diff --git a/.vscode/tasks.json b/.vscode/tasks.json
index 2730f99e87..8cebadd0c3 100644
--- a/.vscode/tasks.json
+++ b/.vscode/tasks.json
@@ -236,6 +236,7 @@
                 "Lambdas",
                 "Language1",
                 "Language2",
+                "Language3",
                 "Literals",
                 "Loops",
                 "Macros",
diff --git a/c/common/src/codingstandards/c/Extensions.qll b/c/common/src/codingstandards/c/Extensions.qll
new file mode 100644
index 0000000000..018359586e
--- /dev/null
+++ b/c/common/src/codingstandards/c/Extensions.qll
@@ -0,0 +1,117 @@
+import cpp
+import codingstandards.cpp.Extensions
+
+/**
+ * Common base class for modeling compiler extensions.
+ */
+abstract class CCompilerExtension extends CompilerExtension { }
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other-Builtins
+abstract class CConditionalDefineExtension extends CCompilerExtension, PreprocessorIfdef {
+  CConditionalDefineExtension() {
+    exists(toString().indexOf("__has_builtin")) or
+    exists(toString().indexOf("__has_constexpr_builtin")) or
+    exists(toString().indexOf("__has_feature")) or
+    exists(toString().indexOf("__has_extension")) or
+    exists(toString().indexOf("__has_attribute")) or
+    exists(toString().indexOf("__has_declspec_attribute")) or
+    exists(toString().indexOf("__is_identifier")) or
+    exists(toString().indexOf("__has_include")) or
+    exists(toString().indexOf("__has_include_next")) or
+    exists(toString().indexOf("__has_warning"))
+  }
+}
+
+// Reference: https://clang.llvm.org/docs/LanguageExtensions.html#builtin-macros
+class CMacroBasedExtension extends CCompilerExtension, Macro {
+  CMacroBasedExtension() {
+    getBody() in [
+        "__BASE_FILE__", "__FILE_NAME__", "__COUNTER__", "__INCLUDE_LEVEL__", "_TIMESTAMP__",
+        "__clang__", "__clang_major__", "__clang_minor__", "__clang_patchlevel__",
+        "__clang_version__", "__clang_literal_encoding__", "__clang_wide_literal_encoding__"
+      ]
+  }
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable-Attributes
+class CAttributeExtension extends CCompilerExtension, Attribute {
+  CAttributeExtension() {
+    getName() in [
+        "ext_vector_type", "vector_size", "access", "aligned", "deprecated", "cold", "unused",
+        "fallthrough", "read_only", "alias"
+      ]
+  }
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/_005f_005fsync-Builtins.html#g_t_005f_005fsync-Builtins
+class CFunctionExtension extends CCompilerExtension, FunctionCall {
+  CFunctionExtension() {
+    // these must be somewhat broad because of how they vary
+    // in implementation / naming
+    getTarget().getName().indexOf("__sync_fetch") = 0 or
+    getTarget().getName().indexOf("__sync_add") = 0 or
+    getTarget().getName().indexOf("__sync_sub") = 0 or
+    getTarget().getName().indexOf("__sync_or") = 0 or
+    getTarget().getName().indexOf("__sync_and") = 0 or
+    getTarget().getName().indexOf("__sync_xor") = 0 or
+    getTarget().getName().indexOf("__sync_nand") = 0 or
+    getTarget().getName().indexOf("__sync_bool") = 0 or
+    getTarget().getName().indexOf("__sync_val") = 0 or
+    getTarget().getName().indexOf("__sync_lock") = 0 or
+    // the built-in extensions
+    getTarget().getName().indexOf("__builtin_") = 0
+  }
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment
+class CFunctionLikeExtension extends CCompilerExtension, AlignofExprOperator {
+  CFunctionLikeExtension() { exists(getValueText().indexOf("__alignof__")) }
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement-Exprs
+class CStmtExprExtension extends CCompilerExtension, StmtExpr { }
+
+// Use of ternary like the following: `int a = 0 ?: 0;` where the
+// one of the branches is omitted
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals
+class CTerseTernaryExtension extends CCompilerExtension, ConditionalExpr {
+  CTerseTernaryExtension() { getCondition() = getElse() or getCondition() = getThen() }
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/_005f_005fint128.html#g_t_005f_005fint128
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Decimal-Float.html#Decimal-Float
+class CRealTypeExtensionExtension extends CCompilerExtension, DeclarationEntry {
+  CRealTypeExtensionExtension() {
+    getType() instanceof Decimal128Type or
+    getType() instanceof Decimal32Type or
+    getType() instanceof Decimal64Type or
+    getType() instanceof Float128Type
+  }
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/_005f_005fint128.html#g_t_005f_005fint128
+class CIntegerTypeExtension extends CCompilerExtension, DeclarationEntry {
+  CIntegerTypeExtension() { getType() instanceof Int128Type }
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long-Long
+class CLongLongType extends CCompilerExtension, DeclarationEntry {
+  CLongLongType() { getType() instanceof LongLongType }
+}
+
+class CZeroLengthArraysExtension extends CCompilerExtension, DeclarationEntry {
+  CZeroLengthArraysExtension() { getType().(ArrayType).getArraySize() = 0 }
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Empty-Structures.html#Empty-Structures
+class CEmptyStructExtension extends CCompilerExtension, Struct {
+  CEmptyStructExtension() { not exists(getAMember(_)) }
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable-Length
+class CVariableLengthArraysExtension extends CCompilerExtension, DeclarationEntry {
+  CVariableLengthArraysExtension() {
+    getType() instanceof ArrayType and
+    not getType().(ArrayType).hasArraySize()
+  }
+}
diff --git a/c/common/src/codingstandards/c/UndefinedBehavior.qll b/c/common/src/codingstandards/c/UndefinedBehavior.qll
new file mode 100644
index 0000000000..49b1ee3e5e
--- /dev/null
+++ b/c/common/src/codingstandards/c/UndefinedBehavior.qll
@@ -0,0 +1,28 @@
+import cpp
+import codingstandards.cpp.UndefinedBehavior
+
+/**
+ * Library for modeling undefined behavior.
