A compile unit can produce a debug_line program consisting of multiple
sequences according to the DWARF standard. The standard guarantees that
addresses monotonically increment within a single sequence but
different sequences may not follow this rule.
This commit changes dwarf/line (in particular PCToLine and
AllPCsBetween) to support debug_line sections containing units with
multiple sequences.
TestPCToLine needs to be changed so that it picks valid addresses (i.e.
addresses covered by a sequence) as values for basePC, instead of just
rounding.
Fixes#1694
Support for position independent executables (PIE) on the native linux
backend, the gdbserver backend on linux and the core backend.
Also implemented in the windows native backend, but it can't be tested
because go doesn't support PIE on windows yet.
Adds a test that compares the output of our state machine with the
output of the debug_line reader in the standard library and checks that
they produce the same output for the debug_line section of grafana as
compiled on macOS (which is the most interesting case since it uses cgo
and therefore goes through dsymutil).
A few bugs were uncovered and fixed:
1. is_stmt was reset improperly after a DW_LNS_end_sequence instruction
2. basic_block, prologue_end and epilogue_begin were not reset after a
DW_LNS_copy instruction
3. some opcodes were not decoded properly if the debug_line section
declares fewer standard opcodes than we know about.
Fixes#1282
