caio/clang-p2996
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

[ELF] Change build-id default to sha1 (#93943)

Browse Source 
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 https://github.com/llvm/llvm-project/issues/43483.

[1]:
b7d427728b/build/files.c (L1883)
This commit is contained in:
Tatsuyuki Ishi
2024-06-11 02:14:44 +09:00
committed by GitHub
parent caf2de76e4
commit 1d96e4bc2d
4 changed files with 15 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
lld/ELF/Options.td
View File

@@ -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)",

3
lld/docs/ReleaseNotes.rst
View File

@@ -48,6 +48,9 @@ ELF Improvements
and combine relocation sections if their relocated section group members are
placed to the same output section.
(`#94704 <https://github.com/llvm/llvm-project/pull/94704>`_)
* ``--build-id`` now defaults to generating a 20-byte digest ("sha1") instead
of 8-byte ("fast"). This improves compatibility with RPM packaging tools.
(`#93943 <https://github.com/llvm/llvm-project/pull/93943>`_)
Breaking changes
----------------

2
lld/docs/ld.lld.1
View File

@@ -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:

19
lld/test/ELF/build-id.s
View File

@@ -6,11 +6,12 @@
# RUN: llvm-readobj -S %t2 | FileCheck -check-prefix=ALIGN %s
# RUN: ld.lld --build-id %t -o %t2
# RUN: llvm-objdump -s %t2 | FileCheck --check-prefix=DEFAULT %s
# RUN: ld.lld --build-id=fast %t -o %t2
# RUN: llvm-objdump -s %t2 | FileCheck --check-prefix=DEFAULT %s
# RUN: llvm-objdump -s %t2 | FileCheck --check-prefix=SHA1 %s
# RUN: ld.lld --build-id %t -o %t2 --threads=1
# RUN: llvm-objdump -s %t2 | FileCheck --check-prefix=DEFAULT %s
# RUN: llvm-objdump -s %t2 | FileCheck --check-prefix=SHA1 %s
# RUN: ld.lld --build-id=fast %t -o %t2
# RUN: llvm-objdump -s %t2 | FileCheck --check-prefix=FAST %s
# RUN: ld.lld --build-id=md5 %t -o %t2
# RUN: llvm-objdump -s %t2 | FileCheck --check-prefix=MD5 %s
@@ -41,7 +42,7 @@
# RUN: ld.lld --build-id --build-id=none %t -o %t2
# RUN: llvm-objdump -s %t2 | FileCheck --check-prefix=NONE %s
# RUN: ld.lld --build-id=none --build-id %t -o %t2
# RUN: llvm-objdump -s %t2 | FileCheck --check-prefix=DEFAULT %s
# RUN: llvm-objdump -s %t2 | FileCheck --check-prefix=SHA1 %s
.globl _start
_start:
@@ -62,10 +63,10 @@ _start:
# ALIGN-NEXT: Info:
# ALIGN-NEXT: AddressAlignment: 4
# DEFAULT: Contents of section .note.test:
# DEFAULT: Contents of section .note.gnu.build-id:
# DEFAULT-NEXT: 04000000 08000000 03000000 474e5500 ............GNU.
# DEFAULT-NEXT: 630bc2f5 a2584763
# FAST: Contents of section .note.test:
# FAST: Contents of section .note.gnu.build-id:
# FAST-NEXT: 04000000 08000000 03000000 474e5500 ............GNU.
# FAST-NEXT: 630bc2f5 a2584763
# MD5: Contents of section .note.gnu.build-id:
# MD5-NEXT: 04000000 10000000 03000000 474e5500 ............GNU.