+ */
+abstract class CUndefinedBehavior extends UndefinedBehavior { }
+
+class C99MainFunction extends Function {
+  C99MainFunction() {
+    this.getNumberOfParameters() = 2 and
+    this.getType() instanceof IntType and
+    this.getParameter(0).getType() instanceof IntType and
+    this.getParameter(1).getType().(PointerType).getBaseType().(PointerType).getBaseType()
+      instanceof CharType
+    or
+    this.getNumberOfParameters() = 0 and
+    this.getType() instanceof VoidType
+  }
+}
+
+class CUndefinedMainDefinition extends CUndefinedBehavior, Function {
+  CUndefinedMainDefinition() {
+    // for testing purposes, we use the prefix ____codeql_coding_standards`
+    (this.getName() = "main" or this.getName().indexOf("____codeql_coding_standards") = 0) and
+    not this instanceof C99MainFunction
+  }
+}
diff --git a/c/misra/src/rules/RULE-1-2/LanguageExtensionsShouldNotBeUsed.ql b/c/misra/src/rules/RULE-1-2/LanguageExtensionsShouldNotBeUsed.ql
new file mode 100644
index 0000000000..f38e41a1b6
--- /dev/null
+++ b/c/misra/src/rules/RULE-1-2/LanguageExtensionsShouldNotBeUsed.ql
@@ -0,0 +1,20 @@
+/**
+ * @id c/misra/language-extensions-should-not-be-used
+ * @name RULE-1-2: Language extensions should not be used
+ * @description Language extensions are not portable to other compilers and should not be used.
+ * @kind problem
+ * @precision high
+ * @problem.severity error
+ * @tags external/misra/id/rule-1-2
+ *       maintainability
+ *       readability
+ *       external/misra/obligation/advisory
+ */
+
+import cpp
+import codingstandards.c.misra
+import codingstandards.c.Extensions
+
+from CCompilerExtension e
+where not isExcluded(e, Language3Package::languageExtensionsShouldNotBeUsedQuery())
+select e, "Is a compiler extension and is not portable to other compilers."
diff --git a/c/misra/src/rules/RULE-1-3/OccurrenceOfUndefinedBehavior.ql b/c/misra/src/rules/RULE-1-3/OccurrenceOfUndefinedBehavior.ql
new file mode 100644
index 0000000000..f6b295bd32
--- /dev/null
+++ b/c/misra/src/rules/RULE-1-3/OccurrenceOfUndefinedBehavior.ql
@@ -0,0 +1,20 @@
+/**
+ * @id c/misra/occurrence-of-undefined-behavior
+ * @name RULE-1-3: There shall be no occurrence of undefined or critical unspecified behavior
+ * @description Relying on undefined or unspecified behavior can result in unreliable programs.
+ * @kind problem
+ * @precision high
+ * @problem.severity error
+ * @tags external/misra/id/rule-1-3
+ *       maintainability
+ *       readability
+ *       external/misra/obligation/required
+ */
+
+import cpp
+import codingstandards.c.misra
+import codingstandards.c.UndefinedBehavior
+
+from CUndefinedBehavior c
+where not isExcluded(c, Language3Package::occurrenceOfUndefinedBehaviorQuery())
+select c, "May result in undefined behavior."
