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exeflat: shrink uncompressed stub size to 64 bytes

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The code still allows for up to 192 bytes, should that
be useful. Simply by re-assembling upxentry.asm then
re-running exeflat, the changes will be picked up.
This commit is contained in:
C. Masloch 2022-05-25 19:28:22 +02:00 committed by Kenneth J Davis
parent 45b3d9ef67
commit 7f38303ade
1 changed files with 22 additions and 20 deletions
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42
utils/exeflat.c
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@ -90,7 +90,7 @@ static void usage(void)
static int exeflat(const char *srcfile, const char *dstfile, static int exeflat(const char *srcfile, const char *dstfile,
const char *start, short *silentSegments, short silentcount, const char *start, short *silentSegments, short silentcount,
int UPX, UWORD entryparagraphs, exe_header *header) int UPX, UWORD stubsize, UWORD entryparagraphs, exe_header *header)
{ {
int i, j; int i, j;
size_t bufsize; size_t bufsize;
@ -231,7 +231,7 @@ static int exeflat(const char *srcfile, const char *dstfile,
} }
/* The biggest .sys file that UPX accepts seems to be 65419 bytes long */ /* The biggest .sys file that UPX accepts seems to be 65419 bytes long */
compress_sys_file = (size - (0xC0 - 0x10)) < 65420; compress_sys_file = (size - (0x20 - 0x10)) < 65420;
if (UPX) { if (UPX) {
printf("Compressing kernel - %s format\n", (compress_sys_file)?"sys":"exe"); printf("Compressing kernel - %s format\n", (compress_sys_file)?"sys":"exe");
if (!compress_sys_file) { if (!compress_sys_file) {
@ -240,13 +240,13 @@ static int exeflat(const char *srcfile, const char *dstfile,
exe_header nheader = *header; exe_header nheader = *header;
nheader.exRelocItems = 0; nheader.exRelocItems = 0;
nheader.exHeaderSize = 2; nheader.exHeaderSize = 2;
realsize = size + 32 - 0xC0; realsize = size + 32 - stubsize;
nheader.exPages = (UWORD)(realsize >> 9); nheader.exPages = (UWORD)(realsize >> 9);
nheader.exExtraBytes = (UWORD)realsize & 511; nheader.exExtraBytes = (UWORD)realsize & 511;
if (nheader.exExtraBytes) if (nheader.exExtraBytes)
nheader.exPages++; nheader.exPages++;
nheader.exInitCS = -0xC; nheader.exInitCS = - (stubsize >> 4);
nheader.exInitIP = 0xC0; nheader.exInitIP = stubsize;
if (fwrite(&nheader, sizeof(nheader), 1, dest) != 1) { if (fwrite(&nheader, sizeof(nheader), 1, dest) != 1) {
printf("Destination file write error\n"); printf("Destination file write error\n");
exit(1); exit(1);
@ -265,9 +265,9 @@ static int exeflat(const char *srcfile, const char *dstfile,
}; };
} }
if (UPX) { if (UPX) {
curbufoffset = 0xC0; curbufoffset = stubsize;
bufsize = BUFSIZE - 0xC0; bufsize = BUFSIZE - stubsize;
to_xfer = size - 0xC0; to_xfer = size - stubsize;
} else { } else {
curbufoffset = 0; curbufoffset = 0;
bufsize = BUFSIZE; bufsize = BUFSIZE;
@ -301,7 +301,7 @@ static int exeflat(const char *srcfile, const char *dstfile,
return compress_sys_file; return compress_sys_file;
} }
static void write_header(FILE *dest, unsigned char * code, static void write_header(FILE *dest, unsigned char * code, UWORD stubsize,
exe_header *header) exe_header *header)
{ {
UWORD stackpointerpatch, stacksegmentpatch, psppatch, csippatch, patchvalue; UWORD stackpointerpatch, stacksegmentpatch, psppatch, csippatch, patchvalue;
@ -312,10 +312,10 @@ static void write_header(FILE *dest, unsigned char * code,
psppatch = code[0x104] + code[0x104 + 1] * 256U; psppatch = code[0x104] + code[0x104 + 1] * 256U;
csippatch = code[0x106] + code[0x106 + 1] * 256U; csippatch = code[0x106] + code[0x106 + 1] * 256U;
end = code[0x108] + code[0x108 + 1] * 256U; end = code[0x108] + code[0x108 + 1] * 256U;
if (stackpointerpatch > (0xC0 - 2) || stackpointerpatch < 32 if (stackpointerpatch > (end - 2) || stackpointerpatch < 32
|| stacksegmentpatch > (0xC0 - 2) || stacksegmentpatch < 32 || stacksegmentpatch > (end - 2) || stacksegmentpatch < 32
