Revert "Revert "linker: get rid of the buddy allocator""

This reverts commit f9a9cda23a6afc1c2dfdfd624cde23b61941eb5e.
This revert is promised once b/5039224, b/5036755, b/5036610 are resolved.
diff --git a/linker/linker.c b/linker/linker.c
index e350d89..4d85064 100644
--- a/linker/linker.c
+++ b/linker/linker.c
@@ -51,8 +51,6 @@
 #include "linker_environ.h"
 #include "linker_format.h"
 
-#include "ba.h"
-
 #define ALLOW_SYMBOLS_FROM_MAIN 1
 #define SO_MAX 128
 
@@ -96,17 +94,6 @@
 #endif
 
 
-/* Set up for the buddy allocator managing the non-prelinked libraries. */
-static struct ba_bits ba_nonprelink_bitmap[(LIBLAST - LIBBASE) / LIBINC];
-static struct ba ba_nonprelink = {
-    .base = LIBBASE,
-    .size = LIBLAST - LIBBASE,
-    .min_alloc = LIBINC,
-    /* max_order will be determined automatically */
-    .bitmap = ba_nonprelink_bitmap,
-    .num_entries = sizeof(ba_nonprelink_bitmap)/sizeof(ba_nonprelink_bitmap[0]),
-};
-
 static inline int validate_soinfo(soinfo *si)
 {
     return (si >= sopool && si < sopool + SO_MAX) ||
@@ -292,7 +279,6 @@
     memset(si, 0, sizeof(soinfo));
     strlcpy((char*) si->name, name, sizeof(si->name));
     sonext->next = si;
-    si->ba_index = -1; /* by default, prelinked */
     si->next = NULL;
     si->refcount = 0;
     sonext = si;
@@ -844,28 +830,25 @@
 {
     if (si->base) {
         /* Attempt to mmap a prelinked library. */
-        si->ba_index = -1;
         return reserve_mem_region(si);
     }
 
-    /* This is not a prelinked library, so we attempt to allocate space
-       for it from the buddy allocator, which manages the area between
-       LIBBASE and LIBLAST.
+    /* This is not a prelinked library, so we use the kernel's default
+       allocator.
     */
-    si->ba_index = ba_allocate(&ba_nonprelink, si->size);
-    if(si->ba_index >= 0) {
-        si->base = ba_start_addr(&ba_nonprelink, si->ba_index);
-        PRINT("%5d mapping library '%s' at %08x (index %d) " \
-              "through buddy allocator.\n",
-              pid, si->name, si->base, si->ba_index);
-        if (reserve_mem_region(si) < 0) {
-            ba_free(&ba_nonprelink, si->ba_index);
-            si->ba_index = -1;
-            si->base = 0;
-            goto err;
-        }
-        return 0;
+
+    void *base = mmap(NULL, si->size, PROT_READ | PROT_EXEC,
+                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    if (base == MAP_FAILED) {
+        DL_ERR("%5d mmap of library '%s' failed: %d (%s)\n",
+              pid, si->name,
+              errno, strerror(errno));
+        goto err;
     }
+    si->base = (unsigned) base;
+    PRINT("%5d mapped library '%s' to %08x via kernel allocator.\n",
+          pid, si->name, si->base);
+    return 0;
 
 err:
     DL_ERR("OOPS: %5d cannot map library '%s'. no vspace available.",
@@ -1154,10 +1137,6 @@
 
     /* Now actually load the library's segments into right places in memory */
     if (load_segments(fd, &__header[0], si) < 0) {
-        if (si->ba_index >= 0) {
-            ba_free(&ba_nonprelink, si->ba_index);
-            si->ba_index = -1;
-        }
         goto fail;
     }
 
@@ -1187,9 +1166,6 @@
     TRACE("[ %5d init_library base=0x%08x sz=0x%08x name='%s') ]\n",
           pid, si->base, si->size, si->name);
 
-    if (si->base < LIBBASE || si->base >= LIBLAST)
-        si->flags |= FLAG_PRELINKED;
-
     if(link_image(si, wr_offset)) {
             /* We failed to link.  However, we can only restore libbase
             ** if no additional libraries have moved it since we updated it.
@@ -1264,12 +1240,6 @@
         }
 
         munmap((char *)si->base, si->size);
-        if (si->ba_index >= 0) {
-            PRINT("%5d releasing library '%s' address space at %08x "\
-                  "through buddy allocator.\n",
-                  pid, si->name, si->base);
-            ba_free(&ba_nonprelink, si->ba_index);
-        }
         notify_gdb_of_unload(si);
         free_info(si);
         si->refcount = 0;
@@ -2213,8 +2183,6 @@
         vecs += 2;
     }
 
-    ba_init(&ba_nonprelink);
-
     si->base = 0;
     si->dynamic = (unsigned *)-1;
     si->wrprotect_start = 0xffffffff;