Do without union of variable length arrays.

Prepare to compile with clang.

A union like
  { T32 a32[n]; T64 a64[n]; } u;
is expanded to
  size_t nbytes = n * MAX(sizeof(T32), sizeof(T64));
  void *data = malloc(nbytes);
  T32 (*a32)[n] = data;
  T64 (*a64)[n] = data;

Signed-off-by: Chih-Hung Hsieh <[email protected]>

3 files changed, 43 insertions, 18 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index daa76cf2..e6744017 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,11 @@
+2015-10-05  Chih-Hung Hsieh <[email protected]>
+
+	* unstrip.c (find_alloc_sections_prelink): Do not allocate
+	on stack union types with variable length arrays; use xmalloc
+	for such dynamic sized objects.
+	* readelf.c (handle_core_item): Likewise, but use alloca
+	for small variable size data object and add assert(count < 128).
+
 2015-10-05  Josh Stone  <[email protected]>
 
 	* Makefile.am (libld_elf_i386.so): Add AM_V_CCLD silencer.
diff --git a/src/readelf.c b/src/readelf.c
index 33274f35..fe7bc392 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -8370,6 +8370,9 @@ handle_core_item (Elf *core, const Ebl_Core_Item *item, const void *desc,
 		  unsigned int colno, size_t *repeated_size)
 {
   uint_fast16_t count = item->count ?: 1;
+  /* Ebl_Core_Item count is always a small number.
+     Make sure the backend didn't put in some large bogus value.  */
+  assert (count < 128);
 
 #define TYPES								      \
   DO_TYPE (BYTE, Byte, "0x%.2" PRIx8, "%" PRId8);			      \
@@ -8379,11 +8382,16 @@ handle_core_item (Elf *core, const Ebl_Core_Item *item, const void *desc,
   DO_TYPE (XWORD, Xword, "0x%.16" PRIx64, "%" PRId64);			      \
   DO_TYPE (SXWORD, Sxword, "%" PRId64, "%" PRId64)
 
-#define DO_TYPE(NAME, Name, hex, dec) GElf_##Name Name[count]
-  union { TYPES; } value;
+#define DO_TYPE(NAME, Name, hex, dec) GElf_##Name Name
+  typedef union { TYPES; } value_t;
+  void *data = alloca (count * sizeof (value_t));
+#undef DO_TYPE
+
+#define DO_TYPE(NAME, Name, hex, dec) \
+    GElf_##Name *value_##Name __attribute__((unused)) = data
+  TYPES;
 #undef DO_TYPE
 
-  void *data = &value;
   size_t size = gelf_fsize (core, item->type, count, EV_CURRENT);
   size_t convsize = size;
   if (repeated_size != NULL)
@@ -8414,7 +8422,7 @@ handle_core_item (Elf *core, const Ebl_Core_Item *item, const void *desc,
 #define DO_TYPE(NAME, Name, hex, dec)					      \
 	  case ELF_T_##NAME:						      \
 	    colno = print_core_item (colno, ',', WRAP_COLUMN,		      \
-				     0, item->name, dec, value.Name[0]); \
+				     0, item->name, dec, value_##Name[0]); \
 	    break
 	  TYPES;
 #undef DO_TYPE
@@ -8430,7 +8438,7 @@ handle_core_item (Elf *core, const Ebl_Core_Item *item, const void *desc,
 #define DO_TYPE(NAME, Name, hex, dec)					      \
 	  case ELF_T_##NAME:						      \
 	    colno = print_core_item (colno, ',', WRAP_COLUMN,		      \
-				     0, item->name, hex, value.Name[0]);      \
+				     0, item->name, hex, value_##Name[0]);      \
 	    break
 	  TYPES;
 #undef DO_TYPE
@@ -8520,8 +8528,8 @@ handle_core_item (Elf *core, const Ebl_Core_Item *item, const void *desc,
 	{
 #define DO_TYPE(NAME, Name, hex, dec)					      \
 	  case ELF_T_##NAME:						      \
-	    sec = value.Name[0];					      \
-	    usec = value.Name[1];					      \
+	    sec = value_##Name[0];					      \
+	    usec = value_##Name[1];					      \
 	    break
 	  TYPES;
 #undef DO_TYPE
@@ -8551,12 +8559,12 @@ handle_core_item (Elf *core, const Ebl_Core_Item *item, const void *desc,
     case 'c':
       assert (count == 1);
       colno = print_core_item (colno, ',', WRAP_COLUMN, 0, item->name,
-			       "%c", value.Byte[0]);
+			       "%c", value_Byte[0]);
       break;
 
