On 4/26/2019 3:25 AM, Jesse Thompson wrote:
I would like to learn how to write assembly programs for the command line that with as little alteration as is feasable will compile both in Cygwin and in other flavors of Unix like Linux and/or FreeBSD.I am targeting only x64 CPUs and I'm perfectly happy to use libc calls instead of direct syscalls or interrupts. I'm hoping to use nasm+gcc, or perhaps fasm to do the deed. Crosspiling is not a concern, I'll build cygwin binaries in cygwin and unix binaries in unix. But I'm confused by the differences in calling convention/ABI between Windows and/or Cygwin and Linux? For example, I can get this to compile and run in Cygwin: ``` global main extern puts section .text main: sub rsp, 20h ; Reserve the shadow space mov rcx, message ; First argument is address of message call puts ; puts(message) add rsp, 20h ; Remove shadow space ret message: db 'Hello', 0 ; C strings need a zero byte at the end ``` but it segfaults in Linux (and complains about "Symbol `puts' causes overflow in R_X86_64_PC32 relocation") and I can get the following to compile and run in Linux: ``` extern puts global main section .text main: mov rdi,message call puts ret message: db "Hello World",0 ``` but *that* segfaults in cygwin. TL;DR: I think I could get a lot more done if I could start from a single Hello World asm file that can compile and run in both places, calling out to puts or something simple like that. Any help would be appreciated, I hope everything about my question makes sense. :)
Der Jesse -- Someone else may be able to speak to the specifics, but register use and calling conventions, and to some extent stack layout, very from platform to platform. Roughly, platform = processor + OS. So (to me anyway) it would not be at all surprising if you have to write code different for each of Windows, Cygwin, and Linux. Cygwin tries to offer library level compatibility for program designed to run under Posix (there are some seams here and there, where Windows differences are hard to hide). But the programs have to be recompiled to the Cygwin ABI. Another thing you may be encountering is the difference between the 32-bit and 64-bit worlds. Recent x86 processor support the x86_64 version as well. Cygwin offers both 32 and 64 bit versions, but they are distinct, and a program needs to be compiled to the one under which you wish to run it. (I have both 32 and 64 bit Cygwin on my computer, and the programs can invoke one another, but the installations need to be in separate file hierarchies.) The same would tend to hold under Linux and Windows, though the OS can determine automatically for a given program whether it is 32 or 64 bit from details of the first bytes of the executable file. Regards - EM -- Problem reports: http://cygwin.com/problems.html FAQ: http://cygwin.com/faq/ Documentation: http://cygwin.com/docs.html Unsubscribe info: http://cygwin.com/ml/#unsubscribe-simple
