Rollup of 4 pull requests #90276
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Rollup of 4 pull requests #90276
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This change adds a new compiler flag that can help reduce the size of ELF binaries that contain many functions. By default, when enabling function sections (which is the default for most targets), the LLVM backend will generate different section names for each function. For example, a function "func" would generate a section called ".text.func". Normally this is fine because the linker will merge all those sections into a single one in the binary. However, starting with LLVM 12 (llvm/llvm-project@ee5d1a0), the backend will also generate unique section names for exception handling, resulting in thousands of ".gcc_except_table.*" sections ending up in the final binary because some linkers don't currently merge or strip these EH sections. This can bloat the ELF headers and string table significantly in binaries that contain many functions. The new option is analogous to Clang's -fno-unique-section-names, and instructs LLVM to generate the same ".text" and ".gcc_except_table" section for each function, resulting in smaller object files and potentially a smaller final binary.
And add a rustdoc-gui test confirming various header sizes.
…, r=jyn514,camelid,notriddle Fix clippy lints in librustdoc I ran clippy on librustdoc and simply fixed the lints. :) r? `@notriddle`
Add -Z no-unique-section-names to reduce ELF header bloat. This change adds a new compiler flag that can help reduce the size of ELF binaries that contain many functions. By default, when enabling function sections (which is the default for most targets), the LLVM backend will generate different section names for each function. For example, a function `func` would generate a section called `.text.func`. Normally this is fine because the linker will merge all those sections into a single one in the binary. However, starting with [LLVM 12](llvm/llvm-project@ee5d1a04), the backend will also generate unique section names for exception handling, resulting in thousands of `.gcc_except_table.*` sections ending up in the final binary because some linkers like LLD don't currently merge or strip these EH sections (see discussion [here](https://reviews.llvm.org/D83655)). This can bloat the ELF headers and string table significantly in binaries that contain many functions. The new option is analogous to Clang's `-fno-unique-section-names`, and instructs LLVM to generate the same `.text` and `.gcc_except_table` section for each function, resulting in a smaller final binary. The motivation to add this new option was because we have a binary that ended up with so many ELF sections (over 65,000) that it broke some existing ELF tools, which couldn't handle so many sections. Here's our old binary: ``` $ readelf --sections old.elf | head -1 There are 71746 section headers, starting at offset 0x2a246508: $ readelf --sections old.elf | grep shstrtab [71742] .shstrtab STRTAB 0000000000000000 2977204c ad44bb 00 0 0 1 ``` That's an 11MB+ string table. Here's the new binary using this option: ``` $ readelf --sections new.elf | head -1 There are 43 section headers, starting at offset 0x29143ca8: $ readelf --sections new.elf | grep shstrtab [40] .shstrtab STRTAB 0000000000000000 29143acc 0001db 00 0 0 1 ``` The whole binary size went down by over 20MB, which is quite significant.
…omez Fix documentation header sizes And add a rustdoc-gui test confirming various header sizes. Split off from rust-lang#90156. This fixes a regression in rust-lang#89506 where the heading level of titles within Markdown was too high (h2) for docblocks under structs, unions, and enum impls. r? ``@camelid`` Demo: https://jacob.hoffman-andrews.com/rust/fix-header-sizes/std/string/struct.String.html#impl-Add%3C%26%27_%20str%3E Stable: https://doc.rust-lang.org/stable/std/string/struct.String.html#impl-Add%3C%26%27_%20str%3E Beta: https://doc.rust-lang.org/beta/std/string/struct.String.html#impl-Add%3C%26%27_%20str%3E
…=lnicola ⬆️ rust-analyzer r? ~~`@ghose~~` sorry, `@ghost`
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@bors r+ p=4 rollup=never |
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📌 Commit 57655d9 has been approved by |
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⌛ Testing commit 57655d9 with merge e3278758c43b4d9d62c5989182c5a76c30407d8a... |
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r? @ghost
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