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bintools-wrapper: specify SHA1 as the build-id hash style explicitly

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NixOS/nixpkgs#146275 has more discussion on this; the abridged version
is that `lld` defaults to using `--build-id=fast` while GNU `ld` defaults
to `--build-id=sha1`. These differ in length and so
`separate-debug-info.sh`, as of this writing, errors on `lld`'s shorter
`--build-id=fast`-generated hashes.

`lld` offers the following `build-id` styles:
  - UUID (random; fast but bad for reproducibility)
  - fast (xxhash; fast but shorter hashes)
  - user provided hexstring
  - SHA1
  - MD5

GNU `ld` supports the latter three options, `mold` supports all of these
plus SHA256.

UUID is out because it's not reproducible, fast isn't supported by GNU
`ld`

Using a nix provided (sourced from the output base hash) hash as the
`build-id` seems tempting but would require a little extra work
(we have to include some characteristic of the binary being hashed
so that binaries within a derivation still have unique hashes; it
seems easy to get this wrong; i.e. a path based approach would make
two otherwise identical binaries that reside at different paths have
different `build-id` hashes)

That leaves SHA1 and MD5 and GNU `ld` already defaults to the former.

This commit adds `$NIX_BUILD_ID_STYLE` as an escape hatch, in case any
packages have strong opinions about which hash to use.

----

Note that if/when NixOS/nixpkgs#146275 goes through, this change can be
reverted if linker speed is a priority.
This commit is contained in:
Rahul Butani 2023-02-25 12:02:24 -06:00
parent 504c4fdc34
commit b41933a1be
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1 changed files with 4 additions and 1 deletions
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5
pkgs/build-support/bintools-wrapper/ld-wrapper.sh
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@ -232,8 +232,11 @@ fi
# Only add --build-id if this is a final link. FIXME: should build gcc # Only add --build-id if this is a final link. FIXME: should build gcc
# with --enable-linker-build-id instead? # with --enable-linker-build-id instead?
#
# Note: `lld` interprets `--build-id` to mean `--build-id=fast`; GNU ld defaults
# to SHA1.
if [ "$NIX_SET_BUILD_ID_@suffixSalt@" = 1 ] && ! (( "$relocatable" )); then if [ "$NIX_SET_BUILD_ID_@suffixSalt@" = 1 ] && ! (( "$relocatable" )); then
extraAfter+=(--build-id) extraAfter+=(--build-id="${NIX_BUILD_ID_STYLE:-sha1}")
fi fi