kernel: add generic wrapper for accessing user memory

This patch adds user_access() which can be used to gracefully handle
page faults that may happen when accessing user memory. It is used
by arch_cpu_user{memcpy, memset, strlcpy}() to allow using optimized
functions from the standard library.

Currently only x64 uses this, but nothing really is arch specific here.

Signed-off-by: Paweł Dziepak <pdziepak@quarnos.org>

x86[-64]: Fix arch_cpu_user_strlcpy() for small buffers

The case for small buffers was broken, since scasb operates on edi/rdi,
not esi/rsi.

x86[-64]: Fix arch_cpu_user_strlcpy() for small buffers

The case for small buffers was broken, since scasb operates on edi/rdi,
not esi/rsi.

x86: move x86_userspace_thread_exit() from user stack to commpage

x86_userspace_thread_exit() is a stub originally placed at the bottom of
each thread user stack that ensures any thread invokes exit_thread() upon
returning from its main higher level function.

Putting anything that is expected to be executed on a stack causes problems
when implementing data execution prevention. Code of x86_userspace_thread_exit()
is now moved to commpage which seems to be much more appropriate place for it.

Implemented threading for x86_64.

* Thread creation and switching is working fine, however threads do not yet
get interrupted because I've not implemented hardware interrupt handling
yet (I'll do that next).
* I've made some changes to struct iframe: I've removed the e/r prefixes
from the member names for both 32/64, so now they're just named ip, ax,
bp, etc. This makes it easier to write code that works with both 32/64
without having to deal with different iframe member names.

Added arch_cpu.cpp to the x86_64 build.

* Some things are currently ifndef'd out completely for x86_64 because
they aren't implemented, there's a few other ifdef's to handle x86_64
differences but most of the code works unchanged.
* Renamed some i386_* functions to x86_*.
* Added a temporary method for setting the current thread on x86_64
(a global variable, not SMP safe). This will be changed to be done
via the GS segment but I've not implemented that yet.

x86_{read,write}_cr{0,4} can just be implemented as macros, put an x86_ prefix on the other read/write macros for consistency.

kernel: add generic wrapper for accessing user memory

This patch adds user_access() which can be used to gracefully handle
page faults that may happen when accessing user memory. It is used
by arch_cpu_user{memcpy, memset, strlcpy}() to allow using optimized
functions from the standard library.

Currently only x64 uses this, but nothing really is arch specific here.

Signed-off-by: Paweł Dziepak <pdziepak@quarnos.org>

x86[-64]: Fix arch_cpu_user_strlcpy() for small buffers

The case for small buffers was broken, since scasb operates on edi/rdi,
not esi/rsi.

x86[-64]: Fix arch_cpu_user_strlcpy() for small buffers

The case for small buffers was broken, since scasb operates on edi/rdi,
not esi/rsi.

x86: move x86_userspace_thread_exit() from user stack to commpage

x86_userspace_thread_exit() is a stub originally placed at the bottom of
each thread user stack that ensures any thread invokes exit_thread() upon
returning from its main higher level function.

Putting anything that is expected to be executed on a stack causes problems
when implementing data execution prevention. Code of x86_userspace_thread_exit()
is now moved to commpage which seems to be much more appropriate place for it.

Implemented threading for x86_64.

* Thread creation and switching is working fine, however threads do not yet
get interrupted because I've not implemented hardware interrupt handling
yet (I'll do that next).
* I've made some changes to struct iframe: I've removed the e/r prefixes
from the member names for both 32/64, so now they're just named ip, ax,
bp, etc. This makes it easier to write code that works with both 32/64
without having to deal with different iframe member names.

Added arch_cpu.cpp to the x86_64 build.

* Some things are currently ifndef'd out completely for x86_64 because
they aren't implemented, there's a few other ifdef's to handle x86_64
differences but most of the code works unchanged.
* Renamed some i386_* functions to x86_*.
* Added a temporary method for setting the current thread on x86_64
(a global variable, not SMP safe). This will be changed to be done
via the GS segment but I've not implemented that yet.

x86_{read,write}_cr{0,4} can just be implemented as macros, put an x86_ prefix on the other read/write macros for consistency.