From 7749e621b85a3a44dd7b629de11ebd3ba91723d2 Mon Sep 17 00:00:00 2001
From: Marian Buschsieweke <marian.buschsieweke@ovgu.de>
Date: Wed, 15 May 2019 14:31:01 +0200
Subject: [PATCH] core: Fix undefined behaviour in C11 atomics

Casting pointers to volatile memory to pointers to regular memory is permitted,
but using those pointers to access the memory results in undefined behavior.
This commit changes the casts to no longer drop the volatile qualifier.

References: https://en.cppreference.com/w/c/language/volatile
---
 core/atomic_c11.c | 44 ++++++++++++++++++++++----------------------
 1 file changed, 22 insertions(+), 22 deletions(-)

diff --git a/core/atomic_c11.c b/core/atomic_c11.c
index eedfd5b2cc..a0d70c83ce 100644
--- a/core/atomic_c11.c
+++ b/core/atomic_c11.c
@@ -64,11 +64,11 @@ typedef uint64_t I8;
 #define TEMPLATE_ATOMIC_LOAD_N(n) \
     I##n __atomic_load_##n (const volatile void *ptr, int memorder) \
     { \
-        (void) memorder;                   \
-        unsigned int mask = irq_disable(); \
-        I##n old = *(I##n *)ptr;           \
-        irq_restore(mask);                 \
-        return old;                        \
+        (void) memorder;                           \
+        unsigned int mask = irq_disable();         \
+        I##n old = *(const volatile I##n *)ptr;    \
+        irq_restore(mask);                         \
+        return old;                                \
     }
 
 /**
@@ -81,7 +81,7 @@ typedef uint64_t I8;
     { \
         (void) memorder;                   \
         unsigned int mask = irq_disable(); \
-        *(I##n *)ptr = val;                \
+        *(volatile I##n *)ptr = val;       \
         irq_restore(mask);                 \
     }
 
@@ -95,8 +95,8 @@ typedef uint64_t I8;
     { \
         (void) memorder;                   \
         unsigned int mask = irq_disable(); \
-        I##n old = *(I##n *)ptr;           \
-        *(I##n *)ptr = desired;            \
+        I##n old = *(volatile I##n *)ptr;  \
+        *(volatile I##n *)ptr = desired;   \
         irq_restore(mask);                 \
         return old;                        \
     }
@@ -114,14 +114,14 @@ typedef uint64_t I8;
         (void) success_memorder;           \
         (void) failure_memorder;           \
         unsigned int mask = irq_disable(); \
-        I##n cur = *(I##n *)ptr;           \
+        I##n cur = *(volatile I##n *)ptr;  \
         if (cur != *(I##n *)expected) {    \
             *(I##n *)expected = cur;       \
             irq_restore(mask);             \
             return false;                  \
         }                                  \
                                            \
-        *(I##n *)ptr = desired;            \
+        *(volatile I##n *)ptr = desired;   \
         irq_restore(mask);                 \
         return true;                       \
     }
@@ -137,12 +137,12 @@ typedef uint64_t I8;
 #define TEMPLATE_ATOMIC_FETCH_OP_N(opname, op, n, prefixop) \
     I##n __atomic_fetch_##opname##_##n(volatile void *ptr, I##n val, int memmodel) \
     { \
-        unsigned int mask = irq_disable();    \
-        (void)memmodel;                       \
-        I##n tmp = *(I##n *)ptr;              \
-        *(I##n *)ptr = prefixop(tmp op val);  \
-        irq_restore(mask);                    \
-        return tmp;                           \
+        unsigned int mask = irq_disable();             \
+        (void)memmodel;                                \
+        I##n tmp = *(volatile I##n *)ptr;              \
+        *(volatile I##n *)ptr = prefixop(tmp op val);  \
+        irq_restore(mask);                             \
+        return tmp;                                    \
     }
 
 /**
@@ -156,12 +156,12 @@ typedef uint64_t I8;
 #define TEMPLATE_ATOMIC_OP_FETCH_N(opname, op, n, prefixop) \
     I##n __atomic_##opname##_fetch_##n(volatile void *ptr, I##n val, int memmodel) \
     { \
-        (void)memmodel;                                 \
-        unsigned int mask = irq_disable();              \
-        I##n tmp = prefixop((*(I##n *)ptr) op val);     \
-        *(I##n *)ptr = tmp;                             \
-        irq_restore(mask);                              \
-        return tmp;                                     \
+        (void)memmodel;                                        \
+        unsigned int mask = irq_disable();                     \
+        I##n tmp = prefixop((*(volatile I##n *)ptr) op val);   \
+        *(volatile I##n *)ptr = tmp;                           \
+        irq_restore(mask);                                     \
+        return tmp;                                            \
     }
 
 /* Template instantiations below */