From 577207a43d5f4eec61de1912a54008153552507d Mon Sep 17 00:00:00 2001
From: Leonard Chan <leonardchan@google.com>
Date: Tue, 18 Mar 2025 11:41:33 -0700
Subject: [PATCH] [sanitizer][Fuchsia] Add callback at end of
 __sanitizer_startup_hook

Sanitizers using this hook on Fuchsia can define this function to do any
extra stuff at the end of the startup hook. For now this is only used by
HWASan which needs to explicitly be initialized before libc extensions
are intitialized.
---
 compiler-rt/lib/asan/asan_fuchsia.cpp                  | 5 +++++
 compiler-rt/lib/hwasan/hwasan_fuchsia.cpp              | 9 +++++++++
 compiler-rt/lib/sanitizer_common/sanitizer_fuchsia.cpp | 2 ++
 compiler-rt/lib/sanitizer_common/sanitizer_fuchsia.h   | 7 +++++++
 compiler-rt/lib/ubsan/ubsan_init_standalone.cpp        | 7 +++++++
 5 files changed, 30 insertions(+)

diff --git a/compiler-rt/lib/asan/asan_fuchsia.cpp b/compiler-rt/lib/asan/asan_fuchsia.cpp
index 96c41e9d42ba6..6876be1dca535 100644
--- a/compiler-rt/lib/asan/asan_fuchsia.cpp
+++ b/compiler-rt/lib/asan/asan_fuchsia.cpp
@@ -25,6 +25,11 @@
 #  include "asan_thread.h"
 #  include "lsan/lsan_common.h"
 
+namespace __sanitizer {
+// ASan doesn't need to do anything else special in the startup hook.
+void EarlySanitizerInit() {}
+}  // namespace __sanitizer
+
 namespace __asan {
 
 // The system already set up the shadow memory for us.
diff --git a/compiler-rt/lib/hwasan/hwasan_fuchsia.cpp b/compiler-rt/lib/hwasan/hwasan_fuchsia.cpp
index d1696f8aa7962..647211bf199e1 100644
--- a/compiler-rt/lib/hwasan/hwasan_fuchsia.cpp
+++ b/compiler-rt/lib/hwasan/hwasan_fuchsia.cpp
@@ -31,6 +31,15 @@
 SANITIZER_INTERFACE_ATTRIBUTE
 THREADLOCAL uptr __hwasan_tls;
 
+namespace __sanitizer {
+void EarlySanitizerInit() {
+  // Setup the hwasan runtime before any `__libc_extensions_init`s are called.
+  // This is needed because libraries which define this function (like fdio)
+  // may be instrumented and either access `__hwasan_tls` or make runtime calls.
+  __hwasan_init();
+}
+}  // namespace __sanitizer
+
 namespace __hwasan {
 
 bool InitShadow() {
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_fuchsia.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_fuchsia.cpp
index acbf3ebfc95c0..1ca50eb186a34 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_fuchsia.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_fuchsia.cpp
@@ -547,6 +547,8 @@ void __sanitizer_startup_hook(int argc, char **argv, char **envp,
   __sanitizer::StoredEnviron = envp;
   __sanitizer::MainThreadStackBase = reinterpret_cast<uintptr_t>(stack_base);
   __sanitizer::MainThreadStackSize = stack_size;
+
+  EarlySanitizerInit();
 }
 
 void __sanitizer_set_report_path(const char *path) {
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_fuchsia.h b/compiler-rt/lib/sanitizer_common/sanitizer_fuchsia.h
index 26c1deab9e5fe..47e7537c1bdf1 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_fuchsia.h
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_fuchsia.h
@@ -32,6 +32,13 @@ struct MemoryMappingLayoutData {
 
 void InitShadowBounds();
 
+// Individual sanitizers can define this to explicitly run something at the end
+// of `__sanitizer_startup_hook`. This can be useful if a sanitizer needs to do
+// extra work after the common startup hook code is called and before module
+// ctors are invoked. For example, hwasan can explicitly call its initializing
+// function here so it can be set up before libc extensions are initialized.
+void EarlySanitizerInit();
+
 }  // namespace __sanitizer
 
 #endif  // SANITIZER_FUCHSIA
diff --git a/compiler-rt/lib/ubsan/ubsan_init_standalone.cpp b/compiler-rt/lib/ubsan/ubsan_init_standalone.cpp
index 91c3f57b424b9..5083246b8b7f3 100644
--- a/compiler-rt/lib/ubsan/ubsan_init_standalone.cpp
+++ b/compiler-rt/lib/ubsan/ubsan_init_standalone.cpp
@@ -19,6 +19,13 @@
 #include "ubsan_init.h"
 #include "ubsan_signals_standalone.h"
 
+#if SANITIZER_FUCHSIA
+namespace __sanitizer {
+// UBSan doesn't need to do anything else special in the startup hook.
+void EarlySanitizerInit() {}
+} // namespace __sanitizer
+#endif // SANITIZER_FUCHSIA
+
 namespace __ubsan {
 
 class UbsanStandaloneInitializer {