Correct rationale in simd_x86_64.S comment

The SIMD operations are written in assembly because loading and operating on indeterminate values is UB in C++ but well-defined in assembly. msan not tracking the loads is a side effect, not the reason. Closes #71
Add .note.gnu.property section for CET/CFI to simd_x86_64.S
2026-08-03 02:37:18 +00:00 · 2026-08-02 22:31:56 -04:00
1 changed files with 15 additions and 3 deletions
@@ -1,7 +1,8 @@
 // SIMD operations on potentially-indeterminate Node16::index[16] bytes.
-// Written in assembly so msan doesn't track the loads. The caller is
-// responsible for masking the returned bitfield to [0, numChildren) before
-// using it.
+// Written in assembly because loading and operating on indeterminate values
+// is UB in C++ but well-defined in assembly. (A side effect is that msan
+// doesn't track the loads.) The caller is responsible for masking the
+// returned bitfield to [0, numChildren) before using it.
 //
 // All functions return a 16-bit bitmask in %eax (bit i set = condition true
 // at index i). The upper 16 bits of %eax are zero.
@@ -71,4 +72,15 @@ mask_in_range_16:
    ret
    .size mask_in_range_16, .-mask_in_range_16

+    .section .note.gnu.property,"a",@note
+    .p2align 3, 0x0
+    .long 4
+    .long 16
+    .long 5
+    .asciz "GNU"
+    .long 0xc0000002
+    .long 4
+    .long 0x3
+    .p2align 3, 0x0
+
    .section .note.GNU-stack,"",@progbits
Author	SHA1	Message	Date
weaselbotandandrew	0b12a037c4	Correct rationale in simd_x86_64.S comment CI / release (arm64, , ubuntu-latest-arm64) (pull_request) Successful in 2m14s Details CI / pre-commit (pull_request) Successful in 1m59s Details CI / test (-DCMAKE_BUILD_TYPE=Debug -DMSAN_TOOLCHAIN_PATH=/opt/msan, debug) (pull_request) Successful in 3m47s Details CI / test (-DCMAKE_CXX_FLAGS=-DUSE_64_BIT=1, 64-bit-versions) (pull_request) Successful in 3m14s Details CI / test (-DCMAKE_C_COMPILER=gcc -DCMAKE_CXX_COMPILER=g++, gcc) (pull_request) Successful in 3m13s Details CI / test (-DUSE_SIMD_FALLBACK=ON, simd-fallback) (pull_request) Successful in 3m17s Details CI / release (amd64, -DMSAN_TOOLCHAIN_PATH=/opt/msan, ubuntu-latest-amd64) (pull_request) Successful in 5m27s Details CI / coverage (pull_request) Successful in 3m42s Details The SIMD operations are written in assembly because loading and operating on indeterminate values is UB in C++ but well-defined in assembly. msan not tracking the loads is a side effect, not the reason. Closes #71	2026-08-03 02:37:18 +00:00
andrew	5c16b8ee90	Add .note.gnu.property section for CET/CFI to simd_x86_64.S CI / release (arm64, , ubuntu-latest-arm64) (push) Successful in 2m21s Details CI / pre-commit (push) Successful in 2m1s Details CI / test (-DCMAKE_BUILD_TYPE=Debug -DMSAN_TOOLCHAIN_PATH=/opt/msan, debug) (push) Successful in 3m48s Details CI / test (-DCMAKE_CXX_FLAGS=-DUSE_64_BIT=1, 64-bit-versions) (push) Successful in 3m18s Details CI / test (-DCMAKE_C_COMPILER=gcc -DCMAKE_CXX_COMPILER=g++, gcc) (push) Successful in 3m15s Details CI / test (-DUSE_SIMD_FALLBACK=ON, simd-fallback) (push) Successful in 3m17s Details CI / release (amd64, -DMSAN_TOOLCHAIN_PATH=/opt/msan, ubuntu-latest-amd64) (push) Successful in 5m33s Details CI / coverage (push) Successful in 3m47s Details The assembly file was missing the GNU property note that records control-flow integrity (CET) support, causing hardening-check to report 'Control flow integrity: no, not found!'. Add the note matching what clang emits with -fcf-protection.	2026-08-02 22:31:56 -04:00