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Merge pull request #221 from smartobjectoriented/217-implementation-of-futex-syscall
Futex syscall implementation
2 parents 37a2f1a + 8be034c commit 774b56e

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10 files changed

+241
-25
lines changed

10 files changed

+241
-25
lines changed

‎so3/include/futex.h‎

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/*
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* Copyright (C) 2014-2025 Daniel Rossier <daniel.rossier@heig-vd.ch>
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* Copyright (C) 2025 Jean-Pierre Miceli <jean-pierre.miceli@heig-vd.ch>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*
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*/
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#ifndef FUTEX_H
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#define FUTEX_H
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#include <timer.h>
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#include <thread.h>
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#include <list.h>
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#include <spinlock.h>
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#include <syscall.h>
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/* Commands */
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#define FUTEX_WAIT 0
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#define FUTEX_WAKE 1
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#define FUTEX_FD 2
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#define FUTEX_REQUEUE 3
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#define FUTEX_CMP_REQUEUE 4
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#define FUTEX_WAKE_OP 5
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#define FUTEX_LOCK_PI 6
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#define FUTEX_UNLOCK_PI 7
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#define FUTEX_TRYLOCK_PI 8
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#define FUTEX_WAIT_BITSET 9
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#define FUTEX_PRIVATE_FLAG 128
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#define FUTEX_CLOCK_REALTIME 256
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#define FUTEX_CMD_MASK ~(FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME)
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/**
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* list of futexes
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*/
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typedef struct futex {
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struct list_head list;
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struct list_head f_element;
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uintptr_t key;
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} futex_t;
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SYSCALL_DECLARE(futex, u32 *uaddr, int op, u32 val, const struct timespec *utime, u32 *uaddr2, u32 val3)
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#endif /* FUTEX_H */

‎so3/include/list.h‎

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@@ -169,6 +169,16 @@ static inline int list_is_last(const struct list_head *list, const struct list_h
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return list->next == head;
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}
171171

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/**
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* list_is_head - tests whether @list is the list @head
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* @list: the entry to test
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* @head: the head of the list
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*/
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static inline int list_is_head(const struct list_head *list, const struct list_head *head)
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{
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return list == head;
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}
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/**
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* list_empty - tests whether a list is empty
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* @head: the list to test.

‎so3/include/mutex.h‎

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Original file line numberDiff line numberDiff line change
@@ -59,8 +59,4 @@ void mutex_lock(struct mutex *lock);
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void mutex_unlock(struct mutex *lock);
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void mutex_init(struct mutex *lock);
6161

62-
SYSCALL_DECLARE(mutex_init, void);
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SYSCALL_DECLARE(mutex_lock, unsigned long number);
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SYSCALL_DECLARE(mutex_unlock, unsigned long number);
65-
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#endif /* MUTEX_H */

‎so3/include/process.h‎

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@@ -29,6 +29,8 @@
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#include <memory.h>
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#include <signal.h>
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#include <ptrace.h>
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#include <spinlock.h>
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#include <futex.h>
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#include <mutex.h>
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#include <syscall.h>
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@@ -106,6 +108,10 @@ struct pcb {
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/* Number of pages required by this process (including binary image) */
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size_t page_count;
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/* List of futexes */
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struct list_head futex;
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spinlock_t futex_lock;
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/* List of frames (physical pages) belonging to this process */
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struct list_head page_list;
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‎so3/kernel/Makefile‎

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Original file line numberDiff line numberDiff line change
@@ -8,6 +8,7 @@ obj-y += main.o \
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thread.o \
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schedule.o \
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mutex.o \
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futex.o \
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spinlock.o \
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syscalls.o \
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softirq.o \

