kernel: do not rely on struct layout when downcasting

Makefile

@@ -10,7 +10,7 @@ export CFLAGS := \
 	-nostdlib -ffreestanding \
 	-fno-omit-frame-pointer \
 	-U_FORTIFY_SOURCE \
-	-Wall -Wextra -pedantic \
+	-Wall -Wextra -pedantic -Wno-gnu-statement-expression-from-macro-expansion \
 	-O2 -g \
 	$(if $(GIT_HASH),-DYAGURA_VERSION=\"$(GIT_HASH)\") \
 	$(EXTRA_CFLAGS)

common/extra.h

@@ -15,6 +15,12 @@
 #define SIZEOF_FIELD(t, f) sizeof(((t*)0)->f)
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
 
+#define CONTAINER_OF(ptr, type, member)                                        \
+    ({                                                                         \
+        const __typeof__(((type*)0)->member)* __mptr = (ptr);                  \
+        (type*)((char*)__mptr - offsetof(type, member));                       \
+    })
+
 #define ROUND_UP(x, align) (((x) + ((align) - 1)) & ~((align) - 1))
 #define ROUND_DOWN(x, align) ((x) & ~((align) - 1))
 #define DIV_CEIL(lhs, rhs) (((lhs) + (rhs) - 1) / (rhs))

kernel/console/tty.c

@@ -1,4 +1,5 @@
 #include "private.h"
+#include <common/extra.h>
 #include <common/string.h>
 #include <kernel/api/signal.h>
 #include <kernel/api/sys/ioctl.h>
@@ -9,20 +10,23 @@
 #include <kernel/safe_string.h>
 #include <kernel/task.h>
 
+static struct tty* tty_from_file(struct file* file) {
+    return CONTAINER_OF(file->inode, struct tty, inode);
+}
+
 static bool can_read(struct tty* tty) {
     return !ring_buf_is_empty(&tty->input_buf);
 }
 
 static bool unblock_read(struct file* file) {
-    struct tty* tty = (struct tty*)file->inode;
-    return can_read(tty);
+    return can_read(tty_from_file(file));
 }
 
 static ssize_t tty_pread(struct file* file, void* buf, size_t count,
                          uint64_t offset) {
     (void)offset;
 
-    struct tty* tty = (struct tty*)file->inode;
+    struct tty* tty = tty_from_file(file);
 
     for (;;) {
         int rc = file_block(file, unblock_read, 0);
@@ -81,15 +85,15 @@ static void processed_echo(struct tty* tty, const char* buf, size_t count) {
 static ssize_t tty_pwrite(struct file* file, const void* buf, size_t count,
                           uint64_t offset) {
     (void)offset;
-    struct tty* tty = (struct tty*)file->inode;
+    struct tty* tty = tty_from_file(file);
     spinlock_lock(&tty->lock);
     processed_echo(tty, buf, count);
     spinlock_unlock(&tty->lock);
     return count;
 }
 
 static int tty_ioctl(struct file* file, int request, void* user_argp) {
-    struct tty* tty = (struct tty*)file->inode;
+    struct tty* tty = tty_from_file(file);
     struct termios* termios = &tty->termios;
     int ret = 0;
     spinlock_lock(&tty->lock);
@@ -157,9 +161,9 @@ static int tty_ioctl(struct file* file, int request, void* user_argp) {
 }
 
 static short tty_poll(struct file* file, short events) {
-    struct tty* tty = (struct tty*)file->inode;
     short revents = 0;
     if (events & POLLIN) {
+        struct tty* tty = tty_from_file(file);
         spinlock_lock(&tty->lock);
         if (can_read(tty))
             revents |= POLLIN;

kernel/fs/fifo.c

@@ -15,8 +15,16 @@ struct fifo {
     atomic_size_t num_writers;
 };
 
+static struct fifo* fifo_from_inode(struct inode* inode) {
+    return CONTAINER_OF(inode, struct fifo, inode);
+}
+
+static struct fifo* fifo_from_file(struct file* file) {
+    return fifo_from_inode(file->inode);
+}
+
 static void fifo_destroy_inode(struct inode* inode) {
-    struct fifo* fifo = (struct fifo*)inode;
+    struct fifo* fifo = fifo_from_inode(inode);
     ring_buf_destroy(&fifo->buf);
     kfree(fifo);
 }
@@ -36,7 +44,7 @@ static bool unblock_open(struct file* file) {
 static int fifo_open(struct file* file, mode_t mode) {
     (void)mode;
 