diff --git a/c/misra/test/rules/RULE-1-2/LanguageExtensionsShouldNotBeUsed.expected b/c/misra/test/rules/RULE-1-2/LanguageExtensionsShouldNotBeUsed.expected
new file mode 100644
index 0000000000..f9f034c980
--- /dev/null
+++ b/c/misra/test/rules/RULE-1-2/LanguageExtensionsShouldNotBeUsed.expected
@@ -0,0 +1,51 @@
+| test.c:34:1:34:23 | #define A __BASE_FILE__ | Is a compiler extension and is not portable to other compilers. |
+| test.c:35:1:35:23 | #define B __FILE_NAME__ | Is a compiler extension and is not portable to other compilers. |
+| test.c:36:1:36:21 | #define C __COUNTER__ | Is a compiler extension and is not portable to other compilers. |
+| test.c:37:1:37:27 | #define D __INCLUDE_LEVEL__ | Is a compiler extension and is not portable to other compilers. |
+| test.c:39:1:39:19 | #define F __clang__ | Is a compiler extension and is not portable to other compilers. |
+| test.c:40:1:40:25 | #define G __clang_major__ | Is a compiler extension and is not portable to other compilers. |
+| test.c:41:1:41:25 | #define H __clang_minor__ | Is a compiler extension and is not portable to other compilers. |
+| test.c:42:1:42:30 | #define I __clang_patchlevel__ | Is a compiler extension and is not portable to other compilers. |
+| test.c:43:1:43:27 | #define J __clang_version__ | Is a compiler extension and is not portable to other compilers. |
+| test.c:44:1:44:36 | #define K __clang_literal_encoding__ | Is a compiler extension and is not portable to other compilers. |
+| test.c:45:1:45:41 | #define L __clang_wide_literal_encoding__ | Is a compiler extension and is not portable to other compilers. |
+| test.c:53:33:53:43 | vector_size | Is a compiler extension and is not portable to other compilers. |
+| test.c:54:33:54:47 | vector_size | Is a compiler extension and is not portable to other compilers. |
+| test.c:55:37:55:51 | ext_vector_type | Is a compiler extension and is not portable to other compilers. |
+| test.c:56:37:56:51 | ext_vector_type | Is a compiler extension and is not portable to other compilers. |
+| test.c:61:3:69:4 | (statement expression) | Is a compiler extension and is not portable to other compilers. |
+| test.c:96:3:96:18 | call to __builtin_setjmp | Is a compiler extension and is not portable to other compilers. |
+| test.c:97:3:97:19 | call to __builtin_longjmp | Is a compiler extension and is not portable to other compilers. |
+| test.c:113:11:113:16 | ... ? ... : ... | Is a compiler extension and is not portable to other compilers. |
+| test.c:124:12:124:12 | definition of a | Is a compiler extension and is not portable to other compilers. |
+| test.c:128:17:128:17 | definition of a | Is a compiler extension and is not portable to other compilers. |
+| test.c:165:8:165:15 | definition of contents | Is a compiler extension and is not portable to other compilers. |
+| test.c:182:8:182:11 | gf19 | Is a compiler extension and is not portable to other compilers. |
+| test.c:214:33:214:35 | declaration of out | Is a compiler extension and is not portable to other compilers. |
+| test.c:215:25:215:26 | declaration of in | Is a compiler extension and is not portable to other compilers. |
+| test.c:268:16:268:21 | access | Is a compiler extension and is not portable to other compilers. |
+| test.c:271:27:271:31 | alias | Is a compiler extension and is not portable to other compilers. |
+| test.c:274:23:274:29 | aligned | Is a compiler extension and is not portable to other compilers. |
+| test.c:285:25:285:34 | deprecated | Is a compiler extension and is not portable to other compilers. |
+| test.c:297:20:297:30 | fallthrough | Is a compiler extension and is not portable to other compilers. |
+| test.c:321:3:321:22 | alignof(<expr>) | Is a compiler extension and is not portable to other compilers. |
+| test.c:340:3:340:31 | call to __builtin_extract_return_addr | Is a compiler extension and is not portable to other compilers. |
+| test.c:341:3:341:28 | call to __builtin_frob_return_addr | Is a compiler extension and is not portable to other compilers. |
+| test.c:342:3:342:25 | call to __builtin_frame_address | Is a compiler extension and is not portable to other compilers. |
+| test.c:363:3:363:22 | call to __sync_fetch_and_add_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:364:3:364:22 | call to __sync_fetch_and_sub_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:365:3:365:21 | call to __sync_fetch_and_or_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:366:3:366:22 | call to __sync_fetch_and_and_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:367:3:367:22 | call to __sync_fetch_and_xor_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:368:3:368:23 | call to __sync_fetch_and_nand_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:369:3:369:22 | call to __sync_add_and_fetch_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:370:3:370:22 | call to __sync_sub_and_fetch_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:371:3:371:21 | call to __sync_or_and_fetch_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:372:3:372:22 | call to __sync_and_and_fetch_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:373:3:373:22 | call to __sync_xor_and_fetch_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:374:3:374:23 | call to __sync_nand_and_fetch_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:376:3:376:30 | call to __sync_bool_compare_and_swap_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:377:3:377:29 | call to __sync_val_compare_and_swap_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:378:3:378:26 | call to __sync_lock_test_and_set_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:379:3:379:21 | call to __sync_lock_release_4 | Is a compiler extension and is not portable to other compilers. |
+| test.c:407:3:407:18 | call to __builtin_alloca | Is a compiler extension and is not portable to other compilers. |
diff --git a/c/misra/test/rules/RULE-1-2/LanguageExtensionsShouldNotBeUsed.qlref b/c/misra/test/rules/RULE-1-2/LanguageExtensionsShouldNotBeUsed.qlref
new file mode 100644
index 0000000000..965c95be2c
--- /dev/null
+++ b/c/misra/test/rules/RULE-1-2/LanguageExtensionsShouldNotBeUsed.qlref
@@ -0,0 +1 @@
+rules/RULE-1-2/LanguageExtensionsShouldNotBeUsed.ql
\ No newline at end of file
diff --git a/c/misra/test/rules/RULE-1-2/options b/c/misra/test/rules/RULE-1-2/options
new file mode 100644
index 0000000000..ea7b68755d
--- /dev/null
+++ b/c/misra/test/rules/RULE-1-2/options
@@ -0,0 +1 @@
+semmle-extractor-options:--clang -fhonor-infinity -std=c11 --edg --diag_error=implicit_func_decl -nostdinc -I../../../../common/test/includes/standard-library
diff --git a/c/misra/test/rules/RULE-1-2/test.c b/c/misra/test/rules/RULE-1-2/test.c
new file mode 100644
index 0000000000..367570f7e7
--- /dev/null
+++ b/c/misra/test/rules/RULE-1-2/test.c
@@ -0,0 +1,409 @@
+#include <stdbool.h>
+#include <stdio.h>
+// Note: Clang aims to support both clang and gcc extensions.
