I traced through ThreadPlanStepRange and ThreadPlanStepRange for this piece
of code:
0x27b2d4 <[J]java.lang.Object.<init>()V>: push {r7, lr}
0x27b2d6 <[J]java.lang.Object.<init>()V+2>: mov r7, sp
0x27b2d8 <[J]java.lang.Object.<init>()V+4>: sub sp, #0x4
0x27b2da <[J]java.lang.Object.<init>()V+6>: movs r2, #0x0
0x27b2dc <[J]java.lang.Object.<init>()V+8>: str r2, [sp]
0x27b2de <[J]java.lang.Object.<init>()V+10>: str r1, [sp]
0x27b2e0 <[J]java.lang.Object.<init>()V+12>: ldr r2, [r1]
0x27b2e2 <[J]java.lang.Object.<init>()V+14>: ldr r2, [r2, #0x30]
0x27b2e4 <[J]java.lang.Object.<init>()V+16>: tst.w r2, #0x100000
0x27b2e8 <[J]java.lang.Object.<init>()V+20>: it ne
0x27b2ea <[J]java.lang.Object.<init>()V+22>: blne 0x466290
; _bcRegisterFinalizer
0x27b2ee <[J]java.lang.Object.<init>()V+26>: add sp, #0x4
0x27b2f0 <[J]java.lang.Object.<init>()V+28>: pop {r7, pc}
0x27b2f2 <[J]java.lang.Object.<init>()V+30>: nop
Execution is halted at 0x27b2e0 when i issue a source-level step. The
ThreadPlanStepRange::DidPush method sets up a breakpoint at 0x27b2ea (2
bytes) successfully after identifying the instruction at 0x27b2ea (blne) as
the next branch instruction in ThreadPlanStepRange
::SetNextBranchBreakpoint.
Next, the threads are then resumed by the command interpreter. We receive
an event from the inferior with stop reason eStopReasonException
(EXC_BAD_INSTRUCTION) right after the resume, stopping the process.
I guess this means i need to figure out how "it" and "blne" work together
(my ARM assembler knowledge is minimal) to then understand why the
breakpoint instruction that's written to the inferior results in a
EXC_BAD_INSTRUCTION. If someone knows what could be the culprit let me know
:)
Thanks,
Mario
On Mon, Dec 1, 2014 at 2:07 PM, Mario Zechner <badlogicga...@gmail.com>
wrote:
> Well, i wrote a very long mail detailing my journey to resolve issue #2
> (hanging after setting target.use-fast-stepping=false), only to eventually
> realize that it doesn't hang but instead just waits for the above loop to
> complete.
>
> This means turning off target.use-fast-stepping is not an option and i'm
> back to square one. I'd be grateful for any pointers on how to fix issue #1
> (EXC_BAD_INSTRUCTION). I guess i'll start by investigating the "run to
> next branch" stepping algorithm in LLDB, though my understanding is
> likely not sufficient to make a dent.
>
> Thanks,
> Mario
>
>
>
>
> On Mon, Dec 1, 2014 at 11:05 AM, Mario Zechner <badlogicga...@gmail.com>
> wrote:
>
>> Hi,
>>
>> setting target.use-fast-stepping to false did indeed solve this issue,
>> albeit at the cost of increased runtime obviously. However, i ran into
>> another issue right after i stepped out of the previously problematic
>> function: http://sht.tl/bdAKRC
>>
>> Trying to source-level step this function (with use-fast-stepping=false)
>> results in 1) the disassembly getting all kinds of messed up and 2) the
>> process not stepping but hanging at the `cmp r1, #0` instruction. The
>> original assembly code around that PC looks like this:
>>
>> LBB24_1: @ %label0
>> @ =>This Inner Loop Header:
>> Depth=1
>> @DEBUG_VALUE:
>> [J]java.lang.Thread.<init>(Ljava/lang/Runnable;Ljava/lang/String;)V:__$env
>> <- R5
>> ldrexd r1, r2, [r0]
>> strexd r1, r6, r6, [r0]
>> cmp r1, #0
>> bne LBB24_1
>> @ BB#2: @ %label0
>> @DEBUG_VALUE:
>> [J]java.lang.Thread.<init>(Ljava/lang/Runnable;Ljava/lang/String;)V:__$env
>> <- R5
>> dmb ish
>> movs r1, #5
>>
>> A simple loop, which is actually part of an inlined function. We had some
>> issues with inlined functions previously, i assume this issue is related.
