Clang is using the wrong memory model

Corinna Vinschen
Sat Aug 17 09:48:00 GMT 2019

Oe Aug 17 07:31, Agner Fog wrote:
> > So errno was a bad example but you can try accessing e.g. __ctype_ptr__,
> > __progname, optarg, h_errno, or use FE_DFL_ENV from another DLL, just
> > for kicks.
> __ctype_ptr__ is a function
> h_errno works like errno with an imported function
> FE_DFL_ENV is a macro
> __progname and optarg are local variables to each exe or dll

That would contradict what, e.g., __progname is for.  Here's a test:

$ cat > dll.c <<EOF
#include <stdio.h>

extern char *__progname;

printprog ()
  printf ("progname: %s\n", __progname);
$ cat > main.c <<EOF
extern void printprog();

main ()
  printprog ();
$ uname -a
CYGWIN_NT-10.0 vmbert10 3.1.0(0.340/5/3) 2019-08-16 14:36 x86_64 Cygwin

Lets try the medium model first:

  $ gcc -g -shared -mcmodel=medium -o dll.dll dll.c
  $ gcc -g -mcmodel=medium -o main main.c dll.dll
  $ ./main
  progname: main

Now let's try the small model:

  $ gcc -g -shared -mcmodel=small -o dll.dll dll.c
  $ gcc -g -mcmodel=small -o main main.c dll.dll
  $ ./main
  Cygwin runtime failure: /home/corinna/main.exe: Invalid relocation.  Offset
  0xfffffffd80348989 at address 0x40000103b doesn't fit into 32 bits

Now let's try without explicit mcmodel on the CLI:

  $ gcc -g -shared -o dll.dll dll.c
  $ gcc -g -o main main.c dll.dll
  $ ./main
  progname: main

> gcc is using the small memory model by default in Cygwin64, and it works.

No, it's not, see above.

> clang is using the small memory by default when cross-compiling for a Cygwin64 target from Linux, and it works. *your* example code.


Corinna Vinschen
Cygwin Maintainer
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