‎so3/kernel/futex.c‎

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@@ -0,0 +1,162 @@
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/*
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* Copyright (C) 2025 Jean-Pierre Miceli <jean-pierre.miceli@heig-vd.ch>
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*
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* This program is free software; you can redistribute it and/or modify
5+
* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful,
9+
* but WITHOUT ANY WARRANTY; without even the implied warranty of
10+
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
11+
* GNU General Public License for more details.
12+
*
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* You should have received a copy of the GNU General Public License
14+
* along with this program; if not, write to the Free Software
15+
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*
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*/
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#include <process.h>
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#include <heap.h>
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#include <errno.h>
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#include <futex.h>
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/**
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* do_futex_wait - block on futex_w
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*
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* @param futex_w address of the futex word
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* @param val expected value of the futex word
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* @return 0 on success or error value
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*/
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static int do_futex_wait(uint32_t *futex_w, uint32_t val)
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{
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unsigned long flags;
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pcb_t *pcb = current()->pcb;
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struct list_head *pos;
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futex_t *futex;
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queue_thread_t f_element;
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flags = spin_lock_irqsave(&pcb->futex_lock);
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if (*futex_w != val) {
42+
spin_unlock_irqrestore(&pcb->futex_lock, flags);
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return -EAGAIN;
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}
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/* look if a futex_w already exists */
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list_for_each(pos, &pcb->futex) {
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futex = list_entry(pos, futex_t, list);
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if ((uintptr_t) futex_w == futex->key)
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break;
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}
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54+
if (list_is_head(pos, &pcb->futex)) {
55+
/* no futex on futex_w */
56+
futex = (futex_t *) calloc(1, sizeof(futex_t));
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if (futex == NULL)
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BUG();
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futex->key = (uintptr_t) futex_w;
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INIT_LIST_HEAD(&futex->f_element);
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list_add_tail(&futex->list, &pcb->futex);
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}
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f_element.tcb = current();
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list_add_tail(&f_element.list, &futex->f_element);
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/* go to sleep. */
71+
spin_unlock(&pcb->futex_lock);
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waiting();
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BUG_ON(local_irq_is_enabled());
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spin_lock(&pcb->futex_lock);
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if (list_empty(&futex->f_element))
79+
free(futex);
80+
81+
spin_unlock_irqrestore(&pcb->futex_lock, flags);
82+
83+
return 0;
84+
}
85+
86+
/**
87+
* do_futex_wake - wake one or more tasks blocked on uaddr
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*
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* @nr_wake wake up to this many tasks
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* @return the number of waiters that were woken up
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*/
92+
static int do_futex_wake(uint32_t *futex_w, uint32_t nr_wake)
93+
{
94+
unsigned long flags;
95+
pcb_t *pcb = current()->pcb;
96+
struct list_head *pos, *p;
97+
futex_t *futex;
98+
queue_thread_t *f_element;
99+
unsigned idx = 0;
100+
101+
flags = spin_lock_irqsave(&pcb->futex_lock);
102+
103+
/* Search for the futex element with futex_w as key */
104+
list_for_each(pos, &pcb->futex) {
105+
futex = list_entry(pos, futex_t, list);
106+
107+
if ((uintptr_t) futex_w == futex->key)
108+
break;
109+
}
110+
111+
/* Check if the wanted key was found in the list */
112+
if (list_is_head(pos, &pcb->futex)) {
113+
/* key does not exists in futex - Error */
114+
spin_unlock_irqrestore(&pcb->futex_lock, flags);
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return -EINVAL;
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}
117+
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/* wakes at most nr_wake of the waiters that are waiting */
119+
list_for_each_safe(pos, p, &futex->list) {
120+
f_element = list_entry(pos, queue_thread_t, list);
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122+
if (idx == nr_wake)
123+
break;
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125+
list_del(&f_element->list);
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ready(f_element->tcb);
127+
128+
idx++;
129+
}
130+
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spin_unlock_irqrestore(&pcb->futex_lock, flags);
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133+
return idx;
134+
}
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SYSCALL_DEFINE6(futex, uint32_t *, uaddr, int, op, uint32_t, val, const struct timespec *, utime, uint32_t *, uaddr2, uint32_t,
137+
val3)
138+
{
139+
int cmd = op & FUTEX_CMD_MASK;
140+
141+
if (utime)
142+
printk("[futex] utime parameter is not used in current implementation\n");
143+
144+
switch (cmd) {
145+
case FUTEX_WAIT:
146+
return do_futex_wait(uaddr, val);
147+
case FUTEX_WAKE:
148+
return do_futex_wake(uaddr, val);
149+
case FUTEX_FD:
150+
case FUTEX_REQUEUE:
151+
case FUTEX_CMP_REQUEUE:
152+
case FUTEX_WAKE_OP:
153+
case FUTEX_LOCK_PI:
154+
case FUTEX_UNLOCK_PI:
155+
case FUTEX_TRYLOCK_PI:
156+
case FUTEX_WAIT_BITSET:
157+
printk("Futex cmd '%d' not supported !\n");
158+
return -EINVAL;
159+
}
160+
161+
return -ENOSYS;
162+
}

‎so3/kernel/mutex.c‎

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Original file line numberDiff line numberDiff line change
@@ -146,27 +146,6 @@ void mutex_unlock(struct mutex *lock)
146146
schedule();
147147
}
148148

149-
/*
150-
* The following syscall implementation are a first attempt, mainly used for debugging kernel mutexes.
151-
*/
152-
SYSCALL_DEFINE1(mutex_lock, unsigned long, number)
153-
{
154-
if (number >= N_MUTEX) {
155-
return -EINVAL;
156-
}
157-
mutex_lock(&current()->pcb->lock[number]);
158-
return 0;
159-
}
160-
161-
SYSCALL_DEFINE1(mutex_unlock, unsigned long, number)
162-
{
163-
if (number >= N_MUTEX) {
164-
return -EINVAL;
165-
}
166-
mutex_unlock(&current()->pcb->lock[number]);
167-
return 0;
168-
}
169-
170149
void mutex_init(struct mutex *lock)
171150
{
172151
memset(lock, 0, sizeof(struct mutex));

‎so3/kernel/process.c‎

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@@ -202,6 +202,10 @@ pcb_t *new_process(void)
202202
/* Init the list of pages */
203203
INIT_LIST_HEAD(&pcb->page_list);
204204

205+
/* Init the futex */
206+
INIT_LIST_HEAD(&pcb->futex);
207+
spin_lock_init(&pcb->futex_lock);
208+
205209
pcb->pid = pid_current++;
206210

207211
/* Init the list of child threads */

‎so3/kernel/syscalls.c‎

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@@ -28,6 +28,7 @@
2828
#include <signal.h>
2929
#include <timer.h>
3030
#include <net.h>
31+
#include <futex.h>
3132
#include <syscall.h>
3233

3334
extern void __get_syscall_args_ext(uint32_t *syscall_no);

‎so3/syscall.tbl‎

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@@ -37,6 +37,7 @@ newfstatat
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mmap
3838
mmap2
3939
nanosleep
40+
futex
4041
pipe IPC_PIPE
4142
pipe2 IPC_PIPE
4243
rt_sigaction IPC_SIGNAL

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