[Pal/FreeBSD] specify loaded address of exec in child process

This is the FreeBSD version of https://reviewable.io/reviews/oscarlab/graphene/372
I haven't tested this PR.

Signed-off-by: Isaku Yamahata <isaku.yamahata@gmail.com>

Pal/src/host/FreeBSD/db_files.c

@@ -63,6 +63,7 @@ static int file_open (PAL_HANDLE * handle, const char * type, const char * uri,
     hdl->file.offset = 0;
     hdl->file.append = 0;
     hdl->file.pass = 0;
+    hdl->file.map_start = NULL;
     char * path = (void *) hdl + HANDLE_SIZE(file);
     memcpy(path, uri, len + 1);
     hdl->file.realpath = path;
@@ -154,6 +155,16 @@ static int file_map (PAL_HANDLE handle, void ** addr, int prot,
 {
     int fd = handle->file.fd;
     void * mem = *addr;
+    /*
+     * work around for fork emulation
+     * the first exec image to be loaded has to be at same address
+     * as parent.
+     */
+    if (mem == NULL && handle->file.map_start != NULL) {
+        mem = (PAL_PTR)handle->file.map_start;
+        /* this address is used. don't over-map it later */
+        handle->file.map_start = NULL;
+    }
     int flags = MAP_FILE|HOST_FLAGS(0, prot)|(mem ? MAP_FIXED : 0);
     prot = HOST_PROT(prot);
 

Pal/src/host/FreeBSD/db_main.c

@@ -242,6 +242,10 @@ void pal_bsd_main (void * args)
     SET_HANDLE_TYPE(file, file);
     file->hdr.flags |= RFD(0)|WFD(0)|WRITEABLE(0);
     file->file.fd = fd;
+    file->file.offset = 0;
+    file->file.append = false;
+    file->file.pass = false;
+    file->file.map_start = NULL;
     char * path = (void *) file + HANDLE_SIZE(file);
     get_norm_path(argv[0], path, 0, len + 1);
     file->file.realpath = path;

Pal/src/host/FreeBSD/db_process.c

@@ -36,6 +36,7 @@
 #include "pal_debug.h"
 #include "pal_error.h"
 #include "pal_security.h"
+#include "pal_rtld.h"
 #include "api.h"
 
 #include <sched.h>
@@ -169,6 +170,20 @@ int _DkProcessCreate (PAL_HANDLE * handle, const char * uri, const char ** args)
             return ret;
 
         handle_set_cloexec(exec, true);
+
+        /* If this process creation is for fork emulation,
+         * map address of executable is already determined.
+         * tell its address to forked process.
+         */
+        size_t len;
+        const char * file_uri = "file:";
+        if (exec_map && exec_map->l_name &&
+            (len = strlen(uri)) >= 5 && !memcmp(uri, file_uri, 5) &&
+            /* skip "file:"*/
+            strlen(exec_map->l_name) == len - 5 &&
+            /* + 1 for lasting * NUL */
+            !memcmp(exec_map->l_name, uri + 5, len - 5 + 1))
+            exec->file.map_start = (PAL_PTR)exec_map->l_map_start;
     }
 
     /* step 2: create parant and child process handle */

Pal/src/host/FreeBSD/pal_host.h

@@ -76,6 +76,12 @@ typedef union pal_handle
         PAL_BOL append;
         PAL_BOL pass;
         PAL_STR realpath;
+        /*
+         * map_start is to request this file should be mapped to this
+         * address. When fork is emulated, the address is already
+         * determined by parent process.
+         */
+        PAL_PTR map_start;
     } file;
 
     struct {