[haiku-bugs] [Haiku] #10459: [Debugger] Investigate anomalous single stepping behavior
- From: "anevilyak" <trac@xxxxxxxxxxxx>
- Date: Thu, 23 Jan 2014 02:42:00 -0000
#10459: [Debugger] Investigate anomalous single stepping behavior
-----------------------------------+------------------------------
Reporter: anevilyak | Owner: anevilyak
Type: bug | Status: new
Priority: normal | Milestone: R1
Component: Applications/Debugger | Version: R1/Development
Keywords: | Blocked By:
Blocking: | Has a Patch: 0
Platform: All |
-----------------------------------+------------------------------
In certain instances, some unusual single stepping behavior can be
observed, as seen in the attached example program. If one steps through
the program until hitting line 19, the next single step would be expected
to jump to either the closing scope line of the current block (line 22),
or the closing line of the function (line 25).
With gcc2, the latter is observed as expected. With gcc4 however, the next
step unexpectedly takes us to line 21 instead. There are some differences
in the generated line number programs between the two compilers, but at
least a cursory glance through our state machine implementation doesn't
reveal any obvious problems in handling the involved opcodes. It should
further be noted that this behavior is only observed when the locally
scoped object is declared at line 15 ; without it, behavior similar to
gcc2 is observed.
Needs further investigation, and probably some additional tracing output
to allow us to better compare our state machine execution with the
corresponding output of objdump for the line number program in question.
One possible candidate that gcc4 emits that gcc2 does not is the
discriminator, but the DWARF specification is quite vague on how to
actually make use of that apart from simply parsing the corresponding
instruction/value.
Objdump output for gcc2:
{{{
Raw dump of debug contents of section .debug_line:
Offset: 0x0
Length: 252
DWARF Version: 2
Prologue Length: 46
Minimum Instruction Length: 4
Initial value of 'is_stmt': 1
Line Base: -10
Line Range: 245
Opcode Base: 10
Opcodes:
Opcode 1 has 0 args
Opcode 2 has 1 args
Opcode 3 has 1 args
Opcode 4 has 1 args
Opcode 5 has 1 args
Opcode 6 has 0 args
Opcode 7 has 0 args
Opcode 8 has 0 args
Opcode 9 has 1 args
The Directory Table is empty.
The File Name Table:
Entry Dir Time Size Name
1 0 0 0 steptest.cpp
2 0 0 0 <internal>
Line Number Statements:
Extended opcode 2: set Address to 0xa30
Special opcode 20: advance Address by 0 to 0xa30 and Line by 10 to 11
Extended opcode 2: set Address to 0xa43
Special opcode 11: advance Address by 0 to 0xa43 and Line by 1 to 12
Extended opcode 2: set Address to 0xa4a
Special opcode 11: advance Address by 0 to 0xa4a and Line by 1 to 13
Extended opcode 2: set Address to 0xa4a
Special opcode 11: advance Address by 0 to 0xa4a and Line by 1 to 14
Extended opcode 2: set Address to 0xa4a
Special opcode 11: advance Address by 0 to 0xa4a and Line by 1 to 15
Extended opcode 2: set Address to 0xa59
Special opcode 11: advance Address by 0 to 0xa59 and Line by 1 to 16
Extended opcode 2: set Address to 0xa5f
Special opcode 11: advance Address by 0 to 0xa5f and Line by 1 to 17
Extended opcode 2: set Address to 0xa80
Special opcode 11: advance Address by 0 to 0xa80 and Line by 1 to 18
Extended opcode 2: set Address to 0xa89
Special opcode 11: advance Address by 0 to 0xa89 and Line by 1 to 19
Extended opcode 2: set Address to 0xaa6
Special opcode 11: advance Address by 0 to 0xaa6 and Line by 1 to 20
Extended opcode 2: set Address to 0xaaf
Special opcode 11: advance Address by 0 to 0xaaf and Line by 1 to 21
Extended opcode 2: set Address to 0xae8
Special opcode 13: advance Address by 0 to 0xae8 and Line by 3 to 24
Extended opcode 2: set Address to 0xb63
Special opcode 11: advance Address by 0 to 0xb63 and Line by 1 to 25
Extended opcode 2: set Address to 0xb6c
Special opcode 14: advance Address by 0 to 0xb6c and Line by 4 to 29
