From ac1a869d608989f1e92e8c909fe2158028f9ccbe Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Marjam=C3=A4ki?= <daniel.marjamaki@gmail.com>
Date: Mon, 5 Sep 2016 17:27:12 +0200
Subject: [PATCH] unused struct members: don't warn about packed structs
 (#3088)

---
 lib/checkunusedvar.cpp |  4 ++++
 lib/token.h            | 13 ++++++++++---
 lib/tokenize.cpp       |  4 ++++
 test/testunusedvar.cpp |  8 ++++++++
 4 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/lib/checkunusedvar.cpp b/lib/checkunusedvar.cpp
index edae3154f..fce780187 100644
--- a/lib/checkunusedvar.cpp
+++ b/lib/checkunusedvar.cpp
@@ -1240,6 +1240,10 @@ void CheckUnusedVar::checkStructMemberUsage()
         if (scope->classStart->fileIndex() != 0 || scope->className.empty())
             continue;
 
+        // Packed struct => possibly used by lowlevel code. Struct members might be required by hardware.
+        if (scope->classEnd->isAttributePacked())
+            continue;
+
         // Bail out if struct/union contains any functions
         if (!scope->functionList.empty())
             continue;
diff --git a/lib/token.h b/lib/token.h
index 0707ec9d0..ae950b634 100644
--- a/lib/token.h
+++ b/lib/token.h
@@ -386,6 +386,12 @@ public:
     void isAttributeNothrow(bool value) {
         setFlag(fIsAttributeNothrow, value);
     }
+    bool isAttributePacked() const {
+        return getFlag(fIsAttributePacked);
+    }
+    void isAttributePacked(bool value) {
+        setFlag(fIsAttributePacked, value);
+    }
     bool isOperatorKeyword() const {
         return getFlag(fIsOperatorKeyword);
     }
@@ -838,9 +844,10 @@ private:
         fIsAttributeNoreturn    = (1 << 12), // __attribute__((noreturn)), __declspec(noreturn)
         fIsAttributeNothrow     = (1 << 13), // __attribute__((nothrow)), __declspec(nothrow)
         fIsAttributeUsed        = (1 << 14), // __attribute__((used))
-        fIsOperatorKeyword      = (1 << 15), // operator=, etc
-        fIsComplex              = (1 << 16), // complex/_Complex type
-        fIsEnumType             = (1 << 17)  // enumeration type
+        fIsAttributePacked      = (1 << 15), // __attribute__((packed))
+        fIsOperatorKeyword      = (1 << 16), // operator=, etc
+        fIsComplex              = (1 << 17), // complex/_Complex type
+        fIsEnumType             = (1 << 18)  // enumeration type
     };
 
     unsigned int _flags;
diff --git a/lib/tokenize.cpp b/lib/tokenize.cpp
index 90f81842d..6b7fc6653 100644
--- a/lib/tokenize.cpp
+++ b/lib/tokenize.cpp
@@ -8585,6 +8585,10 @@ void Tokenizer::simplifyAttribute()
                 }
             }
 
+            else if (Token::simpleMatch(tok->previous(), "} __attribute__ ( ( packed )")) {
+                tok->previous()->isAttributePacked(true);
+            }
+
             Token::eraseTokens(tok, tok->next()->link()->next());
             tok->deleteThis();
         }
diff --git a/test/testunusedvar.cpp b/test/testunusedvar.cpp
index 22d5d39a7..306190f78 100644
--- a/test/testunusedvar.cpp
+++ b/test/testunusedvar.cpp
@@ -48,6 +48,7 @@ private:
         TEST_CASE(structmember10);
         TEST_CASE(structmember11); // #4168 - initialization with {} / passed by address to unknown function
         TEST_CASE(structmember12); // #7179 - FP unused structmember
+        TEST_CASE(structmember13); // #3088 - __attribute__((packed))
         TEST_CASE(structmember_sizeof);
 
         TEST_CASE(localvar1);
@@ -422,6 +423,13 @@ private:
         ASSERT_EQUALS("", errout.str());
     }
 
+    void structmember13() { // #3088 - struct members required by hardware
+        checkStructMemberUsage("struct S {\n"
+                               "  int x;\n"
+                               "} __attribute__((packed));");
+        ASSERT_EQUALS("", errout.str());
+    }
+
     void structmember_extern() {
         // extern struct => no false positive
         checkStructMemberUsage("extern struct AB\n"