[cfe-dev] GNU assembler syntax for strlen

[Andrew Pennebaker]

My Hello World assembler<https://github.com/mcandre/mcandre/tree/master/gas/hello/freebsd>only
works if I hardcode the message length. If I try to use pseudo-ops to
calculate the length, the program either prints extra garbage, or fails to
build.

Code:

msg: .asciz "Hello World!\n"
...
push $14
push $msg
...

Trace:

$ clang -c -o hello.o -arch i386 hello.s
$ ld -o hello -macosx_version_min 10.6 -arch i386 hello.o
$ ./hello
Hello World!

Code:

msg: .asciz "Hello World!\n"
*len: .long .-msg*
...
push $len
push $msg
...

Trace:

$ clang -c -o hello.o -arch i386 hello.s
$ ld -o hello -macosx_version_min 10.6 -arch i386 hello.o
$ ./hello
Hello World!
 ?';? msgstdoutsys_exitsys_writekernel__mh_execute_headerstart

Code:

msg: .asciz "Hello World!\n"
*len = .-msg*
...
push $len
push $msg
...

Trace:

$ clang -c -o hello.o -arch i386 hello.s
$ ld -o hello -macosx_version_min 10.6 -arch i386 hello.o
ld: section __data (address=0x00002000, size=4294967279) would make the
output executable exceed available address range for architecture i386

What is the proper syntax for calculating the length of a hardcoded string
in Clang/Gas? In NASM, I write len equ $-msg

-- 
Cheers,

Andrew Pennebaker
www.yellosoft.us
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