Re: Still stuck with this assembly stuff (amd64)
Brian [EMAIL PROTECTED] writes: I spent the last three days reading through all the archives. And I have no clue what I am doing wrong. I only started down this road because of some of the other posters. I figured I would give assembly a shot. Why? Do you like pain? I read Assembly Step by Step, which is really geared toward DOS and linux, but it's a pretty good overview. Right. And i386 too I suspect, which is a different architecture than amd64, but that just sounds like such a minor problem. There are probably some alpha and sparc examples out there too, try them, they might work. Never mind that the way that code does syscalls is unsupported even on i386. Never mind that the calling conventions on amd64 are different. Never mind that you're using 32-bit pointers on a 64-bit architecture. Never mind that the syscall entry point you're using shouldn't even be there. From what I have read of the history, openBSD went from aout to ELF around 3.0 with the addition of some extra information. Ah, yes. The painful switch from a.out to elf on amd64. Two years before the first processors were released we had a flag day to deal with all the legacy binaries out there. You will find that the tolerance for people who like pain is slightly low on these mailing lists. Find your pain somewhere else, please. //art
Re: Still stuck with this assembly stuff (amd64)
On Thu, Jul 21, 2005 at 11:17:31AM +0200, Artur Grabowski wrote: Never mind that the way that code does syscalls is unsupported even on i386. Never mind that the calling conventions on amd64 are different. Never mind that you're using 32-bit pointers on a 64-bit architecture. Never mind that the syscall entry point you're using shouldn't even be there. Of course Art is right here... what you should be doing is trawling the web with Google looking for the amd64 ABI specification so you can understand how embarressing that code really is. One also wonders why, if you are determined to do this, you don't just compile a hello_world.c and disassemble the output (or just make the compiler output the .s file for you...) -- Brett Lymn
Re: Still stuck with this assembly stuff (amd64)
Thanks. I just wasn't sure if my problem was an openBSD problem or an assembly problem. It's definitely the later. And I just found the amd64 ABI, which is making the problems clear for me. Pushing those args on the stack is definitely wrong. Anyway, I appreciate the feedback. And thanks Art for pointing out that the assembly was wrong. That put me on the right track to finding a solution. The recent threads about the notes section just confused me and put me down the wrong track. Thanks, Brian --- STeve Andre' [EMAIL PROTECTED] wrote: Brian, its always good idea to learn stuff, but this isn't the right place to talk about assembly problems. One of the newsgroups devoted to programming would be a far better source, or one of the many web forums out there. As someone said, compiling programs and looking at the code is a great way of seeing how things are done. Thats one of the ways I learned, quite some time ago with Digital Research C, an awful compiler that gave me lots of pain... The other thing you might want to think about is getting experience on a simpler cpu, perhaps the z80. There are tons and tons of documents on it, and I'm pretty sure that you could write stuff and then run it on an emulator, faster than the hardware I had, back when I used them. At any rate, misc@ isn't the best place for your questions. I'm sure there are some assembler freaks out there who would just love to talk with you and help out. --STeve Andre' Start your day with Yahoo! - make it your home page http://www.yahoo.com/r/hs
Still stuck with this assembly stuff (amd64)
I spent the last three days reading through all the archives.
And I have no clue what I am doing wrong. I only started down
this road because of some of the other posters. I figured I
would give assembly a shot.
I read Assembly Step by Step, which is really geared toward
DOS and linux, but it's a pretty good overview.
From what I have read of the history, openBSD went from aout
to ELF around 3.0 with the addition of some extra information.
I am guessing that my problem is related to doing something
wrong with the amd64. But I'm not sure what to read next.
I did go through the first hundred pages of the amd programmers
guide on the amd website.
I am assembling and linking:
as -o test1.o test1.s
ld -o test1 test1.o
file type reads as:
test1: ELF 64-bit LSB executable, AMD64, version 1, for OpenBSD, statically
linked, not stripped
so it's set as OpenBSD.
And readelf gives me:
ELF Header:
Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
Class: ELF64
Data: 2's complement, little endian
Version: 1 (current)
OS/ABI:UNIX - System V
ABI Version: 0
Type: EXEC (Executable file)
Machine: Advanced Micro Devices X86-64
Version: 0x1
Entry point address: 0x400218
Start of program headers: 64 (bytes into file)
Start of section headers: 664 (bytes into file)
Flags: 0x0
Size of this header: 64 (bytes)
Size of program headers: 56 (bytes)
Number of program headers: 4
Size of section headers: 64 (bytes)
Number of section headers: 10
Section header string table index: 7
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL
0 0 0
[ 1] .text PROGBITS 00400218 0218
0015 AX 0 0 4
[ 2] .data PROGBITS 00600230 0230
000d WA 0 0 4
[ 3] .gotpad0 PROGBITS 0070023d 0240
W 0 0 1
[ 4] .gotpad1 PROGBITS 0070023d 0240
W 0 0 1
[ 5] .bss NOBITS 00800240 0240
WA 0 0 4
[ 6] .note.openbsd.ide NOTE 00400200 0200
0018 A 0 0 4
[ 7] .shstrtab STRTAB 0240
0052 0 0 1
[ 8] .symtab SYMTAB 0518
01b0 0018 9 c 8
[ 9] .strtab STRTAB 06c8
003e 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings)
I (info), L (link order), G (group), x (unknown)
O (extra OS processing required) o (OS specific), p (processor specific)
Program Headers:
Type Offset VirtAddr PhysAddr
FileSizMemSiz Flags Align
LOAD 0x 0x0040 0x0040
0x022d 0x022d R E10
LOAD 0x0230 0x00600230 0x00600230
0x000d 0x000d RW 10
LOAD 0x0240 0x00800240 0x00800240
0x 0x RW 10
NOTE 0x0200 0x00400200 0x00400200
0x0018 0x0018 R 4
Section to Segment mapping:
Segment Sections...
00 .text .note.openbsd.ident
01 .data
02
03 .note.openbsd.ident
There is no dynamic segment in this file.
There are no relocations in this file.
Here is my current code:
.section .note.openbsd.ident, a
.p2align 2
.long 8
.long 4
.long 1
.ascii OpenBSD\0
.long 0
.p2align 2
.section .data
msg: .asciz hello world\n
len = . - msg - 1
.section .text
.global _start
_start:
push $len
push $msg
push $1
movb $4, %al
push %rax
int $0x80
push $0
movb $1, %al
push %rax
int $0x80
Any
