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Oct 1, 2025
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Improve the documentation around ZERO_AR_DATE #146518

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16 changes: 13 additions & 3 deletions compiler/rustc_target/src/spec/base/apple/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -158,12 +158,22 @@ pub(crate) fn base(
SplitDebuginfo::Off,
]),

// Tell the linker that we would like it to avoid irreproducible binaries.
//
// This environment variable is pretty magical but is intended for
// producing deterministic builds. This was first discovered to be used
// by the `ar` tool as a way to control whether or not mtime entries in
// the archive headers were set to zero or not. It appears that
// eventually the linker got updated to do the same thing and now reads
// this environment variable too in recent versions.
// the archive headers were set to zero or not.
//
// In `ld64-351.8`, shipped with Xcode 9.3, the linker was updated to
// read this flag too. Linker versions that don't support this flag
// may embed modification timestamps in binaries (especially in debug
// information).
//
// A cleaner alternative would be to pass the `-reproducible` flag,
// though that is only supported since `ld64-819.6` shipped with Xcode
// 14, which is too new for our minimum supported version:
// https://doc.rust-lang.org/rustc/platform-support/apple-darwin.html#host-tooling
//
// For some more info see the commentary on #47086
link_env: Cow::Borrowed(&[(Cow::Borrowed("ZERO_AR_DATE"), Cow::Borrowed("1"))]),
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