string positional parameter in comparison failure

Now it is possible to compare 2 string variables. I was not able to get the string size so the byte code is quite large. The old comparison between a static string and a variable still the same.
fixes: #450

src/ast/codegen_llvm.cpp

@@ -753,28 +753,37 @@ void CodegenLLVM::visit(Binop &binop)
   Type &type = binop.left->type.type;
   if (type == Type::string)
   {
-    Value *val;
+
+    if (binop.op != bpftrace::Parser::token::EQ && binop.op != bpftrace::Parser::token::NE) {
+      std::cerr << "missing codegen to string operator \"" << opstr(binop) << "\"" << std::endl;
+      abort();
+    }
+
     std::string string_literal("");
-    if (binop.right->is_literal) {
+
+    bool inverse = binop.op == bpftrace::Parser::token::NE;
+
+    if (binop.right->is_literal)
+    {
       binop.left->accept(*this);
-      val = expr_;
-      string_literal = reinterpret_cast<String*>(binop.right)->str;
-    } else {
+      string_literal = static_cast<String *>(binop.right)->str;
+      expr_ = b_.CreateStrcmp(expr_, string_literal, inverse);
+    }
+    else if (binop.left->is_literal)
+    {
       binop.right->accept(*this);
-      val = expr_;
-      string_literal = reinterpret_cast<String*>(binop.left)->str;
+      string_literal = static_cast<String *>(binop.left)->str;
+      expr_ = b_.CreateStrcmp(expr_, string_literal, inverse);
     }
+    else
+    {
+      binop.right->accept(*this);
+      Value * right_string = expr_;
 
-    switch (binop.op) {
-      case bpftrace::Parser::token::EQ:
-        expr_ = b_.CreateStrcmp(val, string_literal);
-        break;
-      case bpftrace::Parser::token::NE:
-        expr_ = b_.CreateStrcmp(val, string_literal, true);
-        break;
-      default:
-        std::cerr << "missing codegen to string operator \"" << opstr(binop) << "\"" << std::endl;
-        abort();
+      binop.left->accept(*this);
+      Value * left_string = expr_;
+
+      expr_ = b_.CreateStrcmp(left_string, right_string, inverse);
     }
   }
   else

src/ast/irbuilderbpf.cpp

@@ -407,6 +407,76 @@ Value *IRBuilderBPF::CreateStrcmp(Value* val, std::string str, bool inverse) {
   return result;
 }
 
+Value *IRBuilderBPF::CreateStrcmp(Value* val1, Value* val2, bool inverse) {
+  /*
+  // This function compares each character of the two string.
+  // It returns true if all are equal and false if any are different
+  // strcmp(String val1, String val2)
+     {
+        for (size_t i = 0; i < bpftrace_.strlen_; i++)
+        {
+
+          if (val1[i] != val2[i])
+          {
+            return false;
+          }
+          if (val1[i] == NULL)
+          {
+            return true;
+          }
+        }
+
+        return true;
+     }
+  */
+  Function *parent = GetInsertBlock()->getParent();
+  BasicBlock *str_ne = BasicBlock::Create(module_.getContext(), "strcmp.false", parent);
+  AllocaInst *store = CreateAllocaBPF(getInt8Ty(), "strcmp.result");
+  BasicBlock *done = BasicBlock::Create(module_.getContext(), "strcmp.done", parent);
+
+  CreateStore(getInt1(inverse), store);
+
+  Value *null_byte = getInt8(0);
+
+  for (size_t i = 0; i < bpftrace_.strlen_; i++)
+  {
+    BasicBlock *char_eq = BasicBlock::Create(module_.getContext(), "strcmp.loop", parent);
+    BasicBlock *loop_null_check = BasicBlock::Create(module_.getContext(), "strcmp.loop_null_cmp", parent);
+
+    AllocaInst *val_char1 = CreateAllocaBPF(getInt8Ty(), "strcmp.char_l");
+    Value *ptr1 = CreateAdd(val1, getInt64(i));
+    CreateProbeRead(val_char1, 1, ptr1);
+    Value *l = CreateLoad(getInt8Ty(), val_char1);
+
+    AllocaInst *val_char2 = CreateAllocaBPF(getInt8Ty(), "strcmp.char_r");
+    Value *ptr2 = CreateAdd(val2, getInt64(i));
+    CreateProbeRead(val_char2, 1, ptr2);
+    Value *r = CreateLoad(getInt8Ty(), val_char2);
+
+    Value *cmp = CreateICmpNE(l, r, "strcmp.cmp");
+    CreateCondBr(cmp, str_ne, loop_null_check);
+
+    SetInsertPoint(loop_null_check);
+
+    Value *cmp_null = CreateICmpEQ(l, null_byte, "strcmp.cmp_null");
+    CreateCondBr(cmp_null, done, char_eq);
+
+    SetInsertPoint(char_eq);
+  }
+
+  CreateBr(done);
+  SetInsertPoint(done);
+  CreateStore(getInt1(!inverse), store);
+
+  CreateBr(str_ne);
+  SetInsertPoint(str_ne);
+
+  Value *result = CreateLoad(store);
+  CreateLifetimeEnd(store);
+
+  return result;
+}
+
 CallInst *IRBuilderBPF::CreateGetNs()
 {
   // u64 ktime_get_ns()

src/ast/irbuilderbpf.h

@@ -46,6 +46,7 @@ class IRBuilderBPF : public IRBuilder<>
   CallInst   *CreateProbeReadStr(Value *dst, size_t size, Value *src);
   Value      *CreateUSDTReadArgument(Value *ctx, AttachPoint *attach_point, int arg_name, Builtin &builtin, int pid);
   Value      *CreateStrcmp(Value* val, std::string str, bool inverse=false);
+  Value      *CreateStrcmp(Value* val1, Value* val2, bool inverse=false);
   CallInst   *CreateGetNs();
   CallInst   *CreateGetPidTgid();
   CallInst   *CreateGetCurrentCgroupId();

src/ast/semantic_analyser.cpp

@@ -540,10 +540,7 @@ void SemanticAnalyser::visit(Binop &binop)
       err_ << "comparing '" << lhs << "' ";
       err_ << "with '" << rhs << "'" << std::endl;
     }
-    else if (lhs == Type::string && !(binop.left->is_literal || binop.right->is_literal)) {
-      err_ << "Comparison between two variables of ";
-      err_ << "type string is not allowed" << std::endl;
-    }
+
     else if (lhs != Type::integer &&
              binop.op != Parser::token::EQ &&
              binop.op != Parser::token::NE) {

tests/runtime/other

@@ -42,3 +42,18 @@ NAME struct keyword optional when casting
 RUN bpftrace -e 'struct Bar { int x; } struct Foo { struct Bar *bar; } i:ms:1 { $foo = (struct Foo *)0; @x = $foo->bar->x; exit()}'
 EXPECT @x: 0
 TIMEOUT 5
+
+NAME struct positional string compare - equal returns true
+RUN bpftrace -e 'BEGIN { if (str($1) == str($2)) { printf("I got %s\n", str($1));}; exit();}' "hello" "hello"
+EXPECT I got hello
+TIMEOUT 5
+
+NAME struct positional string compare - equal returns false
+RUN bpftrace -e 'BEGIN { if (str($1) == str($2)) { printf("I got %s\n", str($1));} else { printf("not equal\n");}; exit();}' "hi" "hello"
+EXPECT not equal
+TIMEOUT 5
+
+NAME struct positional string compare - not equal
+RUN bpftrace -e 'BEGIN { if (str($1) != str($2)) { printf("I got %s\n", str($1));} else { printf("not equal\n");}; exit();}' "hello" "hello"
+EXPECT not equal
+TIMEOUT 5