Update arm/aarch64-related comments

taiki-e · Jul 19, 2024 · 8a3181c · 8a3181c
1 parent 3a3965d
commit 8a3181c
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Showing 3 changed files with 7 additions and 3 deletions.
diff --git a/src/imp/arm_linux.rs b/src/imp/arm_linux.rs
@@ -90,6 +90,9 @@ where
             // This is not single-copy atomic reads, but this is ok because subsequent
             // CAS will check for consistency.
             //
+            // ARM's memory model allow mixed-sized atomic access.
+            // https://github.com/rust-lang/unsafe-code-guidelines/issues/345#issuecomment-1172891466
+            //
             // Note that the C++20 memory model does not allow mixed-sized atomic access,
             // so we must use inline assembly to implement byte_wise_atomic_load.
             // (i.e., byte-wise atomic based on the standard library's atomic types

diff --git a/src/imp/atomic128/detect/aarch64_aa64reg.rs b/src/imp/atomic128/detect/aarch64_aa64reg.rs
@@ -75,8 +75,8 @@ fn _detect(info: &mut CpuInfo) {
             info.set(CpuInfo::HAS_RCPC3);
         }
     }
-    // OpenBSD has an API to get this, but currently always returns 0.
-    // https://github.com/openbsd/src/blob/6a233889798dc3ecb18acc52dce1e57862af2957/sys/arch/arm64/arm64/machdep.c#L371-L377
+    // OpenBSD has an API to get AA64MMFR2, but currently always returns 0.
+    // https://github.com/openbsd/src/blob/1847475460684e4251d673e6b1bceb1b38e699c3/sys/arch/arm64/arm64/machdep.c#L367
     #[cfg_attr(target_os = "openbsd", cfg(test))]
     {
         // ID_AA64MMFR2_EL1, AArch64 Memory Model Feature Register 2

diff --git a/src/imp/atomic128/detect/aarch64_macos.rs b/src/imp/atomic128/detect/aarch64_macos.rs
@@ -5,8 +5,9 @@
 // This module is currently only enabled on tests because aarch64 macOS always supports FEAT_LSE and FEAT_LSE2.
 // https://github.com/llvm/llvm-project/blob/llvmorg-18.1.2/llvm/include/llvm/TargetParser/AArch64TargetParser.h#L728
 //
-// If macOS supporting Armv9.4-a becomes popular in the future, this module will
+// If macOS supporting FEAT_LSE128/FEAT_LRCPC3 becomes popular in the future, this module will
 // be used to support outline-atomics for FEAT_LSE128/FEAT_LRCPC3.
+// M4 is armv9.4-a but I don't know if it supports FEAT_LSE128/FEAT_LRCPC3.
 //
 // Refs: https://developer.apple.com/documentation/kernel/1387446-sysctlbyname/determining_instruction_set_characteristics
 //