diff --git a/arch/amd64/syscall.c b/arch/amd64/syscall.c
index 145fc2a..7a31d62 100644
--- a/arch/amd64/syscall.c
+++ b/arch/amd64/syscall.c
@@ -77,6 +77,7 @@ void *syscall_table[256] = {
     [SYSCALL_NRX_WAITPID] =         sys_waitpid,
     [SYSCALL_NR_GETPGID] =          sys_getpgid,
     [SYSCALL_NR_SETPGID] =          sys_setpgid,
+    [SYSCALL_NR_SIGALTSTACK] =      sys_sigaltstack,
 
     // System
     [SYSCALL_NR_SYNC] =             sys_sync,
diff --git a/include/sys/sys_proc.h b/include/sys/sys_proc.h
index 807ab8a..ba683c1 100644
--- a/include/sys/sys_proc.h
+++ b/include/sys/sys_proc.h
@@ -1,6 +1,8 @@
 #pragma once
 #include "sys/types.h"
 
+struct user_stack;
+
 int sys_kill(pid_t pid, int signum);
 void sys_exit(int status);
 void sys_sigentry(uintptr_t entry);
@@ -14,6 +16,8 @@ gid_t sys_getgid(void);
 int sys_setuid(uid_t uid);
 int sys_setgid(gid_t gid);
 
+int sys_sigaltstack(const struct user_stack *ss, struct user_stack *old_ss);
+
 int sys_waitpid(pid_t pid, int *status, int flags);
 pid_t sys_getpgid(pid_t pid);
 int sys_setpgid(pid_t pid, pid_t pgrp);
diff --git a/include/sys/thread.h b/include/sys/thread.h
index 1344bc5..2ac6902 100644
--- a/include/sys/thread.h
+++ b/include/sys/thread.h
@@ -51,6 +51,11 @@ struct thread {
     struct process *proc;
     struct thread *next_thread;
 
+    // Signal
+    uintptr_t signal_entry;
+    uintptr_t signal_stack_base;
+    size_t signal_stack_size;
+
     uint32_t flags;
 
     // Scheduler
@@ -80,7 +85,6 @@ struct process {
     struct io_notify pid_notify;
 
     // Signal
-    uintptr_t signal_entry;
     uint64_t sigq;
 
     // State
diff --git a/include/user/signum.h b/include/user/signum.h
index 1110760..7278675 100644
--- a/include/user/signum.h
+++ b/include/user/signum.h
@@ -1,4 +1,5 @@
 #pragma once
+#include <sys/types.h>
 
 //#define SIGHUP      1
 //#define SIGINT      2
@@ -57,4 +58,13 @@
 
 #define NSIG        32
 
+struct user_stack {
+    void *ss_sp;
+    size_t ss_size;
+};
+
+#if !defined(__KERNEL__)
+typedef struct user_stack stack_t;
+#endif
+
 int kill(int pid, int signum);
diff --git a/include/user/syscall.h b/include/user/syscall.h
index eb3fb10..1cc469b 100644
--- a/include/user/syscall.h
+++ b/include/user/syscall.h
@@ -51,6 +51,7 @@
 #define SYSCALL_NR_SETGID           106
 #define SYSCALL_NR_SETPGID          109
 #define SYSCALL_NR_GETPGID          121
+#define SYSCALL_NR_SIGALTSTACK      131
 #define SYSCALL_NRX_WAITPID         247
 
 #define SYSCALL_NR_SOCKET           41
diff --git a/sys/execve.c b/sys/execve.c
index d801cec..c717d4c 100644
--- a/sys/execve.c
+++ b/sys/execve.c
@@ -270,7 +270,10 @@ int sys_execve(const char *path, const char **argv, const char **envp) {
     argv_fixup[procv_vecp[0]] = 0;
     envp_fixup[procv_vecp[1]] = 0;
 
-    proc->signal_entry = 0;
+    thr->signal_entry = MM_NADDR;
+    thr->signal_stack_base = MM_NADDR;
+    thr->signal_stack_size = 0;
+
     thr->data.rsp0 = thr->data.rsp0_top;
 
     // Allocate a new user stack
diff --git a/sys/thread.c b/sys/thread.c
index 5143e08..8603e0a 100644
--- a/sys/thread.c
+++ b/sys/thread.c
@@ -234,7 +234,8 @@ int process_init_thread(struct process *proc, uintptr_t entry, void *arg, int us
     proc->first_child = NULL;
     proc->next_child = NULL;
     proc->pgid = -1;
-    proc->pid = -1;
+    proc->pid = process_alloc_pid(user);
+    kdebug("New process #%d with main thread <%p>", proc->pid, main_thread);
 
     proc->sigq = 0;
     proc->proc_state = PROC_ACTIVE;
@@ -277,10 +278,15 @@ int thread_init(struct thread *thr, uintptr_t entry, void *arg, int flags) {
     uintptr_t stack_pages = mm_phys_alloc_contiguous(2); //amd64_phys_alloc_contiguous(2);
     _assert(stack_pages != MM_NADDR);
 