>> Interestingly enough, the back trace is also a bit wonky:
>>
>> (lldb) bt
>>
>> * thread #1: tid = 0x18082, 0x0021a9b4
>> AttachTestIOSDev`[J]java.lang.Thread.<init>(Ljava/lang/Runnable;Ljava/lang/String;)V
>> [inlined] [j]java.lang.Thread.threadPtr(J)[set] + 14 at Thread.java:1, stop
>> reason = trace
>>
>> * frame #0: 0x0021a9b4
>> AttachTestIOSDev`[J]java.lang.Thread.<init>(Ljava/lang/Runnable;Ljava/lang/String;)V
>> [inlined] [j]java.lang.Thread.threadPtr(J)[set] + 14 at Thread.java:1
>>
>> frame #1: 0x0021a9a6
>> AttachTestIOSDev`[J]java.lang.Thread.<init>(__$env=0x01662fc8,
>> __$this=0x64da3833, runnable=0xa4f07400, threadName=0x00286000)V + 46 at
>> Thread.java:138
>> There should be a lot more frame. I'm gonna try to dig up some more
>> details.
>>
>> Thanks a lot!
>> Mario
>>
>>
>>
>> On Sun, Nov 30, 2014 at 1:32 AM, Jason Molenda <ja...@molenda.com> wrote:
>>
>>> The size of the breakpoint instruction is set by
>>> GetSoftwareBreakpointTrapOpcode(). In your case, most likely you're in
>>> PlatformDarwin::GetSoftwareBreakpointTrapOpcode() - lldb uses the symbol
>>> table (from the binary file) to determine if the code in a given function
>>> is arm or thumb. If it's arm, a 4 byte breakpoint is used. If it's thumb,
>>> a 2 byte breakpoint. Of course thumbv2 of T32 instructions can be 4 bytes
>>> -- the blne instruction is in your program -- but I assume the 2 byte
>>> breakpoint instruction still works correctly in these cases; the cpu sees
>>> the 2-byte instruction and stops execution.
>>>
>>> I am a little wary about the fact that this comes after an it
>>> instruction, I kind of vaguely remember issues with that instruction's
>>> behavior.
>>>
>>> It shouldn't make any difference but you might want to try
>>>
>>> (lldb) settings set target.use-fast-stepping false
>>>
>>> which will force lldb to single instruction step through the function.
>>> Right now lldb is looking at the instruction stream and putting breakpoints
>>> on branch/call/jump instructions to do your high-level "step" command,
>>> instead of stopping on every instruction. It is possible there could be a
>>> problem with that approach and the it instruction. Please report back if
>>> this changes the behavior.
>>>
>>> J
>>>
>>>
>>> > On Nov 26, 2014, at 9:22 AM, Mario Zechner <badlogicga...@gmail.com>
>>> wrote:
>>> >
>>> > I dug a little deeper, inspecting the GDB remote packets send by LLDB
>>> to perform the stepping. It appears when sending memory breakpoint commands
>>> used for stepping, the size of the instruction being replaced isn't taken
>>> into account, or writing back the original instruction isn't done properly.
