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--compress-sections is similar to --compress-debug-sections but applies to arbitrary sections. * `--compress-sections <section>=none`: decompress sections * `--compress-sections <section>=[zlib|zstd]`: compress sections with zlib/zstd Like `--remove-section`, the pattern is by default a glob, but a regex when --regex is specified. For `--remove-section` like options, `!` prevents matches and is not dependent on ordering (see `ELF/wildcard-syntax.test`). Since `--compress-sections a=zlib --compress-sections a=none` naturally allows overriding, having an order-independent `!` would be confusing. Therefore, `!` is disallowed. Sections within a segment are effectively immutable. Report an error for an attempt to (de)compress them. `SHF_ALLOC` sections in a relocatable file can be compressed, but linkers usually reject them. Note: Before this patch, a compressed relocation section is recognized as a `RelocationSectionBase` as well and `removeSections` `!ToRemove(*ToRelSec)` may incorrectly interpret a `CompressedSections` as `RelocationSectionBase`, leading to ubsan failure for the new test. Fix this by setting `OriginalFlags` in CompressedSection::CompressedSection. Link: https://discourse.llvm.org/t/rfc-compress-arbitrary-sections-with-ld-lld-compress-sections/71674 Pull Request: https://github.com/llvm/llvm-project/pull/85036