linux-user: Adjust task_unmapped_base for reserved_va

Ensure that the chosen values for mmap_next_start and
task_unmapped_base are within the guest address space.

Tested-by: Helge Deller <deller@gmx.de>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 28 insertions, 0 deletions

diff --git a/linux-user/main.c b/linux-user/main.c
index 556956c363..be621dc792 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -821,6 +821,34 @@ int main(int argc, char **argv, char **envp)
         reserved_va = max_reserved_va;
     }
 
+    /*
+     * Temporarily disable
+     *   "comparison is always false due to limited range of data type"
+     * due to comparison between (possible) uint64_t and uintptr_t.
+     */
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wtype-limits"
+
+    /*
+     * Select an initial value for task_unmapped_base that is in range.
+     */
+    if (reserved_va) {
+        if (TASK_UNMAPPED_BASE < reserved_va) {
+            task_unmapped_base = TASK_UNMAPPED_BASE;
+        } else {
+            /* The most common default formula is TASK_SIZE / 3. */
+            task_unmapped_base = TARGET_PAGE_ALIGN(reserved_va / 3);
+        }
+    } else if (TASK_UNMAPPED_BASE < UINTPTR_MAX) {
+        task_unmapped_base = TASK_UNMAPPED_BASE;
+    } else {
+        /* 32-bit host: pick something medium size. */
+        task_unmapped_base = 0x10000000;
+    }
+    mmap_next_start = task_unmapped_base;
+
+#pragma GCC diagnostic pop
+
     {
         Error *err = NULL;
         if (seed_optarg != NULL) {