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Export ZERO_AR_DATE for macos linker invocations 

This commit attempts to improve reproducibility of builds on macOS by
exporting the `ZERO_AR_DATE=1` environment variable for all invocations
of the linker. While it looks like this env var is targeted at just the
`ar` command (which does actually read this) it appears that recent-ish
versions of the linker *also* read this environment variable. This
env var forces the linker to set a deterministic zero value for the
mtime in the N_OSO field of the object file.

Currently it's believe that older versions of the linker will simply
ignore this env var, while newer versions will read it and produce a
deterministic output for compilations with debuginfo.

Closes #47086
Closes #66568
This commit is contained in:
Alex Crichton 2020-05-05 14:25:58 -07:00
parent cb272d5d21
commit afd88f2a33
2 changed files with 12 additions and 2 deletions
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11
src/librustc_target/spec/apple_base.rs
View File

@ -31,6 +31,17 @@ pub fn opts() -> TargetOptions {
has_elf_tls: version >= (10, 7),
abi_return_struct_as_int: true,
emit_debug_gdb_scripts: false,
// 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.
//
// For some more info see the commentary on #47086
link_env: vec![("ZERO_AR_DATE".to_string(), "1".to_string())],
..Default::default()
}
}

3
src/test/run-make-fulldeps/reproducible-build-2/Makefile
View File

@ -2,7 +2,6 @@
# ignore-musl
# ignore-windows
# ignore-macos (rust-lang/rust#66568)
# Objects are reproducible but their path is not.
all: \
@ -21,7 +20,7 @@ sysroot:
rm -rf $(TMPDIR) && mkdir $(TMPDIR)
$(RUSTC) reproducible-build-aux.rs
$(RUSTC) reproducible-build.rs --crate-type rlib --sysroot $(shell $(RUSTC) --print sysroot) --remap-path-prefix=$(shell $(RUSTC) --print sysroot)=/sysroot
cp -r $(shell $(RUSTC) --print sysroot) $(TMPDIR)/sysroot
cp -R $(shell $(RUSTC) --print sysroot) $(TMPDIR)/sysroot
cp $(TMPDIR)/libreproducible_build.rlib $(TMPDIR)/libfoo.rlib
$(RUSTC) reproducible-build.rs --crate-type rlib --sysroot $(TMPDIR)/sysroot --remap-path-prefix=$(TMPDIR)/sysroot=/sysroot
cmp "$(TMPDIR)/libreproducible_build.rlib" "$(TMPDIR)/libfoo.rlib" || exit 1