spool: Clean up with gcc/clang specific features

.vscode/settings.json

@@ -7,5 +7,5 @@
         "$(workspaceFolder)/include/",
 
     ],
-    "C_Cpp.default.cStandard": "gnu99"
+    "C_Cpp.default.cStandard": "gnu17"
 }

include/ucore/spool.h

@@ -1,5 +1,5 @@
 #ifndef UC_SPOOL_H_
-#define UC_SPOOL_H
+#define UC_SPOOL_H_
 
 #include <stddef.h>
 #include <stdint.h>
@@ -7,6 +7,11 @@
 extern "C" {
 #endif
 
+typedef union UCPoolBlock UCPoolBlock;
+union UCPoolBlock {
+   UCPoolBlock *next; // next free block (when not allocated)
+   unsigned char data[]; // data when allocated
+};
 /** @file
  * Static pool allocator.
  *
@@ -23,12 +28,12 @@ extern "C" {
 */
 typedef struct UCPool UCPool;
 struct UCPool {
-   unsigned char *free_list;   // intrusive free list
+   UCPoolBlock *free_list;   // free list
    size_t block_size; // aligned size of each block
    size_t capacity;   // number of blocks
    size_t align;      // alignment
-   unsigned char *start;       // start of user buffer
+   UCPoolBlock *start;       // start of user buffer
-   unsigned char *end;         // one past end of user buffer
+   UCPoolBlock *end;         // one past end of user buffer
 };
 
 /** Initialize the pool.
@@ -47,6 +52,7 @@ void uc_pool_init(UCPool *pool,
                size_t alignment);
 
 // Allocate a block from the pool. Returns NULL if no more space
+[[gnu::assume_aligned(_Alignof(UCPoolBlock))]]
 void *uc_pool_alloc(UCPool *pool);
 
 // Free @p . Returns memory to the pool

src/spool.c

@@ -11,12 +11,12 @@ void uc_pool_init(UCPool *pool, void *buffer, size_t buffer_size, size_t block_s
 
     // enforce minimum for storing free list pointers
 
-    if (align < _Alignof(unsigned char *)) {
+    if (align < _Alignof(UCPoolBlock)) {
-        align = _Alignof(unsigned char *);
+        align = _Alignof(UCPoolBlock);
     }
 
-    if (block_size < sizeof(unsigned char *)) {
+    if (block_size < sizeof(UCPoolBlock)) {
-        block_size = sizeof(unsigned char *);
+        block_size = sizeof(UCPoolBlock);
     }
     // ensure initial alignment
     size_t stride = UC_ALIGN(block_size, align);
@@ -34,19 +34,21 @@ void uc_pool_init(UCPool *pool, void *buffer, size_t buffer_size, size_t block_s
         pool->capacity = usable / stride;
 
         // build intrusive free list
-        unsigned char *p = (unsigned char *)first_addr;
+        UCPoolBlock *p = (UCPoolBlock*)first_addr;
         for (size_t i = 0; i < pool->capacity - 1; ++i) {
-            *(unsigned char **)p = p + stride;
+            void *punt = __builtin_assume_aligned(&p->data[0] + pool->block_size, _Alignof(UCPoolBlock));
-            p += stride;
+            UCPoolBlock *next = punt;
+            p->next = next;
+            p = next;
         }
-        *(unsigned char **)p = NULL; // last element
+        ((UCPoolBlock *)p)->next = NULL; // last element
-        pool->free_list = (unsigned char *)first_addr;
+        pool->free_list = (UCPoolBlock *)first_addr;
     }
 
     pool->block_size = stride;
     pool->align      = align;
-    pool->start      = (unsigned char *)buffer;
+    pool->start      = buffer;
-    pool->end        = (unsigned char *)buffer + buffer_size;
+    pool->end        = buffer + buffer_size;
 }
 
 
@@ -55,13 +57,13 @@ void *uc_pool_alloc(UCPool *pool)
     if (!pool->free_list) {
         return NULL;
     }
-    unsigned char *block = pool->free_list;
+    UCPoolBlock *block = pool->free_list;
-    pool->free_list = *(unsigned char **)block;
+    pool->free_list = block->next;
 
 #ifdef DEBUG
     memset(block, 0xCB, pool->block_size);
 #endif
-    return block;
+    return block->data;
 }
 #include <stdio.h>
 
@@ -70,12 +72,13 @@ void uc_pool_free(UCPool *pool, void *p)
     if (p == NULL) {
         return;
     }
+    UCPoolBlock *block = p;
 #ifdef DEBUG
-    assert((unsigned char *)p >= pool->start && (unsigned char*)p < pool->end);
+    assert(block >= pool->start && block < pool->end);
     assert(((uintptr_t)p - (uintptr_t)pool->start) % pool->block_size == 0);
 
     // double-free detection
-    for (unsigned char *f = pool->free_list; f; f = *(unsigned char**)f) {
+    for (UCPoolBlock *f = pool->free_list; f; f = f->next) {
         if (f == p) {
             assert(0 && "Double free detected in pool!");
             return;
@@ -85,7 +88,7 @@ void uc_pool_free(UCPool *pool, void *p)
     memset(p, 0xDD, pool->block_size);
 #endif
      // When not in use, store pointer to next free element inline in the block
-    *(unsigned char **)p = pool->free_list;
+    block->next = pool->free_list;
     pool->free_list = p;
 }
 
@@ -98,14 +101,18 @@ void uc_pool_reset(UCPool *pool)
     uintptr_t start_addr = (uintptr_t)pool->start;
     uintptr_t first_addr = UC_ALIGN(start_addr, pool->align);
 
-    unsigned char *p = (unsigned char *)first_addr;
     // build intrusive free list
+    UCPoolBlock *p = (UCPoolBlock*)first_addr;
     for (size_t i = 0; i < pool->capacity - 1; ++i) {
-        *(unsigned char **)p = p + pool->block_size;
+        void *punt = __builtin_assume_aligned(&p->data[0] + pool->block_size, _Alignof(UCPoolBlock));
-        p += pool->block_size;
+        UCPoolBlock *next = punt;
+        p->next = next;
+        p = next;
+
     }
 
-    *(unsigned char **)p = NULL;  // last element
+    p->next = NULL;  // last element
 
-    pool->free_list = (unsigned char *)first_addr;
+    pool->free_list = (UCPoolBlock *)first_addr;
 }
+