[Tinycc-devel] Why does TinyCC fail to link standard C runtime functions in 32-bit mode but works in 64-bit mode?

[Fereydoun Memarzanjany]

If you use TinyCC in its 32-bit mode (`-m32`) to compile a sample
program that uses any CRT function/symbol from `msvcrt.dll` (such as
the snippet provided later in this message), you'll be met with
compilation failures:

`tcc.exe -std=c11 -Wall -Werror -Wl,-subsystem=console -m32 .\main.c`
"tcc: error: undefined symbol '_iob', missing __declspec(dllimport)?"

(This only happens under `-m32`, whereas `-m64` works perfectly fine.)

`_iob` is not the only "unresolved" symbol, either; `printf`,
`freopen`, `freopen_s`, and basically everything from the CRT will
fail to link.

Regardless of whether or not you use `-lmsvcrt`, `#pragma comment(lib,
"msvcrt")`, `_declspec(dllimport)`, `attribute ((dllimport))`,
`-static` or `-shared`, or even `-impdef` on
"C:\Windows\SysWow64\msvcrt.dll" (or earlier versions thereof:
"msvcrt40.dll"), TCC still complains.

I've verified with `DUMPBIN.exe` that both 32- and 64-bit "msvcrt.dll"
do, in fact, define `_iob` and other symbols.

By some arcane logic, the following works perfectly fine: `tcc.exe
-std=c11 -Wall -Werror -Wl,-subsystem=console -m64 .\main.c`

`main.c`
```c
//#pragma comment(lib, "msvcrt")
//__attribute__((dllimport)) extern __declspec(dllimport) FILE _iob[];

#include <windows.h>

// _MSVCRT_ being defined will cause MinGW's stdio.h to use _iob as
// opposed to _imp___iob; only the former is defined in msvcrt.dll.
// However, even though _iob is exported by both the 32- and 64-bit
// versions of said dll, TinyCC still fails to find _iob in the former.
#define _MSVCRT_
#include <stdio.h>

void main() {
    // AllocConsole() and basically everything from kernel32.dll or
    // user32.dll work perfectly fine, both in -m32 and -m64; it's
    // only msvcrt.dll that causes issues with TinyCC.
    AllocConsole();

    // Any CRT function (e.g., freopen, freopen_s, printf, etc.)
    // fail to get linked properly ONLY in -m32; -m64 is fine.
    // Even if I change the -I and -L paths to C:/Windows/SysWow64
    // and/or use tcc.exe -impdef to create .def files from them,
    // TCC still fails in finding _iob and other symbols.
    // Also, using #pragma comment(lib, "msvcrt") or -lmsvcrt
    // doesn't help at all.  Even if you do get TCC to somehow
    // stop complaining about missing symbols, it'd just include
    // a blank IAT.printf or IAT.freopen, causing segfaults.
    freopen("CONOUT$", "w", stdout);
    printf("This only compiles (and prints) under TCC in 64-bit mode.");
}
```

As mentioned earlier, this error in `-m32` happens regardless of other
switches like `-std`, `-shared`, `-static`, `-lmsvcrt`, `-subsyetem`,
etc.  So, at this point, I'm starting to think this might really be a
bug with TinyCC 0.9.27 (Win32 & Win64 builds) itself.