[ELF] Change build-id default to sha1 #93943
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@llvm/pr-subscribers-lld @llvm/pr-subscribers-lld-elf Author: Tatsuyuki Ishi (ishitatsuyuki) ChangesThe current default, build-id=fast, is only 8 bytes due to the usage of 64-bit XXH3. This is incompatible with RPM packaging tools which requires >=16 bytes 1. In Clang the ENABLE_LINKER_BUILD_ID define makes it pass --build-id without a specific hash type. When also defaulting to LLD, this provides a pretty broken default out-of-box. Using XXH3 was a considerable performance advantage when build-id was first implemented, because sha1 was really sha1 and rather slow. Nowadays sha1 is just 160-bit BLAKE3 which is decently fast and not cryptographically broken, so it should be a good default. Note that the default remains "fast" for wasm because sha1 for wasm is still real sha1. Close #43483. Full diff: https://github.com/llvm/llvm-project/pull/93943.diff 2 Files Affected:
diff --git a/lld/ELF/Options.td b/lld/ELF/Options.td
index ff61a566f52f7..54c6f51b28f36 100644
--- a/lld/ELF/Options.td
+++ b/lld/ELF/Options.td
@@ -57,7 +57,7 @@ def Bstatic: F<"Bstatic">, HelpText<"Do not link against shared libraries">;
def build_id: J<"build-id=">, HelpText<"Generate build ID note">,
MetaVarName<"[fast,md5,sha1,uuid,0x<hexstring>]">;
-def : F<"build-id">, Alias<build_id>, AliasArgs<["fast"]>, HelpText<"Alias for --build-id=fast">;
+def : F<"build-id">, Alias<build_id>, AliasArgs<["sha1"]>, HelpText<"Alias for --build-id=sha1">;
defm check_sections: B<"check-sections",
"Check section addresses for overlaps (default)",
diff --git a/lld/docs/ld.lld.1 b/lld/docs/ld.lld.1
index da3b926d02a28..6121ebc924ad4 100644
--- a/lld/docs/ld.lld.1
+++ b/lld/docs/ld.lld.1
@@ -119,7 +119,7 @@ are calculated from the object contents.
is not intended to be cryptographically secure.
.It Fl -build-id
Synonym for
-.Fl -build-id Ns = Ns Cm fast .
+.Fl -build-id Ns = Ns Cm sha1 .
.It Fl -call-graph-profile-sort Ns = Ns Ar algorithm
.Ar algorithm
may be:
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Why not change XXH3 to XXH128? |
There is no XXH3_128 implementation in LLVM and porting it over takes significant work. I'd rather just default to BLAKE3 unless there's a significant performance difference. |
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ishitatsuyuki
changed the title
Removed full-stop. |
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Is this good to merge now? (I don't have committer access) |
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Could you add a release note for this? |
The current default, build-id=fast, is only 8 bytes due to the usage of 64-bit XXH3. This is incompatible with RPM packaging tools which requires >=16 bytes [1]. In Clang the ENABLE_LINKER_BUILD_ID define makes it pass --build-id without a specific hash type. When also defaulting to LLD, this provides a pretty broken default out-of-box. Using XXH3 was a considerable performance advantage when build-id was first implemented, because sha1 was really sha1 and rather slow. Nowadays sha1 is just 160-bit BLAKE3 which is decently fast and not cryptographically broken, so it should be a good default. Note that the default remains "fast" for wasm because sha1 for wasm is still real sha1. Close llvm#43483. [1]: https://github.com/rpm-software-management/rpm/blob/b7d427728b8ba8734ba47d51849a5736bdd727cd/build/files.c#L1883
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Sorry for the delay; added release notes. |
The current default, build-id=fast, is only 8 bytes due to the usage of 64-bit XXH3. This is incompatible with RPM packaging tools which requires >=16 bytes [1]. In Clang the ENABLE_LINKER_BUILD_ID define makes it pass --build-id without a specific hash type. When also defaulting to LLD, this provides a pretty broken default out-of-box. Using XXH3 was a considerable performance advantage when build-id was first implemented, because sha1 was really sha1 and rather slow. Nowadays sha1 is just 160-bit BLAKE3 which is decently fast and not cryptographically broken, so it should be a good default. Note that the default remains "fast" for wasm because sha1 for wasm is still real sha1. Close llvm#43483. [1]: https://github.com/rpm-software-management/rpm/blob/b7d427728b8ba8734ba47d51849a5736bdd727cd/build/files.c#L1883
The current default, build-id=fast, is only 8 bytes due to the usage of 64-bit XXH3. This is incompatible with RPM packaging tools which requires >=16 bytes 1.
In Clang the ENABLE_LINKER_BUILD_ID define makes it pass --build-id without a specific hash type. When also defaulting to LLD, this provides a pretty broken default out-of-box.
Using XXH3 was a considerable performance advantage when build-id was first implemented, because sha1 was really sha1 and rather slow. Nowadays sha1 is just 160-bit BLAKE3 which is decently fast and not cryptographically broken, so it should be a good default.
Note that the default remains "fast" for wasm because sha1 for wasm is still real sha1.
Close #43483.