https://github.com/jroelofs updated
https://github.com/llvm/llvm-project/pull/73685
>From 603983e237e73b2d939bf9ee12e39ecc7983f7f1 Mon Sep 17 00:00:00 2001
From: Jon Roelofs <jonathan_roel...@apple.com>
Date: Wed, 29 Nov 2023 14:21:54 -0800
Subject: [PATCH] add a note about the dispatch_once block
Created using spr 1.3.4
---
compiler-rt/lib/builtins/cpu_model.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/compiler-rt/lib/builtins/cpu_model.c
b/compiler-rt/lib/builtins/cpu_model.c
index 5f5182859080c49..001467a9f7ff511 100644
--- a/compiler-rt/lib/builtins/cpu_model.c
+++ b/compiler-rt/lib/builtins/cpu_model.c
@@ -1285,6 +1285,14 @@ static bool isKnownAndSupported(const char *name) {
}
void __init_cpu_features_resolver(void) {
+ // On Darwin platforms, this may be called concurrently by multiple threads
+ // because the resolvers that use it are called lazily at runtime (unlike on
+ // ELF platforms, where IFuncs are resolved serially at load time). This
+ // function's effect on __aarch64_cpu_features should be idempotent, but even
+ // so we need dispatch_once to resolve the race condition. Dispatch is
+ // available through libSystem, which we need anyway for the sysctl, so this
+ // does not add a new dependency.
+
static dispatch_once_t onceToken = 0;
dispatch_once(&onceToken, ^{
//
https://developer.apple.com/documentation/kernel/1387446-sysctlbyname/determining_instruction_set_characteristics
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