jejak ralat libemu

1) run python dlm gdb(maksudnya, debug mode)

# gdb /usr/bin/python

2) Start python

(gdb) run

3) Jika nama file libemu_test.py, maka

>> import libemu_test
0x401019L hex: A83D asm: test al,0x3d

Program received signal SIGSEGV, Segmentation fault.
0x0000000000000000 in ?? ()

4) Back trace

(gdb) bt
#0  0x0000000000000000 in ?? ()
#1  0x00007ffff58650f6 in emu_cpu_step (c=0xc3fb40) at emu_cpu.c:839
#2  0x00007ffff5b51fbb in __pyx_pf_8pylibemu_8Emulator_25cpu_step (__pyx_v_self=, unused=)
    at src/pylibemu.c:6735
#3  0x000000000042afec in PyEval_EvalFrameEx ()
#4  0x00000000004317f2 in PyEval_EvalCodeEx ()
#5  0x000000000054a078 in PyImport_ExecCodeModuleEx ()
#6  0x000000000050d091 in ?? ()
#7  0x000000000050da8b in ?? ()

5) tukar kepada frame 1  (frame ni refering to stack) (rasanya lah:))

(gdb) frame 1
#1  0x00007ffff58650f6 in emu_cpu_step (c=0xc3fb40) at emu_cpu.c:839
839                     ret = c->cpu_instr_info->function(c, &c->instr.cpu);

6)

(gdb) ptype c
type = struct emu_cpu {
    struct emu *emu;
    struct emu_memory *mem;
    uint32_t debugflags;
    uint32_t eip;
    uint32_t eflags;
    uint32_t reg[8];
    uint16_t *reg16[8];
    uint8_t *reg8[8];
    struct emu_instruction instr;
    struct emu_cpu_instruction_info *cpu_instr_info;
    uint32_t last_fpu_instr[2];
    char *instr_string;
    _Bool repeat_current_instr;
    struct emu_track_and_source *tracking;
} *

7)

(gdb) print c
$1 = (struct emu_cpu *) 0xc3fb40

8)

(gdb) print c->cpu_instr_info
$2 = (struct emu_cpu_instruction_info *) 0x7ffff5aedbc0

9)

(gdb) print c->cpu_instr_info->function
$3 = (int32_t (*)(struct emu_cpu *, struct emu_cpu_instruction *)) 0

sah yang problem adalah kat sini, sebab value adalah 0 (kosong)(yg paling kanan). Maksudnya pointer fungsi 'function' point to null.

Maka kena semak code yang initialize cpu_instr_info-> function

10)

(gdb) ptype c->cpu_instr_info
type = struct emu_cpu_instruction_info {
    int32_t (*function)(struct emu_cpu *, struct emu_cpu_instruction *);
    const char *name;
    struct {
        uint8_t s_bit : 1;
        uint8_t w_bit : 1;
        uint8_t modrm_byte : 4;
        uint8_t imm_data : 3;
        uint8_t disp_data : 3;
        uint8_t level : 2;
        uint8_t type : 2;
        uint8_t fpu_info : 1;
    } format;
} *