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The fun thing is that I found out that these 64-bit call gates are rarely used. Because it does not disable interrupts for example. Back when AMD was developing

by yuhong 9y ago

The fun thing is that I found out that these 64-bit call gates are rarely used. Because it does not disable interrupts for example. Back when AMD was developing x86-64, they were probably focusing on Linux which did not use call gates.

dfox 9y ago
The fact that call gates does not disable interrupts is usually the desired behavior. Linux (and NT for 32 bit code) does not use call gates because they are not that useful for OSes that target the Unix/C flat memory model. You can probably use call gates to implement particularly fast IPC mechanism with semantics similar to QNX's message passing. But probably only real users of call gates are DOS extenders and 32 bit windows for 32/16b thunking (which is to large extent the same use case of mixing 32/16b code in single process).
- yuhong 9y ago
  When SYSCALL added EFLAGS masking, SWAPGS was also created with the assumption that it would be always done when going between kernel and user mode and before enabling interrupts.
- yuhong 9y ago
  And yes, older Unixes also often used call gates too, for example Solaris.