Changeset 1a5eca4 in mainline for kernel/arch/amd64/src/proc/thread.c

Timestamp:

2016-04-27T19:36:56Z (9 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

lfn, master, serial, ticket/834-toolchain-update, topic/msim-upgrade, topic/simplify-dev-export

Children:

af9dd1e

Parents:

d6f9fff

Message:

amd64: Make TLS settable from uspace

The TLS document[1] mandates that %fs[0] is the thread pointer on amd64.
That is good as it allows userspace-only TLS management for fibrils:
fibril_save/restore() simply manipulate the thread pointer in %fs:0 and
don't need to ask the kernel to modify %fs's base. The kernel treats
%fs:0 as another preserved register and preserves it across context
switches. GCC gets in the way a little bit because it by default assumes
that TLS is accessible from negative %fs offsets (which would
necessitate a kernel-assisted solution). Fortunately, there is a GCC
option to suppress this assumption.

• Introduce the concept of virtual registers, with VREG_TP (thread pointer) being the first of them
• Preserve VREG_TP in context_save/restore()
• Stop using sys_tls_set() in favour of using %fs:0 as the thread pointer
• Make GCC generate code that always goes through %gs:0 to access TLS
• Introduce kseg: a per-CPU area accessible from GS_KERNEL that holds the kernel stack, kernel FS base and a scratch space for syscall and int handlers to use

[1] Drepper, U.: ELF Handling For Thread-Local Storage

File:

• kernel/arch/amd64/src/proc/thread.c (modified) (2 diffs)

kernel/arch/amd64/src/proc/thread.c

@@ -35 +35 @@
 #include <proc/thread.h>
 #include <arch/interrupt.h>
+#include <arch/kseg_struct.h>
 
 /** Perform amd64 specific thread initialization.
@@ -43 +44 @@
 void thread_create_arch(thread_t *thread)
 {
-        thread->arch.tls = 0;
-        thread->arch.syscall_rsp[SYSCALL_USTACK_RSP] = 0;
-        
         /*
          * Kernel RSP can be precalculated at thread creation time.
          */
-        thread->arch.syscall_rsp[SYSCALL_KSTACK_RSP] =
+        thread->arch.kstack_rsp =
             (uintptr_t) &thread->kstack[PAGE_SIZE - sizeof(istate_t)];
 }