107 lines
3.4 KiB
C
107 lines
3.4 KiB
C
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/*
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* Copyright (c) 2003 Magnus Lind.
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*
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* This software is provided 'as-is', without any express or implied warranty.
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* In no event will the authors be held liable for any damages arising from
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* the use of this software.
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*
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* Permission is granted to anyone to use this software, alter it and re-
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* distribute it freely for any non-commercial, non-profit purpose subject to
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* the following restrictions:
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*
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* 1. The origin of this software must not be misrepresented; you must not
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* claim that you wrote the original software. If you use this software in a
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* product, an acknowledgment in the product documentation would be
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* appreciated but is not required.
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*
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* 2. Altered source versions must be plainly marked as such, and must not
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* be misrepresented as being the original software.
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*
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* 3. This notice may not be removed or altered from any distribution.
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*
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* 4. The names of this software and/or it's copyright holders may not be
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* used to endorse or promote products derived from this software without
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* specific prior written permission.
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*
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*/
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#include <stdlib.h>
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#include "bprg.h"
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#include "log.h"
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static int
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linkpatch_cb_line_mutate(const unsigned char *in, /* IN */
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unsigned char *mem, /* IN/OUT */
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unsigned short *pos, /* IN/OUT */
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void *priv) /* IN/OUT */
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{
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unsigned short start;
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unsigned short i;
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start = *pos;
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i = 0;
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/* skip link */
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i += 2; in += 2;
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/* copy number */
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mem[start + i++] = *(in++);
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mem[start + i++] = *(in++);
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/* copy line including terminating '\0' */
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while((mem[start + i++] = *(in++)) != '\0');
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/* the purpose of this whole "if" structure is to improve the
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* crunching of the basic program by changing the basic line
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* link pointers to something that crunches better. This is
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* possible since the basic normally recreates the links when
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* loading the basic program anyhow. However if we decrunch
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* the basic program this will not happen. But there is still
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* a nice subroutine that does the job for us that we can call
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* from the basic start trampoline */
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/* link patching begins here */
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if(mem[start + 2] == '\0' && mem[start + 4] != '\0')
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{
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/* mask 1, length 3 offset 3*/
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mem[start + 0] = mem[start + 3];
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mem[start + 1] = mem[start + 4];
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} else if(mem[start + 3] == '\0' && mem[start + 5] != '\0')
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{
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/* mask 2, length 3 offset 4*/
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mem[start + 0] = mem[start + 4];
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mem[start + 1] = mem[start + 5];
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} else if(mem[start + 3] != '\0')
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{
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/* mask 3, length 2 offset 2*/
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mem[start + 0] = mem[start + 2];
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mem[start + 1] = mem[start + 3];
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} else if(mem[start + 4] != '\0')
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{
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/* mask 4, length 2 offset 3*/
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mem[start + 0] = mem[start + 3];
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mem[start + 1] = mem[start + 4];
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} else
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{
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/* if we ever get here I have made a big mistake in
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assuming that the test (mem[start + 4] != '\0') always is true
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since empty basic lines are forbidden */
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LOG(LOG_ERROR, ("Error, can't patch link (should be impossible)"));
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exit(1);
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}
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/* link patching ends here */
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*pos = start + i;
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/* success */
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return 0;
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}
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void
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bprg_link_patch(struct bprg_ctx *ctx)
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{
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bprg_lines_mutate(ctx, linkpatch_cb_line_mutate, NULL);
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LOG(LOG_VERBOSE, ("program length %hu\n", ctx->len));
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}
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