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POSyscall or sysenter on 32 bits Linux?
 

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    <p>Since MS‑DOS, I know system invocation using interrupts. In old papers, I saw reference to <code>int 80h</code> to invoke system functions on Linux. Since a rather long time now, I know <code>int 80h</code> is deprecated in favour of the <code>syscall</code> instruction. But I can't get it working on my 32 bits machine.</p> <h1>The question</h1> <p>Is the <code>syscall</code> instruction to be used on 64 bits platform only? Doesn't 32 bits Linux makes use of <code>syscall</code>?</p> <h1>A sample test</h1> <p>On my 32 bits Linux (Ubuntu Precise), this program terminates with a core dump:</p> <pre><code>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 </code></pre> <p>I've tried with <code>sysenter</code> instead of <code>syscall</code>, but it crashes the same way.</p>
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    1. COpossible duplicate of [What is better "int 0x80" or "syscall"?](http://stackoverflow.com/questions/12806584/what-is-better-int-0x80-or-syscall)
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    2. COThere is indeed something related, [here](http://stackoverflow.com/a/12806910/279335), but which does not answer the question. He says `syscall` isn't available in 32 bits mode of Intel CPUs, but the assembler compiled it in 32 bits mode; either the assertion is unclear or it is wrong. Then, I get a core‑dump due to an illegal instruction, but this instruction is available on all Intel CPU starting with Pentium II, and mine is far above that. He mention `sysenter`, which I tried with the same result. Anyway, I've never seen any mention of `sysenter` in Linux ABI, only `int 80h` or `syscall`.
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    3. COWell, according to “[System Calls (wiki.osdev.org)](http://wiki.osdev.org/System_Calls)”, `syscall` is the AMD equivalent of the Intel `sysenter`. It says “*On Intel CPU, starting from the Pentium II, a new instruction pair sysenter/sysexit has appeared. It allows a faster switch from user mode to kernel mode, by limiting the overhead of changing mode. **A similar instruction pair has been created by AMD: Syscall/Sysret**. However the behaviour of these instructions are different from Intel's.*”
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