+// This test case has been designed using lists compiled from:
+// - https://clang.llvm.org/docs/LanguageExtensions.html
+// - https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other-Builtins
+#ifdef __has_builtin // NON_COMPLIANT[FALSE_NEGATIVE]
+#endif
+#ifdef __has_constexpr_builtin // NON_COMPLIANT[FALSE_NEGATIVE]
+#endif
+#ifdef __has_feature // NON_COMPLIANT[FALSE_NEGATIVE]
+#endif
+#ifdef __has_extension // NON_COMPLIANT[FALSE_NEGATIVE]
+#endif
+#ifdef __has_c_attribute // NON_COMPLIANT[FALSE_NEGATIVE]
+#endif
+#ifdef __has_attribute // NON_COMPLIANT[FALSE_NEGATIVE]
+#endif
+#ifdef __has_declspec_attribute // NON_COMPLIANT[FALSE_NEGATIVE]
+#endif
+#ifdef __is_identifier // NON_COMPLIANT[FALSE_NEGATIVE]
+#endif
+#ifdef __has_include // NON_COMPLIANT[FALSE_NEGATIVE]
+#endif
+#ifdef __has_include_next // NON_COMPLIANT[FALSE_NEGATIVE]
+#endif
+#ifdef __has_warning // NON_COMPLIANT[FALSE_NEGATIVE]
+#endif
+
+// Reference: https://clang.llvm.org/docs/LanguageExtensions.html#builtin-macros
+#define A __BASE_FILE__                   // NON_COMPLIANT
+#define B __FILE_NAME__                   // NON_COMPLIANT
+#define C __COUNTER__                     // NON_COMPLIANT
+#define D __INCLUDE_LEVEL__               // NON_COMPLIANT
+#define E__TIMESTAMP__                    // NON_COMPLIANT
+#define F __clang__                       // NON_COMPLIANT
+#define G __clang_major__                 // NON_COMPLIANT
+#define H __clang_minor__                 // NON_COMPLIANT
+#define I __clang_patchlevel__            // NON_COMPLIANT
+#define J __clang_version__               // NON_COMPLIANT
+#define K __clang_literal_encoding__      // NON_COMPLIANT
+#define L __clang_wide_literal_encoding__ // NON_COMPLIANT
+
+// Requires additional compiler flags to change the architecture
+// typedef __attribute__((neon_vector_type(8))) int8_t int8x8_t;
+// typedef __attribute__((neon_polyvector_type(16))) poly8_t poly8x16_t;
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable-Attributes
+typedef int int4 __attribute__((vector_size(4 * sizeof(int)))); // NON_COMPLIANT
+typedef int v4si __attribute__((__vector_size__(16)));          // NON_COMPLIANT
+typedef float float4 __attribute__((ext_vector_type(4)));       // NON_COMPLIANT
+typedef float float2 __attribute__((ext_vector_type(2)));       // NON_COMPLIANT
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html#Statement-Exprs
+void gf1() {
+  ({ // NON_COMPLIANT
+    int y = 1;
+    int z;
+    if (y > 0)
+      z = y;
+    else
+      z = -y;
+    z;
+  });
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Local-Labels.html#Local-Labels
+void gf2() {
+  // __label__ found; // NON_COMPLIANT[FALSE_NEGATIVE] -- local labels not
+  // supported by clang
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Labels-as-Values.html#Labels-as-Values
+void gf3() {
+  void *ptr;
+  // goto *ptr; // NON_COMPLIANT[FALSE_NEGATIVE]  -- not supported in clang
+}
+
+// Referfence:
+// https://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html#Nested-Functions
+void gf4() {
+  // void gf4a(){  // NON_COMPLIANT[FALSE_NEGATIVE]  -- not supported in clang
+  //
+  // }
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Nonlocal-Gotos.html#Nonlocal-Gotos
+void gf5() {
+  __builtin_setjmp(0);     // NON_COMPLIANT
+  __builtin_longjmp(0, 1); // NON_COMPLIANT
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Constructing-Calls.html#Constructing-Calls
+void gf6() {
+  // not supported by clang
+  //__builtin_apply_args(); // NON_COMPLIANT[FALSE_NEGATIVE]
+  //__builtin_apply(0, 0, 0); // NON_COMPLIANT[FALSE_NEGATIVE]
+  //__builtin_return(0); // NON_COMPLIANT[FALSE_NEGATIVE]
+  //__builtin_va_arg_pack(); // NON_COMPLIANT[FALSE_NEGATIVE]
+  //__builtin_va_arg_pack_len(); // NON_COMPLIANT[FALSE_NEGATIVE]
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Conditionals.html#Conditionals
+void gf7() {
+  int a = 0 ?: 0; // NON_COMPLIANT
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Typeof.html#Typeof
+void gf8() {
+  typeof(int *); // NON_COMPLIANT[FALSE_NEGATIVE]
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/_005f_005fint128.html#g_t_005f_005fint128
+void gf9() {
+  __int128 a; // NON_COMPLIANT
+}
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Long-Long.html#Long-Long
+void gf10() {
+  long long int a; // NON_COMPLIANT
