Assure dwarf debug info stays correct in dist builds

[drahnr]

With the recently landed PR #116 we have basic support.

One of the remaining questions, is the effect on debug info paths.

If they are intact, that's awesome! If not, well.. parsing the return object file and parsing the paths and manually remapping them by usage of i.e. gimli might be an option.

[montekki]

AFAIU the only thing in DWARF pointing to compdir would be the DW_AT_comp_dir variable and it looks like --remap-path-prefix successfully modifies it.

In my case --remap-path-prefix /home/$USERNAME/=/tmp creates this info:

llvm-dwarfdump ./target/debug/ttt | head -n 20
./target/debug/ttt:     file format elf64-x86-64

.debug_info contents:
0x00000000: Compile Unit: length = 0x0000004c, format = DWARF32, version = 0x0004, abbr_offset = 0x0000, addr_size = 0x08 (next unit at 0x00000050)

0x0000000b: DW_TAG_compile_unit
              DW_AT_producer    ("clang LLVM (rustc version 1.58.1 (db9d1b20b 2022-01-20))")
              DW_AT_language    (DW_LANG_Rust)
              DW_AT_name        ("src/main.rs")
              DW_AT_stmt_list   (0x00000000)
              DW_AT_comp_dir    ("/tmp/ttt")
              DW_AT_GNU_pubnames        (true)
              DW_AT_low_pc      (0x00000000000085d0)
              DW_AT_high_pc     (0x00000000000085d2)

0x0000002a:   DW_TAG_namespace
                DW_AT_name      ("core")

0x0000002f:     DW_TAG_namespace
                  DW_AT_name    ("hint")

[drahnr]

That'd mean we could just modify the comp_dir on retrieval and modify that for local debug symbol resolution, or do we need to touch that at all?

[montekki]

As soon as you command cachepot to do directory remapping as in #116 cachepot you will end up with the intended paths in DWARF as well. In other words you do not need to do anything extra atm.