upx/src/stub/fold_sh86.asm

;  fold_sh86.asm -- Linux program entry point & decompressor (shell script)
;
;  This file is part of the UPX executable compressor.
;
;  Copyright (C) 1996-2004 Markus Franz Xaver Johannes Oberhumer
;  Copyright (C) 1996-2004 Laszlo Molnar
;  Copyright (C) 2000-2004 John F. Reiser
;  All Rights Reserved.
;
;  UPX and the UCL library are free software; you can redistribute them
;  and/or modify them under the terms of the GNU General Public License as
;  published by the Free Software Foundation; either version 2 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 General Public License for more details.
;
;  You should have received a copy of the GNU General Public License
;  along with this program; see the file COPYING.
;  If not, write to the Free Software Foundation, Inc.,
;  59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
;
;  Markus F.X.J. Oberhumer              Laszlo Molnar
;  <mfx@users.sourceforge.net>          <ml1050@users.sourceforge.net>
;
;  John F. Reiser
;  <jreiser@users.sourceforge.net>
;


                BITS    32
                SECTION .text
                CPU     386

%define PAGE_SIZE ( 1<<12)
%define szElf32_Ehdr 0x34
%define szElf32_Phdr 8*4
%define e_entry  (16 + 2*2 + 4)
%define p_memsz  5*4
%define szl_info 12
%define szp_info 12
%define a_type 0
%define a_val  4
%define sz_auxv 8

fold_begin:     ; enter: %ebx= uncDst
                ; also edx= szElf32_Ehdr + 2*szElf32_Phdr + &Elf32_Ehdr
        pop eax  ; discard &sz_uncompressed
        pop eax  ; discard  sz_uncompressed

; Move argc,argv,envp down to make room for complete Elf_auxv table.
; Linux kernel 2.4.2 and earlier give only AT_HWCAP and AT_PLATFORM
; because we have no PT_INTERP.  Linux kernel 2.4.5 (and later?)
; give not quite everything.  It is simpler and smaller code for us
; to generate a "complete" table where Elf_auxv[k -1].a_type = k.
; ld-linux.so.2 depends on AT_PHDR and AT_ENTRY, for instance

%define AT_NULL   0
%define AT_IGNORE 1
%define AT_PHDR   3
%define AT_NUMBER (5+ 23)
; 2002-11-09  glibc-2.2.90  AT_IGNOREPPC==22  plus 5 for future growth

        mov esi, esp
        sub esp, sz_auxv * AT_NUMBER  ; more than 128 bytes
        mov edi, esp
do_auxv:  ; entry: %esi=src = &argc; %edi=dst.  exit: %edi= &AT_NULL
        ; cld

L10:  ; move argc+argv
        lodsd
        stosd
        test eax,eax
        jne L10

L20:  ; move envp
        lodsd
        stosd
        test eax,eax
        jne L20

; complete Elf_auxv table full of AT_IGNORE
        push edi  ; save base of resulting table
        inc eax  ; convert 0 to AT_IGNORE
        push byte 2 * (AT_NUMBER -1)  ; less than 128
        pop ecx
        rep stosd
        dec eax  ; convert AT_IGNORE into AT_NULL
        stosd  ; terminate Elf_auxv
        stosd
        pop edi  ; base of resulting table

L30:  ; distribute existing Elf32_auxv into new table
        lodsd
        test eax,eax  ; AT_NULL ?
        xchg eax,ecx  ; edx is busy, do not use
        lodsd
        je L40
        mov [a_type + sz_auxv*(ecx -1) + edi], ecx
        mov [a_val  + sz_auxv*(ecx -1) + edi], eax
        jmp L30
L40:

%define OVERHEAD 2048
%define MAX_ELF_HDR 512

        sub esp, dword MAX_ELF_HDR + OVERHEAD

        xchg eax, ebx  ; eax= uncDst
        lea edx, [szl_info + szp_info + edx]  ; cprSrc
        mov ecx, [   edx]  ; sz_unc
        mov ebx, [4+ edx]  ; sz_cpr
        mov esi, eax  ; extra copy of uncDst
        pusha  ; (AT_table,uncDst,f_decpr,&ehdr,{sz_cpr,cprSrc},{sz_unc,uncDst})
EXTERN upx_main
        call upx_main  ; entry = upx_main(...)
        pop ecx  ; junk
        push eax  ; save entry address
        popa  ; edi= entry address; esi= uncDst
        add esp, dword MAX_ELF_HDR + OVERHEAD  ; remove temp space

        pop ecx  ; argc
        pop edx  ; $0 filename, to become argv[0]
        push edx  ; restore $0 filename

        inc ecx
        push esi  ; &uncompressed shell script
        sub esi, byte 3

        mov [esi], word 0x632d  ; "-c"
        inc ecx
        push esi  ; &"-c"

        inc ecx
        push edx  ; argv[0] is duplicate of $0

        push ecx  ; new argc
        push edi  ; save entry address

; _dl_start and company (ld-linux.so.2) assumes that it has virgin stack,
; and does not initialize all its stack local variables to zero.
; Ulrich Drepper (drepper@cyngus.com) has refused to fix the bugs.
; See GNU wwwgnats libc/1165 .

%define  N_STKCLR (0x100 + MAX_ELF_HDR + OVERHEAD)/4
        lea edi, [esp - 4*N_STKCLR]
        pusha  ; values will be zeroed
        mov ebx,esp  ; save
        mov esp,edi  ; Linux does not grow stack below esp
        mov ecx, N_STKCLR
        xor eax,eax
        rep stosd
        mov esp,ebx  ; restore

; Because the decompressed shell script occupies low memory anyway,
; there isn't much payback to unmapping the compressed script and
; ourselves the stub.  We would need a place to put the escape hatch
; "int $0x80; popa; ret", and some kernels do not allow execution
; on the stack.  So, we would have to dirty a page of the shell
; or of /lib/ld-linux.so.  It's simpler just to omit the unapping.
        popa
        ret


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