[PATCH] bsd-user: Properly allocate guest virtual address space

[Richard Henderson]

Do not hard-code guest_base at 32GB.
Do not override mmap_next_start for reserved_va.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---

Hi Warner,

With the blitz-trial branch you provided, the host libc allocates
thread-local storage within the [32GB, 36GB) region that you currently
assume is free.

The armv7-hello program happens to map on top of this thread-local
storage, and then we crash later accessing some host TLS variable.

While the linux-user probe_guest_base is significantly more complex,
we are also trying to handle 32-bit hosts.  I think freebsd is always
assuming 64-bit hosts, which makes this simpler.


r~
---
 bsd-user/main.c | 37 +++++++++++++++++++------------------
 1 file changed, 19 insertions(+), 18 deletions(-)

diff --git a/bsd-user/main.c b/bsd-user/main.c
index f500ec292b..9760aad9f6 100644
--- a/bsd-user/main.c
+++ b/bsd-user/main.c
@@ -50,20 +50,8 @@
 
 int do_strace;
 
-/*
- * Going hand in hand with the va space needed (see below), we need
- * to find a host address to map the guest to. Assume that qemu
- * itself doesn't need memory above 32GB (or that we don't collide
- * with anything interesting). This is selected rather arbitrarily,
- * but seems to produce good results in tests to date.
- */
-# if HOST_LONG_BITS >= 64
-uintptr_t guest_base = 0x800000000ul;    /* at 32GB */
-bool have_guest_base = true;
-#else
-uintptr_t guest_base;    /* TODO: use sysctl to find big enough hole */
+uintptr_t guest_base;
 bool have_guest_base;
-#endif
 static bool opt_one_insn_per_tb;
 static const char *cpu_model;
 static const char *cpu_type;
@@ -522,10 +510,6 @@ int main(int argc, char **argv)
     target_environ = envlist_to_environ(envlist, NULL);
     envlist_free(envlist);
 
-    if (reserved_va) {
-        mmap_next_start = reserved_va + 1;
-    }
-
     {
         Error *err = NULL;
         if (seed_optarg != NULL) {
@@ -543,7 +527,24 @@ int main(int argc, char **argv)
      * Now that page sizes are configured we can do
      * proper page alignment for guest_base.
      */
-    guest_base = HOST_PAGE_ALIGN(guest_base);
+    if (have_guest_base) {
+       if (guest_base & ~qemu_host_page_mask) {
+            error_report("Selected guest base not host page aligned");
+            exit(1);
+        }
+    } else if (reserved_va) {
+        void *p = mmap(NULL, reserved_va + 1, PROT_NONE, MAP_GUARD, -1, 0);
+        if (p == MAP_FAILED) {
+            const char *err = strerror(errno);
+            char *sz = size_to_str(reserved_va + 1);
+
+            error_report("Cannot allocate %s bytes for guest address space: 
%s",
+                         sz, err);
+            exit(1);
+        }
+        guest_base = (uintptr_t)p;
+        have_guest_base = true;
+    }
 
     if (loader_exec(filename, argv + optind, target_environ, regs, info,
                     &bprm) != 0) {
-- 
2.41.0