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Re: [Tinycc-devel] Libtcc and existing variables

From: grischka
Subject: Re: [Tinycc-devel] Libtcc and existing variables
Date: Thu, 28 Sep 2017 09:22:58 +0200
User-agent: Thunderbird (Windows/20090812)

Joel Bodenmann wrote:
Hello folks,

I am successfully using libtcc in an application. I'm very happy with it and
I thank you for providing this awesome tool.

So far, my needs were basically completely covered by the libtcc_test.c
example program that uses tcc_add_symbol() to give the compiled program
access to a function that exists in the host application (I'm sorry if my
terminology is off here). However, now I have a case where I need to give
the client application (the program that gets compiled) access to a variable
that already exists in the host application.

See CURRENT libtcc_test.c for an example how to access variables.

(JIT snippet needs to declare it like
    [ __attribute((dllimport)) ] extern myStruct a;

-- gr

Specifically, my client program
needs a pointer to a struct that already exists in the host application
during runtime. This is a basic illustration of what's going on:

// Struct declaration (known in the host program and the client program)

typedef struct myStruct_t {


} myStruct;

// Creating an instance of said struct in the host program

myStruct a;

// Using that struct in the client program (this gets compiled by libtcc)


When I compile this with libtcc, I get the compilation error "a is
undeclared". Initially I was confused by that because I properly added the
struct instance using this:   tcc_add_symbol(s, "a", &a);

However, upon thinking about it (and reading the documentation) I figured
out that tcc_add_symbol only affects linking time and the tcc compiler
simply doesn't know what a is.

My question: Is there any way to give a client program access to a variable
that exists in the host program? All I could think of so far is generating a
wrapper function that gets compiled with the client program that returns a
pointer to a. However, I'd like to avoid that if possible.

Any kind of comments would be greatly appreciated.

Best regards,

~ Joel Bodenmann


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