Support debug fission using -Csplit-debuginfo=post-link

[bjorn3]

Proposal

On macOS and Windows -Csplit-debuginfo=packed puts all debuginfo in a separate file. This avoids leaking sensitive information into release executables while still allowing debugging with those debuginfo files and reduces file size. On Linux however we make use of dwarf split debuginfo, which puts a fair amount of information into the executable itself, leaking sensitive data like build paths, and increases the size of executables. Instead I propose to add an option to use debug fission where the debuginfo sections are copied out of the executable into a separate file and buildid is used to be able to locate the right debuginfo file. This is what all major linux distros use for debuginfo. This disadvantage over the current scheme is longer linking time, but for local development -Csplit-debuginfo=unpacked is a better choice anyway, which I propose to keep using dwarf split debuginfo as is. This way -Csplit-debuginfo=unpacked is the best choice for local development and the new -Csplit-debuginfo=post-link is the best choice for release builds across all platforms that support the respective options. -Csplit-debuginfo=post-link would be equivalent to -Csplit-debuginfo=packed on Windows and macOS.

Mentors or Reviewers

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[rustbot]

This issue is not meant to be used for technical discussion. There is a Zulip stream for that. Use this issue to leave procedural comments, such as volunteering to review, indicating that you second the proposal (or third, etc), or raising a concern that you would like to be addressed.

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cc @rust-lang/compiler @rust-lang/compiler-contributors

[michaelwoerister]

@rustbot second

Thanks, @bjorn3!

[apiraino]

@rustbot label -final-comment-period +major-change-accepted