Re: Calling convention that gets frame pointer register clobbered

[Etienne Lorrain <etienne_lorrain at yahoo dot fr>]

 --- Jim Wilson wrote:
> Etienne Lorrain wrote:
> >  You cannot compile the logical (%si containning the address of a
> >  structure to be filled by the disk BIOS service int $0x13):
> 
> I don't understand what the complaint is here.  The example you gave 
> doesn't compile because ebiosinfo_t is undefined.  If I add a simple 
> structure, then it does compiler.  I don't get an error with gcc-3.3 or 
> current mainline.  I don't see anything obviously wrong with the 
> resulting assembly code.

  The code is compiling if the structure is small enough to fit in
 a 32 bits register, not if it has to be in memory - I should have
 said it. With the compiler I have nearby, this code is only
 compiling if the line "//    unsigned c, d, e, f;" is commented out:

---------------------------
typedef struct {
    unsigned char a,b;
//    unsigned c, d, e, f;
    } ebiosinfo_t;

unsigned char
_EBIOSDISK_getparam (unsigned char disk, ebiosinfo_t *ebiosinfo,
                     unsigned char *status)
  {
  unsigned char carry;

  asm (
"       int     $0x13           # _EBIOSDISK_getparam   \n"
"       mov     %%ah,%1                                 \n"
"       setc    %0                                      \n"
        : "=qm" (carry), "=qm" (*status)
        : "a"((unsigned short)0x4800), "d" (disk), "S" (*ebiosinfo)
        );

  return carry;
  }
---------------------------

$ gcc -v
Reading specs from /usr/lib/gcc-lib/i686-pc-cygwin/3.3.1/specs
Configured with: /GCC/gcc-3.3.1-3/configure --with-gcc --with-gnu-ld
--with-gnu-as --prefix=/usr --e
xec-prefix=/usr --sysconfdir=/etc --libdir=/usr/lib --libexecdir=/usr/sbin
--mandir=/usr/share/man -
-infodir=/usr/share/info --enable-languages=c,ada,c++,f77,pascal,java,objc
--enable-libgcj --enable-
threads=posix --with-system-zlib --enable-nls --without-included-gettext
--enable-interpreter --enab
le-sjlj-exceptions --disable-version-specific-runtime-libs --enable-shared
--disable-win32-registry
--enable-java-gc=boehm --disable-hash-synchronization --verbose
--target=i686-pc-cygwin --host=i686-
pc-cygwin --build=i686-pc-cygwin
Thread model: posix
gcc version 3.3.1 (cygming special)

$ gcc -O2 tmp.c
/usr/lib/gcc-lib/i686-pc-cygwin/3.3.1/../../../libcygwin.a(libcmain.o)(.text+0x7c):
undefined refere
nce to `_WinMain@16'
collect2: ld returned 1 exit status

$ vi tmp.c # to uncomment line 3:

$ gcc -O2 tmp.c
tmp.c: In function `_EBIOSDISK_getparam':
tmp.c:12: internal compiler error: in emit_move_insn, at expr.c:3159
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.

  Note that I did not notice the change of message in later versions,
 and cygwin is not my usual reference - but this code does not compile
 since at least gcc-2.95.

  Etienne.

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