Re: [Tinycc-devel] Feature requests and bug report

[grischka]

Arlen Keshabyan wrote:
> Hello,
>
> My name is Arlen. I'm a programmer from Russia, so I'm sorry for my
> bad English in advance.
>
> First, let me thank you all (to whom it concerns) for TCC, for the
> little precious Perl among the open source projects. Honestly, I've
> used it as a scripting engine for my project. It shows great speed
> results, it's easy and flexible to use. It exactly matches my
> conceptions of a tool like TCC. While using it for awhile, I've
> noticed some shortcomings. The first one is critical. It's about a
> structure alignment. Consider the following code:
>
> struct TestStructure
> {
>         char *_data;
>         long long _size;
> };
>
> GCC tells me that this structure aligned by 8 bytes because 'long
> long' type's size is 8 bytes. So, GCC used the longest type's size for
> the structure alignment. Well, TCC aligned the same structure by 4
> bytes. Because of this, this structure cannot be used for passing data
> between my application and the TCC compiled code. The _size structure
> member is inaccessible due to its different addresses (a shift from
> the beginning of the structure) in TCC and GCC. So, I think TCC has to
> align the structure by 8 bytes too, like GCC does it.

I have committed a fix for this:
http://repo.or.cz/w/tinycc.git?a=commitdiff;h=b8621527

> The second thing is about runtime behavior. If I include 'tcc.c' file
> into my application with LIBTCC defined then compilation goes OK, but
> an error comes out while runtime. The library requests the 'libtcc1.a'
> file to be somewhere around. I do not want the standard c-runtime
> 'libtcc1' to be included in libtcc and I want to provide my own
> runtime library by adding my symbols or using shared libraries. Can
> you provide a way to choose whether to load libtcc1 library runtime or
> not to?

libtcc1.a is not "the standard c-runtime" but tcc specific compiler
support for long long arithmetics (mostly).  If you don't need
that you can set the s->nostdlib flag or just comment out the line
where it is loaded.

That said, maybe libtcc could have a more general function like
   tcc_set_option(s, ...)
which could also replace tcc_enable_debug() and tcc_set_warning().
Just currently there isn't something like that.

> The third one is a feature request. Can you provide a way to set a
> callback function to process pragmas in a source code while parsing
> it. For instance, a function called 'tcc_set_pragma_callback'. This
> function is supposed to get a single string parameter that is a string
> right after the pragma directive. And this callback function is
> supposed to return an integer value that tells a parser to do
> something or not to. This way we can extend functionality a bit. For
> example:
>
> #pragma shared(user32.dll, kernel32.dll, gdi32.dll, "C:/myfolder/myshared.dll")
>
> This way I can add some libraries with 'tcc_add_library' function
> requested in a source code. Or
>
> #pragma once
>
> I can tell a parser to skip the rest of a source code file by
> returning a special value from my callback when it meets '#pragma
> once' directive second time in the same file.
>
> Anyway, a parser is supposed to call pragma callback function when it
> meets an unknown pragma directive and I'm supposed to tell it what to
> do – ignore the directive, ignore the whole file, stop parsing issuing
> an error or do something else.

Well, you can push any new features on our "mob" branch anytime:
    git push ssh://address@hidden/srv/git/tinycc.git my-feature-xyz:mob

It's otherwise hard to see whether it's useful and still simple (tiny)
enough that we want it for everyone ;)

> The fourth thing is about shared libraries. When I use tcc_add_library
> function to load an executable file with exported functions then the
> function fails to load it until you provide a .def file for the
> executable. As far as I know it only understands .dll, .def and .a
> file extensions. Right? 

TCC-PE loads only .def and .a.  I know the gnu linker can load .dll
and maybe .exe.  It would be possible for TCC in theory,  basically
by merging tiny_impdef.c into tccpe.c.  The advantage with .def files
is that it works for dll's that aren't present on the host-system.

> If yes, can you do something to let load an
> executable file as a shared library? As far as I know it's not so hard
> to retrieve a list of exported functions from a shared library or
> executable.

You cannot load exe's as "shared library" because there can be only
one exe-module in a process and it is already loaded by the OS.

If you want to load symbols at runtime from the exe where libtcc
is compiled in, then you could modify tccpe.c:resolve_sym such that
it tries to load any unknown symbols from the main module:

  addr = GetProcAddress(GetModuleHandle(NULL), symbol);

Also "tcc_add_symbol()" can be used to make symbols known to libtcc.

> Telling the truth, TCC is almost the most amazing thing I've ever seen and used.
> Thank you ever so much for this great experience.

Thank you.

> I'm impatient to see your C++ additions, since using simple classes,
> 'new' and 'delete' operators, and a simple string object are the great
> additions to TCC.

C++? What's that? ;)

IIRC I've seen string objects, in some project derived from TinyCC,
somewhere ...

--- grischka