[RFC][PATCH v12 1/8] Define a new dynamic section tag - DT_GNU_FLAGS_1 (bug 22745)

["Vivek Das Mohapatra via Libc-alpha" <libc-alpha@sourceware.org>]

Define a new flags section DT_GNU_FLAGS_1 (no more bits are available
in DT_GNU_FLAGS).

One flag is currently defined: DF_GNU_1_UNIQUE.

libc and its companion DSOs (libpthread et al) should have this
section and flag set.
---
 elf/elf.h              |  7 ++++++-
 elf/get-dynamic-info.h | 12 ++++++++++++
 include/elf.h          |  2 ++
 include/link.h         |  1 +
 4 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/elf/elf.h b/elf/elf.h
index 2a62b98d4a..448c275d10 100644
--- a/elf/elf.h
+++ b/elf/elf.h
@@ -896,6 +896,7 @@ typedef struct
    Dyn.d_un.d_val field of the Elf*_Dyn structure.  This follows Sun's
    approach.  */
 #define DT_VALRNGLO	0x6ffffd00
+#define DT_GNU_FLAGS_1   0x6ffffdf4	/* GNU extension flags */
 #define DT_GNU_PRELINKED 0x6ffffdf5	/* Prelinking timestamp */
 #define DT_GNU_CONFLICTSZ 0x6ffffdf6	/* Size of conflict section */
 #define DT_GNU_LIBLISTSZ 0x6ffffdf7	/* Size of library list */
@@ -910,7 +911,7 @@ typedef struct
 #define DT_SYMINENT	0x6ffffdff	/* Entry size of syminfo */
 #define DT_VALRNGHI	0x6ffffdff
 #define DT_VALTAGIDX(tag)	(DT_VALRNGHI - (tag))	/* Reverse order! */
-#define DT_VALNUM 12
+#define DT_VALNUM 13
 
 /* DT_* entries which fall between DT_ADDRRNGHI & DT_ADDRRNGLO use the
    Dyn.d_un.d_ptr field of the Elf*_Dyn structure.
@@ -999,6 +1000,10 @@ typedef struct
 #define	DF_1_WEAKFILTER 0x20000000
 #define	DF_1_NOCOMMON   0x40000000
 
+/* State flags selectable in the `d_un.d_val' element of the DT_GNU_FLAGS_1
+   entry in the dynamic section.  */
+#define DF_GNU_1_UNIQUE 0x00000001	/* Load max 1 copy of this DSO.  */
+
 /* Flags for the feature selection in DT_FEATURE_1.  */
 #define DTF_1_PARINIT	0x00000001
 #define DTF_1_CONFEXP	0x00000002
diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
index d8ec32377d..8082d84ba1 100644
--- a/elf/get-dynamic-info.h
+++ b/elf/get-dynamic-info.h
@@ -175,6 +175,18 @@ elf_get_dynamic_info (struct link_map *l, ElfW(Dyn) *temp)
       if (l->l_flags_1 & DF_1_NOW)
 	info[DT_BIND_NOW] = info[VERSYMIDX (DT_FLAGS_1)];
     }
+  if (info[DT_VALTAGIDX (DT_GNU_FLAGS_1)
+           + DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGNUM + DT_EXTRANUM] != NULL)
+    {
+      l->l_gnu_flags_1 = info[DT_VALTAGIDX (DT_GNU_FLAGS_1)
+                              + DT_NUM + DT_THISPROCNUM
+                              + DT_VERSIONTAGNUM + DT_EXTRANUM]->d_un.d_val;
+
+      if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_FILES)
+	  && l->l_gnu_flags_1 & ~DT_GNU_1_SUPPORTED_MASK)
+	_dl_debug_printf ("\nWARNING: Unsupported flag value(s) of 0x%x in DT_GNU_FLAGS_1.\n",
+			  l->l_gnu_flags_1 & ~DT_GNU_1_SUPPORTED_MASK);
+    }
   if (info[DT_RUNPATH] != NULL)
     /* If both RUNPATH and RPATH are given, the latter is ignored.  */
     info[DT_RPATH] = NULL;
diff --git a/include/elf.h b/include/elf.h
index 14ed67ff67..5eee37c294 100644
--- a/include/elf.h
+++ b/include/elf.h
@@ -25,5 +25,7 @@
    (DF_1_NOW | DF_1_NODELETE | DF_1_INITFIRST | DF_1_NOOPEN \
     | DF_1_ORIGIN | DF_1_NODEFLIB | DF_1_PIE)
 
+#define DT_GNU_1_SUPPORTED_MASK DF_GNU_1_UNIQUE
+
 #endif /* !_ISOMAC */
 #endif /* elf.h */
diff --git a/include/link.h b/include/link.h
index 4af16cb596..6ed35eb808 100644
--- a/include/link.h
+++ b/include/link.h
@@ -283,6 +283,7 @@ struct link_map
     unsigned int l_used;
 
     /* Various flag words.  */
+    ElfW(Word) l_gnu_flags_1;
     ElfW(Word) l_feature_1;
     ElfW(Word) l_flags_1;
     ElfW(Word) l_flags;
-- 
2.20.1