ARM PC Rear Panel Offset

Question

The ARM manual states that:

At run time, the PC does not contain the address of the current instruction execution. The address of the currently executing command is usually PC-8 for ARM or PC-4 for Thumb.

Does this also apply to PC values ​​in reverse traces?

For example, if I have the following backtrace (from an Android armv7 device using ARM commands):

 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 ??? 

Should I look for a failure instruction inside libSomeLib.so in 0xd4ea1f24-0xd47cb000=0x006D6F24 or 0xd4ea1f24-0xd47cb000-8=0x006D6F1C ?

Answer 1

I made a deliberate crash for an investigation. Source:

 int* crashPointer = nullptr; *crashPointer = 7; 

Generated assembly:

 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 trying to dereference r1 which is #0 

Predicted 11fed4 Address 11fed4

Actual emergency reset:

 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 

Conclusion: ea696ed4-ea577000=11fed4 , which is equal to the predicted address.

To summarize: there is no need to add an offset to the value of the PC in the crash dump (for Android armv7 at least).