+    thr->signal_entry = MM_NADDR;
+    thr->signal_stack_base = MM_NADDR;
+    thr->signal_stack_size = 0;
+
     thr->data.rsp0_base = MM_VIRTUALIZE(stack_pages);
     thr->data.rsp0_size = MM_PAGE_SIZE * 2;
     thr->data.rsp0_top = thr->data.rsp0_base + thr->data.rsp0_size;
     thr->flags = (flags & THR_INIT_USER) ? 0 : THREAD_KERNEL;
+    thr->next_thread = NULL;
 
     if (flags & THR_INIT_USER) {
         thr->data.fxsave = kmalloc(FXSAVE_REGION);
@@ -427,7 +433,6 @@ int sys_fork(struct sys_fork_frame *frame) {
     thread_wait_io_init(&dst->pid_notify);
     dst->flags = 0;
     strcpy(dst->name, src->name);
-    dst->signal_entry = src->signal_entry;
     process_ioctx_fork(dst, src);
     dst->parent = src;
     dst->next_child = src->first_child;
@@ -439,6 +444,7 @@ int sys_fork(struct sys_fork_frame *frame) {
     dst->first_thread = dst_thread;
     dst->thread_count = 1;
     dst->proc_state = PROC_ACTIVE;
+    kdebug("New process #%d with main thread <%p>\n", dst->pid, dst_thread);
 
     // Initialize dst thread
     dst_thread->proc = dst;
@@ -452,10 +458,15 @@ int sys_fork(struct sys_fork_frame *frame) {
     dst_thread->data.rsp0_size = MM_PAGE_SIZE * 2;
     dst_thread->data.rsp0_top = dst_thread->data.rsp0_base + dst_thread->data.rsp0_size;
     dst_thread->flags = 0;
+    dst_thread->next_thread = NULL;
 
     dst_thread->data.rsp3_base = src_thread->data.rsp3_base;
     dst_thread->data.rsp3_size = src_thread->data.rsp3_size;
 
+    dst_thread->signal_entry = src_thread->signal_entry;
+    dst_thread->signal_stack_base = src_thread->signal_stack_base;
+    dst_thread->signal_stack_size = src_thread->signal_stack_size;
+
     dst_thread->data.cr3 = MM_PHYS(space);
 
     dst_thread->data.fxsave = kmalloc(FXSAVE_REGION);
@@ -554,11 +565,14 @@ void thread_sigenter(int signum) {
 
         return;
     }
-    uintptr_t old_rsp0_top = thr->data.rsp0_top;
-    // XXX: Either use a separate stack or ensure stuff doesn't get overwritten
-    uintptr_t signal_rsp3 = thr->data.rsp3_base + 0x800;
 
-    context_sigenter(thr->proc->signal_entry, signal_rsp3, signum);
+    assert(thr->signal_entry != MM_NADDR, "Thread hasn't set its signal entry!\n");
+    assert(thr->signal_stack_base != MM_NADDR, "Thread hasn't set its signal stack!\n");
+
+    uintptr_t old_rsp0_top = thr->data.rsp0_top;
+    uintptr_t signal_rsp3 = thr->signal_stack_base + thr->signal_stack_size;
+
+    context_sigenter(thr->signal_entry, signal_rsp3, signum);
 
     thr->data.rsp0_top = old_rsp0_top;
 }
@@ -704,7 +718,23 @@ int sys_kill(pid_t pid, int signum) {
 }
 
 void sys_sigentry(uintptr_t entry) {
-    thread_self->proc->signal_entry = entry;
+    thread_self->signal_entry = entry;
+}
+
+int sys_sigaltstack(const struct user_stack *ss, struct user_stack *old_ss) {
+    struct thread *thr = thread_self;
+    _assert(thr);
+
+    if (old_ss) {
+        old_ss->ss_sp = (void *) thr->signal_stack_base;
+        old_ss->ss_size = thr->signal_stack_size;
+    }
+    if (ss) {
+        thr->signal_stack_base = (uintptr_t) ss->ss_sp;
+        thr->signal_stack_size = ss->ss_size;
+    }
+
+    return 0;
 }
 
 pid_t sys_getpid(void) {