Changeset d6f9fff in mainline for kernel/arch/ia32/src/context.S

Timestamp:

2016-04-27T12:39:14Z (8 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

File:

• kernel/arch/ia32/src/context.S (modified) (3 diffs)

kernel/arch/ia32/src/context.S

@@ -29 +29 @@
 #include <abi/asmtool.h>
 #include <arch/context_struct.h>
+#include <arch/vreg.h>
 
 .text
@@ -48 +49 @@
         movl %edi, CONTEXT_OFFSET_EDI(%edx)     # %edi -> ctx->edi
         movl %ebp, CONTEXT_OFFSET_EBP(%edx)     # %ebp -> ctx->ebp
+
+        mov vreg_ptr, %ecx
+        movl %gs:VREG_TP(%ecx), %ecx
+        movl %ecx, CONTEXT_OFFSET_TP(%edx)
 
         xorl %eax, %eax         # context_save returns 1
@@ -72 +77 @@
 
         movl %edx, 0(%esp)      # put saved pc on stack
+
+        mov vreg_ptr, %ecx
+        movl CONTEXT_OFFSET_TP(%eax), %edx
+        movl %edx, %gs:VREG_TP(%ecx)
+
         xorl %eax, %eax         # context_restore returns 0
         ret
-FUNCTION_END(context_restore_arch)