From a0540658f66feb32c1abe71d9d7589b854e9aaa5 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Sun, 30 Jun 2024 23:51:40 -0400
Subject: kernel/amd64: proc: Add stack init func for exec

Add stack initialization code for exec functions. This new code
initializes values on the stack, including argc, argv, and the
auxiliary vector.

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/arch/amd64/amd64/proc_machdep.c | 60 +++++++++++++++++++++++++++++++++++++
 sys/include/sys/exec.h              | 16 ++++++++++
 sys/include/sys/proc.h              |  5 ++++
 3 files changed, 81 insertions(+)

(limited to 'sys')

diff --git a/sys/arch/amd64/amd64/proc_machdep.c b/sys/arch/amd64/amd64/proc_machdep.c
index ee38f21..2b4368b 100644
--- a/sys/arch/amd64/amd64/proc_machdep.c
+++ b/sys/arch/amd64/amd64/proc_machdep.c
@@ -31,6 +31,7 @@
 #include <sys/types.h>
 #include <sys/param.h>
 #include <sys/errno.h>
+#include <sys/exec.h>
 #include <machine/frame.h>
 #include <machine/gdt.h>
 #include <vm/physmem.h>
@@ -38,6 +39,65 @@
 #include <vm/map.h>
 #include <string.h>
 
+void
+md_td_stackinit(struct proc *td, void *stack_top, struct exec_prog *prog)
+{
+    uintptr_t *sp = stack_top;
+    uintptr_t old_sp;
+    size_t argc, envc, len;
+    char **argvp = prog->argp;
+    char **envp = prog->envp;
+    struct auxval auxval = prog->auxval;
+    struct trapframe *tfp;
+
+    /* Copy strings */
+    old_sp = (uintptr_t)sp;
+    for (argc = 0; argvp[argc] != NULL; ++argc) {
+        len = strlen(argvp[argc]) + 1;
+        sp = (void *)((char *)sp - len);
+        memcpy((char *)sp, argvp[argc], len);
+    }
+    for (envc = 0; envp[envc] != NULL; ++envc) {
+        len = strlen(envp[envc]) + 1;
+        sp = (void *)((char *)sp - len);
+        memcpy((char *)sp, envp[envc], len);
+    }
+
+    /* Ensure the stack is aligned */
+    sp = (void *)ALIGN_DOWN((uintptr_t)sp, 16);
+    if (((argc + envc + 1) & 1) != 0)
+        --sp;
+
+    AUXVAL(sp, AT_NULL, 0x0);
+    AUXVAL(sp, AT_SECURE, 0x0);
+    AUXVAL(sp, AT_ENTRY, auxval.at_entry);
+    AUXVAL(sp, AT_PHDR, auxval.at_phdr);
+    AUXVAL(sp, AT_PHNUM, auxval.at_phnum);
+    AUXVAL(sp, AT_PAGESIZE, DEFAULT_PAGESIZE);
+    STACK_PUSH(sp, 0);
+
+    /* Copy envp pointers */
+    sp -= envc;
+    for (int i = 0; i < envc; ++i) {
+        len = strlen(envp[i]) + 1;
+        old_sp -= len;
+        sp[i] = (uintptr_t)old_sp - VM_HIGHER_HALF;
+    }
+
+    /* Copy argvp pointers */
+    STACK_PUSH(sp, 0);
+    sp -= argc;
+    for (int i = 0; i < argc; ++i) {
+        len = strlen(argvp[i]) + 1;
+        old_sp -= len;
+        sp[i] = (uintptr_t)old_sp - VM_HIGHER_HALF;
+    }
+
+    STACK_PUSH(sp, argc);
+    tfp = &td->tf;
+    tfp->rsp = (uintptr_t)sp - VM_HIGHER_HALF;
+}
+
 void
 setregs(struct proc *td, struct exec_prog *prog, uintptr_t stack)
 {
diff --git a/sys/include/sys/exec.h b/sys/include/sys/exec.h
index 4910ff2..73eae01 100644
--- a/sys/include/sys/exec.h
+++ b/sys/include/sys/exec.h
@@ -34,7 +34,23 @@
 
 #if defined(_KERNEL)
 
+/* Danger: Do not change these !! */
+#define AT_NULL 0
+#define AT_ENTRY 1
+#define AT_PHDR 2
+#define AT_PHENT 3
+#define AT_PHNUM 4
+#define AT_EXECPATH 5
+#define AT_SECURE 6
+#define AT_RANDOM 7
+#define AT_EXECFN 8
+#define AT_PAGESIZE 9
+
 #define MAX_PHDRS 32
+#define STACK_PUSH(PTR, VAL) *(--(PTR)) = VAL
+#define AUXVAL(PTR, TAG, VAL)   \
+    STACK_PUSH(PTR, VAL);       \
+    STACK_PUSH(PTR, TAG);
 
 struct exec_range {
     uintptr_t start;
diff --git a/sys/include/sys/proc.h b/sys/include/sys/proc.h
index 5303072..0c3cd33 100644
--- a/sys/include/sys/proc.h
+++ b/sys/include/sys/proc.h
@@ -43,6 +43,8 @@
 #define PROC_STACK_PAGES 8
 #define PROC_STACK_SIZE  (PROC_STACK_PAGES * DEFAULT_PAGESIZE)
 
+struct exec_prog;
+
 struct proc {
     pid_t pid;
     struct trapframe tf;
@@ -57,6 +59,9 @@ struct proc {
 
 struct proc *this_td(void);
 int md_fork(struct proc *p, struct proc *parent, uintptr_t ip);
+
+void md_td_stackinit(struct proc *td, void *stack_top, struct exec_prog *prog);
+
 int fork1(struct proc *cur, int flags, void(*ip)(void), struct proc **newprocp);
 int exit1(struct proc *td);
 
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