From: Jakub Jelinek <jakub@redhat.com>
Date: Tue, 3 Feb 2026 08:18:34 +0000 (+0100)
Subject: c++: Don't call cpp_translate_string on NULL string [PR123918]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=31ca0008418821367eaec1fa7750c18442d18c5e;p=thirdparty%2Fgcc.git

c++: Don't call cpp_translate_string on NULL string [PR123918]

My P2246R1 patch caused diagnostics reported by running ubsan
instrumented compiler on cpp26/static_assert1.C - if len is 0,
we don't bother to allocate msg, so it stays NULL, and when I've added
cpp_translate_string call, that can invoke memcpy (something, NULL, 0);
in that case.
While that is no longer UB in C2Y since N3322, libsanitizer doesn't
know that yet and reports it anyway.
While we could just do
      if (len)
        {
...
        }
      else
        msg = "";
there is really no point in trying to translate "" and allocate memory
for that, so the following patch instead by passes that translation for
len == 0.

2026-02-03  Jakub Jelinek  <jakub@redhat.com>

	PR c++/123918
	* semantics.cc (cexpr_str::extract): Bypass cpp_translate_string
	for len == 0.
---

diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 3e1a86fae6c..fb1be25edf5 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -12860,7 +12860,10 @@ cexpr_str::extract (location_t location, const char * & msg, int &len)
       cpp_string istr, ostr;
       istr.len = len;
       istr.text = (const unsigned char *) msg;
-      if (!cpp_translate_string (parse_in, &istr, &ostr, CPP_STRING, true))
+      if (len == 0)
+	;
+      else if (!cpp_translate_string (parse_in, &istr, &ostr, CPP_STRING,
+				      true))
 	{
 	  error_at (location, "could not convert constexpr string from "
 			      "ordinary literal encoding to source character "