>>> The following log shows what happens when stepping into the previously
>>> mentioned function:
>>> >
>>> > (lldb) s
>>> > Process 166 stopped
>>> > * thread #1: tid = 0x0fd9, 0x002602e0
>>> AttachTestIOSDev`[J]java.lang.Object.<init>(__$env=0x016bffc8,
>>> __$this=0x017864b0)V + 12 at Object.java:136, queue =
>>> 'com.apple.main-thread', stop reason = step in
>>> > frame #0: 0x002602e0
>>> AttachTestIOSDev`[J]java.lang.Object.<init>(__$env=0x016bffc8,
>>> __$this=0x017864b0)V + 12 at Object.java:136
>>> > (lldb) disassemble -p
>>> > AttachTestIOSDev`[J]java.lang.Object.<init>()V + 12 at Object.java:136:
>>> > -> 0x2602e0: ldr r2, [r1]
>>> > 0x2602e2: ldr r2, [r2, #0x30]
>>> > 0x2602e4: tst.w r2, #0x100000
>>> > 0x2602e8: it ne
>>> > (lldb) s
>>> > Process 166 stopped
>>> > * thread #1: tid = 0x0fd9, 0x002602ec
>>> AttachTestIOSDev`[J]java.lang.Object.<init>(__$env=0x016bffc8,
>>> __$this=0x017864b0)V + 24 at Object.java:136, queue =
>>> 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION
>>> (code=EXC_ARM_UNDEFINED, subcode=0xffd1b001)
>>> > frame #0: 0x002602ec
>>> AttachTestIOSDev`[J]java.lang.Object.<init>(__$env=0x016bffc8,
>>> __$this=0x017864b0)V + 24 at Object.java:136
>>> > (lldb) disassemble -p
>>> > AttachTestIOSDev`[J]java.lang.Object.<init>()V + 24 at Object.java:136:
>>> > -> 0x2602ec: .long 0xb001ffd1 ; unknown opcode
>>> > 0x2602f0: pop {r7, pc}
>>> >
>>> > AttachTestIOSDev`[J]java.lang.Object.<init>()V + 30:
>>> > 0x2602f2: nop
>>> >
>>> > AttachTestIOSDev`[J]java.lang.Object.clone()Ljava/lang/Object; at
>>> Object.java:154:
>>> > 0x2602f4: push {r4, r5, r7, lr}
>>> > (lldb) disassemble -f
>>> > AttachTestIOSDev`[J]java.lang.Object.<init>()V at Object.java:136:
>>> > 0x2602d4: push {r7, lr}
>>> > 0x2602d6: mov r7, sp
>>> > 0x2602d8: sub sp, #0x4
>>> > 0x2602da: movs r2, #0x0
>>> > 0x2602dc: str r2, [sp]
>>> > 0x2602de: str r1, [sp]
>>> > 0x2602e0: ldr r2, [r1]
>>> > 0x2602e2: ldr r2, [r2, #0x30]
>>> > 0x2602e4: tst.w r2, #0x100000
>>> > 0x2602e8: it ne
>>> > 0x2602ea: blne 0x44b290 ; _bcRegisterFinalizer
>>> > 0x2602ee: add sp, #0x4
>>> > 0x2602f0: pop {r7, pc}
>>> >
>>> > AttachTestIOSDev`[J]java.lang.Object.<init>()V + 30:
>>> > 0x2602f2: nop
>>> >
>>> > The first step succeeds and ends up right after the prologue, at
>>> 0x2602e0: ldr r2, [r1]. The next step ends up at 0x2602ec: .long
>>> 0xb001ffd1 which is wrong, it should be 0x2602ea: blne 0x44b290.
>>> >
>>> > The GDB remote conversation between lldb and the debugserver on the
>>> device (only relevant parts):
>>> >
>>> > # First step
>>> > lldb->debugserver: $Z0,2602e0,2#73
>>> > debugserver->lldb: $OK#00
>>> > lldb->debugserver: $vCont;c:0fd9#15
>>> > debugserver->lldb: (320)
>>> $T05thread:fd9;qaddr:37ebfad0;threads:fd9,ffa,ffb,ffd,fff,1009,100a,100b;00:c8ff6b01;01:b0647801;02:00000000;03:c87d6a00;04:00000000;05:c8ff6b01;06:fc6a6501;07:0c6a6501;08:90e96b01;09:28000000;0a:74a0ea37;0b:c8ff6b01;0c:b09e5b00;0d:086a6501;0e:d1b22000;0f:
>>> >
>>> > # Second step
>>> > lldb->debugserver: $Z0,2602ea,2#a4
>>> > debugserver->lldb: $OK#00
>>> > lldb->debugserver: $vCont;c:0fd9#15
>>> > debugserver->lldb: (324)
>>> $T92thread:fd9;qaddr:37ebfad0;threads:fd9,ffa,ffb,ffd,fff,1009,100a,100b;00:c8ff6b01;01:b0647801;02:01004300;03:c87d6a00;04:00000000;05:c8ff6b01;06:fc6a6501;07:0c6a6501;08:90e96b01;09:28000000;0a:74a0ea37;0b:c8ff6b01;0c:b09e5b00;0d:086a6501;0e:d1b22000;0f:
>>> >
>>> > For the first step, a 2 byte memory breakpoint is written to 0x2602e0
>>> ($Z0,2602e0,2#73), which is where the first step ended up. The instruction
>>> that got replaced is 2 bytes long. The GDB command wrote a 2 bytes memory
>>> breakpoint to the address, so all is good.
