preprocessor: add macroExpandDepth guard to bound MacroExpand recursion

MacroExpand can call PrescanMacroArg (to pre-expand function-like macro
arguments), which in turn calls MacroExpand for any macros found in the
argument token stream.  With deeply nested macro invocations in the
source, this creates a call chain of depth proportional to the nesting
level.  At 200+ levels the native C++ stack overflows.

Add macroExpandDepth to TPpContext (initialized to 0) and a RAII
DepthGuard in MacroExpand that increments it on entry and decrements on
exit.  If the depth reaches maxMacroExpandDepth (200) MacroExpand emits
a preprocessor error and returns MacroExpandNotStarted, unwinding the
recursion cleanly instead of crashing.

Add test preprocessor.macro.recursion.vert: F(x)=x nested 210 times
triggers the guard 10 times with 'macro expansion depth limit exceeded'
errors; without the guard the same input causes a stack overflow.

Author: ashketchumwashere

Test/baseResults/preprocessor.macro.recursion.vert.err

@@ -0,0 +1,13 @@
+ERROR: 0:15: 'macro expansion' : macro expansion depth limit exceeded F
+ERROR: 0:15: 'macro expansion' : macro expansion depth limit exceeded F
+ERROR: 0:15: 'macro expansion' : macro expansion depth limit exceeded F
+ERROR: 0:15: 'macro expansion' : macro expansion depth limit exceeded F
+ERROR: 0:15: 'macro expansion' : macro expansion depth limit exceeded F
+ERROR: 0:15: 'macro expansion' : macro expansion depth limit exceeded F
+ERROR: 0:15: 'macro expansion' : macro expansion depth limit exceeded F
+ERROR: 0:15: 'macro expansion' : macro expansion depth limit exceeded F
+ERROR: 0:15: 'macro expansion' : macro expansion depth limit exceeded F
+ERROR: 0:15: 'macro expansion' : macro expansion depth limit exceeded F
+ERROR: 10 compilation errors.  No code generated.
+
+

Test/baseResults/preprocessor.macro.recursion.vert.out

@@ -0,0 +1,17 @@
+// Test: macroExpandDepth guard prevents stack overflow via
+// deeply nested function-like macro expansion.
+//
+// Without the macroExpandDepth counter (and macro->busy set before
+// PrescanMacroArg), F(F(F(...F(1)...))) causes MacroExpand to call
+// PrescanMacroArg which calls MacroExpand again for each nested F,
+// growing the C stack without bound until stack overflow.
+//
+// With the fix, expansion is terminated at depth 200 with an error.
+
+#version 450
+
+#define F(x) x
+
+int a = F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(F(1))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))));
+
+void main() {}

Test/preprocessor.macro.recursion.vert

@@ -1237,6 +1237,20 @@ MacroExpandResult TPpContext::MacroExpand(TPpToken* ppToken, bool expandUndef, b
 {
     ppToken->space = false;
     int macroAtom = atomStrings.getAtom(ppToken->name);
+
+    // Bound total MacroExpand nesting depth to prevent stack overflow
+    // via unbounded MacroExpand <-> PrescanMacroArg mutual recursion.
+    if (macroExpandDepth >= maxMacroExpandDepth) {
+        parseContext.ppError(ppToken->loc, "macro expansion depth limit exceeded",
+                             "macro expansion", ppToken->name);
+        return MacroExpandNotStarted;
+    }
+    struct DepthGuard {
+        int& d;
+        explicit DepthGuard(int& d_) : d(d_) { ++d; }
+        ~DepthGuard() { --d; }
+    } guard(macroExpandDepth);
+
     if (ppToken->fullyExpanded)
         return MacroExpandNotStarted;
 

glslang/MachineIndependent/preprocessor/Pp.cpp

@@ -466,6 +466,10 @@ class TPpContext {
     std::vector<tInput*> inputStack;
     bool errorOnVersion;
     bool versionSeen;
+    // Current nesting depth of MacroExpand() calls; bounded to prevent
+    // stack overflow via unbounded MacroExpand <-> PrescanMacroArg recursion.
+    int macroExpandDepth = 0;
+    static const int maxMacroExpandDepth = 200;
 
     //
     // from Pp.cpp

glslang/MachineIndependent/preprocessor/PpContext.h

@@ -73,6 +73,7 @@ INSTANTIATE_TEST_SUITE_P(
         "preprocessor.paste_stringify.vert",
         "preprocessor.stringify_invalid.vert",
         "preprocessor.elseseen.oob.vert",
+        "preprocessor.macro.recursion.vert",
     })),
     FileNameAsCustomTestSuffix
 );