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex
+void gf11() {
+  __real__(0); // NON_COMPLIANT[FALSE_NEGATIVE]
+  __imag__(0); // NON_COMPLIANT[FALSE_NEGATIVE]
+}
+
+void gf12() {}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Floating-Types.html#Floating-Types
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Decimal-Float.html#Decimal-Float
+void gf13() {
+  // not supported on clang
+  //_Decimal32 a; // NON_COMPLIANT[FALSE_NEGATIVE]
+  //_Decimal64 b; // NON_COMPLIANT[FALSE_NEGATIVE]
+  //_Decimal128 c; // NON_COMPLIANT[FALSE_NEGATIVE]
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Complex.html#Complex
+void gf14() {
+  // Do not work in clang
+  // typedef _Complex float __attribute__((mode(TC))) _Complex128; //
+  // NON_COMPLIANT[FALSE_NEGATIVE] typedef _Complex float
+  // __attribute__((mode(XC))) _Complex80; // NON_COMPLIANT[FALSE_NEGATIVE]
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Hex-Floats.html#Hex-Floats
+void gf15() {
+  float f = 0x1.fp3; // NON_COMPLIANT[FALSE_NEGATIVE]
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html#Zero-Length
+void gf16() {
+  char contents[0]; // NON_COMPLIANT
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Named-Address-Spaces.html#Named-Address-Spaces
+void gf17() {
+  // const __flash char ** p; // NON_COMPLIANT[FALSE_NEGATIVE] --  not supported
+  // in clang
+}
+
+void gf18() {
+  // not supported by extractor - checked by looking for flags.
+
+  // short _Fract, _Fract; // NON_COMPLIANT[FALSE_NEGATIVE] -
+  // long _Fract; // NON_COMPLIANT[FALSE_NEGATIVE]
+}
+
+struct gf19 {}; // NON_COMPLIANT
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable-Length
+void gf20(int n) {
+  // struct S { int x[n]; }; // NON_COMPLIANT[FALSE_NEGATIVE] - will never be
+  // supported in clang
+}
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Variadic-Macros.html#Variadic-Macros
+#define gf21(format, args...)                                                  \
+  printf(format, args) // NON_COMPLIANT[FALSE_NEGATIVE] -- note
+                       // the issue here is explicitly naming the arguments.
+#define gf21a(format, ...) printf(format, __VA_ARGS__) // COMPLIANT
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Escaped-Newlines.html#Escaped-Newlines
+#define gf22                                                                   \
+  "a"                                                                          \
+  \     
+"b" // NON_COMPLIANT[FALSE_NEGATIVE] - additional spaces after a backslash --
+    // stripped by extractor
+#define gf22a                                                                  \
+  "a"                                                                          \
+  "b" // COMPLIANT
+
+void gf24(int f, int g) {
+  float beat_freqs[2] = {f - g, f + g}; // NON_COMPLIANT
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html#Variable-Length
+void gf25t(int N, int M, double out[M][N], // NON_COMPLIANT
+           const double in[N][M]);         // NON_COMPLIANT
+void gf25() {
+  double x[3][2];
+  double y[2][3];
+  gf25t(3, 2, y,
+        x); // in ISO C the const qualifier is formally attached
+            // to the element type of the array and not the array itself
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html#Compound-Literals
+struct gf26t {
+  int a;
+  char b[2];
+} gf26v;
+void gf26(int x, int y) {
+  gf26v = ((struct gf26t){
+      x + y, 'z', 0}); // NON_COMPLIANT[FALSE_NEGATIVE] - compound literal
+}
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html#Case-Ranges
+void gf28() {
+  int a;
+
+  // switch(a){
+  //     case: 0 ... 5:  // NON_COMPLIANT[FALSE_NEGATIVE] -  Not supported in
+  //     clang.
+  //         ;;
+  //         break;
+  //     default:
+  //         ;;
+  //         break;
+  // }
+}
+
+union gf29u {
+  int i;
+  double j;
+};
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Cast-to-Union.html#Cast-to-Union
+void gf29() {
+  int x;
+  int y;
+  union gf29u z;
+  z = (union gf29u)x; // NON_COMPLIANT[FALSE_NEGATIVE]
+  z = (union gf29u)y; // NON_COMPLIANT[FALSE_NEGATIVE]
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Variable-Attributes.html#Variable-Attributes
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#Function-Attributes
+__attribute__((access(read_only, 1))) int
+gf30(const char *); // NON_COMPLIANT -- attributes are not portable.
