src/video/SDL_stretch.c
author Sam Lantinga <slouken@libsdl.org>
Sun, 18 Oct 2009 17:31:37 +0000
branchSDL-1.2
changeset 4355 9b464226e541
parent 4159 a1b03ba2fcd0
child 4356 ab2dfac9d5c1
permissions -rw-r--r--
Fixed bug #855 Ludwig Nussel 2009-10-18 06:31:52 PDT an mprotect call was added to fix bug 528. However that results in a buffer that allows writing and code execution. Ie the no-execute security features of modern operating systems are defeated this way. Two mprotect calls are needed. One to make the buffer executable but not writeable when done and another one to make the buffer writeable again if the content needs to be changed.

/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997-2009 Sam Lantinga

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    Sam Lantinga
    slouken@libsdl.org
*/
#include "SDL_config.h"

/* This a stretch blit implementation based on ideas given to me by
   Tomasz Cejner - thanks! :)

   April 27, 2000 - Sam Lantinga
*/

#include "SDL_video.h"
#include "SDL_blit.h"

/* This isn't ready for general consumption yet - it should be folded
   into the general blitting mechanism.
*/

#if ((defined(_MFC_VER) && defined(_M_IX86)/* && !defined(_WIN32_WCE) still needed? */) || \
     defined(__WATCOMC__) || \
     (defined(__GNUC__) && defined(__i386__))) && SDL_ASSEMBLY_ROUTINES
#define USE_ASM_STRETCH
#endif

#ifdef USE_ASM_STRETCH

#ifdef HAVE_MPROTECT
#include <sys/types.h>
#include <sys/mman.h>
#endif
#ifdef __GNUC__
#define PAGE_ALIGNED __attribute__((__aligned__(4096)))
#else
#define PAGE_ALIGNED
#endif

#if defined(_M_IX86) || defined(i386)
#define PREFIX16	0x66
#define STORE_BYTE	0xAA
#define STORE_WORD	0xAB
#define LOAD_BYTE	0xAC
#define LOAD_WORD	0xAD
#define RETURN		0xC3
#else
#error Need assembly opcodes for this architecture
#endif

static unsigned char copy_row[4096] PAGE_ALIGNED;

static int generate_rowbytes(int src_w, int dst_w, int bpp)
{
	static struct {
		int bpp;
		int src_w;
		int dst_w;
		int status;
	} last;

	int i;
	int pos, inc;
	unsigned char *eip;
	unsigned char load, store;

	/* See if we need to regenerate the copy buffer */
	if ( (src_w == last.src_w) &&
	     (dst_w == last.dst_w) && (bpp == last.bpp) ) {
		return(last.status);
	}
	last.bpp = bpp;
	last.src_w = src_w;
	last.dst_w = dst_w;
	last.status = -1;

	switch (bpp) {
	    case 1:
		load = LOAD_BYTE;
		store = STORE_BYTE;
		break;
	    case 2:
	    case 4:
		load = LOAD_WORD;
		store = STORE_WORD;
		break;
	    default:
		SDL_SetError("ASM stretch of %d bytes isn't supported\n", bpp);
		return(-1);
	}
#ifdef HAVE_MPROTECT
	/* Make the code writeable */
	if ( mprotect(copy_row, sizeof(copy_row), PROT_READ|PROT_WRITE) < 0 ) {
		SDL_SetError("Couldn't make copy buffer writeable");
		return(-1);
	}
#endif
	pos = 0x10000;
	inc = (src_w << 16) / dst_w;
	eip = copy_row;
	for ( i=0; i<dst_w; ++i ) {
		while ( pos >= 0x10000L ) {
			if ( bpp == 2 ) {
				*eip++ = PREFIX16;
			}
			*eip++ = load;
			pos -= 0x10000L;
		}
		if ( bpp == 2 ) {
			*eip++ = PREFIX16;
		}
		*eip++ = store;
		pos += inc;
	}
	*eip++ = RETURN;

	/* Verify that we didn't overflow (too late!!!) */
	if ( eip > (copy_row+sizeof(copy_row)) ) {
		SDL_SetError("Copy buffer overflow");
		return(-1);
	}
#ifdef HAVE_MPROTECT
	/* Make the code executable but not writeable */
	if ( mprotect(copy_row, sizeof(copy_row), PROT_READ|PROT_EXEC) < 0 ) {
		SDL_SetError("Couldn't make copy buffer executable");
		return(-1);
	}
#endif
	last.status = 0;
	return(0);
}

#endif /* USE_ASM_STRETCH */

#define DEFINE_COPY_ROW(name, type)			\
void name(type *src, int src_w, type *dst, int dst_w)	\
{							\
	int i;						\
	int pos, inc;					\
	type pixel = 0;					\
							\
	pos = 0x10000;					\
	inc = (src_w << 16) / dst_w;			\
	for ( i=dst_w; i>0; --i ) {			\
		while ( pos >= 0x10000L ) {		\
			pixel = *src++;			\
			pos -= 0x10000L;		\
		}					\
		*dst++ = pixel;				\
		pos += inc;				\
	}						\
}
DEFINE_COPY_ROW(copy_row1, Uint8)
DEFINE_COPY_ROW(copy_row2, Uint16)
DEFINE_COPY_ROW(copy_row4, Uint32)

