linux-user: Use elf_et_dyn_base for ET_DYN with interpreter

Follow the lead of the linux kernel in fs/binfmt_elf.c,
in which an ET_DYN executable which uses an interpreter
(usually a PIE executable) is loaded away from where the
interpreter itself will be loaded.

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

linux-user/elfload.c

@@ -3106,6 +3106,8 @@ static void load_elf_image(const char *image_name, int image_fd,
         }
     }
 
+    load_addr = loaddr;
+
     if (pinterp_name != NULL) {
         /*
          * This is the main executable.
@@ -3135,11 +3137,32 @@ static void load_elf_image(const char *image_name, int image_fd,
              */
             probe_guest_base(image_name, loaddr, hiaddr);
         } else {
+            abi_ulong align;
+
             /*
              * The binary is dynamic, but we still need to
              * select guest_base.  In this case we pass a size.
              */
             probe_guest_base(image_name, 0, hiaddr - loaddr);
+
+            /*
+             * Avoid collision with the loader by providing a different
+             * default load address.
+             */
+            load_addr += elf_et_dyn_base;
+
+            /*
+             * TODO: Better support for mmap alignment is desirable.
+             * Since we do not have complete control over the guest
+             * address space, we prefer the kernel to choose some address
+             * rather than force the use of LOAD_ADDR via MAP_FIXED.
+             * But without MAP_FIXED we cannot guarantee alignment,
+             * only suggest it.
+             */
+            align = pow2ceil(info->alignment);
+            if (align) {
+                load_addr &= -align;
+            }
         }
     }
 
@@ -3154,13 +3177,13 @@ static void load_elf_image(const char *image_name, int image_fd,
      *
      * Otherwise this is ET_DYN, and we are searching for a location
      * that can hold the memory space required.  If the image is
-     * pre-linked, LOADDR will be non-zero, and the kernel should
+     * pre-linked, LOAD_ADDR will be non-zero, and the kernel should
      * honor that address if it happens to be free.
      *
      * In both cases, we will overwrite pages in this range with mappings
      * from the executable.
      */
-    load_addr = target_mmap(loaddr, (size_t)hiaddr - loaddr + 1, PROT_NONE,
+    load_addr = target_mmap(load_addr, (size_t)hiaddr - loaddr + 1, PROT_NONE,
                             MAP_PRIVATE | MAP_ANON | MAP_NORESERVE |
                             (ehdr->e_type == ET_EXEC ? MAP_FIXED_NOREPLACE : 0),
                             -1, 0);