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Honor dos_header_t.e_cparhdr for small header

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... and cleanup PackDjgpp2::readFileHeader()
https://github.com/upx/upx/issues/881

	modified:   p_djgpp2.cpp
	modified:   p_djgpp2.h
This commit is contained in:
John Reiser
2025-02-11 10:29:53 -08:00
committed by Markus F.X.J. Oberhumer
parent 8c9e04daaf
commit bd67677389
2 changed files with 21 additions and 15 deletions
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22
src/p_djgpp2.cpp
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@ -150,27 +150,23 @@ static void handle_allegropak(InputFile *fi, OutputFile *fo) {
}
int PackDjgpp2::readFileHeader() {
byte hdr[0x1c];
byte magic[8];
dos_header_t dos_hdr;
fi->seek(0, SEEK_SET);
fi->readx(hdr, sizeof(hdr));
if (get_le16(hdr) == 0x5a4d) // MZ exe signature, stubbed?
{
coff_offset = 512 * get_le16(hdr + 4);
if (get_le16(hdr + 2) != 0)
coff_offset += get_le16(hdr + 2) - 512;
fi->seek(512, SEEK_SET);
fi->readx(&dos_hdr, sizeof(dos_hdr));
if (get_le16(&dos_hdr.e_magic) == 0x5a4d) { // MZ exe signature, stubbed?
byte magic[8];
fi->seek(16 * get_le16(&dos_hdr.e_cparhdr), SEEK_SET);
fi->readx(magic, 8);
if (memcmp("go32stub", magic, 8) != 0)
return 0; // not V2 image
}
coff_offset = 512 * get_le16(&dos_hdr.e_cp);
if (get_le16(&dos_hdr.e_cblp) != 0)
coff_offset += get_le16(&dos_hdr.e_cblp) - 512;
fi->seek(coff_offset, SEEK_SET);
if (fi->read(&coff_hdr, sizeof(coff_hdr)) != sizeof(coff_hdr))
throwCantPack("skipping djgpp symlink");
} else {
fi->seek(coff_offset, SEEK_SET);
fi->readx(&coff_hdr, 0xa8);
}
if (coff_hdr.f_magic != 0x014c) // I386MAGIC
return 0;
if ((coff_hdr.f_flags & 2) == 0) // F_EXEC - COFF executable

10
src/p_djgpp2.h
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@ -62,6 +62,16 @@ protected:
unsigned coff_offset;
// based on https://dox.ipxe.org/PeImage_8h_source.html
struct alignas(1) dos_header_t {
LE16 e_magic;
LE16 e_cblp; // Bytes on last page of file
LE16 e_cp; // Pages in file
LE16 e_crlc; // Relocations
LE16 e_cparhdr; // Size of header in paragraphs
LE16 e_OMITTED[32 - 5 * 2];
}; // 64 bytes
struct alignas(1) external_scnhdr_t {
byte _[12]; // name, paddr
LE32 vaddr;