ld.so: Decorate BSS mappings

Decorate BSS mappings with [anon: glibc: .bss <file>], for example
[anon: glibc: .bss /lib/libc.so.6]. The string ".bss" is already used
by bionic so use the same, but add the filename as well. If the name
would be longer than what the kernel allows, drop the directory part
of the path.

Refactor glibc.mem.decorate_maps check to a separate function and use
it to avoid assembling a name, which would not be used later.

Signed-off-by: Petr Malat <oss@malat.biz>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

elf/dl-map-segments.h

@@ -18,6 +18,7 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <dl-load.h>
+#include <setvmaname.h>
 
 /* Map a segment and align it properly.  */
 
@@ -182,12 +183,41 @@ _dl_map_segments (struct link_map *l, int fd,
           if (zeroend > zeropage)
             {
               /* Map the remaining zero pages in from the zero fill FD.  */
+              char bssname[ANON_VMA_NAME_MAX_LEN] = " glibc: .bss";
+
               caddr_t mapat;
               mapat = __mmap ((caddr_t) zeropage, zeroend - zeropage,
                               c->prot, MAP_ANON|MAP_PRIVATE|MAP_FIXED,
                               -1, 0);
               if (__glibc_unlikely (mapat == MAP_FAILED))
                 return DL_MAP_SEGMENTS_ERROR_MAP_ZERO_FILL;
+              if (__is_decorate_maps_enabled ())
+                {
+                  if (l->l_name != NULL && *l->l_name != '\0')
+                    {
+                      int i = strlen (bssname), j = 0;
+                      int namelen = strlen (l->l_name);
+
+                      bssname[i++] = ' ';
+                      if (namelen > sizeof (bssname) - i - 1)
+                        for (j = namelen - 1; j > 0; j--)
+                          if (l->l_name[j - 1] == '/')
+                            break;
+
+                      for (; l->l_name[j] != '\0' && i < sizeof (bssname) - 1;
+                           i++, j++)
+                        {
+                          char ch = l->l_name[j];
+                          /* Replace non-printable characters and
+                             \, `, $, [ and ].  */
+                          if (ch <= 0x1f || ch >= 0x7f || strchr("\\`$[]", ch))
+                            ch = '!';
+                          bssname[i] = ch;
+                        }
+                      bssname[i] = 0;
+                    }
+                  __set_vma_name ((void*)zeropage, zeroend - zeropage, bssname);
+                }
             }
         }
 

nptl/allocatestack.c

@@ -638,10 +638,6 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
   return 0;
 }
 
-/* Maximum supported name from initial kernel support, not exported
-   by user API.  */
-#define ANON_VMA_NAME_MAX_LEN 80
-
 #define SET_STACK_NAME(__prefix, __stack, __stacksize, __tid)		\
   ({									\
      char __stack_name[sizeof (__prefix) +				\

sysdeps/generic/setvmaname.h

@@ -19,6 +19,18 @@
 #ifndef __SETVMANAME_H
 #define __SETVMANAME_H
 
+#include <stdbool.h>
+
+/* Set this to small value to not waste memory on systems, which do
+ * not support VMA name. */
+#define ANON_VMA_NAME_MAX_LEN 16
+
+static inline bool
+__is_decorate_maps_enabled (void)
+{
+  return false;
+}
+
 static inline
 void __set_vma_name (void *start, size_t len, const char *name)
 {

sysdeps/unix/sysv/linux/setvmaname.c

@@ -22,6 +22,33 @@
 #include <sysdep.h>
 #include <elf/dl-tunables.h>
 
+static enum {
+  decorate_unknown = -1,
+  decorate_off,
+  decorate_on
+} decorate_maps = decorate_unknown;
+
+bool
+__is_decorate_maps_enabled (void)
+{
+  switch (atomic_load_relaxed (&decorate_maps))
+    {
+    case decorate_unknown:
+      if (TUNABLE_GET (glibc, mem, decorate_maps, int32_t, NULL) != 0)
+        {
+          atomic_store_relaxed (&decorate_maps, decorate_on);
+          return true;
+        }
+      atomic_store_relaxed (&decorate_maps, decorate_off);
+      return false;
+    case decorate_off:
+      return false;
+    case decorate_on:
+      return true;
+    }
+  __builtin_unreachable ();
+}
+
 /* If PR_SET_VMA_ANON_NAME is not supported by the kernel, prctl returns
    EINVAL.  However, it also returns the same error for invalid argument.
    Since it is an internal-only API, it assumes well formatted input:
@@ -31,19 +58,13 @@
 void
 __set_vma_name (void *start, size_t len, const char *name)
 {
-  static int prctl_supported = 1;
-  if (atomic_load_relaxed (&prctl_supported) == 0)
-    return;
-
-  /* Set the prctl as not supported to avoid checking the tunable on every
-     call.  */
-  if (TUNABLE_GET (glibc, mem, decorate_maps, int32_t, NULL) != 0)
+  if (__is_decorate_maps_enabled ())
     {
       int r = INTERNAL_SYSCALL_CALL (prctl, PR_SET_VMA, PR_SET_VMA_ANON_NAME,
-				     start, len, name);
-      if (r == 0 || r != -EINVAL)
-	return;
+                                     start, len, name);
+
+      /* Disable further attempts if not supported by the kernel.  */
+      if (r == -EINVAL)
+        atomic_store_relaxed (&decorate_maps, decorate_off);
     }
-  atomic_store_relaxed (&prctl_supported, 0);
-  return;
 }

sysdeps/unix/sysv/linux/setvmaname.h

@@ -19,9 +19,17 @@
 #ifndef __SETVMANAME_H
 #define __SETVMANAME_H
 
+/* Maximum supported name from initial kernel support, not exported
+   by user API.  */
+#define ANON_VMA_NAME_MAX_LEN 80
+
 /* Set the NAME to the anonymous memory map START with size of LEN.
    It assumes well-formatted input.  */
 #if IS_IN(libc) || IS_IN(rtld)
+#include <stdbool.h>
+
+bool __is_decorate_maps_enabled (void) attribute_hidden;
+
 void __set_vma_name (void *start, size_t len, const char *name)
   attribute_hidden;
 #else