Add exe2ico extractor

1 files changed, 165 insertions, 0 deletions

diff --git a/tools/exe2ico.c b/tools/exe2ico.c
new file mode 100644
index 0000000..5d92994
--- /dev/null
+++ b/tools/exe2ico.c
@@ -0,0 +1,165 @@
+/* Copyright (C) 2022  June McEnroe <june@causal.agency>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <SDL_rwops.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static void errx(int eval, const char *fmt, ...) {
+	va_list ap;
+	va_start(ap, fmt);
+	vfprintf(stderr, fmt, ap);
+	va_end(ap);
+	putc('\n', stderr);
+	exit(eval);
+}
+static void err(int eval, const char *fmt, ...) {
+	va_list ap;
+	va_start(ap, fmt);
+	vfprintf(stderr, fmt, ap);
+	va_end(ap);
+	fprintf(stderr, ": %s\n", SDL_GetError());
+	exit(eval);
+}
+
+int main(int argc, char *argv[]) {
+	if (argc < 2) return 1;
+	const char *exePath = argv[1];
+	const char *name = strrchr(exePath, '/');
+	name = (name ? &name[1] : exePath);
+	char icoPath[256];
+	snprintf(
+		icoPath, sizeof(icoPath), "%.*s.ICO", (int)strcspn(name, "."), name
+	);
+
+	SDL_RWops *exe = SDL_RWFromFile(exePath, "rb");
+	if (!exe) err(1, "%s", exePath);
+	SDL_RWops *ico = SDL_RWFromFile(icoPath, "wb");
+	if (!ico) err(1, "%s", icoPath);
+
+	// Read the EXE header
+	if (SDL_ReadU8(exe) != 'M' || SDL_ReadU8(exe) != 'Z') {
+		errx(1, "%s: invalid MZ signature", exePath);
+	}
+	SDL_RWseek(exe, 0x3C, RW_SEEK_SET);
+	Uint16 neOffset = SDL_ReadLE16(exe);
+	SDL_RWseek(exe, neOffset, RW_SEEK_SET);
+	Uint8 sig[2] = { SDL_ReadU8(exe), SDL_ReadU8(exe) };
+	if (sig[0] == 'P' && sig[1] == 'E') {
+		errx(1, "%s: not implemented for PE", exePath);
+	}
+	if (sig[0] != 'N' || sig[1] != 'E') {
+		errx(1, "%s: invalid NE/PE signature", exePath);
+	}
+
+	// Read the NE header
+	SDL_RWseek(exe, neOffset + 0x24, RW_SEEK_SET);
+	Uint16 resourceTableOffset = neOffset + SDL_ReadLE16(exe);
+
+	// Find the RT_GROUP_ICON resource
+	SDL_RWseek(exe, resourceTableOffset, RW_SEEK_SET);
+	Uint16 alignmentShift = SDL_ReadLE16(exe);
+	for (;;) {
+		Uint16 typeID = SDL_ReadLE16(exe);
+		Uint16 count = SDL_ReadLE16(exe);
+		SDL_ReadLE32(exe); // reserved
+		if (!typeID) {
+			errx(1, "%s: no group icon resource", exePath);
+		}
+		if (typeID == 0x800E) break;
+		SDL_RWseek(exe, 0x0C * count, RW_SEEK_CUR);
+	}
+
+	// Copy the ICONHEADER
+	// https://devblogs.microsoft.com/oldnewthing/20101018-00/?p=12513
+	SDL_RWseek(exe, (Uint32)SDL_ReadLE16(exe) << alignmentShift, RW_SEEK_SET);
+	SDL_WriteLE16(ico, SDL_ReadLE16(exe)); // reserved
+	SDL_WriteLE16(ico, SDL_ReadLE16(exe)); // type
+	Uint16 iconDirCount = SDL_ReadLE16(exe);
+	SDL_WriteLE16(ico, iconDirCount);
+
+	// Copy ICONDIRENTRY's. The entries in the RT_GROUP_ICON resource differ
+	// from those in ICO in their last field. In ICO, it is a 32-bit offset
+	// of the icon data in the ICO file. In the resource, it is a 16-bit
+	// resource ID of an RT_ICON resource. Here we assume the resources are
+	// in the same order as the entries referencing them. We translate the
+	// resource IDs into data offsets by simply tallying up the data lengths
+	// so far. The data offsets need to be aligned to alignmentShift to match
+	// up with the lengths of the icon resources.
+	Uint32 iconDirLength = 0x06 + 0x10 * iconDirCount;
+	Uint32 dataOffset = iconDirLength;
+	dataOffset += -dataOffset & ((1 << alignmentShift) - 1);
+	for (Uint16 i = 0; i < iconDirCount; ++i) {
+		SDL_WriteU8(ico, SDL_ReadU8(exe)); // width
+		SDL_WriteU8(ico, SDL_ReadU8(exe)); // height
+		SDL_WriteU8(ico, SDL_ReadU8(exe)); // colors
+		SDL_WriteU8(ico, SDL_ReadU8(exe)); // reserved
+		SDL_WriteLE16(ico, SDL_ReadLE16(exe)); // color planes
+		SDL_WriteLE16(ico, SDL_ReadLE16(exe)); // bits per pixel
+		Uint32 dataLength = SDL_ReadLE32(exe);
+		SDL_ReadLE16(exe); // resource ID, assumed sequential
+		SDL_WriteLE32(ico, dataLength);
+		SDL_WriteLE32(ico, dataOffset);
+		dataOffset += dataLength;
+		dataOffset += -dataOffset & ((1 << alignmentShift) - 1);
+	}
+	// Padding before the first aligned data offset
+	for (Uint8 i = 0; i < (-iconDirLength & ((1 << alignmentShift) - 1)); ++i) {
+		SDL_WriteU8(ico, 0);
+	}
+
+	// Find the RT_ICON resources
+	SDL_RWseek(exe, resourceTableOffset + 0x02, RW_SEEK_SET);
+	Uint16 resourceCount;
+	for (;;) {
+		Uint16 typeID = SDL_ReadLE16(exe);
+		resourceCount = SDL_ReadLE16(exe);
+		SDL_ReadLE32(exe); // reserved
+		if (!typeID) {
+			errx(1, "%s: no icon resources", exePath);
+		}
+		if (typeID == 0x8003) break;
+		SDL_RWseek(exe, 0x0C * resourceCount, RW_SEEK_CUR);
+	}
+
+	// Copy all icon data sequentially
+	Uint8 *data = NULL;
+	for (Uint16 i = 0; i < resourceCount; ++i) {
+		Uint32 dataOffset = (Uint32)SDL_ReadLE16(exe) << alignmentShift;
+		Uint32 dataLength = (Uint32)SDL_ReadLE16(exe) << alignmentShift;
+		SDL_ReadLE16(exe); // flags
+		SDL_ReadLE16(exe); // resource ID
+		SDL_ReadLE32(exe); // reserved
+		Sint64 nextResource = SDL_RWtell(exe);
+		if (nextResource < 0) err(1, "%s", exePath);
+
+		SDL_RWseek(exe, dataOffset, RW_SEEK_SET);
+		data = realloc(data, dataLength);
+		if (!data) errx(1, "malloc failed");
+		size_t num = SDL_RWread(exe, data, dataLength, 1);
+		if (!num) err(1, "%s", exePath);
+		num = SDL_RWwrite(ico, data, dataLength, 1);
+		if (!num) err(1, "%s", icoPath);
+
+		SDL_RWseek(exe, nextResource, RW_SEEK_SET);
+	}
+	free(data);
+
+	SDL_RWclose(ico);
+	SDL_RWclose(exe);
+}