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

Timestamp:

2016-04-27T19:36:56Z (8 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/scheduler.c (modified) (2 diffs)

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

@@ -42 +42 @@
 #include <arch/pm.h>
 #include <arch/ddi/ddi.h>
+#include <arch/kseg_struct.h>
 
 /** Perform amd64 specific tasks needed before the new task is run.
@@ -55 +56 @@
 void before_thread_runs_arch(void)
 {
-        CPU->arch.tss->rsp0 =
-            (uintptr_t) &THREAD->kstack[STACK_SIZE];
-        
-        /*
-         * Syscall support.
-         */
-        swapgs();
-        write_msr(AMD_MSR_GS, (uintptr_t) THREAD->arch.syscall_rsp);
-        swapgs();
-        
-        /* TLS support - set FS to thread local storage */
-        write_msr(AMD_MSR_FS, THREAD->arch.tls);
+        CPU->arch.tss->rsp0 = (uintptr_t) &THREAD->kstack[STACK_SIZE];
+
+        kseg_t *kseg = (kseg_t *) read_msr(AMD_MSR_GS_KERNEL);  
+        kseg->kstack_rsp = THREAD->arch.kstack_rsp;
 }