guix: map the whole DISTSRC in -fdebug-prefix-map #36708

Fixes #34414.

Why

The Guix build scripts set -fdebug-prefix-map=${DISTSRC}/src=.. Generated sources (for example the capnp proxies) are in the build tree, outside ${DISTSRC}/src, so their debug info kept the absolute /distsrc-base/distsrc-<commit>-<host>/build/... path. Sources from src/ were relative. With two kinds of paths, it is hard to set up source path mapping in a debugger.

This maps ${DISTSRC} instead, in build_linux.sh, build_linux_gui.sh, build_win.sh and build_win_gui.sh. The macOS scripts do not set -fdebug-prefix-map, so this PR does not change them.

What changes in the debug paths

All source paths are now relative to the repository root:

To find the sources in gdb, use the repository root as the source directory (directory /path/to/bitcoin) instead of src/.

How I checked

• Guix build of this change on an x86_64 build machine, for the six Linux and Windows hosts.
• readelf --debug-dump=info, --debug-dump=rawline and --debug-dump=str of libexec/bitcoin-node.dbg (x86_64-linux-gnu): no distsrc string. Sources show as ./src/..., generated capnp files as ./build/src/....
• bitcoind.exe.dbg from the Windows debug zip: no distsrc string.
• The only absolute paths left come from the Guix toolchain (glibc, libgcc). This change does not affect them.

I will post the Guix hashes for this commit in a comment. I do not have an aarch64 build machine at the moment, so a build from someone with one is welcome.

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External sites

• Code coverage & benchmarks: https://corecheck.dev/bitcoin/bitcoin/pulls/36708
• Ralph review <img src=https://review.fish.foo/assets/bitcoin/bitcoin/36708.png alt="Ralph review status"> https://git.fish.foo/bitcoin/bitcoin/pulls/36708#author-ralph

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #36270 _{<img src="https://drahtbot.space/ack_count/bitcoin/bitcoin/36270.svg">} (build: ensure release binaries don't contain depends references by fanquake)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

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Guix build of 00867d70c01b (x86_64 build machine):

x86_64
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Guix builds (on x86_64) [untrusted test-only build, possibly unsafe, not for production use]

Hmm, I was thinking this is a nice change, but I am not so sure now. Maybe this and the issue should just be closed?

Recall that there is still plenty of stuff not mapped, like /bitcoin/depends/..., or /usr/include/.... So mapping capnp seems like a rounding error that doesn't really matter? (Recall a user won't have the build dir anyway for this guix release build)

So I think this can still be done, but I think it would mostly be a "style cleanup".

Hmm, I was thinking this is a nice change, but I am not so sure now. Maybe this and the issue should just be closed?

Recall that there is still plenty of stuff not mapped, like /bitcoin/depends/..., or /usr/include/.... So mapping capnp seems like a rounding error that doesn't really matter? (Recall a user won't have the build dir anyway for this guix release build)

So I think this can still be done, but I think it would mostly be a "style cleanup".

Fair point. I checked the line tables of bitcoin-node.dbg from my build, and after this change about a third of the source directories are still absolute (/bitcoin/depends/..., /usr/include/..., plus the toolchain's /tmp/guix-build-...). So the capnp mapping alone does not give fully relative debug info, and it is mostly cosmetic. Feel free to close this one.

do you think mapping of all paths, including depends, be worth it, or is it not worth the review? I'm ok to do update this one if you think so.

#36709 is separate: it fixes a real build failure with --system, which I hit while trying to test this PR.

See also #36270, but that just re-writes the path and the user would still have to fetch the sources themselves (and likely rewrite the debug paths themselves again)

I think I'll close this for now. The changes are fine, but as a pure style cleanup, it may be not worth it. Let's wait until the motivation is stronger and then re-open.