[glibc/maskray/grte] For b/18243822, fix dlopen_with_offset to not reuse the same link_map entry when called on the same

[glibc/maskray/grte] For b/18243822, fix dlopen_with_offset to not reuse the same link_map entry when called on the same

[Fangrui Song]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=6f9557ac2ebba75161875563ba43fcd4a881e149

commit 6f9557ac2ebba75161875563ba43fcd4a881e149
Author: Paul Pluzhnikov <ppluzhnikov@google.com>
Date:   Mon Nov 10 10:56:25 2014 -0800

    For b/18243822, fix dlopen_with_offset to not reuse the same link_map entry when called on the same file with different offsets.

Diff:
---
 elf/dl-load.c  | 24 ++++++++++++++++++++++--
 include/link.h |  6 ++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/elf/dl-load.c b/elf/dl-load.c
index e49d0862f9..b6c4aa8da0 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -840,7 +840,8 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd, off_t of
 
   /* Look again to see if the real name matched another already loaded.  */
   for (l = GL(dl_ns)[nsid]._ns_loaded; l != NULL; l = l->l_next)
-    if (!l->l_removed && _dl_file_id_match_p (&l->l_file_id, &id))
+    if (!l->l_removed && _dl_file_id_match_p (&l->l_file_id, &id)
+        && l->l_off == offset)
       {
 	/* The object is already loaded.
 	   Just bump its reference count and return it.  */
@@ -947,8 +948,25 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd, off_t of
   else
     assert (r->r_state == RT_ADD);
 
+  if (offset != 0)
+    {
+      /* Google-specific: to help GDB, and for b/18243822, turn realname
+         into "realname/@0x<offset>"  */
+      realname = realloc (realname, strlen(realname) + 16 + 4 /* "/@0x" */);
+      if (realname == NULL)
+	{
+	  errstring = N_("unable to realloc");
+	  goto call_lose_errno;
+	}
+      strcat(realname, "/@0x");
+
+      char tmp[20];
+      tmp[19] = '\0';
+      strcat(realname, _itoa(offset, &tmp[18], 16, 0));
+    }
+
   /* Enter the new object in the list of loaded objects.  */
-  l = _dl_new_object (realname, name, l_type, loader, mode, nsid);
+  l = _dl_new_object (realname, (offset ? realname : name), l_type, loader, mode, nsid);
   if (__glibc_unlikely (l == NULL))
     {
 #ifdef SHARED
@@ -1320,6 +1338,8 @@ cannot enable executable stack as shared object requires");
   assert (origname == NULL);
 #endif
 
+  l->l_off = offset;
+
   /* When we profile the SONAME might be needed for something else but
      loading.  Add it right away.  */
   if (__glibc_unlikely (GLRO(dl_profile) != NULL)
diff --git a/include/link.h b/include/link.h
index 5924594548..22c3eec73d 100644
--- a/include/link.h
+++ b/include/link.h
@@ -246,6 +246,12 @@ struct link_map
        object is the same as one already loaded.  */
     struct r_file_id l_file_id;
 
+    /* Google-specific extension, intended to be part of public interface
+       to the debugger.  As such, it belongs right after l_prev... except
+       putting it there causes Google libunwind to crash due to its own
+       peeking into glibc internals (see grte_v1_glibc_link_map).  */
+    size_t l_off;  /* File offset to Elf_Ehdr.  */
+
     /* Collected information about own RUNPATH directories.  */
     struct r_search_path_struct l_runpath_dirs;