[clang] Fix preprocessor output from #embed (#126742)

[Fznamznon]

When bytes with negative signed char values appear in the data, make sure to use raw bytes from the data string when preprocessing, not char values.

Fixes #102798

[llvmbot]

@llvm/pr-subscribers-clang

Author: Mariya Podchishchaeva (Fznamznon)

Changes

When bytes with negative signed char values appear in the data, make sure to use raw bytes from the data string when preprocessing, not char values.

Fixes #102798

---

Full diff: https://github.com/llvm/llvm-project/pull/127222.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+2)
• (modified) clang/lib/Frontend/PrintPreprocessedOutput.cpp (+2-3)
• (modified) clang/test/Preprocessor/embed_preprocess_to_file.c (+8)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index ad1a5e7ae282e..08f8491e2928d 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -897,6 +897,8 @@ Bug Fixes in This Version
 - No longer return ``false`` for ``noexcept`` expressions involving a
   ``delete`` which resolves to a destroying delete but the type of the object
   being deleted has a potentially throwing destructor (#GH118660).
+- Clang now outputs correct values when #embed data contains bytes with negative
+  signed char values (#GH102798).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Frontend/PrintPreprocessedOutput.cpp b/clang/lib/Frontend/PrintPreprocessedOutput.cpp
index 1005825441b3e..2ae355fb33885 100644
--- a/clang/lib/Frontend/PrintPreprocessedOutput.cpp
+++ b/clang/lib/Frontend/PrintPreprocessedOutput.cpp
@@ -974,11 +974,10 @@ static void PrintPreprocessedTokens(Preprocessor &PP, Token &Tok,
       // Loop over the contents and print them as a comma-delimited list of
       // values.
       bool PrintComma = false;
-      for (auto Iter = Data->BinaryData.begin(), End = Data->BinaryData.end();
-           Iter != End; ++Iter) {
+      for (unsigned char Byte : Data->BinaryData.bytes()) {
         if (PrintComma)
           *Callbacks->OS << ", ";
-        *Callbacks->OS << static_cast<unsigned>(*Iter);
+        *Callbacks->OS << static_cast<int>(Byte);
         PrintComma = true;
       }
     } else if (Tok.isAnnotation()) {
diff --git a/clang/test/Preprocessor/embed_preprocess_to_file.c b/clang/test/Preprocessor/embed_preprocess_to_file.c
index 9895d958cf96d..b3c99d36f784a 100644
--- a/clang/test/Preprocessor/embed_preprocess_to_file.c
+++ b/clang/test/Preprocessor/embed_preprocess_to_file.c
@@ -37,3 +37,11 @@ const char even_more[] = {
 // DIRECTIVE-NEXT: #embed <jk.txt> prefix(4, 5,) suffix(, 6, 7) /* clang -E -dE */
 // DIRECTIVE-NEXT:  , 8, 9, 10
 // DIRECTIVE-NEXT: };
+
+constexpr char big_one[] = {
+#embed <big_char.txt>
+};
+
+// EXPANDED: constexpr char big_one[] = {255
+// DIRECTIVE: constexpr char big_one[] = {
+// DIRECTIVE-NEXT: #embed <big_char.txt>

[AaronBallman]

LGTM!

[github-actions]

@Fznamznon (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.