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#ifndef __HOOK_H
#define __HOOK_H
bool insert_function_redirect(void *function, void *redirect, uint32_t flags);
bool remove_function_redirect(void *function);
bool redirect_call_within_function(void *function, void *target, void *redirect);
// Flags recognised by insert_function_redirect.
enum {
HOOK_DEFAULT = 0,
HOOK_REPLACE_FUNCTION = (1 << 0), // Replace call, don't hook.
HOOK_FASTCALL = (1 << 1), // Try to minimize damage to registers.
};
// Convenient representation of an x86 near call. The immediate operand is the
// relative, displaced branch target, thus actual address is something like:
//
// target = (uintptr_t)(&call) + sizeof(struct call) + call->operand.i;
//
struct __attribute__((packed)) branch {
uint8_t opcode;
union {
uintptr_t i;
void *p;
} operand;
uint8_t data[0]; // Used to chain instructions together.
};
#define X86_OPCODE_CALL_NEAR 0xE8
#define X86_OPCODE_JMP_NEAR 0xE9
#define X86_OPCODE_NOP 0x90
#define X86_OPCODE_RET 0xC3
#define X86_OPCODE_MOV_EAX_IMM 0xB8
#define X86_OPCODE_PUSH_EBP 0x55
#define X86_PREFIX_DATA16 0x66
// This is used to save an arbitrary 2 byte integer in the instuction stream
// without disrupting disassemblers.
struct __attribute__((packed)) encodedsize {
uint8_t prefix; // 0x66
uint8_t opcode; // 0xB8
uint16_t operand;
};
static int __stub_zero() { return 0; }
static int __stub_one() { return 1; }
static int __stub_false(){ return false; }
static int __stub_true() { return true; }
static int __stub_neg() { return -1; }
// Callee clears stubs, common on Windows.
static int __attribute__((stdcall)) __stub_zero_std_4(int a) { return 0; }
static int __attribute__((stdcall)) __stub_zero_std_8(int a, int b) { return 0; }
static int __attribute__((stdcall)) __stub_zero_std_12(int a, int b, int c) { return 0; }
static int __attribute__((stdcall)) __stub_zero_std_16(int a, int b, int c, int d) { return 0; }
// This allows you to call stubs like __stub_zero_std(4) to specify how many bytes to clear.
#define __stub_zero_std(n) __stub_zero_std_ ## n
#endif
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