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>

diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
index 203b6c7b0bdb282f935be43c756d906bc33b90c6..ee68dda550a8220362731195fc378bac212dfd2b 100644 (file)
--- a/elf/dl-map-segments.h
+++ b/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);
+                }
             }
         }
 

diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index cffcd3d42187ea0494a80e86531c175f805e7078..800ca89720d6278c3fd2f27d1dc6fc907d5b6f03 100644 (file)
--- a/nptl/allocatestack.c
+++ b/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) +                             \

diff --git a/sysdeps/generic/setvmaname.h b/sysdeps/generic/setvmaname.h
index baca984a540954220a4aba7d980c195c78225f10..496fcca33ba4aeca27d00c39f02f93eb3bdb9f06 100644 (file)
--- a/sysdeps/generic/setvmaname.h
+++ b/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)
 {

diff --git a/sysdeps/unix/sysv/linux/setvmaname.c b/sysdeps/unix/sysv/linux/setvmaname.c
index 749c587f129cb5775f85b7ab6f7469e0c2336e96..ea93a5ffbebc9e5a7e32a297138f465724b4725f 100644 (file)
--- a/sysdeps/unix/sysv/linux/setvmaname.c
+++ b/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;
 }

diff --git a/sysdeps/unix/sysv/linux/setvmaname.h b/sysdeps/unix/sysv/linux/setvmaname.h
index 715b0967998382c8020a0673e4a7951a550c2146..48643d0dad9004405e8fca210d78e0cc37ac0e03 100644 (file)
--- a/sysdeps/unix/sysv/linux/setvmaname.h
+++ b/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