libs/libc/symtab: fix bogus symbol names for out-of-range addresses

allsyms_findbyvalue()/%pS printed a bogus name/offset for addresses
outside the real symbol table's coverage, due to the boundary sentinels
being matchable as real symbols.

Compute the high sentinel from the actual symbol range and treat a
sentinel match as "not found".

Signed-off-by: liang.huang <liang.huang@houmo.ai>
Assisted-by: Claude Code:claude-sonnet-5

libs/libc/symtab/symtab_allsyms.c

@@ -61,6 +61,18 @@ allsyms_lookup(FAR const char *name, FAR void *value,
   else if (value)
     {
       symbol = symtab_findbyvalue(g_allsyms, value, g_nallsyms);
+
+      /* g_allsyms[0] and g_allsyms[g_nallsyms - 1] are boundary sentinels,
+       * not real symbols.  A match against either one means 'value' falls
+       * outside the range covered by real symbols, so treat it as not
+       * found instead of reporting a bogus name/offset.
+       */
+
+      if (symbol == &g_allsyms[0] ||
+          symbol == &g_allsyms[g_nallsyms - 1])
+        {
+          symbol = NULL;
+        }
     }
 
   if (symbol && symbol != &g_allsyms[g_nallsyms - 1])

tools/mkallsyms.py

@@ -47,6 +47,7 @@ class SymbolTables(object):
             self.elffile = None
         self.output = output
         self.symbol_list = []
+        self.max_address = 0
 
     def symbol_filter(self, symbol):
         if symbol["st_info"]["type"] != "STT_FUNC":
@@ -78,7 +79,9 @@ class SymbolTables(object):
             self.emitline(
                 '  { "%s", (FAR %s void *)%s },' % (symbol[1], noconst, hex(symbol[0]))
             )
-        self.emitline('  { "Unknown", (FAR %s void *)0xffffffff }\n};' % (noconst))
+        self.emitline(
+            '  { "Unknown", (FAR %s void *)%s }\n};' % (noconst, hex(self.max_address))
+        )
 
     def get_symtable(self):
         symbol_tables = [
@@ -111,7 +114,12 @@ class SymbolTables(object):
                     func_name = re.sub(r"\(.*$", "", symbol_name)
                 except cxxfilt.InvalidName:
                     symbol_name = symbol.name
-                self.symbol_list.append((symbol["st_value"], func_name))
+                self.symbol_list.append(
+                    (symbol["st_value"], func_name, symbol["st_size"])
+                )
+                end = symbol["st_value"] + symbol["st_size"]
+                if end > self.max_address:
+                    self.max_address = end
         if orderbyname:
             self.symbol_list = sorted(self.symbol_list, key=lambda item: item[1])
         else: