[llvm-dev] How to create a sprintf call in IR

[zhi chen via llvm-dev]

Hi,

I created a global char array, char buffer[1024]. I want to call a function
to append the string information to the buffer repeatedly. For example, I
need to implement the following code, where length, a, b, c, are global
variables.

int length = 0;
length += sprintf(buffer+length, "str%d", a);
length += sprintf(buffer+length, "str%c", b);
length += sprintf(buffer+length, "str%d", c);

I did it in the following way.
1. Create the global array:
    IntegerType CHARTYPE = IntegerType::get(llvm::getGlobalContext(), 8);
    ArrayType* ty = ArrayType::get(CHARTYPE, 1024);

    GlobalVariable* buffer = new GlobalVariable(mod, ty, false,
GlobalValue::ExternalLinkage, 0, "buffer");

2. Create sprintf
    std::vector<Type*> agrs(2, Type::getInt8PtrTy(ctxt));
    FunctionType* sprintfFT = FunctionType::get(Type::getInt32Ty(ctxt),
args, true);
    Constant* sprintf = mod->getOrInsertFunction("sprintf", sprintfFT);

    Now, I got stuck to create teh function call for sprintf.

    I didn't it like the following:
   Value* str = builder.CreateGlobalStringPtr("str", "");
   Value* data  = builder.CreateLoad(a);  //load a, b, or c
   Value* buf = builder.CreateLoad(buffer);
   builder.CreateCall3((value*)sprintf, buf, str, data);

I want to test the sprintf function before adding the offset, but it didn't
work. The error information is "llvm.sys:PrintStackTrace(_IO_FILE)". Any
help will be appreciated.

Best,
Zhi
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