linux-user/FLAT: fix auto-stack sizing

The current auto-stack sizing works like it does on a NOMMU system; the
problem is that this only works if the envp/argv arrays are fairly slim.
On a desktop system, this is rarely the case, and can easily blow past
the stack and into data/text regions as the default stack for FLAT progs
is a mere 4KiB.  So rather than rely on the NOMMU calculation (which is
only there because NOMMU can't easily allocate gobs of contiguous mem),
calc the full space actually needed and let the MMU host make space.

Signed-off-by: Mike Frysinger <[email protected]>
Signed-off-by: Riku Voipio <[email protected]>

Author: vapier

linux-user/flatload.c

@@ -733,8 +733,15 @@ int load_flt_binary(struct linux_binprm * bprm, struct target_pt_regs * regs,
      * pedantic and include space for the argv/envp array as it may have
      * a lot of entries.
      */
-#define TOP_OF_ARGS (TARGET_PAGE_SIZE * MAX_ARG_PAGES - sizeof(void *))
-    stack_len = TOP_OF_ARGS - bprm->p;             /* the strings */
+    stack_len = 0;
+    for (i = 0; i < bprm->argc; ++i) {
+        /* the argv strings */
+        stack_len += strlen(bprm->argv[i]);
+    }
+    for (i = 0; i < bprm->envc; ++i) {
+        /* the envp strings */
+        stack_len += strlen(bprm->envp[i]);
+    }
     stack_len += (bprm->argc + 1) * 4; /* the argv array */
     stack_len += (bprm->envc + 1) * 4; /* the envp array */