Implement split debug symbols

[michaelforney]

It would be really nice to have oasis build everything with debug symbols, and split them off into separate files.

This way, you could select whether you want debug symbols per-package using patterns in config.fs.

[angry-otter]

Hmm, I can take on this one, compiled gdb with pkgsrc, (had to struggle with autoconf and GCC 15 being strict about implicit declarations), when I got gdb compiled, I actually tried passing -ggdb to pax cflags yesterday, to no avail. Ended up with printf :)

[rnpnr]

This way, you could select whether you want debug symbols per-package using patterns in config.fs.

That definitely sounds useful, but in that case wouldn't you also want to be able to specify cflags separately? I find that debug info for optimized programs isn't really that much more useful than not specifying -s in your linker flags (granted I tend to work in single translation unit code where most things get inlined).

[michaelforney]

when I got gdb compiled, I actually tried passing -ggdb to pax cflags yesterday, to no avail. Ended up with printf :)

The problem is probably -s in ldflags, which will strip all the symbols that -ggdb added. Usually my go-to for building debug binaries is adding -O0 -g ta the package/library's cflags, and set('ldflags', '') in the package that built the exe.

I looked at this briefly a few years ago. I think the tricky part is that our link rule now would produce multiple outputs. Either that, or we split it into three actions (link, strip, split). We also need to do something with file to avoid having to specify all the binaries twice.

I had a scripts/split-debug.sh

#!/bin/sh

objcopy --only-keep-debug "$1" "$1.debug"
strip -g "$1"

and then changed the link rule to

rule link
  command = $cc $ldflags -o $out $in $ldlibs && sh $basedir/scripts/split-debug.sh $out
  description =         LINK    $out

[michaelforney]

This way, you could select whether you want debug symbols per-package using patterns in config.fs.

That definitely sounds useful, but in that case wouldn't you also want to be able to specify cflags separately? I find that debug info for optimized programs isn't really that much more useful than not specifying -s in your linker flags (granted I tend to work in single translation unit code where most things get inlined).

That's true, it is pretty difficult to debug with -O2. But, it at least helps you find where something is crashing and gives you a stack trace, which is quite useful. Edit: you probably get most of that without -s, but I still think it's useful to find generally what's going wrong (until you hit the dreaded <optimized out>).

I think per-package cflags might be nice. Are there other use-cases you can think of besides -O0?

[angry-otter]

The problem is probably -s in ldflags, which will strip all the symbols that -ggdb added. Usually my go-to for building debug binaries is adding -O0 -g ta the package/library's cflags, and set('ldflags', '') in the package that built the exe.

yep, it is probably -s... that forces the executable to be stripped, It was late, did a fallback on printfs. :-) But willing to work on this feature.