/* The ASM code doesn't handle 24-bpp stretch blits */
void copy_row3(Uint8 *src, int src_w, Uint8 *dst, int dst_w)
{
	int i;
	int pos, inc;
	Uint8 pixel[3] = { 0, 0, 0 };

	pos = 0x10000;
	inc = (src_w << 16) / dst_w;
	for ( i=dst_w; i>0; --i ) {
		while ( pos >= 0x10000L ) {
			pixel[0] = *src++;
			pixel[1] = *src++;
			pixel[2] = *src++;
			pos -= 0x10000L;
		}
		*dst++ = pixel[0];
		*dst++ = pixel[1];
		*dst++ = pixel[2];
		pos += inc;
	}
}

/* Perform a stretch blit between two surfaces of the same format.
   NOTE:  This function is not safe to call from multiple threads!
*/
int SDL_SoftStretch(SDL_Surface *src, SDL_Rect *srcrect,
                    SDL_Surface *dst, SDL_Rect *dstrect)
{
	int src_locked;
	int dst_locked;
	int pos, inc;
	int dst_width;
	int dst_maxrow;
	int src_row, dst_row;
	Uint8 *srcp = NULL;
	Uint8 *dstp;
	SDL_Rect full_src;
	SDL_Rect full_dst;
#ifdef USE_ASM_STRETCH
	SDL_bool use_asm = SDL_TRUE;
#ifdef __GNUC__
	int u1, u2;
#endif
#endif /* USE_ASM_STRETCH */
	const int bpp = dst->format->BytesPerPixel;

	if ( src->format->BitsPerPixel != dst->format->BitsPerPixel ) {
		SDL_SetError("Only works with same format surfaces");
		return(-1);
	}

	/* Verify the blit rectangles */
	if ( srcrect ) {
		if ( (srcrect->x < 0) || (srcrect->y < 0) ||
		     ((srcrect->x+srcrect->w) > src->w) ||
		     ((srcrect->y+srcrect->h) > src->h) ) {
			SDL_SetError("Invalid source blit rectangle");
			return(-1);
		}
	} else {
		full_src.x = 0;
		full_src.y = 0;
		full_src.w = src->w;
		full_src.h = src->h;
		srcrect = &full_src;
	}
	if ( dstrect ) {
		if ( (dstrect->x < 0) || (dstrect->y < 0) ||
		     ((dstrect->x+dstrect->w) > dst->w) ||
		     ((dstrect->y+dstrect->h) > dst->h) ) {
			SDL_SetError("Invalid destination blit rectangle");
			return(-1);
		}
	} else {
		full_dst.x = 0;
		full_dst.y = 0;
		full_dst.w = dst->w;
		full_dst.h = dst->h;
		dstrect = &full_dst;
	}

	/* Lock the destination if it's in hardware */
	dst_locked = 0;
	if ( SDL_MUSTLOCK(dst) ) {
		if ( SDL_LockSurface(dst) < 0 ) {
			SDL_SetError("Unable to lock destination surface");
			return(-1);
		}
		dst_locked = 1;
	}
	/* Lock the source if it's in hardware */
	src_locked = 0;
	if ( SDL_MUSTLOCK(src) ) {
		if ( SDL_LockSurface(src) < 0 ) {
			if ( dst_locked ) {
				SDL_UnlockSurface(dst);
			}
			SDL_SetError("Unable to lock source surface");
			return(-1);
		}
		src_locked = 1;
	}

	/* Set up the data... */
	pos = 0x10000;
	inc = (srcrect->h << 16) / dstrect->h;
	src_row = srcrect->y;
	dst_row = dstrect->y;
	dst_width = dstrect->w*bpp;

#ifdef USE_ASM_STRETCH
	/* Write the opcodes for this stretch */
	if ( (bpp == 3) ||
	     (generate_rowbytes(srcrect->w, dstrect->w, bpp) < 0) ) {
		use_asm = SDL_FALSE;
	}
#endif

	/* Perform the stretch blit */
	for ( dst_maxrow = dst_row+dstrect->h; dst_row<dst_maxrow; ++dst_row ) {
		dstp = (Uint8 *)dst->pixels + (dst_row*dst->pitch)
		                            + (dstrect->x*bpp);
		while ( pos >= 0x10000L ) {
			srcp = (Uint8 *)src->pixels + (src_row*src->pitch)
			                            + (srcrect->x*bpp);
			++src_row;
			pos -= 0x10000L;
		}
#ifdef USE_ASM_STRETCH
		if (use_asm) {
#ifdef __GNUC__
			__asm__ __volatile__ (
			"call *%4"
			: "=&D" (u1), "=&S" (u2)
			: "0" (dstp), "1" (srcp), "r" (copy_row)
			: "memory" );
#elif defined(_MSC_VER) || defined(__WATCOMC__)
		{ void *code = copy_row;
			__asm {
				push edi
				push esi
	
				mov edi, dstp
				mov esi, srcp
				call dword ptr code

				pop esi
				pop edi
			}
		}
#else
#error Need inline assembly for this compiler
#endif
		} else
#endif
		switch (bpp) {
		    case 1:
			copy_row1(srcp, srcrect->w, dstp, dstrect->w);
			break;
		    case 2:
			copy_row2((Uint16 *)srcp, srcrect->w,
			          (Uint16 *)dstp, dstrect->w);
			break;
		    case 3:
			copy_row3(srcp, srcrect->w, dstp, dstrect->w);
			break;
		    case 4:
			copy_row4((Uint32 *)srcp, srcrect->w,
			          (Uint32 *)dstp, dstrect->w);
			break;
		}
		pos += inc;
	}

	/* We need to unlock the surfaces if they're locked */
	if ( dst_locked ) {
		SDL_UnlockSurface(dst);
	}
	if ( src_locked ) {
		SDL_UnlockSurface(src);
	}
	return(0);
}