llvm/llvm-project

llvm-objcopy crashes with unreachable error when (de)compression requested without selected value available

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#197877 opened on May 15, 2026

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good first issuetools:llvm-objcopy/strip

Description

llvm-objcopy crashes due to calling llvm_unreachable when compression::compress or compression::decompress is called without the selected compression type being installed on the machine.

The problem is that the tool doesn't call compression::getReasonIfUnsupported before compression::compress or compression::decompress. The correct thing to do is to call that first, then check the result and either report an Error based on the result or continuing and (de)compress as requested.

Discovered while triaging #197813.

I'll label this with good first issue as it's a trivial fix (but I don't have the personal time to fix it and put a PR up myself). There should be two tests for it. The first test should test that the correct error is emitted for zlib compression and decompression and the second the same for zstd. Each test should only run if zlib/zstd is NOT enabled on the target (i.e. something like UNSUPPORTED: zlib, but check other examples for REQUIRES/UNSUPPORTED tags to see the exact way of writing that).

Contributor guide

Tech stack
cpp
Domain
clitooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
C++LLVM basicstesting fundamentals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
80
Research direction
Modify llvm objcopy to call compression::getReasonIfUnsupported before compression::compress or decompress, and report any error returned. Create two test files in llvm/test/tools/llvm objcopy for zlib and zstd, using UNSUPPORTED tags to ensure they run only when the respective library is not enabled. Refer to existing tests for the exact syntax of UNSUPPORTED and REQUIRES.