symtabs: improve handling of symbol lookups

When CONFIG_SYMTAB_ORDEREDBYNAME is selected most code will use
the ordered search function. When it is not selected no code will
use the ordered search function. This change merges the two
functions and varies its behaviour based on the config setting,
such that all callers can simply call the one search function
and get the best behaviour.

An additional configuration option allows leading underscores to
be stripped from symbols being relocated in loaded objects. This
allows toolchains which prefix C symbol with underscores to make
loadable ELF objects.

Documentation/components/binfmt.rst

@@ -283,6 +283,11 @@ symbol by its name and to provide the address associated with the symbol
 as needed to perform the dynamic linking of the binary object to the
 base FLASH code.
 
+Some toolchains will prefix symbols with an underscore. To support these
+toolchains the ``CONFIG_SYMTAB_DECORATED`` setting may be defined. This
+will cause a leading underscore to be ignored on *undefined* symbols
+during dynamic linking.
+
 Symbol Table Header Files
 -------------------------
 
@@ -323,33 +328,24 @@ Symbol Table Function Interfaces
 .. c:function:: FAR const struct symtab_s *symtab_findbyname(FAR const struct symtab_s *symtab, FAR const char *name, int nsyms);
 
   Find the symbol in the symbol table with the matching name.
-  This version assumes that table is not ordered with respect to
-  symbol name and, hence, access time will be linear with respect
-  to ``nsyms``.
-
-  :return:
-    A reference to the symbol table entry if an entry with the matching name is found; NULL is returned if the entry is not found.
-
-.. c:function:: FAR const struct symtab_s *symtab_findorderedbyname(FAR const struct symtab_s *symtab, FAR const char *name, int nsyms);
-
-  Find the symbol in the symbol table with the matching name.
-  This version assumes that table ordered with respect to symbol name.
+  The implementation will be linear with respect to ``nsyms`` if
+  ``CONFIG_SYMTAB_ORDEREDBYNAME`` is not selected, and logarithmic
+  if it is.
 
   :return:
     A reference to the symbol table entry if an entry with
     the matching name is found; NULL is returned if the entry is not found.
 
-
 .. c:function:: FAR const struct symtab_s *symtab_findbyvalue(FAR const struct symtab_s *symtab, FAR void *value, int nsyms);
 
   Find the symbol in the symbol table whose value closest
   (but not greater than), the provided value. This version assumes
-  that table is not ordered with respect to symbol name and, hence,
+  that table is not ordered with respect to symbol value and, hence,
   access time will be linear with respect to ``nsyms``.
 
   :return:
     A reference to the symbol table entry if an entry with the matching
-    name is found; ``NULL`` is returned if the entry is not found.
+    value is found; ``NULL`` is returned if the entry is not found.
 
 Configuration Variables
 =======================
@@ -358,6 +354,7 @@ Configuration Variables
     This logic may be suppressed be defining this setting.
   - ``CONFIG_BINFMT_CONSTRUCTORS``: Build in support for C++ constructors in loaded modules.
   - ``CONFIG_SYMTAB_ORDEREDBYNAME``: Symbol tables are order by name (rather than value).
+  - ``CONFIG_SYMTAB_DECORATED``: Symbols will have a leading underscore in object files.
 
 Additional configuration options may be required for the each enabled
 binary format.

binfmt/Kconfig

@@ -66,12 +66,3 @@ config BINFMT_CONSTRUCTORS
 	---help---
 		Built-in support for C++ constructors in loaded modules.  Currently
 		only support for ELF binary formats.
-
-config SYMTAB_ORDEREDBYNAME
-	bool "Symbol Tables Ordered by Name"
-	default n
-	---help---
-		Select if the symbol table is ordered by symbol name.  In this case,
-		the logic can perform faster lookups using a binary search.
-		Otherwise, the symbol table is assumed to be un-ordered and only
-		slow, linear searches are supported.

binfmt/libelf/libelf_symbols.c

@@ -290,14 +290,8 @@ int elf_symvalue(FAR struct elf_loadinfo_s *loadinfo, FAR Elf_Sym *sym,
 
         /* Check if the base code exports a symbol of this name */
 
-#ifdef CONFIG_SYMTAB_ORDEREDBYNAME
-        symbol = symtab_findorderedbyname(exports,
-                                          (FAR char *)loadinfo->iobuffer,
-                                          nexports);
-#else
         symbol = symtab_findbyname(exports, (FAR char *)loadinfo->iobuffer,
                                    nexports);
-#endif
         if (!symbol)
           {
             berr("SHN_UNDEF: Exported symbol \"%s\" not found\n",

binfmt/libnxflat/libnxflat_bind.c

@@ -461,11 +461,7 @@ static inline int nxflat_bindimports(FAR struct nxflat_loadinfo_s *loadinfo,
 
           /* Find the exported symbol value for this symbol name. */
 
-#ifdef CONFIG_SYMTAB_ORDEREDBYNAME
-          symbol = symtab_findorderedbyname(exports, symname, nexports);
-#else
           symbol = symtab_findbyname(exports, symname, nexports);
-#endif
           if (!symbol)
             {
               berr("Exported symbol \"%s\" not found\n", symname);

include/nuttx/symtab.h

@@ -73,8 +73,9 @@ extern "C"
  *
  * Description:
  *   Find the symbol in the symbol table with the matching name.
- *   This version assumes that table is not ordered with respect to symbol
- *   name and, hence, access time will be linear with respect to nsyms.
+ *   The implementation will be linear with respect to nsyms if
+ *   CONFIG_SYMTAB_ORDEREDBYNAME is not selected, and logarithmic
+ *   if it is.
  *
  * Returned Value:
  *   A reference to the symbol table entry if an entry with the matching
@@ -86,30 +87,13 @@ FAR const struct symtab_s *
 symtab_findbyname(FAR const struct symtab_s *symtab,
                   FAR const char *name, int nsyms);
 