Extended opcode 2: set Address to 0xb7f
Special opcode 11: advance Address by 0 to 0xb7f and Line by 1 to 30
Extended opcode 2: set Address to 0xb84
Special opcode 12: advance Address by 0 to 0xb84 and Line by 2 to 32
Extended opcode 2: set Address to 0xb8c
Special opcode 11: advance Address by 0 to 0xb8c and Line by 1 to 33
Extended opcode 2: set Address to 0xb97
Extended opcode 1: End of Sequence
Extended opcode 2: set Address to 0xb98
Special opcode 12: advance Address by 0 to 0xb98 and Line by 2 to 3
Extended opcode 2: set Address to 0xbc7
Extended opcode 1: End of Sequence
Extended opcode 2: set Address to 0xbd0
Special opcode 13: advance Address by 0 to 0xbd0 and Line by 3 to 4
Extended opcode 2: set Address to 0xc1d
Extended opcode 1: End of Sequence
Extended opcode 2: set Address to 0xc20
Special opcode 42: advance Address by 0 to 0xc20 and Line by 32 to 33
Extended opcode 2: set Address to 0xc6c
Extended opcode 1: End of Sequence
}}}
Objdump output for gcc4:
{{{
Raw dump of debug contents of section .debug_line:
Offset: 0x0
Length: 127
DWARF Version: 2
Prologue Length: 35
Minimum Instruction Length: 1
Initial value of 'is_stmt': 1
Line Base: -5
Line Range: 14
Opcode Base: 13
Opcodes:
Opcode 1 has 0 args
Opcode 2 has 1 args
Opcode 3 has 1 args
Opcode 4 has 1 args
Opcode 5 has 1 args
Opcode 6 has 0 args
Opcode 7 has 0 args
Opcode 8 has 0 args
Opcode 9 has 1 args
Opcode 10 has 0 args
Opcode 11 has 0 args
Opcode 12 has 1 args
The Directory Table is empty.
The File Name Table:
Entry Dir Time Size Name
1 0 0 0 steptest.cpp
Line Number Statements:
Extended opcode 2: set Address to 0x952
Special opcode 7: advance Address by 0 to 0x952 and Line by 2 to 3
Special opcode 201: advance Address by 14 to 0x960 and Line by 0 to 3
Advance PC by 26 to 0x97a
Extended opcode 1: End of Sequence
Extended opcode 2: set Address to 0x97a
Special opcode 8: advance Address by 0 to 0x97a and Line by 3 to 4
Advance PC by constant 17 to 0x98b
Special opcode 19: advance Address by 1 to 0x98c and Line by 0 to 4
Extended opcode 4: set Discriminator to 1
Set is_stmt to 0
Advance PC by 36 to 0x9b0
Special opcode 5: advance Address by 0 to 0x9b0 and Line by 0 to 4
Special opcode 201: advance Address by 14 to 0x9be and Line by 0 to 4
Advance PC by 5 to 0x9c3
Extended opcode 1: End of Sequence
Extended opcode 2: set Address to 0x9c4
Special opcode 8: advance Address by 0 to 0x9c4 and Line by 3 to 4
Advance PC by constant 17 to 0x9d5
Special opcode 19: advance Address by 1 to 0x9d6 and Line by 0 to 4
Advance PC by 33 to 0x9f7
Extended opcode 1: End of Sequence
Extended opcode 2: set Address to 0x898
Advance Line by 10 to 11
Copy
Advance PC by constant 17 to 0x8a9
Special opcode 48: advance Address by 3 to 0x8ac and Line by 1 to 12
Special opcode 106: advance Address by 7 to 0x8b3 and Line by 3 to 15
Special opcode 216: advance Address by 15 to 0x8c2 and Line by 1 to 16
Special opcode 90: advance Address by 6 to 0x8c8 and Line by 1 to 17
Special opcode 174: advance Address by 12 to 0x8d4 and Line by 1 to 18
Special opcode 132: advance Address by 9 to 0x8dd and Line by 1 to 19
Special opcode 174: advance Address by 12 to 0x8e9 and Line by 1 to 20
Special opcode 132: advance Address by 9 to 0x8f2 and Line by 1 to 21
Advance PC by 37 to 0x917
Special opcode 8: advance Address by 0 to 0x917 and Line by 3 to 24
Special opcode 104: advance Address by 7 to 0x91e and Line by 1 to 25
Special opcode 121: advance Address by 8 to 0x926 and Line by 4 to 29
Advance PC by constant 17 to 0x937
Special opcode 132: advance Address by 9 to 0x940 and Line by 1 to 30
Special opcode 77: advance Address by 5 to 0x945 and Line by 2 to 32
Special opcode 76: advance Address by 5 to 0x94a and Line by 1 to 33
Advance PC by 7 to 0x951
Extended opcode 1: End of Sequence
}}}
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Ticket URL: <https://dev.haiku-os.org/ticket/10459>
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