linux-user: init_guest_space: Don't try to align if we'll reject it

If the ensure-alignment code gets triggered, then the
"if (host_start && real_start != current_start)" check will always trigger,
so save 2 syscalls and put that check first.

Note that we can't just switch to using MAP_FIXED for that check, because
then we couldn't differentiate between a failure because "there isn't
enough space" and "there isn't enough space *here*".

Signed-off-by: Luke Shumaker <lukeshu@parabola.nu>
Message-Id: <20171228180814.9749-9-lukeshu@lukeshu.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index c6491a8..5c64299 100644 (file)
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -1845,6 +1845,11 @@ unsigned long init_guest_space(unsigned long host_start,
             return (unsigned long)-1;
         }
 
+        /* Check to see if the address is valid.  */
+        if (host_start && real_start != current_start) {
+            goto try_again;
+        }
+
         /* Ensure the address is properly aligned.  */
         if (real_start & ~qemu_host_page_mask) {
             /* Ideally, we adjust like
@@ -1879,11 +1884,6 @@ unsigned long init_guest_space(unsigned long host_start,
             aligned_start = real_start;
         }
 
-        /* Check to see if the address is valid.  */
-        if (host_start && aligned_start != current_start) {
-            goto try_again;
-        }
-
 #if defined(TARGET_ARM) && !defined(TARGET_AARCH64)
         /* On 32-bit ARM, we need to also be able to map the commpage.  */
         int valid = init_guest_commpage(aligned_start - guest_start,