Hi,
I wanted to relay a few issues found in 'command.com' , FreeDos version 1.2.
(1) After a successful build (using Turbo C 2.01), the system would hang after
entering a command ... I tracked the hangup to "realloc()" call in static void
docommand(char *line)
#ifdef FEATURE_INSTALLABLE_COMMANDS
cp = realloc(buf, ARGS_BUFFER_SIZE);
#ifndef NDEBUG
if(cp != buf) {
dprintf( ("[INTERNAL error: realloc() returned wrong result]") );
buf = cp;
}
#endif
#else
free(buf); buf = 0; /* no further useage of this buffer */
#endif
The only way to resolve this problem without changing code in 'docommand()'
was to replace realloc() with my own -- (see below) -- once done, the command
processor accepted commands. This may be a compiler related problem -- I
empirically determined the size of the heap block since I didn't have the Turbo
C source code of malloc() and related functions.
#define USE_MY_REALLOC
#ifdef USE_MY_REALLOC
/*
*----------------------------------------------------------------------
*
* realloc --
*
* Change the size of the block referenced by ptr to "size",
* possibly moving the block to a larger storage area.
*
* Results:
* The return value is a pointer to the new area of memory.
* The contents of this block will be unchanged up to the
* lesser of the new and old sizes.
*
* Side effects:
* The old block of memory may be released.
*
*----------------------------------------------------------------------
*/
static int malloc_size(char *ptr)
{
unsigned short size;
/* empirically determined size of memory block */
ptr -= 4;
size = *(unsigned short*)ptr;
size -= 9;
return (size);
}
void * _Cdecl realloc(void *ptr, size_t newSize)
/* Ptr to currently allocated block. If
* it's 0, then this procedure behaves
* identically to malloc. */
/* Size of block after it is extended */
{
char *newPtr;
unsigned int curSize;
if (ptr == 0)
{
return malloc(newSize);
}
curSize = malloc_size(ptr);
if (newSize <= curSize)
{
return ptr;
}
newPtr = malloc(newSize);
memcpy(newPtr, ptr, curSize);
free(ptr);
return(newPtr);
}
#endif /* USE_MY_REALLOC */
(2) Copying a file (via DOS 'copy' command) failed. I tracked this issue down
to code in farread.c. The Int21 DOS call (via DOSreadwrite()) for WRITE and
READ used the same command parameter (0x3F). I changed this to 0x40 for WRITE
which resolved the problem.
size_t farread(int fd, void far*buf, size_t length)
{
/* Use DOS API in order to read the strings directly to the far address */
return( DOSreadwrite( fd, buf, length, 0x3F00 ) );
}
size_t farwrite(int fd, void far*buf, size_t length)
{
/*
Originally ..
return( DOSreadwrite( fd, buf, length, 0x3F00 ) );
Change 0x3F00 to 0x4000 for WRITE
*/
return( DOSreadwrite( fd, buf, length, 0x4000 ) );
}
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