upx_itoa() in assembler to enforce no relocation

Makefile l_lx_exec.c upx_itoa.asm

committer: jreiser <jreiser> 1037070863 +0000

src/stub/Makefile

@@ -322,11 +322,14 @@ fold_elf86.h: l_lx_elf.o fold_elf86.o l_lx_elf86.lds
 l_lx_exec.o: l_lx_exec.c
 	$(CC_LINUX_I386) -c $<
 
+upx_itoa.o: upx_itoa.asm
+	$(NASM) -f elf -o $@ $<
+
 fold_exec86.o: fold_exec86.asm
 	$(NASM) -f elf -o $@ $<
 
-fold_exec86.h: l_lx_exec.o fold_exec86.o l_lx_exec86.lds
+fold_exec86.h: l_lx_exec.o upx_itoa.o fold_exec86.o l_lx_exec86.lds
-	ld -T $(srcdir)/l_lx_exec86.lds -Map $T.map -o $T.bin $T.o l_lx_exec.o
+	ld -T $(srcdir)/l_lx_exec86.lds -Map $T.map -o $T.bin $T.o l_lx_exec.o upx_itoa.o
 	objcopy -S -R .comment -R .note $T.bin
 	$(STRIPELF) $T.bin
 	$(BRANDELF) $T.bin

src/stub/l_lx_exec.c

@@ -73,33 +73,35 @@ static __inline__ int xwrite(int fd, const void *buf, int count)
 // util
 **************************************************************************/
 
-// FIXME: all code in this source file must be relocatible, so
+extern char *
-//  we have to use `volatile' here.
+__attribute__ ((regparm(2), stdcall))  // be ruthless
-// FIXME: rewrite upx_itoa() in assembly
+upx_itoa(unsigned long v, char *buf);
-static char *upx_itoa(char *buf, unsigned long v)
+//  Some versions of gcc optimize the division and/or remainder using
-{
+//  a multiplication by (2**32)/10, and use a relocatable 32-bit address
-//    const unsigned TEN = 10;
+//  to reference the constant.  We require no relocations because we move
-    volatile unsigned TEN = 10;
+//  the code at runtime.  See upx_itoa.asm for replacement [also smaller.]
-    char *p = buf;
+//static char *upx_itoa(unsigned long v, char *buf)
-    {
+//{
-        unsigned long k = v;
+//    volatile unsigned TEN = 10;  // an ugly way to achieve no relocation
-        do {
+//    char *p = buf;
-            p++;
+//    {
-            k /= TEN;
+//        unsigned long k = v;
-        } while (k > 0);
+//        do {
-    }
+//            p++;
-    buf = p;
+//            k /= TEN;
-    *p = 0;
+//        } while (k > 0);
-    {
+//    }
-        unsigned long k = v;
+//    buf = p;
-        do {
+//    *p = 0;
-            *--p = '0' + k % TEN;
+//    {
-            k /= TEN;
+//        unsigned long k = v;
-        } while (k > 0);
+//        do {
-    }
+//            *--p = '0' + k % TEN;
-    return buf;
+//            k /= TEN;
-}
+//        } while (k > 0);
-
+//    }
+//    return buf;
+//}
 
 static uint32_t ascii5(char *p, uint32_t v, unsigned n)
 {
@@ -159,9 +161,9 @@ go_self(char const *tmpname, char *argv[], char *envp[])
         SET4(procself_buf + 0, '/', 'p', 'r', 'o');
         SET4(procself_buf + 4, 'c', '/',  0 ,  0 );
         {
-            char *const procself = upx_itoa(procself_buf + 6, getpid());
+            char *const procself = upx_itoa(getpid(), procself_buf + 6);
             SET4(procself, '/', 'f', 'd', '/');
-            upx_itoa(procself + 4, fdi);
+            upx_itoa(fdi, procself + 4);
         }
 
         // Check for working /proc/self/fd/X by accessing the

src/stub/upx_itoa.asm

@@ -0,0 +1,54 @@
+;  l_lx_itoa.asm -- decimal print; smaller than gcc, and no relocations
+;
+;  This file is part of the UPX executable compressor.
+;
+;  Copyright (C) 2002 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.
+;
+;  John F. Reiser
+;  <jreiser@users.sourceforge.net>
+;
+
+
+        BITS    32
+        SECTION .text
+	GLOBAL upx_itoa
+
+upx_itoa:  ; char *upx_itoa(eax= unsigned v, edx= char *buf)  /* 0<=(int)v */
+	push edi  ; save register
+	mov edi,edx  ; output ptr
+	push byte 10
+	cld
+	pop ecx  ; radix
+	call recur
+	mov [edi],ah  ; NUL terminate
+	xchg eax,edi  ; eax= continuation point
+	pop edi  ; restore register
+	ret
+recur:
+	cdq  ; zero extend eax into edx [use "sub edx,edx" if eax < 0 ]
+	div ecx  ; eax=quo, edx=rem;  flags are undefined
+	push edx
+	test eax,eax
+	je quo0
+	call recur
+quo0:
+	pop eax  ; remainder
+	add al, byte '0'
+	stosb
+	ret