[Qemu-devel] [PATCH 08/10] linux-user: Factor out guest space probing into a function

[Peter Maydell]

From: Meador Inge <address@hidden>

Signed-off-by: Meador Inge <address@hidden>
Reviewed-by: Peter Maydell <address@hidden>
Signed-off-by: Peter Maydell <address@hidden>
---
 linux-user/elfload.c |  110 +++++++++++++++++++++++++++++++++++---------------
 linux-user/qemu.h    |   13 ++++++
 2 files changed, 90 insertions(+), 33 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index 6b622d4..cbc7617 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -1426,6 +1426,73 @@ bool guest_validate_base(unsigned long guest_base)
 }
 #endif
 
+unsigned long init_guest_space(unsigned long host_start,
+                               unsigned long host_size,
+                               unsigned long guest_start,
+                               bool fixed)
+{
+    unsigned long current_start, real_start;
+    int flags;
+
+    assert(host_start || host_size);
+
+    /* If just a starting address is given, then just verify that
+     * address.  */
+    if (host_start && !host_size) {
+        if (guest_validate_base(host_start)) {
+            return host_start;
+        } else {
+            return (unsigned long)-1;
+        }
+    }
+
+    /* Setup the initial flags and start address.  */
+    current_start = host_start & qemu_host_page_mask;
+    flags = MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE;
+    if (fixed) {
+        flags |= MAP_FIXED;
+    }
+
+    /* Otherwise, a non-zero size region of memory needs to be mapped
+     * and validated.  */
+    while (1) {
+        /* Do not use mmap_find_vma here because that is limited to the
+         * guest address space.  We are going to make the
+         * guest address space fit whatever we're given.
+         */
+        real_start = (unsigned long)
+            mmap((void *)current_start, host_size, PROT_NONE, flags, -1, 0);
+        if (real_start == (unsigned long)-1) {
+            return (unsigned long)-1;
+        }
+
+        if ((real_start == current_start)
+            && guest_validate_base(real_start - guest_start)) {
+            break;
+        }
+
+        /* That address didn't work.  Unmap and try a different one.
+         * The address the host picked because is typically right at
+         * the top of the host address space and leaves the guest with
+         * no usable address space.  Resort to a linear search.  We
+         * already compensated for mmap_min_addr, so this should not
+         * happen often.  Probably means we got unlucky and host
+         * address space randomization put a shared library somewhere
+         * inconvenient.
+         */
+        munmap((void *)real_start, host_size);
+        current_start += qemu_host_page_size;
+        if (host_start == current_start) {
+            /* Theoretically possible if host doesn't have any suitably
+             * aligned areas.  Normally the first mmap will fail.
+             */
+            return (unsigned long)-1;
+        }
+    }
+
+    return real_start;
+}
+
 static void probe_guest_base(const char *image_name,
                              abi_ulong loaddr, abi_ulong hiaddr)
 {
@@ -1452,46 +1519,23 @@ static void probe_guest_base(const char *image_name,
             }
         }
         host_size = hiaddr - loaddr;
-        while (1) {
-            /* Do not use mmap_find_vma here because that is limited to the
-               guest address space.  We are going to make the
-               guest address space fit whatever we're given.  */
-            real_start = (unsigned long)
-                mmap((void *)host_start, host_size, PROT_NONE,
-                     MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE, -1, 0);
-            if (real_start == (unsigned long)-1) {
-                goto exit_perror;
-            }
-            guest_base = real_start - loaddr;
-            if ((real_start == host_start) &&
-                guest_validate_base(guest_base)) {
-                break;
-            }
-            /* That address didn't work.  Unmap and try a different one.
-               The address the host picked because is typically right at
-               the top of the host address space and leaves the guest with
-               no usable address space.  Resort to a linear search.  We
-               already compensated for mmap_min_addr, so this should not
-               happen often.  Probably means we got unlucky and host
-               address space randomization put a shared library somewhere
-               inconvenient.  */
-            munmap((void *)real_start, host_size);
-            host_start += qemu_host_page_size;
-            if (host_start == loaddr) {
-                /* Theoretically possible if host doesn't have any suitably
-                   aligned areas.  Normally the first mmap will fail.  */
-                errmsg = "Unable to find space for application";
-                goto exit_errmsg;
-            }
+
+        /* Setup the initial guest memory space with ranges gleaned from
+         * the ELF image that is being loaded.
+         */
+        real_start = init_guest_space(host_start, host_size, loaddr, false);
+        if (real_start == (unsigned long)-1) {
+            errmsg = "Unable to find space for application";
+            goto exit_errmsg;
         }
+        guest_base = real_start - loaddr;
+
         qemu_log("Relocating guest address space from 0x"
                  TARGET_ABI_FMT_lx " to 0x%lx\n",
                  loaddr, real_start);
     }
     return;
 
-exit_perror:
-    errmsg = strerror(errno);
 exit_errmsg:
     fprintf(stderr, "%s: %s\n", image_name, errmsg);
     exit(-1);
diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 7b299b7..7d4e23e 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -210,6 +210,19 @@ void fork_end(int child);
  */
 bool guest_validate_base(unsigned long guest_base);
 
+/* Creates the initial guest address space in the host memory space using
+ * the given host start address hint and size.  The guest_start parameter
+ * specifies the start address of the guest space.  guest_base will be the
+ * difference between the host start address computed by this function and
+ * guest_start.  If fixed is specified, then the mapped address space must
+ * start at host_start.  The real start address of the mapped memory space is
+ * returned or -1 if there was an error.
+ */
+unsigned long init_guest_space(unsigned long host_start,
+                               unsigned long host_size,
+                               unsigned long guest_start,
+                               bool fixed);
+
 #include "qemu-log.h"
 
 /* strace.c */
-- 
1.7.9.5