Restructure GDT. Add sysenter support #290
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This allows us to use syscall from inline asm without clobbering all callee-clobbered registers. Saving/restoring all registers also prevents "leaking" kernel register values into userland. Signed-off-by: Johannes Wikner <[email protected]>
The GDT entries needed to be re-organized to support sysexit. While
doing so, better document why they exist in the first place, and their
particular order.
Rename __KERN_{CS,DS}16 -> __RMODE_{CS,DS}16 to clearly indicate that
these entries only exist in the real mode GDT.
Omit entries that are unused in i386 or unused for a particular gdt.
Signed-off-by: Johannes Wikner <[email protected]>
user_cs should point to USER_CS32 so that correct %cs and %ss are set upon sysret and sysretq. This fixes a subtle bug which where branches using %cs (e.g., intra-mode iret) would crash after a syscall. Signed-off-by: Johannes Wikner <[email protected]>
Introduces the necessary MSRs, and sets them to handle sysenter and sysexits. Add macro to choose approriate instruction depending on build. When adding compatibility mode support, we need to use either sysexit or sysexitq depending on what usermode is executing. Same for sysret and sysretq. Signed-off-by: Johannes Wikner <[email protected]>
To give usermode the option to choose sysenter instead of syscall, we expose syscall_mode(enum syscall_mode), which is by default using syscall. Signed-off-by: Johannes Wikner <[email protected]>
From usermode's perspective it works the same as syscall. Signed-off-by: Johannes Wikner <[email protected]> Signed-off-by: Pawel Wieczorkiewicz <[email protected]>
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Based on #284. Request for comments on this.
In particular the GDT bit that had to be reworked a bit. Also, whether and how we should give the option to use sysenter instead of syscall.