From 5ac10820ea011514bb1eab9d398fd6f0364a8f14 Mon Sep 17 00:00:00 2001
From: Hannah Lyons <7751607+babyhuey@users.noreply.github.com>
Date: Thu, 8 Oct 2026 11:24:12 -0400
Subject: [PATCH] feat(libScePosixForWebKit): implement arc4random_buf

---
 core/libs/CMakeLists.txt                      | 10 +++++
 core/libs/prx/libScePosixForWebKit/Export.cpp | 13 +++++++
 core/libs/tests/GuestPosixRandom.cpp          | 37 +++++++++++++++++++
 3 files changed, 60 insertions(+)
 create mode 100644 core/libs/tests/GuestPosixRandom.cpp

diff --git a/core/libs/CMakeLists.txt b/core/libs/CMakeLists.txt
index 32eb46fa5..bae33c894 100644
--- a/core/libs/CMakeLists.txt
+++ b/core/libs/CMakeLists.txt
@@ -238,4 +238,14 @@ if(BUILD_TESTING)
         set_tests_properties(savedata_native_write_replacement PROPERTIES ENVIRONMENT_MODIFICATION
             "PATH=path_list_prepend:$<TARGET_FILE_DIR:libSceSaveData.native>")
     endif()
+
+    add_test_executable(guest_posix_random_tests tests/GuestPosixRandom.cpp)
+    target_include_directories(guest_posix_random_tests PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
+    target_link_libraries(guest_posix_random_tests PRIVATE libScePosixForWebKit)
+    configure_windows_unwind(guest_posix_random_tests)
+    add_test(NAME guest_posix_random COMMAND guest_posix_random_tests)
+    if(WIN32)
+        set_tests_properties(guest_posix_random PROPERTIES ENVIRONMENT_MODIFICATION
+            "PATH=path_list_prepend:$<TARGET_FILE_DIR:libScePosixForWebKit>")
+    endif()
 endif()
diff --git a/core/libs/prx/libScePosixForWebKit/Export.cpp b/core/libs/prx/libScePosixForWebKit/Export.cpp
index 71f7b26f6..509ea37a9 100644
--- a/core/libs/prx/libScePosixForWebKit/Export.cpp
+++ b/core/libs/prx/libScePosixForWebKit/Export.cpp
@@ -1,5 +1,9 @@
 #include "prx/libc/include/general/VabiMacros.hpp"
+#include <algorithm>
 #include <cctype>
+#include <cstddef>
+#include <cstring>
+#include <random>
 
 extern "C" {
 
@@ -19,4 +23,13 @@ char* APS5_VABI strcasestr_nid_postfix(const char* text, const char* needle) {
     return nullptr;
 }
 
+void APS5_VABI arc4random_buf_nid_postfix(void* buffer, std::size_t size) {
+    static thread_local std::random_device device;
+    auto* bytes = static_cast<unsigned char*>(buffer);
+    for (std::size_t offset = 0; offset < size; offset += sizeof(unsigned int)) {
+        const unsigned int value = device();
+        std::memcpy(bytes + offset, &value, std::min(sizeof(value), size - offset));
+    }
+}
+
 }
diff --git a/core/libs/tests/GuestPosixRandom.cpp b/core/libs/tests/GuestPosixRandom.cpp
new file mode 100644
index 000000000..43526c711
--- /dev/null
+++ b/core/libs/tests/GuestPosixRandom.cpp
@@ -0,0 +1,37 @@
+#include "prx/libc/include/general/VabiMacros.hpp"
+#include <algorithm>
+#include <array>
+#include <cstddef>
+#include <cstdio>
+#include <cstdlib>
+#include <source_location>
+
+extern "C" void APS5_VABI arc4random_buf_nid_postfix(void*, std::size_t);
+
+void Require(bool condition, std::source_location location = std::source_location::current()) {
+    if (!condition) {
+        std::fprintf(stderr, "Posix random check failed at line %u\n", location.line());
+        std::abort();
+    }
+}
+
+int main() {
+    std::array<unsigned char, 4099> first{};
+    std::array<unsigned char, 4099> second{};
+    first.fill(0xa5);
+    arc4random_buf_nid_postfix(first.data(), 0);
+    Require(std::all_of(first.begin(), first.end(), [](unsigned char value) { return value == 0xa5; }));
+    for (const std::size_t size : {1u, 3u, 5u, 4098u}) {
+        first.fill(0xa5);
+        arc4random_buf_nid_postfix(first.data(), size);
+        Require(std::all_of(first.begin() + static_cast<std::ptrdiff_t>(size), first.end(),
+            [](unsigned char value) { return value == 0xa5; }));
+    }
+    arc4random_buf_nid_postfix(first.data(), first.size());
+    arc4random_buf_nid_postfix(second.data(), second.size());
+    Require(first != second);
+    std::array<std::size_t, 256> counts{};
+    for (const auto value : first) ++counts[value];
+    Require(*std::max_element(counts.begin(), counts.end()) < 64);
+    return 0;
+}