Subversion Repositories Kolibri OS

; Check whether PE module has been loaded at preferred address.

; If not, relocate the module.

;

; in: esi = PE base address

; in: [esp+4] = module name for debug print

; out: CF=1 - fail

proc fixup_pe_relocations uses edi ebp

; 1. Fetch some data from PE header or stripped PE header.

; We need:

; * ImageBase - preferred address, compare with esi = actual load address;

;   ebp will keep the delta

; * RVA and size of fixups directory

; * flag IMAGE_FILE_RELOCS_STRIPPED from Characteristics

; If the actual address equals the preferred address, do nothing.

; If fixups directory is present, proceed to 2.

; If there is no fixups directory, there are two options:

; * either the directory has not been created

; * or the module has no fixups (data-only module, for example).

; In the first case, IMAGE_FILE_RELOCS_STRIPPED is set, and this is an error.

; In the second case, IMAGE_FILE_RELOCS_STRIPPED is not set; do nothing.

        mov     ebp, esi

        cmp     word [esi], 'MZ'

        jz      .parse_mz

        sub     ebp, [esi+STRIPPED_PE_HEADER.ImageBase]

        jnz     @f

.nothing:

        ret

@@:

        mov     dl, byte [esi+STRIPPED_PE_HEADER.Characteristics]

        lea     eax, [esi+sizeof.STRIPPED_PE_HEADER+SPE_DIRECTORY_BASERELOC*sizeof.IMAGE_DATA_DIRECTORY]

        cmp     [esi+STRIPPED_PE_HEADER.NumberOfRvaAndSizes], SPE_DIRECTORY_BASERELOC

        ja      .common

.norelocs:

        test    dl, IMAGE_FILE_RELOCS_STRIPPED

        jz      .nothing

        stc

        ret

.parse_mz:

        mov     eax, [esi+3Ch]

        add     eax, esi

        sub     ebp, [eax+IMAGE_NT_HEADERS.OptionalHeader.ImageBase]

        jz      .nothing

        mov     dl, byte [esi+IMAGE_NT_HEADERS.FileHeader.Characteristics]

        cmp     [eax+IMAGE_NT_HEADERS.OptionalHeader.NumberOfDirectories], IMAGE_DIRECTORY_ENTRY_BASERELOC

        jbe     .norelocs

        add     eax, IMAGE_NT_HEADERS.OptionalHeader.DataDirectory+IMAGE_DIRECTORY_ENTRY_BASERELOC*sizeof.IMAGE_DATA_DIRECTORY

.common:

        mov     edi, [eax+IMAGE_DATA_DIRECTORY.VirtualAddress]

        push    [eax+IMAGE_DATA_DIRECTORY.isize]

virtual at esp

.sizeleft       dd      ?

end virtual

        add     edi, esi

        cmp     [.sizeleft], 0

        jz      .norelocs

; 2. We need to relocate and we have the relocation table.

; esi = PE base address

; edi = pointer to current data of relocation table

; 2a. Relocation table is organized into blocks describing every page.

; End of table is defined from table size fetched from the header.

; Loop 2b-2g over all blocks until no more data is left.

.pageloop:

; 2b. Load the header of the current block: address and size.

; Advance total size.

; Size in the block includes size of the header, subtract it.

; If there is no data in this block, go to 2g.

        mov     edx, [edi+IMAGE_BASE_RELOCATION.VirtualAddress]

        mov     ecx, [edi+IMAGE_BASE_RELOCATION.SizeOfBlock]

        sub     [.sizeleft], ecx

        add     edi, sizeof.IMAGE_BASE_RELOCATION

        sub     ecx, sizeof.IMAGE_BASE_RELOCATION

        jbe     .pagedone

; 2c. We are going to modify data, so mprotect the current page to be writable.

; Save the old protection, we will restore it after the block is processed.

; Ignore any error.

PROT_READ = 1

PROT_WRITE = 2

PROT_EXEC = 4

        push    esi ecx

        mov     eax, 68

        mov     ebx, 30

        mov     ecx, PROT_READ+PROT_WRITE

        add     edx, esi

        mov     esi, 0x1000

        call    FS_SYSCALL_PTR

        pop     ecx

        push    eax

; 2d. Block data is an array of word values. Repeat 2e for every of those.

.relocloop:

        sub     ecx, 2

        jb      .relocdone

; 2e. Every value consists of a 4-bit type and 12-bit offset in the page.

; x86 uses two types: 0 = no data (used for padding), 3 = 32-bit relative.

        movzx   eax, word [edi]

        add     edi, 2

        mov     ebx, eax

        and     ebx, 0xFFF

        shr     eax, 12

        jz      .relocloop

        cmp     al, IMAGE_REL_BASED_HIGHLOW

        jnz     .badreloc

        add     [edx+ebx], ebp

        jmp     .relocloop

.relocdone:

; 2f. Restore memory protection changed in 2c.

        pop     ecx

        cmp     ecx, -1

        jz      @f

        mov     eax, 68

        mov     ebx, 30

        mov     esi, 0x1000

        call    FS_SYSCALL_PTR

@@:

        pop     esi

.pagedone:

        cmp     [.sizeleft], 0

        jnz     .pageloop

        pop     eax ; pop .sizeleft

; 3. For performance reasons, relocation should be avoided

; by choosing an appropriate preferred address.

; If we have actually relocated something, yell to the debug board,

; so the programmer can notice that.

        mov     ecx, msg_relocated1

        call    sys_msg_board_str

        mov     ecx, [esp+4]

        call    sys_msg_board_str

        mov     ecx, msg_relocated2

        call    sys_msg_board_str

        clc

        ret

.badreloc:

        pop     eax

        mov     ecx, msg_bad_relocation1

        call    sys_msg_board_str

        mov     ecx, [esp+4]

        call    sys_msg_board_str

        mov     ecx, msg_newline

        call    sys_msg_board_str

        stc

        ret

endp