[Lldb-commits] [PATCH] D57781: Fix strlen() of unbound array undefined behavior

Jan Kratochvil via Phabricator via lldb-commits lldb-commits at lists.llvm.org
Tue Feb 5 13:21:43 PST 2019

jankratochvil created this revision.
jankratochvil added a project: LLDB.
Herald added subscribers: abidh, aprantl.

LLDB testsuite fails when built by GCC8 on:

  LLDB :: SymbolFile/DWARF/find-basic-namespace.cpp

This is because this code in LLDB codebase has undefined behavior:

  #include <algorithm>
  #include <string.h>
  // lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp:1731
  static struct section_64 {
    char sectname[16];
    char segname[16];
  } sect64 = { {'_','_','a','p','p','l','e','_','n','a','m','e','s','p','a','c'}, "__DWARF" };
  int main() {
    return std::min<size_t>(strlen(sect64.sectname), sizeof(sect64.sectname));

It has been discussed as a (false) bugreport to GCC: wrong-code: LLDB testcase fails: SymbolFile/DWARF/find-basic-namespace.cpp <https://bugzilla.redhat.com/show_bug.cgi?id=1672436>

I will check it in if there are no comments as it looks obvious enough to me.




Index: lldb/source/Utility/ConstString.cpp
--- lldb/source/Utility/ConstString.cpp
+++ lldb/source/Utility/ConstString.cpp
@@ -143,7 +143,7 @@
   const char *GetConstTrimmedCStringWithLength(const char *cstr,
                                                size_t cstr_len) {
     if (cstr != nullptr) {
-      const size_t trimmed_len = std::min<size_t>(strlen(cstr), cstr_len);
+      const size_t trimmed_len = strnlen(cstr, cstr_len);
       return GetConstCStringWithLength(cstr, trimmed_len);
     return nullptr;
Index: lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
--- lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
+++ lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp
@@ -1609,8 +1609,7 @@
   bool add_section = true;
   bool add_to_unified = true;
   ConstString const_segname(
-      load_cmd.segname,
-      std::min<size_t>(strlen(load_cmd.segname), sizeof(load_cmd.segname)));
+      load_cmd.segname, strnlen(load_cmd.segname, sizeof(load_cmd.segname)));
   SectionSP unified_section_sp(
@@ -1729,8 +1728,7 @@
     if (add_section) {
       ConstString section_name(
-          sect64.sectname,
-          std::min<size_t>(strlen(sect64.sectname), sizeof(sect64.sectname)));
+          sect64.sectname, strnlen(sect64.sectname, sizeof(sect64.sectname)));
       if (!const_segname) {
         // We have a segment with no name so we need to conjure up segments
         // that correspond to the section's segname if there isn't already such

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