-    struct fifo* fifo = (struct fifo*)file->inode;
+    struct fifo* fifo = fifo_from_file(file);
     switch (file->flags & O_ACCMODE) {
     case O_RDONLY:
         ++fifo->num_readers;
@@ -61,7 +69,7 @@ static int fifo_open(struct file* file, mode_t mode) {
 }
 
 static int fifo_close(struct file* file) {
-    struct fifo* fifo = (struct fifo*)file->inode;
+    struct fifo* fifo = fifo_from_file(file);
     switch (file->flags & O_ACCMODE) {
     case O_RDONLY:
         --fifo->num_readers;
@@ -76,15 +84,15 @@ static int fifo_close(struct file* file) {
 }
 
 static bool unblock_read(struct file* file) {
-    const struct fifo* fifo = (const struct fifo*)file->inode;
+    const struct fifo* fifo = fifo_from_file(file);
     return fifo->num_writers == 0 || !ring_buf_is_empty(&fifo->buf);
 }
 
 static ssize_t fifo_pread(struct file* file, void* buffer, size_t count,
                           uint64_t offset) {
     (void)offset;
 
-    struct fifo* fifo = (struct fifo*)file->inode;
+    struct fifo* fifo = fifo_from_file(file);
     struct ring_buf* buf = &fifo->buf;
 
     for (;;) {
@@ -115,7 +123,7 @@ static ssize_t fifo_pwrite(struct file* file, const void* buffer, size_t count,
                            uint64_t offset) {
     (void)offset;
 
-    struct fifo* fifo = (struct fifo*)file->inode;
+    struct fifo* fifo = fifo_from_file(file);
     struct ring_buf* buf = &fifo->buf;
 
     for (;;) {
@@ -190,5 +198,5 @@ struct inode* fifo_create(void) {
     inode->mode = S_IFIFO;
     inode->ref_count = 1;
 
-    return (struct inode*)fifo;
+    return inode;
 }

kernel/fs/fs.c

@@ -9,6 +9,7 @@
 #include <kernel/panic.h>
 #include <kernel/safe_string.h>
 #include <kernel/sched.h>
+#include <kernel/socket.h>
 
 void inode_ref(struct inode* inode) {
     ASSERT(inode);
@@ -27,7 +28,7 @@ void inode_destroy(struct inode* inode) {
     ASSERT(inode->ref_count == 0 && inode->num_links == 0);
     ASSERT(inode->fops->destroy_inode);
     inode_unref(inode->fifo);
-    inode_unref((struct inode*)inode->bound_socket);
+    inode_unref(&inode->bound_socket->inode);
     inode->fops->destroy_inode(inode);
 }
 

kernel/fs/proc/pid.c

@@ -22,8 +22,12 @@ typedef struct {
     pid_t pid;
 } proc_pid_item_inode;
 
+static proc_pid_item_inode* item_from_file(struct file* file) {
+    return CONTAINER_OF(file->inode, proc_pid_item_inode, item_inode.inode);
+}
+
 static int populate_cmdline(struct file* file, struct vec* vec) {
-    proc_pid_item_inode* node = (proc_pid_item_inode*)file->inode;
+    proc_pid_item_inode* node = item_from_file(file);
     struct task* task = task_find_by_tid(node->pid);
     if (!task)
         return -ENOENT;
@@ -57,7 +61,7 @@ static int populate_cmdline(struct file* file, struct vec* vec) {
 }
 
 static int populate_comm(struct file* file, struct vec* vec) {
-    proc_pid_item_inode* node = (proc_pid_item_inode*)file->inode;
+    proc_pid_item_inode* node = item_from_file(file);
     struct task* task = task_find_by_tid(node->pid);
     if (!task)
         return -ENOENT;
@@ -74,7 +78,7 @@ static int populate_comm(struct file* file, struct vec* vec) {
 }
 
 static int populate_cwd(struct file* file, struct vec* vec) {
-    proc_pid_item_inode* node = (proc_pid_item_inode*)file->inode;
+    proc_pid_item_inode* node = item_from_file(file);
     struct task* task = task_find_by_tid(node->pid);
     if (!task)
         return -ENOENT;
@@ -96,7 +100,7 @@ static int populate_cwd(struct file* file, struct vec* vec) {
 }
 
 static int populate_environ(struct file* file, struct vec* vec) {
-    proc_pid_item_inode* node = (proc_pid_item_inode*)file->inode;
+    proc_pid_item_inode* node = item_from_file(file);
     struct task* task = task_find_by_tid(node->pid);
     if (!task)
         return -ENOENT;
@@ -130,7 +134,7 @@ static int populate_environ(struct file* file, struct vec* vec) {
 }
 
 static int populate_maps(struct file* file, struct vec* vec) {
-    proc_pid_item_inode* node = (proc_pid_item_inode*)file->inode;
+    proc_pid_item_inode* node = item_from_file(file);
     struct task* task = task_find_by_tid(node->pid);
     if (!task)
         return -ENOENT;
@@ -159,7 +163,7 @@ static int add_item(proc_dir_inode* parent, const proc_item_def* item_def,
                     pid_t pid) {
     proc_pid_item_inode* node = kmalloc(sizeof(proc_pid_item_inode));
     if (!node) {
-        inode_unref((struct inode*)parent);
+        inode_unref(&parent->inode);
         return -ENOMEM;
     }
     *node = (proc_pid_item_inode){0};
@@ -174,7 +178,7 @@ static int add_item(proc_dir_inode* parent, const proc_item_def* item_def,
     inode->ref_count = 1;
 
     int rc = dentry_append(&parent->children, item_def->name, inode);
-    inode_unref((struct inode*)parent);
+    inode_unref(&parent->inode);
     return rc;
 }
 