>>> >
>>> > For the second step, a 2 byte memory breakpoint is written to 0x2602ea
>>> ($Z0,2602ea,2#a4). But instead of ending up at 0x2602ec, which is in the
>>> middle of the 4-byte blne instruction.
>>> >
>>> > Is it correct for LLDB to set a 2 byte memory breakpoint instead of a
>>> 4-byte memory breakpoint in this case? The PC will be set to an invalid
>>> address, which then causes the EXC_BAD_INSTRUCTION.
>>> >
>>> > Am i understanding this correctly? Is there a way for me to fix this?
>>> >
>>> > On Wed, Nov 26, 2014 at 5:26 PM, Mario Zechner <
>>> badlogicga...@gmail.com> wrote:
>>> > Hi,
>>> >
>>> > we generate thumbv7 binaries for iOS devices. We deploy, launch and
>>> debug those via LLDB. Stepping into functions seems to almost always
>>> generate a EXC_BAD_INSTRUCTION signal. The signal is not generated when
>>> running the app without the debugger attached. It is also not generated
>>> when we attach a debugger, but simply let the app run without breakpoints
>>> or any stepping.
>>> >
>>> > Here's one of these function's LLVM IR:
>>> >
>>> > =======================
>>> > define external void @"[J]java.lang.Object.<init>()V"(%Env* %p0,
>>> %Object* %p1) nounwind noinline optsize {
>>> > label0:
>>> > call void @"llvm.dbg.declare"(metadata !{%Env* %p0}, metadata
>>> !19), !dbg !{i32 136, i32 0, metadata !{i32 786478, metadata !0, metadata
>>> !1, metadata !"[J]java.lang.Object.<init>()V", metadata
>>> !"[J]java.lang.Object.<init>()V", metadata !"", i32 136, metadata !15, i1
>>> false, i1 true, i32 0, i32 0, null, i32 256, i1 false, void (%Env*,
>>> %Object*)* @"[J]java.lang.Object.<init>()V", null, null, metadata !17, i32
>>> 136}, null}
>>> > %r0 = alloca %Object*
>>> > store %Object* null, %Object** %r0
>>> > call void @"llvm.dbg.declare"(metadata !{%Object** %r0}, metadata
>>> !21), !dbg !{i32 136, i32 0, metadata !14, null}
>>> > store %Object* %p1, %Object** %r0
>>> > call void @"register_finalizable"(%Env* %p0, %Object* %p1), !dbg
>>> !{i32 136, i32 0, metadata !18, null}
>>> > ret void, !dbg !{i32 136, i32 0, metadata !18, null}
>>> > }
>>> > =======================
>>> >
>>> > The corresponding thumbv7 assembler code as generated by LLVM:
>>> >
>>> > =======================
>>> > .globl "_[J]java.lang.Object.<init>()V"
>>> > .align 2
>>> > .code 16 @
>>> @"[J]java.lang.Object.<init>()V"
>>> > .thumb_func "_[J]java.lang.Object.<init>()V"
>>> > "_[J]java.lang.Object.<init>()V":
>>> > .cfi_startproc
>>> > Lfunc_begin18:
>>> > .loc 1 136 0 @ Object.java:136:0
>>> > @ BB#0: @ %label0
>>> > .loc 1 136 0 @ Object.java:136:0
>>> > push {r7, lr}
>>> > mov r7, sp
>>> > sub sp, #4
>>> > @DEBUG_VALUE: [J]java.lang.Object.<init>()V:__$env <- R0
>>> > movs r2, #0
>>> > str r2, [sp]
