From 8401230be6a396b10659de62639792f149daf811 Mon Sep 17 00:00:00 2001
From: Steven Moreland <smoreland@google.com>
Date: Sat, 27 Apr 2024 01:17:21 +0000
Subject: [PATCH] bionic: max_android_page_size to 16384

The maximum page size Android supports
now is 16384, and Art only supports 16kB,
so we can save a bit of space.

Bug: 332556665
Test: N/A
Change-Id: I23df607bcc5cf9e96d7b6a66169413cd1a883f7e
---
 libc/bionic/pthread_internal.h |  2 +-
 libc/platform/bionic/page.h    |  6 ++++--
 libc/private/WriteProtected.h  | 10 +++++-----
 libdl/libdl_cfi.cpp            |  6 +++---
 4 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/libc/bionic/pthread_internal.h b/libc/bionic/pthread_internal.h
index 091f711eb..c2abdea29 100644
--- a/libc/bionic/pthread_internal.h
+++ b/libc/bionic/pthread_internal.h
@@ -240,7 +240,7 @@ __LIBC_HIDDEN__ void pthread_key_clean_all(void);
 // On LP64, we could use more but there's no obvious advantage to doing
 // so, and the various media processes use RLIMIT_AS as a way to limit
 // the amount of allocation they'll do.
-#define PTHREAD_GUARD_SIZE max_page_size()
+#define PTHREAD_GUARD_SIZE max_android_page_size()
 
 // SIGSTKSZ (8KiB) is not big enough.
 // An snprintf to a stack buffer of size PATH_MAX consumes ~7KiB of stack.
diff --git a/libc/platform/bionic/page.h b/libc/platform/bionic/page.h
index 65faba4f0..4dbe4baea 100644
--- a/libc/platform/bionic/page.h
+++ b/libc/platform/bionic/page.h
@@ -32,11 +32,13 @@ inline size_t page_size() {
 #endif
 }
 
-constexpr size_t max_page_size() {
+// The maximum page size supported on any Android device. As
+// of API level 35, this is limited by ART.
+constexpr size_t max_android_page_size() {
 #if defined(PAGE_SIZE)
   return PAGE_SIZE;
 #else
-  return 65536;
+  return 16384;
 #endif
 }
 
diff --git a/libc/private/WriteProtected.h b/libc/private/WriteProtected.h
index bbe35e529..f26912546 100644
--- a/libc/private/WriteProtected.h
+++ b/libc/private/WriteProtected.h
@@ -30,11 +30,11 @@
 template <typename T>
 union WriteProtectedContents {
   T value;
-  char padding[max_page_size()];
+  char padding[max_android_page_size()];
 
   WriteProtectedContents() = default;
   BIONIC_DISALLOW_COPY_AND_ASSIGN(WriteProtectedContents);
-} __attribute__((aligned(max_page_size())));
+} __attribute__((aligned(max_android_page_size())));
 
 // Write protected wrapper class that aligns its contents to a page boundary,
 // and sets the memory protection to be non-writable, except when being modified
@@ -42,8 +42,8 @@ union WriteProtectedContents {
 template <typename T>
 class WriteProtected {
  public:
-  static_assert(sizeof(T) < max_page_size(),
-                "WriteProtected only supports contents up to max_page_size()");
+  static_assert(sizeof(T) < max_android_page_size(),
+                "WriteProtected only supports contents up to max_android_page_size()");
 
   WriteProtected() = default;
   BIONIC_DISALLOW_COPY_AND_ASSIGN(WriteProtected);
@@ -89,7 +89,7 @@ class WriteProtected {
     // ourselves.
     addr = untag_address(addr);
 #endif
-    if (mprotect(reinterpret_cast<void*>(addr), max_page_size(), prot) == -1) {
+    if (mprotect(reinterpret_cast<void*>(addr), max_android_page_size(), prot) == -1) {
       async_safe_fatal("WriteProtected mprotect %x failed: %s", prot, strerror(errno));
     }
   }
diff --git a/libdl/libdl_cfi.cpp b/libdl/libdl_cfi.cpp
index 23cd7f53a..8adc342ac 100644
--- a/libdl/libdl_cfi.cpp
+++ b/libdl/libdl_cfi.cpp
@@ -26,15 +26,15 @@ __attribute__((__weak__, visibility("default"))) extern "C" void __loader_cfi_fa
 // dlopen/dlclose.
 static struct {
   uintptr_t v;
-  char padding[max_page_size() - sizeof(v)];
-} shadow_base_storage alignas(max_page_size());
+  char padding[max_android_page_size() - sizeof(v)];
+} shadow_base_storage alignas(max_android_page_size());
 
 // __cfi_init is called by the loader as soon as the shadow is mapped. This may happen very early
 // during startup, before libdl.so global constructors, and, on i386, even before __libc_sysinfo is
 // initialized. This function should not do any system calls.
 extern "C" uintptr_t* __cfi_init(uintptr_t shadow_base) {
   shadow_base_storage.v = shadow_base;
-  static_assert(sizeof(shadow_base_storage) == max_page_size(), "");
+  static_assert(sizeof(shadow_base_storage) == max_android_page_size(), "");
   return &shadow_base_storage.v;
 }