[crt0] Actually pass argc, argv, envp to main()s

With the new SysV style process init args, it's a bit easier to finally
parse out argc, argv, and envp from the stack and pass them on to main
functions.

src/libraries/libc/arch/amd64/crt/crt0.s

@@ -87,11 +87,16 @@ _libc_crt0_start:
 
     call __run_global_ctors
 
+    ; argc
     mov rdi, [r15]
+
+    ; argv
     mov rsi, r15
     add rsi, 8
-    mov rdx, 0    ; TODO: actually parse stack for argc, argv, envp
-    mov rcx, rbx
+
+    ; envp
+    lea rdx, [rsi + rdi*8 + 8]
+
     lookup_GOT main
     call rax
 

src/user/drv.uart/main.cpp

@@ -20,7 +20,7 @@
 #include "serial.h"
 
 extern "C" {
-    int main(int, const char **);
+    int main(int, const char **, const char **envp);
 }
 
 j6_handle_t g_handle_sys = j6_handle_invalid;
@@ -36,7 +36,7 @@ uint8_t com2_out[out_buf_size];
 constexpr uintptr_t stack_top = 0xf80000000;
 
 int
-main(int argc, const char **argv)
+main(int argc, const char **argv, const char **envp)
 {
     j6::syslog(j6::logs::srv, j6::log_level::info, "uart driver starting");
 

src/user/srv.init/loader.cpp

@@ -71,6 +71,8 @@ public:
     }
 
     void build() {
+        *push<uint64_t, 16>() = 0;
+
         if ((m_argv.count() + m_envp.count()) % 2 == 0)
             *push<uint64_t>() = 0; // Pad for 16-byte alignment
 
@@ -268,6 +270,9 @@ load_program(
         stack_top,
     };
 
+    stack.add_arg(path);
+    stack.add_env("jsix_version", GIT_VERSION);
+
     static constexpr size_t nhandles = 3;
     static constexpr size_t handles_extra = 3 * sizeof(j6_arg_handle_entry);
     j6_arg_handles *handles_arg = stack.add_aux_data<j6_arg_handles>(j6_aux_handles, handles_extra);