+
+extern int __attribute__((alias("var_target")))
+gf31; // NON_COMPLIANT -- attributes are not portable.
+
+struct __attribute__((aligned(8))) gf32 {
+  short f[3];
+}; // NON_COMPLIANT -- attributes are not portable.
+
+void gf33() {
+gf33l:
+  __attribute__((cold, unused)); // NON_COMPLIANT
+  return;
+}
+
+enum gf34 {
+  oldval __attribute__((deprecated)), // NON_COMPLIANT
+  newval
+};
+
+void gf35() {
+  int x;
+  // __attribute__((assume(x == 42))); // NON_COMPLIANT[FALSE_NEGATIVE] - Not
+  // supported in clang
+
+  switch (x) {
+  case 1:
+    printf("");
+    __attribute__((fallthrough)); // NON_COMPLIANT
+  case 2:
+    break;
+  }
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html#Dollar-Signs
+void gf37() {
+  int a$1; // NON_COMPLIANT[FALSE_NEGATIVE]
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Character-Escapes.html#Character-Escapes
+void gf38() {
+  const char *c = "test\e"; // NON_COMPLIANT[FALSE_NEGATIVE]
+}
+
+struct gf39s {
+  int x;
+  char y;
+} gf39v;
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Alignment.html#Alignment
+void gf39() {
+  __alignof__(gf39v.x); // NON_COMPLIANT
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Incomplete-Enums.html#Incomplete-Enums
+// enum gf40 {}; // NON_COMPLIANT[FALSE_NEGATIVE] - not supported in clang
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Function-Names.html#Function-Names
+void gf41() {
+  printf("__FUNCTION__ = %s\n", __FUNCTION__); // NON_COMPLIANT[FALSE_NEGATIVE]
+  printf("__PRETTY_FUNCTION__ = %s\n",
+         __PRETTY_FUNCTION__); // NON_COMPLIANT[FALSE_NEGATIVE]
+}
+
+// Reference: https://clang.llvm.org/docs/LanguageExtensions.html#builtin-macros
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other-Builtins
+void gf42() {
+  __builtin_extract_return_addr(0); // NON_COMPLIANT
+  __builtin_frob_return_addr(0);    // NON_COMPLIANT
+  __builtin_frame_address(0);       // NON_COMPLIANT
+}
+
+struct gf43s {
+  int x;
+  char y;
+} gf43v;
+
+void gf43() {
+  __builtin_offsetof(struct gf43s, x); // NON_COMPLIANT
+}
+
+struct gf44s {
+  int x;
+  char y;
+} gf44v;
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/_005f_005fsync-Builtins.html#g_t_005f_005fsync-Builtins
+void gf44() {
+  int i;
+  __sync_fetch_and_add(&i, 0);  // NON_COMPLIANT
+  __sync_fetch_and_sub(&i, 0);  // NON_COMPLIANT
+  __sync_fetch_and_or(&i, 0);   // NON_COMPLIANT
+  __sync_fetch_and_and(&i, 0);  // NON_COMPLIANT
+  __sync_fetch_and_xor(&i, 0);  // NON_COMPLIANT
+  __sync_fetch_and_nand(&i, 0); // NON_COMPLIANT
+  __sync_add_and_fetch(&i, 0);  // NON_COMPLIANT
+  __sync_sub_and_fetch(&i, 0);  // NON_COMPLIANT
+  __sync_or_and_fetch(&i, 0);   // NON_COMPLIANT
+  __sync_and_and_fetch(&i, 0);  // NON_COMPLIANT
+  __sync_xor_and_fetch(&i, 0);  // NON_COMPLIANT
+  __sync_nand_and_fetch(&i, 0); // NON_COMPLIANT
+
+  __sync_bool_compare_and_swap(&i, 0, 0);
+  __sync_val_compare_and_swap(&i, 0, 0);
+  __sync_lock_test_and_set(&i, 0, 0);
+  __sync_lock_release(&i, 0);
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Binary-constants.html#Binary-constants
+void gf45() {
+  int i = 0b101010; // NON_COMPLIANT[FALSE_NEGATIVE]
+}
+
+// Reference: https://gcc.gnu.org/onlinedocs/gcc/Thread-Local.html#Thread-Local
+__thread int gf46; // NON_COMPLIANT[FALSE_NEGATIVE]
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Unnamed-Fields.html#Unnamed-Fields
+void gf47() { // NON_COMPLIANT in versions < C11.
+  struct {
+    int a;
+    union {
+      int b;
+      float c;
+    };
+    int d;
+  } f;
+}
+
+// Reference:
+// https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#Other-Builtins
+void gf48() {
+  __builtin_alloca(
+      0); // NON_COMPLIANT (all __builtin functions are non-compliant.)
