https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95574
Bug ID: 95574
Summary: line table entry in sequence with address after
sequence
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: vries at gcc dot gnu.org
Target Milestone: ---
When doing a build from current trunk, I get the following in the .debug_line
section of build/x86_64-pc-linux-gnu/libgcc/libgcc_s.so.1:
...
[0x000006f5] Special opcode 75: advance Address by 5 to 0x2faa and Line by 0
to 246
[0x000006f6] Advance PC by 0 to 0x2faa
[0x000006f8] Extended opcode 1: End of Sequence
...
This is nonsensical dwarf: both the special opcode and the End-Of-Sequence
declare a row in the matrix, each with the same address.
The special opcode declares a target instruction at that address.
The End-of-Sequence declares that the sequence ends before that address.
It's a contradiction that the target instruction is both part of the sequence
(according to Copy) and not part of the sequence (according to
End-of-Sequence).
[ Relevant dwarf standard bits:
end_sequence:
A boolean indicating that the current address is that of the first byte
after the end of a sequence of target machine instructions. end_sequence
terminates a sequence of lines; therefore other information in the same
row is not meaningful.
Special Opcodes
Each ubyte special opcode has the following effect on the state machine:
1. Add a signed integer to the line register.
2. Modify the operation pointer by incrementing the address and op_index
registers as described below.
3. Append a row to the matrix using the current values of the state machine
registers.
DW_LNE_end_sequence:
The DW_LNE_end_sequence opcode takes no operands. It sets the
end_sequence register of the state machine to “true” and appends a row
to the matrix using the current values of the state-machine registers.
Then it resets the registers to the initial values specified above (see
Section 6.2.2). Every line number program sequence must end with a
DW_LNE_end_sequence instruction which creates a row whose address is
that of the byte after the last target machine instruction of the sequence.
]
