
    return (uint16_t)(ax_reg >> 8);
}
#endif

static inline zx_status_t inst_test8(const instruction_t* inst, uint8_t inst_val, uint8_t value) {
    if (inst->type != INST_TEST || inst->mem != 1u || inst_val8(inst) != inst_val)
        return ZX_ERR_NOT_SUPPORTED;
#if __x86_64__
    *inst->flags &= ~X86_FLAGS_STATUS;
    *inst->flags |= x86_flags_for_test8(inst_val, value);
    return ZX_OK;
#else // __x86_64__
    return ZX_ERR_NOT_SUPPORTED;
#endif // __x86_64__
}

__END_CDECLS