+}
\ No newline at end of file
diff --git a/c/misra/test/rules/RULE-1-3/OccurrenceOfUndefinedBehavior.expected b/c/misra/test/rules/RULE-1-3/OccurrenceOfUndefinedBehavior.expected
new file mode 100644
index 0000000000..68216d500f
--- /dev/null
+++ b/c/misra/test/rules/RULE-1-3/OccurrenceOfUndefinedBehavior.expected
@@ -0,0 +1,5 @@
+| test.c:8:6:8:35 | ____codeql_coding_standards_m2 | May result in undefined behavior. |
+| test.c:11:5:11:34 | ____codeql_coding_standards_m3 | May result in undefined behavior. |
+| test.c:15:5:15:34 | ____codeql_coding_standards_m4 | May result in undefined behavior. |
+| test.c:19:5:19:34 | ____codeql_coding_standards_m5 | May result in undefined behavior. |
+| test.c:23:5:23:34 | ____codeql_coding_standards_m6 | May result in undefined behavior. |
diff --git a/c/misra/test/rules/RULE-1-3/OccurrenceOfUndefinedBehavior.qlref b/c/misra/test/rules/RULE-1-3/OccurrenceOfUndefinedBehavior.qlref
new file mode 100644
index 0000000000..b579db05b1
--- /dev/null
+++ b/c/misra/test/rules/RULE-1-3/OccurrenceOfUndefinedBehavior.qlref
@@ -0,0 +1 @@
+rules/RULE-1-3/OccurrenceOfUndefinedBehavior.ql
\ No newline at end of file
diff --git a/c/misra/test/rules/RULE-1-3/test.c b/c/misra/test/rules/RULE-1-3/test.c
new file mode 100644
index 0000000000..190cff4000
--- /dev/null
+++ b/c/misra/test/rules/RULE-1-3/test.c
@@ -0,0 +1,25 @@
+void main(void) { // COMPLIANT
+}
+
+int ____codeql_coding_standards_m1(int argc, char **argv) { // NON_COMPLIANT
+  return 0;
+}
+
+void ____codeql_coding_standards_m2(char *argc, char **argv) { // NON_COMPLIANT
+}
+
+int ____codeql_coding_standards_m3(int argc, char *argv) { // NON_COMPLIANT
+  return 0;
+}
+
+int ____codeql_coding_standards_m4() { // NON_COMPLIANT
+  return 0;
+}
+
+int ____codeql_coding_standards_m5(int argc, int *argv) { // NON_COMPLIANT
+  return 0;
+}
+
+int ____codeql_coding_standards_m6(int argc, int **argv) { // NON_COMPLIANT
+  return 0;
+}
diff --git a/cpp/common/src/codingstandards/cpp/Extensions.qll b/cpp/common/src/codingstandards/cpp/Extensions.qll
new file mode 100644
index 0000000000..5ca6cea4f6
--- /dev/null
+++ b/cpp/common/src/codingstandards/cpp/Extensions.qll
@@ -0,0 +1,11 @@
+import cpp
+
+/**
+ * Common base class for modeling compiler extensions.
+ */
+abstract class CompilerExtension extends Locatable { }
+
+/**
+ * Common base class for modeling compiler extensions in CPP.
+ */
+abstract class CPPCompilerExtension extends CompilerExtension { }
diff --git a/cpp/common/src/codingstandards/cpp/UndefinedBehavior.qll b/cpp/common/src/codingstandards/cpp/UndefinedBehavior.qll
new file mode 100644
index 0000000000..85e2f64612
--- /dev/null
+++ b/cpp/common/src/codingstandards/cpp/UndefinedBehavior.qll
@@ -0,0 +1,8 @@
+import cpp
+
+/**
+ * Library for modeling undefined behavior.
