[RFC,v4,11/15] Use the DSO search helper to check for preloaded DF_1_UNIQUE DSOs

Message ID 53ddc0d7ea9da7df9bab1cc47e0150223cf2bf3d.1585588166.git.vivek@collabora.com
State New
Headers show
Series
  • Proof-of-Concept implementation of RTLD_SHARED for dlmopen
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Commit Message

Sergei Trofimovich via Libc-alpha March 30, 2020, 5:43 p.m.
If a DSO already exists (with the same name) in the base namespace
and it is flagged DF_1_UNIQUE then we should behave as if a proxy
had been requested.
---
 elf/dl-open.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

-- 
2.11.0

Patch

diff --git a/elf/dl-open.c b/elf/dl-open.c
index 9265b4239a..0197cd07e0 100644
--- a/elf/dl-open.c
+++ b/elf/dl-open.c
@@ -476,6 +476,7 @@  dl_open_worker (void *a)
   const char *file = args->file;
   int mode = args->mode;
   struct link_map *call_map = NULL;
+  struct link_map *preloaded = NULL;
   int want_proxy = mode & RTLD_SHARED;
   Lmid_t proxy_ns = LM_ID_BASE;
 
@@ -510,6 +511,22 @@  dl_open_worker (void *a)
      may not be true if this is a recursive call to dlopen.  */
   _dl_debug_initialize (0, args->nsid);
 
+  /* Target Lmid is not the base and we haven't explicitly asked for a proxy:
+     We need to check for a matching DSO in the base Lmid in case it is flagged
+     DF_1_UNIQUE in which case we add RTLD_SHARED to the mode and set
+     want_proxy.  */
+  if (__glibc_unlikely (args->nsid != LM_ID_BASE) &&
+      __glibc_likely (!want_proxy))
+    {
+      preloaded = _dl_find_dso (file, LM_ID_BASE);
+
+      if (preloaded && (preloaded->l_flags_1 & DF_1_UNIQUE))
+        {
+          want_proxy = RTLD_SHARED;
+          mode |= RTLD_SHARED;
+        }
+    }
+
   /* Load the named object.  */
   struct link_map *new;
   args->map = new = _dl_map_object (call_map, file, lt_loaded, 0,