@@ -215,6 +219,6 @@ struct inode* proc_pid_dir_inode_create(proc_dir_inode* parent, pid_t pid) {
             return ERR_PTR(rc);
     }
 
-    inode_unref((struct inode*)parent);
+    inode_unref(&parent->inode);
     return inode;
 }

kernel/fs/proc/private.h

@@ -26,6 +26,10 @@ typedef struct {
     struct dentry* children;
 } proc_dir_inode;
 
+static inline proc_dir_inode* proc_dir_from_inode(struct inode* inode) {
+    return CONTAINER_OF(inode, proc_dir_inode, inode);
+}
+
 void proc_dir_destroy_inode(struct inode* inode);
 struct inode* proc_dir_lookup_child(struct inode* inode, const char* name);
 int proc_dir_getdents(struct file*, getdents_callback_fn callback, void* ctx);

kernel/fs/proc/proc.c

@@ -14,7 +14,7 @@ static int proc_item_open(struct file* file, mode_t mode) {
         return -ENOMEM;
     *vec = (struct vec){0};
 
-    proc_item_inode* node = (proc_item_inode*)file->inode;
+    proc_item_inode* node = CONTAINER_OF(file->inode, proc_item_inode, inode);
     int rc = node->populate(file, vec);
     if (IS_ERR(rc)) {
         vec_destroy(vec);
@@ -45,21 +45,21 @@ const struct file_ops proc_item_fops = {
 };
 
 void proc_dir_destroy_inode(struct inode* inode) {
-    proc_dir_inode* node = (proc_dir_inode*)inode;
+    proc_dir_inode* node = proc_dir_from_inode(inode);
     dentry_clear(node->children);
     kfree(node);
 }
 
 struct inode* proc_dir_lookup_child(struct inode* inode, const char* name) {
-    proc_dir_inode* node = (proc_dir_inode*)inode;
+    proc_dir_inode* node = proc_dir_from_inode(inode);
     struct inode* child = dentry_find(node->children, name);
     inode_unref(inode);
     return child;
 }
 
 int proc_dir_getdents(struct file* file, getdents_callback_fn callback,
                       void* ctx) {
-    proc_dir_inode* node = (proc_dir_inode*)file->inode;
+    proc_dir_inode* node = proc_dir_from_inode(file->inode);
     mutex_lock(&file->offset_lock);
     int rc = dentry_getdents(file, node->children, callback, ctx);
     mutex_unlock(&file->offset_lock);

kernel/fs/proc/root.c

@@ -168,15 +168,16 @@ static proc_item_def root_items[] = {
 static struct inode* proc_root_lookup_child(struct inode* inode,
                                             const char* name) {
     if (str_is_uint(name)) {
+        proc_dir_inode* parent = proc_dir_from_inode(inode);
         pid_t pid = atoi(name);
-        return proc_pid_dir_inode_create((proc_dir_inode*)inode, pid);
+        return proc_pid_dir_inode_create(parent, pid);
     }
     return proc_dir_lookup_child(inode, name);
 }
 
 static int proc_root_getdents(struct file* file, getdents_callback_fn callback,
                               void* ctx) {
-    proc_dir_inode* node = (proc_dir_inode*)file->inode;
+    proc_dir_inode* node = CONTAINER_OF(file->inode, proc_dir_inode, inode);
 
     mutex_lock(&file->offset_lock);
     if ((size_t)file->offset < NUM_ITEMS) {
@@ -218,7 +219,7 @@ static int proc_root_getdents(struct file* file, getdents_callback_fn callback,
 static int add_item(proc_dir_inode* parent, const proc_item_def* item_def) {
     proc_item_inode* node = kmalloc(sizeof(proc_item_inode));
     if (!node) {
-        inode_unref((struct inode*)parent);
+        inode_unref(&parent->inode);
         return -ENOMEM;
     }
     *node = (proc_item_inode){0};
@@ -232,7 +233,7 @@ static int add_item(proc_dir_inode* parent, const proc_item_def* item_def) {
     inode->ref_count = 1;
 
     int rc = dentry_append(&parent->children, item_def->name, inode);
-    inode_unref((struct inode*)parent);
+    inode_unref(&parent->inode);
     return rc;
 }