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[COFF] Make the DOS stub a real DOS program 

It only adds a few bytes and is nice for backward compatibility.

Differential Revision: https://reviews.llvm.org/D44018

llvm-svn: 327001
This commit is contained in:
Hans Wennborg 2018-03-08 14:27:28 +00:00
parent 1ba49ee897
commit aee5881a85
2 changed files with 52 additions and 8 deletions
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50
lld/COFF/Writer.cpp
View File

@ -42,8 +42,40 @@ using namespace llvm::support::endian;
using namespace lld;
using namespace lld::coff;
/* To re-generate DOSProgram:
$ cat > /tmp/DOSProgram.asm
org 0
; Copy cs to ds.
push cs
pop ds
; Point ds:dx at the $-terminated string.
mov dx, str
; Int 21/AH=09h: Write string to standard output.
mov ah, 0x9
int 0x21
; Int 21/AH=4Ch: Exit with return code (in AL).
mov ax, 0x4C01
int 0x21
str:
db 'This program cannot be run in DOS mode.$'
align 8, db 0
$ nasm -fbin /tmp/DOSProgram.asm -o /tmp/DOSProgram.bin
$ xxd -i /tmp/DOSProgram.bin
*/
static unsigned char DOSProgram[] = {
0x0e, 0x1f, 0xba, 0x0e, 0x00, 0xb4, 0x09, 0xcd, 0x21, 0xb8, 0x01, 0x4c,
0xcd, 0x21, 0x54, 0x68, 0x69, 0x73, 0x20, 0x70, 0x72, 0x6f, 0x67, 0x72,
0x61, 0x6d, 0x20, 0x63, 0x61, 0x6e, 0x6e, 0x6f, 0x74, 0x20, 0x62, 0x65,
0x20, 0x72, 0x75, 0x6e, 0x20, 0x69, 0x6e, 0x20, 0x44, 0x4f, 0x53, 0x20,
0x6d, 0x6f, 0x64, 0x65, 0x2e, 0x24, 0x00, 0x00
};
static_assert(sizeof(DOSProgram) % 8 == 0,
"DOSProgram size must be multiple of 8");
static const int SectorSize = 512;
static const int DOSStubSize = 64;
static const int DOSStubSize = sizeof(dos_header) + sizeof(DOSProgram);
static_assert(DOSStubSize % 8 == 0, "DOSStub size must be multiple of 8");
static const int NumberfOfDataDirectory = 16;
namespace {
@ -657,15 +689,27 @@ void Writer::assignAddresses() {
}
template <typename PEHeaderTy> void Writer::writeHeader() {
// Write DOS stub
// Write DOS header. For backwards compatibility, the first part of a PE/COFF
// executable consists of an MS-DOS MZ executable. If the executable is run
// under DOS, that program gets run (usually to just print an error message).
// When run under Windows, the loader looks at AddressOfNewExeHeader and uses
// the PE header instead.
uint8_t *Buf = Buffer->getBufferStart();
auto *DOS = reinterpret_cast<dos_header *>(Buf);
Buf += DOSStubSize;
Buf += sizeof(dos_header);
DOS->Magic[0] = 'M';
DOS->Magic[1] = 'Z';
DOS->UsedBytesInTheLastPage = DOSStubSize % 512;
DOS->FileSizeInPages = divideCeil(DOSStubSize, 512);
DOS->HeaderSizeInParagraphs = sizeof(dos_header) / 16;
DOS->AddressOfRelocationTable = sizeof(dos_header);
DOS->AddressOfNewExeHeader = DOSStubSize;
// Write DOS program.
memcpy(Buf, DOSProgram, sizeof(DOSProgram));
Buf += sizeof(DOSProgram);
// Write PE magic
memcpy(Buf, PEMagic, sizeof(PEMagic));
Buf += sizeof(PEMagic);

10
lld/test/COFF/hello32.test
View File

@ -40,7 +40,7 @@ HEADER-NEXT: MinorImageVersion: 0
HEADER-NEXT: MajorSubsystemVersion: 6
HEADER-NEXT: MinorSubsystemVersion: 0
HEADER-NEXT: SizeOfImage: 20480
HEADER-NEXT: SizeOfHeaders: 512
HEADER-NEXT: SizeOfHeaders: 1024
HEADER-NEXT: Subsystem: IMAGE_SUBSYSTEM_WINDOWS_CUI (0x3)
HEADER-NEXT: Characteristics [ (0x9540)
HEADER-NEXT: IMAGE_DLL_CHARACTERISTICS_APPCONTAINER (0x1000)
@ -91,10 +91,10 @@ HEADER-NEXT: }
HEADER-NEXT: }
HEADER-NEXT: DOSHeader {
HEADER-NEXT: Magic: MZ
HEADER-NEXT: UsedBytesInTheLastPage: 0
HEADER-NEXT: FileSizeInPages: 0
HEADER-NEXT: UsedBytesInTheLastPage: 120
HEADER-NEXT: FileSizeInPages: 1
HEADER-NEXT: NumberOfRelocationItems: 0
HEADER-NEXT: HeaderSizeInParagraphs: 0
HEADER-NEXT: HeaderSizeInParagraphs: 4
HEADER-NEXT: MinimumExtraParagraphs: 0
HEADER-NEXT: MaximumExtraParagraphs: 0
HEADER-NEXT: InitialRelativeSS: 0
@ -106,7 +106,7 @@ HEADER-NEXT: AddressOfRelocationTable: 64
HEADER-NEXT: OverlayNumber: 0
HEADER-NEXT: OEMid: 0
HEADER-NEXT: OEMinfo: 0
HEADER-NEXT: AddressOfNewExeHeader: 64
HEADER-NEXT: AddressOfNewExeHeader: 120
HEADER-NEXT: }
IMPORTS: Format: COFF-i386