Changeset d6f9fff in mainline for kernel/arch/ia32/src/asm.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/asm.S (modified) (7 diffs)

kernel/arch/ia32/src/asm.S

@@ -183 +183 @@
 
         /*
-         * Save TLS.
-         */
-        movl %gs, %edx
-        movl %edx, ISTATE_OFFSET_GS(%esp)
-
-        /*
          * Switch to kernel selectors.
          */
-        movw $(GDT_SELECTOR(KDATA_DES)), %ax
-        movw %ax, %ds
-        movw %ax, %es
+        movl $(GDT_SELECTOR(KDATA_DES)), %eax
+        movl %eax, %ds
+        movl %eax, %es
+        movl $(GDT_SELECTOR(VREG_DES)), %eax
+        movl %eax, %gs
         
         /*
@@ -213 +209 @@
         
         /*
-         * Restore TLS.
-         */
-        movl ISTATE_OFFSET_GS(%esp), %edx
-        movl %edx, %gs
-        
-        /*
          * Prepare return address and userspace stack for SYSEXIT.
          */
@@ -252 +242 @@
 
         /*
-         * Save the selector registers.
+         * Save the segment registers.
          */
         movl %gs, %ecx
@@ -272 +262 @@
         movl %eax, %ds
         movl %eax, %es
+        movl $(GDT_SELECTOR(VREG_DES)), %eax
+        movl %eax, %gs
                 
         movl $0, ISTATE_OFFSET_EBP_FRAME(%esp)
@@ -284 +276 @@
                         
         /*
-         * Restore the selector registers.
+         * Restore the segment registers.
          */
         movl ISTATE_OFFSET_GS(%esp), %ecx
@@ -354 +346 @@
         
         /*
-         * Save the selector registers.
+         * Save the segment registers.
          */
         movl %gs, %ecx
@@ -374 +366 @@
         movl %eax, %ds
         movl %eax, %es
+        movl $(GDT_SELECTOR(VREG_DES)), %eax
+        movl %eax, %gs
         
         /*