Crate rucc_debug 

DWARF 5 generation.

Design: spec/11-asm-objects-debug.md. Layer rank 10, see spec/18-package-layout.md.

Status

The line table and nothing else. write() takes one unit’s worth of addresses and the places in the source they came from and gives back the sections that say so, which is enough for addr2line to answer a program counter with a file and a line and not enough for a debugger to print a variable. The rest of M8 is tamnd/rucc#9.

The reason that part came first is tamnd/rucc#1558. A report from the safety monitor carries a program counter and deliberately carries no source location, because spec/safe-memory/06-instrumentation.md section 6.5 would rather have one line table than two that can disagree, and that only works once there is one. Until there was, every report out of a corpus run had to be read backwards out of a disassembly.

Every crate in the workspace is published, and publishing implies a promise. This one is tier 3: its Rust API is explicitly unstable and will change without a major version bump. Depend on the rucc binary’s behaviour, not on this.

Two things still waiting

Options::prefix_map in rucc-session holds a debug list, which is what -fdebug-prefix-map= and -ffile-prefix-map= put there. Every path that reaches Unit has already been through PrefixMap::apply, because that is the whole reason a distribution passes those flags and because a build is only reproducible if all of the paths in it are rewritten rather than most. The rewriting is the driver’s rather than this crate’s for one reason: the driver is where a path is still a path, and by the time one arrives here it is a string in a table that nothing is allowed to reinterpret.

Options::compress is the other, and it is what -gz put there. Every debug section this crate hands to the object writer has to be compressed the way that field says, which for Compress::ZlibGnu also means the section is named .zdebug_info rather than .debug_info and carries a ZLIB tag and a length instead of an Elf64_Chdr. Compressing the sections is worth more than anything else a distribution shipping debug symbols passes, so a build that asked for it and got a file twice the size it expected has a real complaint. Nothing reads it yet, and on a line table alone the saving is smaller than it will be.

Structs

Function

One function, and where each of its instructions came from.

Row

One row of the table: an address, and where the code at it came from.

Unit

One compilation unit’s worth of line information.

Enums

Error

What went wrong while the sections were being built.

Constants

MILESTONE

The milestone in spec/17-milestones.md that fills this crate in.

Functions

write

The sections a unit’s line information goes in.