Changeset d6f9fff in mainline for kernel/arch/ia32/src/proc

Timestamp:

2016-04-27T12:39:14Z (10 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

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

Children:

1a5eca4

Parents:

8a36bc1e

Message:

ia32: Make TLS settable from uspace

The TLS document[1] mandates that %gs[0] is the thread pointer on ia32.
That is good as it allows userspace-only TLS management for fibrils:
fibril_save/restore() simply manipulate the thread pointer in %gs:0 and
don't need to ask the kernel to modify %gs's base. The kernel treats
%gs: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 %gs 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 %gs:0 as the thread pointer
• Make GCC generate code that always goes through %gs:0 to access TLS

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

Location:

kernel/arch/ia32/src/proc

Files:

• scheduler.c (modified) (1 diff)
• thread.c (modified) (1 diff)

kernel/arch/ia32/src/proc/scheduler.c

@@ -70 +70 @@
         CPU->arch.tss->esp0 = kstk;
         CPU->arch.tss->ss0 = GDT_SELECTOR(KDATA_DES);
-        
-        /* Set up TLS in GS register */
-        set_tls_desc(THREAD->arch.tls);
 }
 

kernel/arch/ia32/src/proc/thread.c

@@ -41 +41 @@
 void thread_create_arch(thread_t *t)
 {
-        t->arch.tls = 0;
 }