Syscall or sysenter on 32 bits Linux?
32-bit, assembly, linux, sysenter, system-calls
Solution
After some web searching, I landed to this other topic on StackOverflow: Linux invoke a system call via sysenter tutorial. It says the recommended way to invoke the system, is neither using `int 80h` nor `syscall` nor `sysenter`, but `linux-gate.so`.
Still remains the question about the crash and core‑dump. My guess is finally that although either `syscall` or `sysenter` instructions are available as a CPU instruction, may be the Linux kernel just does not set‑up properly this “entry point” when it decide it's not really useful on a given hardware platform.
Seems on 32 bits platform, `sysenter` or `syscall` may be available, while it's always available, only on 64 bits platform.
Although I feel this answer my question, I still welcome more material, like an authoritative reference for my above guess.
-- update --
At least, I could find this which confirm the above. That's still not an authoritative reference but seems trustable enough I believe.
What is linux-gate.so.1?, says:
The preferred way of invoking a system call is determined by the kernel at boot time, and evidently this box uses sysenter.
Also, from another source, a sample FASM assembly source (needs some translations if you use NASM), to call a system function via `linux-gate.so`: Finding linux-gate.so.1 in Assembly .
Problem
Since MS‑DOS, I know system invocation using interrupts. In old papers, I saw reference to `int 80h` to invoke system functions on Linux. Since a rather long time now, I know `int 80h` is deprecated in favour of the `syscall` instruction. But I can't get it working on my 32 bits machine. The question Is the `syscall` instruction to be used on 64 bits platform only? Doesn't 32 bits Linux makes use of `syscall`? A sample test On my 32 bits Linux (Ubuntu Precise), this program terminates with a core dump: ``` global _start _start: mov eax, 4 ; 4 is write mov ebx, 1 ; 1 is stdout mov ecx, message ; address of string mov edx, length ; number of bytes syscall mov eax, 1 ; 1 is exit xor ebx, ebx ; return code 0 syscall message: db 10,"Hello, World",10,10 length equ $ - message ``` I've tried with `sysenter` instead of `syscall`, but it crashes the same way.