>>> > str r1, [sp]
>>> > .loc 1 136 0 prologue_end @ Object.java:136:0
>>> > Ltmp6:
>>> > ldr r2, [r1]
>>> > ldr r2, [r2, #48]
>>> > tst.w r2, #1048576
>>> > Ltmp7:
>>> > @DEBUG_VALUE: [J]java.lang.Object.<init>()V:__$env <- R0
>>> > it ne
>>> > blxne __bcRegisterFinalizer
>>> > add sp, #4
>>> > pop {r7, pc}
>>> > Ltmp8:
>>> > Lfunc_end18:
>>> > "L_[J]java.lang.Object.<init>()V_end":
>>> >
>>> > .cfi_endproc
>>> > =======================
>>> >
>>> > Now, when stepping into this function, LLDB receives a signal from the
>>> debug server:
>>> >
>>> > =======================
>>> > (lldb) s
>>> > Process 176 stopped
>>> > * thread #1: tid = 0x11f5, 0x0023e2ec
>>> AttachTestIOSDev`[J]java.lang.Object.<init>(__$env=0x0169efc8,
>>> __$this=0x0174cd10)V + 24 at Object.java:136, queue =
>>> 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION
>>> (code=EXC_ARM_UNDEFINED, subcode=0xffd1b001)
>>> > frame #0: 0x0023e2ec
>>> AttachTestIOSDev`[J]java.lang.Object.<init>(__$env=0x0169efc8,
>>> __$this=0x0174cd10)V + 24 at Object.java:136
>>> > =======================
>>> >
>>> > Disassembling around the PC gives:
>>> >
>>> > =======================
>>> > (lldb) disassemble --pc
>>> > AttachTestIOSDev`[J]java.lang.Object.<init>()V + 24 at Object.java:136:
>>> > -> 0x23e2ec: .long 0xb001ffd1 ; unknown opcode
>>> > 0x23e2f0: pop {r7, pc}
>>> >
>>> > AttachTestIOSDev`[J]java.lang.Object.<init>()V + 30:
>>> > 0x23e2f2: nop
>>> >
>>> > Disassembling until the beginning of the frame gives:
>>> >
>>> > (lldb) disassemble -f
>>> > AttachTestIOSDev`[J]java.lang.Object.<init>()V at Object.java:136:
>>> > 0x23e2d4: push {r7, lr}
>>> > 0x23e2d6: mov r7, sp
>>> > 0x23e2d8: sub sp, #0x4
>>> > 0x23e2da: movs r2, #0x0
>>> > 0x23e2dc: str r2, [sp]
>>> > 0x23e2de: str r1, [sp]
>>> > 0x23e2e0: ldr r2, [r1]
>>> > 0x23e2e2: ldr r2, [r2, #0x30]
>>> > 0x23e2e4: tst.w r2, #0x100000
>>> > 0x23e2e8: it ne
>>> > 0x23e2ea: blne 0x429290 ; _bcRegisterFinalizer
>>> > 0x23e2ee: add sp, #0x4
>>> > 0x23e2f0: pop {r7, pc}
>>> >
>>> > Accprding to this, execution should never end up at address 0x23e2ec.
>>> That's right in the middle of the blne and add instructions in the second
>>> disassembly. I have a hunch that the debugserver on the device may
>>> interfere here, e.g. add a trap instruction to implement the stepping. I'm
>>> not quite sure what to make of it.
>>> >
>>> > I'd appreciate any hints. If you require more information, i got
>>> plenty of logs :)
>>> >
>>> > Thanks,
>>> > Mario
>>> >
>>> > _______________________________________________
>>> > lldb-dev mailing list
>>> > lldb-dev@cs.uiuc.edu
>>> > http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev
>>>
>>>
>>
>
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