+ */
+abstract class UndefinedBehavior extends Locatable { }
+
+abstract class CPPUndefinedBehavior extends UndefinedBehavior { }
diff --git a/cpp/common/src/codingstandards/cpp/exclusions/c/Language3.qll b/cpp/common/src/codingstandards/cpp/exclusions/c/Language3.qll
new file mode 100644
index 0000000000..836f8f7010
--- /dev/null
+++ b/cpp/common/src/codingstandards/cpp/exclusions/c/Language3.qll
@@ -0,0 +1,44 @@
+//** THIS FILE IS AUTOGENERATED, DO NOT MODIFY DIRECTLY.  **/
+import cpp
+import RuleMetadata
+import codingstandards.cpp.exclusions.RuleMetadata
+
+newtype Language3Query =
+  TLanguageExtensionsShouldNotBeUsedQuery() or
+  TOccurrenceOfUndefinedBehaviorQuery()
+
+predicate isLanguage3QueryMetadata(Query query, string queryId, string ruleId, string category) {
+  query =
+    // `Query` instance for the `languageExtensionsShouldNotBeUsed` query
+    Language3Package::languageExtensionsShouldNotBeUsedQuery() and
+  queryId =
+    // `@id` for the `languageExtensionsShouldNotBeUsed` query
+    "c/misra/language-extensions-should-not-be-used" and
+  ruleId = "RULE-1-2" and
+  category = "advisory"
+  or
+  query =
+    // `Query` instance for the `occurrenceOfUndefinedBehavior` query
+    Language3Package::occurrenceOfUndefinedBehaviorQuery() and
+  queryId =
+    // `@id` for the `occurrenceOfUndefinedBehavior` query
+    "c/misra/occurrence-of-undefined-behavior" and
+  ruleId = "RULE-1-3" and
+  category = "required"
+}
+
+module Language3Package {
+  Query languageExtensionsShouldNotBeUsedQuery() {
+    //autogenerate `Query` type
+    result =
+      // `Query` type for `languageExtensionsShouldNotBeUsed` query
+      TQueryC(TLanguage3PackageQuery(TLanguageExtensionsShouldNotBeUsedQuery()))
+  }
+
+  Query occurrenceOfUndefinedBehaviorQuery() {
+    //autogenerate `Query` type
+    result =
+      // `Query` type for `occurrenceOfUndefinedBehavior` query
+      TQueryC(TLanguage3PackageQuery(TOccurrenceOfUndefinedBehaviorQuery()))
+  }
+}
diff --git a/cpp/common/src/codingstandards/cpp/exclusions/c/RuleMetadata.qll b/cpp/common/src/codingstandards/cpp/exclusions/c/RuleMetadata.qll
index 9dfb52fb84..4a25016843 100644
--- a/cpp/common/src/codingstandards/cpp/exclusions/c/RuleMetadata.qll
+++ b/cpp/common/src/codingstandards/cpp/exclusions/c/RuleMetadata.qll
@@ -33,6 +33,7 @@ import IO4
 import InvalidMemory1
 import Language1
 import Language2
+import Language3
 import Memory1
 import Misc
 import Pointers1
@@ -84,6 +85,7 @@ newtype TCQuery =
   TInvalidMemory1PackageQuery(InvalidMemory1Query q) or
   TLanguage1PackageQuery(Language1Query q) or
   TLanguage2PackageQuery(Language2Query q) or
+  TLanguage3PackageQuery(Language3Query q) or
   TMemory1PackageQuery(Memory1Query q) or
   TMiscPackageQuery(MiscQuery q) or
   TPointers1PackageQuery(Pointers1Query q) or
@@ -135,6 +137,7 @@ predicate isQueryMetadata(Query query, string queryId, string ruleId, string cat
   isInvalidMemory1QueryMetadata(query, queryId, ruleId, category) or
   isLanguage1QueryMetadata(query, queryId, ruleId, category) or
   isLanguage2QueryMetadata(query, queryId, ruleId, category) or
+  isLanguage3QueryMetadata(query, queryId, ruleId, category) or
   isMemory1QueryMetadata(query, queryId, ruleId, category) or
   isMiscQueryMetadata(query, queryId, ruleId, category) or
   isPointers1QueryMetadata(query, queryId, ruleId, category) or
diff --git a/rule_packages/c/Language3.json b/rule_packages/c/Language3.json
new file mode 100644
index 0000000000..d48444a4ab
--- /dev/null
+++ b/rule_packages/c/Language3.json
@@ -0,0 +1,50 @@
+{
+  "MISRA-C-2012": {
+    "RULE-1-2": {
+      "properties": {
+        "obligation": "advisory"
+      },
+      "queries": [
+        {
+          "description": "Language extensions are not portable to other compilers and should not be used.",
+          "kind": "problem",
+          "name": "Language extensions should not be used",
+          "precision": "high",
+          "severity": "error",
+          "short_name": "LanguageExtensionsShouldNotBeUsed",
+          "tags": [
+            "maintainability",
+            "readability" 
+          ],
+          "implementation_scope": {
+            "description": "This implementation attempts to cover a broad section of the compiler specific extensions documented in: https://clang.llvm.org/docs/LanguageExtensions.html and https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html but is not comprehensive. The following topics are addressed in this query: Builtin macros, Variable Attributes, Function Attributes, Statement Expressions, Non-Local Gotos, Conditionals, Extended Integer / Numeric Types, Zero Length Structures, Zero Length Arrays, Variable Length Arrays, Case Attributes, Alignment, __sync and __fetch builtins. Other topics listed in the extension references are not covered by this query."
+          }
+        }
+      ],
+      "title": "Language extensions should not be used"
+    },
+    "RULE-1-3": {
+      "properties": {
+        "obligation": "required"
+      },
+      "queries": [
+        {
+          "description": "Relying on undefined or unspecified behavior can result in unreliable programs.",
+          "kind": "problem",
+          "name": "There shall be no occurrence of undefined or critical unspecified behavior",
+          "precision": "high",
+          "severity": "error",
+          "short_name": "OccurrenceOfUndefinedBehavior",
+          "tags": [
+            "maintainability",
+            "readability" 
+          ],
+          "implementation_scope": {
+            "description": "This implementation only considers alternate forms of `main` and the undefined behavior that results. Note that the current version of CodeQL is not able to detect this issue if a function is named `main` since it will assume the return type and formal parameters. Additional cases from Appendix J of the C99 standard are not currently considered."
+          }
+        }
+      ],
+      "title": "There shall be no occurrence of undefined or critical unspecified behavior"
+    }
+  }
+}
\ No newline at end of file