-/****************************************************************************
- * Name: symtab_findorderedbyname
- *
- * Description:
- *   Find the symbol in the symbol table with the matching name.
- *   This version assumes that table ordered with respect to symbol name.
- *
- * Returned Value:
- *   A reference to the symbol table entry if an entry with the matching
- *   name is found; NULL is returned if the entry is not found.
- *
- ****************************************************************************/
-
-FAR const struct symtab_s *
-symtab_findorderedbyname(FAR const struct symtab_s *symtab,
-                         FAR const char *name, int nsyms);
-
 /****************************************************************************
  * Name: symtab_findbyvalue
  *
  * Description:
  *   Find the symbol in the symbol table whose value closest (but not greater
  *   than), the provided value. This version assumes that table is not
- *   ordered with respect to symbol name and, hence, access time will be
+ *   ordered with respect to symbol value and, hence, access time will be
  *   linear with respect to nsyms.
  *
  * Returned Value:

libs/libc/modlib/modlib_symbols.c

@@ -174,15 +174,9 @@ static int modlib_symcallback(FAR struct module_s *modp, FAR void *arg)
 
   /* Check if this module exports a symbol of that name */
 
-#ifdef CONFIG_SYMTAB_ORDEREDBYNAME
-  exportinfo->symbol = symtab_findorderedbyname(modp->modinfo.exports,
-                                                exportinfo->name,
-                                                modp->modinfo.nexports);
-#else
   exportinfo->symbol = symtab_findbyname(modp->modinfo.exports,
                                          exportinfo->name,
                                          modp->modinfo.nexports);
-#endif
 
   if (exportinfo->symbol != NULL)
     {
@@ -381,13 +375,8 @@ int modlib_symvalue(FAR struct module_s *modp,
         if (symbol == NULL)
           {
             modlib_getsymtab(&symbol, &nsymbols);
-#ifdef CONFIG_SYMTAB_ORDEREDBYNAME
-            symbol = symtab_findorderedbyname(symbol, exportinfo.name,
-                                              nsymbols);
-#else
             symbol = symtab_findbyname(symbol, exportinfo.name,
                                        nsymbols);
-#endif
           }
 
         /* Was the symbol found from any exporter? */

libs/libc/symtab/Make.defs

@@ -20,8 +20,7 @@
 
 # Symbol table source files
 
-CSRCS += symtab_findbyname.c symtab_findbyvalue.c
-CSRCS += symtab_findorderedbyname.c symtab_sortbyname.c
+CSRCS += symtab_findbyname.c symtab_findbyvalue.c symtab_sortbyname.c
 
 # Add the symtab directory to the build
 

libs/libc/symtab/symtab_findbyname.c

@@ -53,7 +53,65 @@ FAR const struct symtab_s *
 symtab_findbyname(FAR const struct symtab_s *symtab,
                   FAR const char *name, int nsyms)
 {
+#ifdef CONFIG_SYMTAB_ORDEREDBYNAME
+  int low  = 0;
+  int high = nsyms - 1;
+  int mid;
+  int cmp;
+#endif
+
+#ifdef CONFIG_SYMTAB_DECORATED
+  if (name[0] == '_')
+    {
+      name++;
+    }
+#endif
+
   DEBUGASSERT(symtab != NULL && name != NULL);
+
+#ifdef CONFIG_SYMTAB_ORDEREDBYNAME
+  while (low < high)
+    {
+      /* Compare the name to the one in the middle.  (or just below
+       * the middle in the case where one is even and one is odd).
+       */
+
+      mid = (low + high) >> 1;
+      cmp = strcmp(name, symtab[mid].sym_name);
+      if (cmp < 0)
+        {
+          /* name < symtab[mid].sym_name
+           *
+           * NOTE: Because of truncation in the calculation of 'mid'.
+           * 'mid' could be equal to 'low'
+           */
+
+          high = mid > low ? mid - 1 : low;
+        }
+      else if (cmp > 0)
+        {
+          /* name > symtab[mid].sym_name */
+
+          low = mid + 1;
+        }
+      else
+        {
+          /* symtab[mid].sym_name == name */
+
+          return &symtab[mid];
+        }
+    }
+
+  /* low == high... One final check.  We might not have actually tested
+   * the final symtab[] name.
+   *
+   *   Example: Only the last pass through loop, suppose low = 1, high = 2,
+   *   mid = 1, and symtab[high].sym_name == name.  Then we would get here
+   *   with low = 2, high = 2, but symtab[2].sym_name was never tested.
+   */
+
+  return strcmp(name, symtab[low].sym_name) == 0 ? &symtab[low] : NULL;
+#else
   for (; nsyms > 0; symtab++, nsyms--)
     {
       if (strcmp(name, symtab->sym_name) == 0)
@@ -63,4 +121,5 @@ symtab_findbyname(FAR const struct symtab_s *symtab,
     }
 
   return NULL;
+#endif
 }

libs/libc/symtab/symtab_findbyvalue.c

@@ -41,12 +41,12 @@
  * Description:
  *   Find the symbol in the symbol table whose value closest (but not greater
  *   than), the provided value. This version assumes that table is not
- *   ordered with respect to symbol name and, hence, access time will be
+ *   ordered with respect to symbol value and, hence, access time will be
  *   linear with respect to nsyms.
  *
  * Returned Value:
  *   A reference to the symbol table entry if an entry with the matching
- *   name is found; NULL is returned if the entry is not found.
+ *   value is found; NULL is returned if the entry is not found.
  *
  ****************************************************************************/