kernel: exec: Add execve()

Signed-off-by: Ian Moffett <ian@osmora.org>

4 files changed, 161 insertions, 3 deletions

diff --git a/sys/include/sys/exec.h b/sys/include/sys/exec.h
index 73eae01..f5fac97 100644
--- a/sys/include/sys/exec.h
+++ b/sys/include/sys/exec.h
@@ -72,7 +72,15 @@ struct exec_prog {
     char **envp;
 };
 
+struct execve_args {
+    const char *pathname;
+    char **argv;
+    char **envp;
+};
+
+int execve(struct proc *td, const struct execve_args *args);
 int elf64_load(const char *pathname, struct proc *td, struct exec_prog *prog);
+
 void elf_unload(struct proc *td, struct exec_prog *prog);
 void setregs(struct proc *td, struct exec_prog *prog, uintptr_t stack);
 
diff --git a/sys/include/sys/proc.h b/sys/include/sys/proc.h
index 0c3cd33..ba931f3 100644
--- a/sys/include/sys/proc.h
+++ b/sys/include/sys/proc.h
@@ -56,6 +56,8 @@ struct proc {
 };
 
 #define PROC_EXITING    BIT(0)  /* Exiting */
+#define PROC_EXEC       BIT(1)  /* Exec called (cleared by sched) */
+#define PROC_INEXEC     BIT(2)  /* Exec in progress */
 
 struct proc *this_td(void);
 int md_fork(struct proc *p, struct proc *parent, uintptr_t ip);
diff --git a/sys/kern/kern_exec.c b/sys/kern/kern_exec.c
new file mode 100644
index 0000000..b21404b
--- /dev/null
+++ b/sys/kern/kern_exec.c
@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) 2023-2024 Ian Marco Moffett and the Osmora Team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of Hyra nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/exec.h>
+#include <sys/types.h>
+#include <sys/errno.h>
+#include <sys/proc.h>
+#include <sys/sched.h>
+#include <vm/vm.h>
+#include <vm/map.h>
+#include <vm/physmem.h>
+#include <machine/pcb.h>
+
+/*
+ * Release the memory of the old stack
+ *
+ * @td: Target thread.
+ */
+static void
+release_stack(struct proc *td)
+{
+    struct pcb *pcbp = &td->pcb;
+    uintptr_t base = td->stack_base;
+
+    if (base >= VM_HIGHER_HALF) {
+        base -= VM_HIGHER_HALF;
+        vm_free_frame(base, PROC_STACK_PAGES);
+    } else {
+        vm_unmap(pcbp->addrsp, base, PROC_STACK_SIZE);
+        vm_free_frame(base, PROC_STACK_PAGES);
+    }
+}
+
+int
+execve(struct proc *td, const struct execve_args *args)
+{
+    int error;
+    struct exec_prog prog;
+    struct pcb *pcbp = &td->pcb;
+    uintptr_t stack_top, stack;
+
+    if (td == NULL || args == NULL)
+        return -EINVAL;
+    if ((error = elf64_load(args->pathname, td, &prog)) != 0)
+        return error;
+
+    /* Mark the thread as running exec */
+    td->flags |= (PROC_EXEC | PROC_INEXEC);
+
+    /* Create the new stack */
+    stack = vm_alloc_frame(PROC_STACK_PAGES);
+    if (stack == 0) {
+        elf_unload(td, &prog);
+        return -ENOMEM;
+    }
+
+    /* Release the old stack if it exists */
+    if (td->stack_base != 0)
+        release_stack(td);
+
+    /* Set new stack and map it to userspace */
+    td->stack_base = stack;
+    vm_map(pcbp->addrsp, td->stack_base, td->stack_base,
+        (PROT_READ | PROT_WRITE | PROT_USER), PROC_STACK_SIZE);
+
+    prog.argp = args->argv;
+    prog.envp = args->envp;
+    stack_top = td->stack_base + (PROC_STACK_SIZE - 1);
+
+    /* Setup registers and stack */
+    md_td_stackinit(td, (void *)(stack_top + VM_HIGHER_HALF), &prog);
+    setregs(td, &prog, stack_top);
+
+    /*
+     * Done, reset flags and yield
+     *
+     * XXX: PROC_EXEC is unset by the scheduler so it
+     *      can properly start the new exec'd program.
+     */
+    td->flags &= ~PROC_INEXEC;
+    sched_enter();
+}
diff --git a/sys/kern/kern_sched.c b/sys/kern/kern_sched.c
index 9df541e..278eba2 100644
--- a/sys/kern/kern_sched.c
+++ b/sys/kern/kern_sched.c
@@ -74,6 +74,24 @@ sched_oneshot(bool now)
     timer.oneshot_us(usec);
 }
 
+/*
+ * Save thread state and enqueue it back into one
+ * of the ready queues.
+ */
+static void
+sched_save_td(struct proc *td, struct trapframe *tf)
+{
+    /*
+     * Save trapframe to process structure only
+     * if PROC_EXEC is not set.
+     */
+    if (!ISSET(td->flags, PROC_EXEC)) {
+        memcpy(&td->tf, tf, sizeof(td->tf));
+    }
+
+    sched_enqueue_td(td);
+}
+
 static struct proc *
 sched_dequeue_td(void)
 {
@@ -137,6 +155,21 @@ sched_switch(struct trapframe *tf)
     ci = this_cpu();
     td = ci->curtd;
 
+    if (td != NULL) {
+        inexec = ISSET(td->flags, PROC_INEXEC);
+
+        /*
+         * If both PROC_INEXEC and PROC_EXEC are set,
+         * an exec is in progress. However, if PROC_INEXEC is
+         * unset and PROC_EXEC is set, an exec has completed
+         * and we can unset PROC_EXEC and copy the new trapframe.
+         */
+        if (ISSET(td->flags, PROC_EXEC) && !inexec) {
+            memcpy(tf, &td->tf, sizeof(*tf));
+            td->flags &= ~PROC_EXEC;
+        }
+    }
+
     /*
      * Get the next thread and use it only if it isn't
      * in the middle of an exit, exec, or whatever.
@@ -148,6 +181,14 @@ sched_switch(struct trapframe *tf)
         }
 
         /*
+         * If we are in the middle of an exec, don't use this
+         * thread.
+         */
+        if (ISSET(next_td->flags, PROC_EXEC)) {
+            use_current = false;
+        }
+
+        /*
          * Don't use this thread if we are currently
          * exiting.
          */
@@ -156,10 +197,9 @@ sched_switch(struct trapframe *tf)
         }
     } while (!use_current);
 
-    /* Re-enqueue the old thread */
+    /* Save the previous thread */
     if (td != NULL) {
-        memcpy(&td->tf, tf, sizeof(td->tf));
-        sched_enqueue_td(td);
+        sched_save_td(td, tf);
     }
 
     memcpy(tf, &next_td->tf, sizeof(*tf));