From 433bf1ebc2debf27cee3ba0f56a1c531cdb4cb52 Mon Sep 17 00:00:00 2001
From: Yunus Shaikh <75296019+yunusshaikh7@users.noreply.github.com>
Date: Sat, 10 Oct 2026 01:07:23 -0700
Subject: [PATCH] fix(libc): map _Towctrans descriptors 1 and 2 to lower and
 upper case

_Towctrans passed the guest's descriptor to the host towctrans.
Dinkumware's <wctype.h> (xwcc.h) defines towlower(wc) as
_Towctrans(wc, 1) and towupper(wc) as _Towctrans(wc, 2), the values
FreeBSD's wctrans.c also uses for "tolower" and "toupper". UCRT reads
1 as toupper and other nonzero values as tolower, so on Windows
towlower(L'A') returned L'A' and towupper(L'a') returned L'a', while
towlower(L'a') returned L'A'. The host wint_t is 16 bits there, which
also turned WEOF into 0xffff. glibc's wctrans_t is a pointer to a
table that towctrans reads, so on Linux descriptor 1 or 2 is
dereferenced as an address.

_Towctrans now takes the guest's 32-bit wint_t and size_t descriptor.
1 and 2 map 0..255 through the C locale tables behind _Getptolower and
_Getptoupper and return other values unchanged. Any other descriptor
sets errno to EINVAL and returns wc unchanged, as FreeBSD's
towctrans_l does.
---
 core/libs/prx/libc/src/LocaleSupport.cpp | 13 +++++++++---
 core/libs/tests/GuestLocale.cpp          | 26 ++++++++++++++++++++++++
 2 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/core/libs/prx/libc/src/LocaleSupport.cpp b/core/libs/prx/libc/src/LocaleSupport.cpp
index d0a70841a..a21ce8227 100644
--- a/core/libs/prx/libc/src/LocaleSupport.cpp
+++ b/core/libs/prx/libc/src/LocaleSupport.cpp
@@ -4,7 +4,7 @@
 #include <cstdio>
 #include <cstdint>
 #include <cwchar>
-#include <cwctype>
+#include <cerrno>
 #include <ios>
 #include <locale>
 #include <mutex>
@@ -323,8 +323,15 @@ mbstate_t* APS5_VABI _Getpwcstate_nid_postfix() {
     return &state;
 }
 
-wint_t APS5_VABI _Towctrans_nid_postfix(wint_t c, wctrans_t desc) {
-    return std::towctrans(c, desc);
+std::uint32_t APS5_VABI _Towctrans_nid_postfix(std::uint32_t c, std::uint64_t desc) {
+    constexpr std::uint64_t ToLower = 1;
+    constexpr std::uint64_t ToUpper = 2;
+    if (desc != ToLower && desc != ToUpper) {
+        errno = 22;
+        return c;
+    }
+    if (c > UCHAR_MAX) return c;
+    return static_cast<std::uint32_t>((desc == ToLower ? g_lowerTable : g_upperTable)[c + 1]);
 }
 
 // Locale ids and stream objects the title imports besides the ones above; the streams are zeroed
diff --git a/core/libs/tests/GuestLocale.cpp b/core/libs/tests/GuestLocale.cpp
index 632670181..93cf43ff1 100644
--- a/core/libs/tests/GuestLocale.cpp
+++ b/core/libs/tests/GuestLocale.cpp
@@ -1,5 +1,6 @@
 #include "prx/libc/include/GuestLocale.hpp"
 #include <array>
+#include <cstdint>
 #include <cstring>
 #include <cwchar>
 #include <climits>
@@ -23,6 +24,8 @@ int APS5_VABI _Mbtowcx_nid_postfix(std::uint16_t* dst, const char* src, std::siz
 int APS5_VABI _Wctombx_nid_postfix(char* dst, std::uint16_t src, std::mbstate_t* st);
 void APS5_VABI _Locksyslock_nid_postfix();
 void APS5_VABI _Unlocksyslock_nid_postfix();
+std::uint32_t APS5_VABI _Towctrans_nid_postfix(std::uint32_t wc, std::uint64_t desc);
+int* APS5_VABI __error_nid_postfix();
 
 }
 
@@ -144,12 +147,35 @@ static void CheckStreamDestruction() {
     Require(object.stream.locale == &_ZSt21_sceLibcClassicLocale_nid_postfix);
 }
 
+static void CheckWideCaseTranslation() {
+    const auto* lower = _Getptolower_nid_postfix();
+    const auto* upper = _Getptoupper_nid_postfix();
+    Require(_Towctrans_nid_postfix(u'A', 1) == u'a' && _Towctrans_nid_postfix(u'a', 2) == u'A');
+    *__error_nid_postfix() = 0;
+    for (std::uint32_t value = 0; value < 256; ++value) {
+        Require(_Towctrans_nid_postfix(value, 1) == static_cast<std::uint32_t>(lower[value]));
+        Require(_Towctrans_nid_postfix(value, 2) == static_cast<std::uint32_t>(upper[value]));
+    }
+    const std::uint32_t uncased[] = {0x100u, 0x391u, 0x3b1u, 0xffffu, 0xffffffffu};
+    for (const std::uint32_t value : uncased) {
+        Require(_Towctrans_nid_postfix(value, 1) == value && _Towctrans_nid_postfix(value, 2) == value);
+    }
+    Require(*__error_nid_postfix() == 0);
+    const std::uint64_t invalidDescriptors[] = {0, 3};
+    for (const std::uint64_t descriptor : invalidDescriptors) {
+        *__error_nid_postfix() = 0;
+        Require(_Towctrans_nid_postfix(u'A', descriptor) == u'A' && _Towctrans_nid_postfix(u'7', descriptor) == u'7');
+        Require(*__error_nid_postfix() == 22);
+    }
+}
+
 int main() {
     CheckGuestCalls();
     CheckLocinfoAlignment();
     CheckCharacterTables();
     CheckCharacterConversions();
     CheckStreamDestruction();
+    CheckWideCaseTranslation();
     _Locksyslock_nid_postfix();
     _Locksyslock_nid_postfix();
     _Unlocksyslock_nid_postfix();