Re: Preliminary questions for sponsoring a compiler

[Albert van der Horst <albert@spenarnc.xs4all.nl>]

Christian Seiler schreef op 2016-07-25 18:14:
> On 07/25/2016 02:51 PM, Albert van der Horst wrote:
> > The problem is: ld is not stable w.r.t. linking pure assembler files.
>
> How so?
>
> $ cat write.s
> .text
>
> .global _start
> .type   _start, @function
>
> _start:
>         mov     $1, %rax
>         mov     %rax, %rdi
>         lea     str, %rsi
>         mov     strsize, %rdx
>         syscall
>         xor     %rdi, %rdi
>         mov     $60, %rax
>         syscall
>
> .data
> str:
>         .string "Hello World!\n"
> strsize:
>         .quad   .-str
> $ gcc -Wall -c -o write.o write.s && ld -o write write.o
> $ ./write
> Hello World!
> $ strace ./write
> execve("./write", ["./write"], [/* 58 vars */]) = 0
> write(1, "Hello World!\n\0", 14Hello World!
> )        = 14
> _exit(0)                                = ?
> +++ exited with 0 +++
> $ cat write-nasm.s
> section .text
> global  _start
>
> _start:
>         mov     rax, 0x1
>         mov     rdi, rax
>         lea     rsi, [hello]
>         mov     rdx, length
>         syscall
>         xor     edi, edi
>         mov     rax, 60
>         syscall
>
>
> section .data
> hello   db      'Hello World!', 10, 0
> length  equ     $ - hello
> $ nasm -f elf64 -o write-nasm.o write-nasm.s
> $ ld -o write-nasm write-nasm.o
> $ ./write-nasm
> Hello World!
> $ strace ./write-nasm
> execve("./write-nasm", ["./write-nasm"], [/* 58 vars */]) = 0
> write(1, "Hello World!\n\0", 14Hello World!
> )        = 14
> _exit(0)                                = ?
> +++ exited with 0 +++
>
> I don't quite get what you mean, I never had any problem with
> that.

{Probably going off topic here]
A pure assembler file means full control over section names, their 
properties (in particular, readable, writable *and* executable) and 
where they are located. My compilation feature requires a stable layout 
for the ELF header.
 gcc and ld are intended for c and if you try to do the things I want, 
it feels like remote controlling a robot that must drive a car.

I will not bore you with all the details. One detail, .text and .data 
have predefined properties. Now look how many options ld has. One is 
appropriate
called -nmagic . It sometimes helps to turn those properties around,
at other times it failed.

By the way write.s gives me  `` bad register name `%rax' ''

> Regards,
> Christian

Groetjes Albert

--
Suffering is the prerogative of the strong, the weak -- perish.
Albert van der Horst