Add basic futex implementation

siloam72761 · Apr 6, 2018 · b9c0f6a · b9c0f6a
1 parent 498ecfe
commit b9c0f6a
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Showing 7 changed files with 122 additions and 3 deletions.
diff --git a/emu/memory.c b/emu/memory.c
@@ -141,7 +141,7 @@ static __no_instrument void set_dirty_page(struct mem *mem, page_t page) {
     mem->dirty_page = page;
 }
 
-char *mem_ptr(struct mem *mem, addr_t addr, int type) {
+void *mem_ptr(struct mem *mem, addr_t addr, int type) {
     page_t page = PAGE(addr);
     struct pt_entry *entry = &mem->pt[page];
 

diff --git a/emu/memory.h b/emu/memory.h
@@ -76,7 +76,7 @@ int pt_copy_on_write(struct mem *src, page_t src_start, struct mem *dst, page_t
 
 #define MEM_READ 0
 #define MEM_WRITE 1
-char *mem_ptr(struct mem *mem, addr_t addr, int type);
+void *mem_ptr(struct mem *mem, addr_t addr, int type);
 
 extern size_t real_page_size;
 

diff --git a/kernel/calls.c b/kernel/calls.c
@@ -97,6 +97,7 @@ syscall_t syscall_table[] = {
     [228] = (syscall_t) sys_fsetxattr,
     [238] = (syscall_t) sys_tkill,
     [239] = (syscall_t) sys_sendfile64,
+    [240] = (syscall_t) sys_futex,
     [243] = (syscall_t) sys_set_thread_area,
     [252] = (syscall_t) sys_exit_group,
     [258] = (syscall_t) sys_set_tid_address,

diff --git a/kernel/calls.h b/kernel/calls.h
@@ -173,7 +173,8 @@ struct sys_info {
 };
 dword_t sys_sysinfo(addr_t info_addr);
 
-// time
+// futexes
+dword_t sys_futex(addr_t uaddr, dword_t op, dword_t val);
 
 // crap that ideally shouldn't exist
 struct pollfd_ {

diff --git a/kernel/futex.c b/kernel/futex.c
@@ -0,0 +1,115 @@
+#include "kernel/calls.h"
+
+struct futex {
+    atomic_uint refcount;
+    struct mem *mem;
+    addr_t addr;
+    lock_t lock;
+    pthread_cond_t cond;
+    struct list chain; // locked by futex_hash_lock
+};
+
+#define FUTEX_HASH_BITS 12
+#define FUTEX_HASH_SIZE (1 << FUTEX_HASH_BITS)
+static lock_t futex_hash_lock;
+static struct list futex_hash[FUTEX_HASH_SIZE];
+
+static void __attribute__((constructor)) init_futex_hash() {
+    for (int i = 0; i < FUTEX_HASH_SIZE; i++)
+        list_init(&futex_hash[i]);
+}
+
+// returns the futex for the current process at the given addr, and locks it
+static struct futex *futex_get(addr_t addr) {
+    int hash = (addr ^ (unsigned long) current->cpu.mem) % FUTEX_HASH_SIZE;
+    lock(&futex_hash_lock);
+    struct list *bucket = &futex_hash[hash];
+    struct futex *futex;
+    list_for_each_entry(bucket, futex, chain) {
+        if (futex->addr == addr) {
+            futex->refcount++;
+            goto have_futex;
+        }
+    }
+
+    futex = malloc(sizeof(struct futex));
+    if (futex == NULL)
+        return NULL;
+    futex->refcount = 0;
+    futex->mem = current->cpu.mem;
+    futex->addr = addr;
+    lock_init(&futex->lock);
+    pthread_cond_init(&futex->cond, NULL);
+    list_add(bucket, &futex->chain);
+
+have_futex:
+    lock(&futex->lock);
+    unlock(&futex_hash_lock);
+    return futex;
+}
+
+// must be called on the result of futex_get when you're done with it
+static void futex_put(struct futex *futex) {
+    unlock(&futex->lock);
+    if (--futex->refcount == 0) {
+        lock(&futex_hash_lock);
+        list_remove(&futex->chain);
+        unlock(&futex_hash_lock);
+    }
+}
+
+static int futex_load(struct futex *futex, dword_t *out) {
+    dword_t *ptr = mem_ptr(futex->mem, futex->addr, MEM_READ);
+    if (ptr == NULL)
+        return 1;
+    *out = *ptr;
+    return 0;
+}
+
+int futex_wait(addr_t uaddr, dword_t val) {
+    struct futex *futex = futex_get(uaddr);
+    int err = 0;
+    dword_t tmp;
+    if (futex_load(futex, &tmp))
+        err = _EFAULT;
+    else if (tmp != val)
+        err = _EAGAIN;
+    else
+        pthread_cond_wait(&futex->cond, &futex->lock);
+    futex_put(futex);
+    return err;
+}
+
+int futex_wake(addr_t uaddr, dword_t val) {
+    struct futex *futex = futex_get(uaddr);
+    if (val == 1)
+        pthread_cond_signal(&futex->cond);
+    else if (val != 0x7fffffff)
+        pthread_cond_broadcast(&futex->cond);
+    else
+        TODO("invalid number of futex wakes %d", val);
+    futex_put(futex);
+    return val; // FIXME wrong if val is INT_MAX
+}
+
+#define FUTEX_WAIT_ 0
+#define FUTEX_WAKE_ 1
+#define FUTEX_PRIVATE_FLAG_ 128
+#define FUTEX_CMD_MASK_ ~(FUTEX_PRIVATE_FLAG_)
+
+dword_t sys_futex(addr_t uaddr, dword_t op, dword_t val) {
+    if (!(op & FUTEX_PRIVATE_FLAG_)) {
+        FIXME("no support for shared futexes");
+        return _ENOSYS;
+    }
+    switch (op & FUTEX_CMD_MASK_) {
+        case FUTEX_WAIT_:
+            STRACE("futex_wait(0x%x, %d)", uaddr, val);
+            return futex_wait(uaddr, val);
+        case FUTEX_WAKE_:
+            STRACE("futex_wake(0x%x, %d)", uaddr, val);
+            return futex_wake(uaddr, val);
+    }
+    FIXME("unsupported futex operation %d", op);
+    return _ENOSYS;
+}
diff --git a/kernel/tls.c b/kernel/tls.c
@@ -32,6 +32,7 @@ int task_set_thread_area(struct task *task, addr_t u_info) {
 }
 
 int sys_set_thread_area(addr_t u_info) {
+    STRACE("set_thread_area(0x%x)", u_info);
     return task_set_thread_area(current, u_info);
 }
 

diff --git a/meson.build b/meson.build
@@ -49,6 +49,7 @@ src = [
     'kernel/mmap.c',
     'kernel/uname.c',
     'kernel/tls.c',
+    'kernel/futex.c',
     'kernel/getset.c',
     'kernel/signal.c',
     'kernel/resource.c',
-Original file line number
+Diff line change
@@ Expand Up / @@ -32,6 +32,7 @@ int task_set_thread_area(struct task *task, addr_t u_info) { @@
     }
     int sys_set_thread_area(addr_t u_info) {
+        STRACE("set_thread_area(0x%x)", u_info);
         return task_set_thread_area(current, u_info);
     }
@@ Expand Down @@