[review v4] Only make a nullterminated string if we need to

["Christian Biesinger (Code Review)" <gerrit at gnutoolchain-gerrit dot osci dot io>]

Change URL: https://gnutoolchain-gerrit.osci.io/r/c/binutils-gdb/+/222
......................................................................

Only make a nullterminated string if we need to

As of 7bb43059820c5febb4509b15202a93efde442bc6, we no longer need
a nullterminated linkage_name to look up the entry in the hash table.

So this patch makes it so we only make the copy if the entry was
not found.

By auditing all callers of symbol_set_names, I found out that all cases
where the string may not be nullterminated already pass true for COPY_NAME.
So here, I am documenting that as a requirement and am removing the code
that relies on undefined behavior in symbol_set_names (it accessed the string
past the provided length to check for nulltermination). Note that the Ada
case at the beginning of symbol_set_names was already relying on this.

gdb/ChangeLog:

2019-10-28  Christian Biesinger  <cbiesinger@google.com>

	* symtab.h (symbol_set_names): Document that copy_name must be
	set to true for non-nullterminated strings.
	* symtab.c (symbol_set_names): Only make a nullterminated copy of
	linkage_name if the entry was not found and we need to demangle.

Change-Id: I183302e1f51483ff6dff0fd5c3b0f32f0f04a5d2
---
M gdb/symtab.c
M gdb/symtab.h
2 files changed, 21 insertions(+), 19 deletions(-)



diff --git a/gdb/symtab.c b/gdb/symtab.c
index 79c5fde..a6a9dc9 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -832,8 +832,6 @@
 		  struct objfile_per_bfd_storage *per_bfd)
 {
   struct demangled_name_entry **slot;
-  /* A 0-terminated copy of the linkage name.  */
-  const char *linkage_name_copy;
 
   if (gsymbol->language == language_ada)
     {
@@ -858,20 +856,7 @@
   if (per_bfd->demangled_names_hash == NULL)
     create_demangled_names_hash (per_bfd);
 
-  if (linkage_name[len] != '\0')
-    {
-      char *alloc_name;
-
-      alloc_name = (char *) alloca (len + 1);
-      memcpy (alloc_name, linkage_name, len);
-      alloc_name[len] = '\0';
-
-      linkage_name_copy = alloc_name;
-    }
-  else
-    linkage_name_copy = linkage_name;
-
-  struct demangled_name_entry entry (gdb::string_view (linkage_name_copy, len));
+  struct demangled_name_entry entry (gdb::string_view (linkage_name, len));
   slot = ((struct demangled_name_entry **)
 	  htab_find_slot (per_bfd->demangled_names_hash.get (),
 			  &entry, INSERT));
@@ -882,6 +867,21 @@
 	 This happens to, e.g., main.init (__go_init_main).  Cope.  */
       || (gsymbol->language == language_go && (*slot)->demangled == nullptr))
     {
+      /* A 0-terminated copy of the linkage name.  Callers must set COPY_NAME
+         to true if the string might not be nullterminated.  We have to make
+         this copy because demangling needs a nullterminated string.  */
+      const char *linkage_name_copy;
+      if (copy_name)
+	{
+	  char *alloc_name = (char *) alloca (len + 1);
+	  memcpy (alloc_name, linkage_name, len);
+	  alloc_name[len] = '\0';
+
+	  linkage_name_copy = alloc_name;
+	}
+      else
+	linkage_name_copy = linkage_name;
+
       gdb::unique_xmalloc_ptr<char> demangled_name_ptr
 	(symbol_find_demangled_name (gsymbol, linkage_name_copy));
 
@@ -894,7 +894,7 @@
 	 It turns out that it is actually important to still save such
 	 an entry in the hash table, because storing this name gives
 	 us better bcache hit rates for partial symbols.  */
-      if (!copy_name && linkage_name_copy == linkage_name)
+      if (!copy_name)
 	{
 	  *slot
 	    = ((struct demangled_name_entry *)
@@ -912,7 +912,8 @@
 	       obstack_alloc (&per_bfd->storage_obstack,
 			      sizeof (demangled_name_entry) + len + 1));
 	  char *mangled_ptr = reinterpret_cast<char *> (*slot + 1);
-	  strcpy (mangled_ptr, linkage_name_copy);
+	  memcpy (mangled_ptr, linkage_name, len);
+	  mangled_ptr [len] = '\0';
 	  new (*slot) demangled_name_entry
 	    (gdb::string_view (mangled_ptr, len));
 	}
diff --git a/gdb/symtab.h b/gdb/symtab.h
index 5300383..131a74d 100644
--- a/gdb/symtab.h
+++ b/gdb/symtab.h
@@ -504,7 +504,8 @@
   (symbol)->ginfo.name = (linkage_name)
 
 /* Set the linkage and natural names of a symbol, by demangling
-   the linkage name.  */
+   the linkage name.  If linkage_name may not be nullterminated,
+   copy_name must be set to true.  */
 #define SYMBOL_SET_NAMES(symbol,linkage_name,len,copy_name,objfile)	\
   symbol_set_names (&(symbol)->ginfo, linkage_name, len, copy_name, \
 		    (objfile)->per_bfd)

-- 
Gerrit-Project: binutils-gdb
Gerrit-Branch: master
Gerrit-Change-Id: I183302e1f51483ff6dff0fd5c3b0f32f0f04a5d2
Gerrit-Change-Number: 222
Gerrit-PatchSet: 4
Gerrit-Owner: Christian Biesinger <cbiesinger@google.com>
Gerrit-Reviewer: Christian Biesinger <cbiesinger@google.com>
Gerrit-Reviewer: Luis Machado <luis.machado@linaro.org>
Gerrit-CC: Tom Tromey <tromey@sourceware.org>
Gerrit-MessageType: newpatchset