cmd/link: debug_line incomplete when using cgo with some versions of dsymutil [Debugging] #25451
Description
This is a duplicate of #25392, I actually posted this on that issue yesterday but it was already closed and I think nobody saw it. I think that issue should be reopened.
It looks like some (most?) versions of dsymutil do not support (but see below) version 3 for debug_line, including the most recent version of dsymutil on 10.12.
If 10.12 is still considered supported this breaks backwards compatibility.
Now, Saying that dsymutil doesn't support v3 is incomplete, it seems that it actually does, but only if you lie to it and say it's v2. For example this is what the line table of a compilation unit produced by clang looks like in the final executable:
Offset: 0x2b3fc
Length: 154
DWARF Version: 2
Prologue Length: 30
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
Note how it says version 2 but has more than 9 standard opcodes.
The choice is between lying, pretending 10.12 doesn't exist or reverting the prologueEnd thing.