android - ARM 汇编回溯 PC 偏移量

Question

ARM 手册提到:

During execution, PC does not contain the address of the currently executing instruction. The address of the currently executing instruction is typically PC-8 for ARM, or PC-4 for Thumb.

这是否也适用于崩溃回溯中的 PC 值？

例如，如果我有以下回溯(来自使用 ARM 指令的 Android armv7 设备):

libSomeLib.so!SomeClass::someMethod [someFile.cpp : 638 + 0x4]
    r0 = 0x00000001    r1 = 0xffffffff    r2 = 0x00000000    r3 = 0xd4fcd71c
    r4 = 0xd39b9284    r5 = 0xd39b927c    r6 = 0xd39b9278    r7 = 0xc7025520
    r8 = 0xc5e1d7b0    r9 = 0xe01136a8   r10 = 0x00000012   r12 = 0xd39b9268
    fp = 0xd39b92d4    sp = 0xd39b9268    lr = 0xd4ea1f24    pc = 0xd4ea1f24
...
0xd47cb000 - 0xd5079fff  libSomeLib.so  ???

我应该在 0xd4ea1f24-0xd47cb000=0x006D6F24 还是 0xd4ea1f24-0xd47cb000-8=0x006D6F1C 处寻找 libSomeLib.so 中的崩溃指令？

Answer 1

我故意撞车进行调查。源代码:

int* crashPointer = nullptr;
*crashPointer = 7;

生成的程序集:

11feb8: e3005007    movw    r5, #7
11febc: e3006000    movw    r6, #0 <--- r6 is #0
11fec0: e50b0014    str r0, [fp, #-20]  ; 0xffffffec
11fec4: e50b1018    str r1, [fp, #-24]  ; 0xffffffe8
11fec8: e51b0014    ldr r0, [fp, #-20]  ; 0xffffffec
    int* crashPointer = nullptr;
11fecc: e50b601c    str r6, [fp, #-28]  ; 0xffffffe4 <--- Stores #0 to [fp, #-28] from r6
    *crashPointer = 7;
11fed0: e51b101c    ldr r1, [fp, #-28]  ; 0xffffffe4 <--- Loads #0 from [fp, #-28] to r1
11fed4: e5815000    str r5, [r1] <--- This should crash since it's trying to dereference r1 which is #0

预测的崩溃地址是11fed4

实际故障转储:

signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x0
    r0 ea408800  r1 00000000  r2 00000006  r3 ea6ccfa0
    r4 ea6d1b2a  r5 00000007  r6 00000000  r7 ea3ff904
    r8 00000001  r9 e8b22ec0  sl ea6b5be9  fp ea3ff5c0
    ip ea6d1af8  sp ea3ff550  lr ea6d09aa  pc ea696ed4  cpsr 600f0010
...
ea577000-ea6d7000 r-xp 00000000 fe:01 1556782   libSomeLib.so

结论: ea696ed4-ea577000=11fed4，等于预测地址。

总而言之:无需向故障转储中的 PC 值添加偏移量(至少对于 Android armv7)。