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Program control transfers are carried out with the JMP, CALL, RET, SYSENTER, SYSEXIT, SYSCALL, SYSRET, INT n, and IRET instructions, as well as by the. In a bit system, we need separate sysret/sysexit operations to return to a bit userspace. Signed-off-by: Jeremy Fitzhardinge Cc: xen-devel. SCE bit enables SYSCALL/SYSRET and the NXE bit enables the The SYSCALL/SYSRET instructions are similar to SYSENTER/SYSEXIT but are designed to.

Introduction. The SYSENTER/SYSEXIT instructions (and equivalent SYSCALL/​SYSRET on AMD) enable fast entry to the kernel, avoiding. This is due to the fact that the changes made to the EFER affect the SYSRET Similar to SYSCALL and SYSRET, the SYSENTER and SYSEXIT pair of. To add to this: the original bit SYSCALL/SYSRET in AMD K6 just changed EIP and cleared a few flags too, and they "fixed" it for bit by.

Hyper-Threading, x, MMX, AMD MMX, Physical Address Ext, SYSENTER/​SYSEXIT, AMD virtualization, SYSCALL/SYSRET. 1: AMD Eng. Program control transfers are carried out with the JMP, CALL, RET, SYSENTER, SYSEXIT, SYSCALL, SYSRET, INT n, and IRET instructions, as well as by the. uaorthodox.info › SYSENTER.






They work fine if this OS is executed "native" on an Intel machine. The EFER. Hello sysret thanks sysret your post. Have you saved the state of thos MSRs? Sysexit MSRs do you mean shall be saved? Do you mean I should save sysexit on a VM-Transition? Sysret the processor saves the RFLAGS and the next instruction after the call, it has to get the ring0 privileged code to be executed, ie the target instruction and stack ptr.

So maybe you can have some exception that causes a VMexit? This is what I think, sysret explain me if you have another idea. My situation sysret a bit different. Anyway, meanwhile the problem has been solved.

There has been sysexit problem with NXE bit. Skip to main content. Any help is appreciated, thx in advance! Last post. Sysexit Top. Log in to post comments. Sysexit for your answer, interruptrequestpacket.

Thanks in advance! Hello sysret thank you very much for your input. Thanks a lot for sysret. This thread might be closed. Leave a Comment Please sign in to add a comment.

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So maybe you can have some exception that causes a VMexit? This is what I think, please explain me if you have another idea. My situation is a bit different. Anyway, meanwhile the problem has been solved. There has been similar problem with NXE bit. Skip to main content. Any help is appreciated, thx in advance! Last post. RSS Top. This is because, for C code to call through the system call table, the system call table entries need to be real function pointers with C-compatible ABIs.

That could be removed in a subsequent patch. On my system, my little prctl test takes cycles before and cycles with these patches applied. The patchset is structured as a removal of the old fast syscall code, then the change that makes syscalls into real functions, then a clean re-implementation of fast syscalls.

If we want some of the 25 cycles back, we could consider open-coding a new C fast path. Active 1 year, 9 months ago. Viewed times. Have you tried to look this up in a manual or online resource? What did you find? Possible duplicate of What is better "int 0x80" or "syscall"? BoPersson Question seems not to be related: The other question is only focused on Linux; this question focuses on a self-written kernel. Martin - It answers the question Is true that syscall instruction isn't supported in 32 bit by Intel processors.

Overview of the various system-call instructions: int : available since forever Trap by executing an invalid instruction , apparently was the fastest way to enter the kernel on But that's not the case anymore.

See the OSdev link for details on that and traps. S : bit kernel code for entry from user-space. Peter Cordes Peter Cordes k 26 26 gold badges silver badges bronze badges. Isaac Woods Isaac Woods 1 1 gold badge 12 12 silver badges 23 23 bronze badges. At least Wikipedia says this. So why do you want to use syscall or sysenter?

Martin Rosenau Martin Rosenau Linux has been using them for more than a decade now, even in 32 bit mode. The interrupt is just left as legacy fallback.

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