|| psppatch > (0xC0 - 2) || psppatch < 32 || psppatch > (end - 2) || psppatch < 32
|| csippatch > (0xC0 - 4) || csippatch < 32 || csippatch > (end - 4) || csippatch < 32
|| end > 0xC0 || end < 32) { || end > 0xC0 || end < 32) {
printf("Invalid entry file patch offsets\n"); printf("Invalid entry file patch offsets\n");
exit(1); exit(1);
@ -326,17 +326,17 @@ static void write_header(FILE *dest, unsigned char * code,
code[stackpointerpatch] = patchvalue & 0xFF; code[stackpointerpatch] = patchvalue & 0xFF;
code[stackpointerpatch + 1] = (patchvalue >> 8) & 0xFF; code[stackpointerpatch + 1] = (patchvalue >> 8) & 0xFF;
patchvalue = code[stacksegmentpatch] + code[stacksegmentpatch + 1] * 256U; patchvalue = code[stacksegmentpatch] + code[stacksegmentpatch + 1] * 256U;
patchvalue += header->exInitSS + 0x6C; patchvalue += header->exInitSS + 0x60 + (stubsize >> 4);
code[stacksegmentpatch] = patchvalue & 0xFF; code[stacksegmentpatch] = patchvalue & 0xFF;
code[stacksegmentpatch + 1] = (patchvalue >> 8) & 0xFF; code[stacksegmentpatch + 1] = (patchvalue >> 8) & 0xFF;
patchvalue = code[psppatch] + code[psppatch + 1] * 256U; patchvalue = code[psppatch] + code[psppatch + 1] * 256U;
patchvalue += 0x6C; patchvalue += 0x60 + (stubsize >> 4);
code[psppatch] = patchvalue & 0xFF; code[psppatch] = patchvalue & 0xFF;
code[psppatch + 1] = (patchvalue >> 8) & 0xFF; code[psppatch + 1] = (patchvalue >> 8) & 0xFF;
patchvalue = header->exInitIP; patchvalue = header->exInitIP;
code[csippatch] = patchvalue & 0xFF; code[csippatch] = patchvalue & 0xFF;
code[csippatch + 1] = (patchvalue >> 8) & 0xFF; code[csippatch + 1] = (patchvalue >> 8) & 0xFF;
patchvalue = header->exInitCS + 0x6C; patchvalue = header->exInitCS + 0x60 + (stubsize >> 4);
code[csippatch + 2] = patchvalue & 0xFF; code[csippatch + 2] = patchvalue & 0xFF;
code[csippatch + 3] = (patchvalue >> 8) & 0xFF; code[csippatch + 3] = (patchvalue >> 8) & 0xFF;
@ -353,7 +353,7 @@ static void write_header(FILE *dest, unsigned char * code,
} }
fseek(dest, 0, SEEK_SET); fseek(dest, 0, SEEK_SET);
if (fwrite(code, 1, 0xC0, dest) != 0xC0) { if (fwrite(code, 1, stubsize, dest) != stubsize) {
printf("Error writing header code to output file\n"); printf("Error writing header code to output file\n");
exit(1); exit(1);
} }
@ -373,6 +373,7 @@ int main(int argc, char **argv)
static unsigned char code[256 + 10 + 1]; static unsigned char code[256 + 10 + 1];
FILE * entryf = NULL; FILE * entryf = NULL;
UWORD end; UWORD end;
UWORD stubsize = 0;
/* if no arguments provided, show usage and exit */ /* if no arguments provided, show usage and exit */
if (argc < 4) usage(); if (argc < 4) usage();
@ -426,6 +427,7 @@ int main(int argc, char **argv)
printf("Invalid entry file patch offsets\n"); printf("Invalid entry file patch offsets\n");
exit(1); exit(1);
} }
stubsize = (end + 15U) & ~15U;
} }
/* arguments left : /* arguments left :
@ -433,7 +435,7 @@ int main(int argc, char **argv)
compress_sys_file = exeflat(argv[1], argv[2], argv[3], compress_sys_file = exeflat(argv[1], argv[2], argv[3],
silentSegments, silentcount, silentSegments, silentcount,
UPX, 0, &header); UPX, stubsize, 0, &header);
if (!UPX) if (!UPX)
exit(0); exit(0);
@ -480,7 +482,7 @@ int main(int argc, char **argv)
{ {
exeflat(tmpexe, argv[2], argv[3], exeflat(tmpexe, argv[2], argv[3],
silentSegments, silentcount, silentSegments, silentcount,
FALSE, 0xC, &header); FALSE, stubsize, stubsize >> 4, &header);
} }
/* argv[2] now contains the final flattened file: just /* argv[2] now contains the final flattened file: just
@ -506,7 +508,7 @@ int main(int argc, char **argv)
exit(1); exit(1);
} }
write_header(dest, code, &header); write_header(dest, code, stubsize, &header);
do { do {
size = fread(buffer, 1, 32 * 1024, source); size = fread(buffer, 1, 32 * 1024, source);
if (fwrite(buffer, 1, size, dest) != size) { if (fwrite(buffer, 1, size, dest) != size) {