From 8607a7fb338d81a3e5692d1aafd0951e7fd603c5 Mon Sep 17 00:00:00 2001
From: Alex <93446519+AlexOn1ine@users.noreply.github.com>
Date: Sat, 17 Aug 2024 18:19:22 +0200
Subject: [PATCH] Fixes UB in Cmd_averagestats (#5191)

* Fixes UB in Cmd_averagestats

* fix test and align default case
---
 src/battle_script_commands.c          | 23 ++++++++++++++++-------
 test/battle/move_effect/guard_split.c | 22 ++++++++++++++++++++++
 test/battle/move_effect/power_split.c | 22 ++++++++++++++++++++++
 3 files changed, 60 insertions(+), 7 deletions(-)
 create mode 100644 test/battle/move_effect/guard_split.c
 create mode 100644 test/battle/move_effect/power_split.c

diff --git a/src/battle_script_commands.c b/src/battle_script_commands.c
index 394a455b3a..9165d7b7e4 100644
--- a/src/battle_script_commands.c
+++ b/src/battle_script_commands.c
@@ -15669,17 +15669,26 @@ static void Cmd_swapstatstages(void)
     gBattlescriptCurrInstr = cmd->nextInstr;
 }
 
+static u16 *GetBattlerStat(struct BattlePokemon *battler, u32 stat)
+{
+    switch (stat)
+    {
+    case STAT_ATK:   return &battler->attack;
+    case STAT_DEF:   return &battler->defense;
+    case STAT_SPATK: return &battler->spAttack;
+    case STAT_SPDEF: return &battler->spDefense;
+    default:         return NULL;
+    }
+}
+
 static void Cmd_averagestats(void)
 {
     CMD_ARGS(u8 stat);
 
-    u8 stat = cmd->stat;
-    u16 atkStat = *(u16 *)((&gBattleMons[gBattlerAttacker].attack) + (stat - 1));
-    u16 defStat = *(u16 *)((&gBattleMons[gBattlerTarget].attack) + (stat - 1));
-    u16 average = (atkStat + defStat) / 2;
-
-    *(u16 *)((&gBattleMons[gBattlerAttacker].attack) + (stat - 1)) = average;
-    *(u16 *)((&gBattleMons[gBattlerTarget].attack) + (stat - 1)) = average;
+    u16 *stat1 = GetBattlerStat(&gBattleMons[gBattlerAttacker], cmd->stat);
+    u16 *stat2 = GetBattlerStat(&gBattleMons[gBattlerTarget], cmd->stat);
+    u16 avg = (*stat1 + *stat2) / 2;
+    *stat1 = *stat2 = avg;
 
     gBattlescriptCurrInstr = cmd->nextInstr;
 }
diff --git a/test/battle/move_effect/guard_split.c b/test/battle/move_effect/guard_split.c
new file mode 100644
index 0000000000..3f012ab6e2
--- /dev/null
+++ b/test/battle/move_effect/guard_split.c
@@ -0,0 +1,22 @@
+#include "global.h"
+#include "test/battle.h"
+
+ASSUMPTIONS
+{
+    ASSUME(gMovesInfo[MOVE_GUARD_SPLIT].effect == EFFECT_GUARD_SPLIT);
+}
+
+SINGLE_BATTLE_TEST("Guard Split averages users and targets Def and Sp. Def stats")
+{
+    GIVEN {
+        PLAYER(SPECIES_BULBASAUR);
+        OPPONENT(SPECIES_IVYSAUR);
+    } WHEN {
+        TURN { MOVE(player, MOVE_GUARD_SPLIT); }
+    } SCENE {
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_GUARD_SPLIT, player);
+    } THEN {
+        EXPECT_EQ(player->defense, opponent->defense);
+        EXPECT_EQ(player->spDefense, opponent->spDefense);
+    }
+}
diff --git a/test/battle/move_effect/power_split.c b/test/battle/move_effect/power_split.c
new file mode 100644
index 0000000000..70d1bfd5ea
--- /dev/null
+++ b/test/battle/move_effect/power_split.c
@@ -0,0 +1,22 @@
+#include "global.h"
+#include "test/battle.h"
+
+ASSUMPTIONS
+{
+    ASSUME(gMovesInfo[MOVE_POWER_SPLIT].effect == EFFECT_POWER_SPLIT);
+}
+
+SINGLE_BATTLE_TEST("Power Split averages user and targets Atk and Sp. Atk stats")
+{
+    GIVEN {
+        PLAYER(SPECIES_BULBASAUR);
+        OPPONENT(SPECIES_IVYSAUR);
+    } WHEN {
+        TURN { MOVE(player, MOVE_POWER_SPLIT); }
+    } SCENE {
+        ANIMATION(ANIM_TYPE_MOVE, MOVE_POWER_SPLIT, player);
+    } THEN {
+        EXPECT_EQ(player->attack, opponent->attack);
+        EXPECT_EQ(player->spAttack, opponent->spAttack);
+    }
+}