Re: Reproducible rust builds

[Joe Hillenbrand <joehillen@gmail.com>]

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Hi Nikolai,

I've been trying to make rust reproducible as well.

I starting with version 1.19, but I think you're right to just skip
anything older than 1.25 as it looks like a bunch of reproducibility fixes were
added to cargo and rust around 1.22.

What kind of differences are you getting from between the builds?
For me, it has been liblibc. I've attached the output of the following command:

$ diffoscope --exclude-directory-metadata
/gnu/store/hv2wb30jgzhhgfvlhrfpk3qcwr38igg4-rust-1.22.1
/gnu/store/hv2wb30jgzhhgfvlhrfpk3qcwr38igg4-rust-1.22.1-check --html
diffoscope-rust.html

On Fri, Oct 12, 2018 at 3:44 PM Nikolai Merinov
<nikolai.merinov@member.fsf.org> wrote:
> 2. Rust 1.26.2 reproducible with LLVM 6.0.1 regardless of which LLVM
> used for rust 1.25.0. I failed to find any specific changes that allow
> this version to be built in reproducible manner with LLVM 6.0.1.

How sure are you that 1.26.2 is reproducible? I noticed that sometimes it will
work after 2 rounds and sometimes it won't.

I've pulled your repo and started a build with 4 rounds just to check.
It will probably take a couple of days.

You might also try adding the attached patch I grabbed from Debian.
I haven't gotten it to work yet, but maybe it will help you.

Thanks,
-Joe

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Description: Don't split dwarf debug for a fully-reproducible build
Author: Ximin Luo <infinity0@debian.org>
Bug: https://github.com/rust-lang/rust/issues/34902

--- a/src/librustc_llvm/build.rs
+++ b/src/librustc_llvm/build.rs
@@ -140,6 +140,11 @@
     let mut cfg = cc::Build::new();
     cfg.warnings(false);
     for flag in cxxflags.split_whitespace() {
+        // Split-dwarf gives unreproducible DW_AT_GNU_dwo_id so don't do it
+        if flag == "-gsplit-dwarf" {
+            continue;
+        }
+
         // Ignore flags like `-m64` when we're doing a cross build
         if is_crossed && flag.starts_with("-m") {
             continue;