     case 's':
       colno = print_core_item (colno, ',', WRAP_COLUMN, 0, item->name,
-			       "%.*s", (int) count, value.Byte);
+			       "%.*s", (int) count, value_Byte);
       break;
 
     case '\n':
diff --git a/src/unstrip.c b/src/unstrip.c
index d193708a..2a35deca 100644
--- a/src/unstrip.c
+++ b/src/unstrip.c
@@ -54,6 +54,10 @@
 # define _(str) gettext (str)
 #endif
 
+#ifndef MAX
+# define MAX(a, b) ((a) > (b) ? (a) : (b))
+#endif
+
 /* Name and version of program.  */
 static void print_version (FILE *stream, struct argp_state *state);
 ARGP_PROGRAM_VERSION_HOOK_DEF = print_version;
@@ -1013,13 +1017,17 @@ find_alloc_sections_prelink (Elf *debug, Elf_Data *debug_shstrtab,
 	error (EXIT_FAILURE, 0, _("invalid contents in '%s' section"),
 	       ".gnu.prelink_undo");
 
-      union
-      {
-	Elf32_Shdr s32[shnum - 1];
-	Elf64_Shdr s64[shnum - 1];
-      } shdr;
-      dst.d_buf = &shdr;
-      dst.d_size = sizeof shdr;
+      if (unlikely ((shnum - 1) >
+                    SIZE_MAX / MAX (sizeof (Elf32_Shdr), sizeof (Elf64_Shdr))))
+	error (EXIT_FAILURE, 0, _("overflow with shnum = %zu in '%s' section"),
+	       (size_t) shnum, ".gnu.prelink_undo");
+      const size_t shdr_bytes =
+          (shnum - 1) * MAX (sizeof (Elf32_Shdr), sizeof (Elf64_Shdr));
+      void *shdr = xmalloc (shdr_bytes);
+      Elf32_Shdr (*s32)[shnum - 1] = shdr;
+      Elf64_Shdr (*s64)[shnum - 1] = shdr;
+      dst.d_buf = shdr;
+      dst.d_size = shdr_bytes;
       ELF_CHECK (gelf_xlatetom (main, &dst, &src,
 				main_ehdr->e_ident[EI_DATA]) != NULL,
 		 _("cannot read '.gnu.prelink_undo' section: %s"));
@@ -1030,7 +1038,7 @@ find_alloc_sections_prelink (Elf *debug, Elf_Data *debug_shstrtab,
 	  struct section *sec = &undo_sections[undo_nalloc];
 	  if (ehdr.e32.e_ident[EI_CLASS] == ELFCLASS32)
 	    {
-#define COPY(field) sec->shdr.field = shdr.s32[i].field
+#define COPY(field) sec->shdr.field = (*s32)[i].field
 	      COPY (sh_name);
 	      COPY (sh_type);
 	      COPY (sh_flags);
@@ -1044,7 +1052,7 @@ find_alloc_sections_prelink (Elf *debug, Elf_Data *debug_shstrtab,
 #undef	COPY
 	    }
 	  else
-	    sec->shdr = shdr.s64[i];
+	    sec->shdr = (*s64)[i];
 	  if (sec->shdr.sh_flags & SHF_ALLOC)
 	    {
 	      sec->shdr.sh_addr += bias;
@@ -1057,6 +1065,7 @@ find_alloc_sections_prelink (Elf *debug, Elf_Data *debug_shstrtab,
 	}
       qsort (undo_sections, undo_nalloc,
 	     sizeof undo_sections[0], compare_sections_nonrel);
+      free (shdr);
     }
 
   bool fail = false;