Changeset 1a5eca4 in mainline for kernel/arch/amd64/src/context.S

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/context.S (modified) (3 diffs)

kernel/arch/amd64/src/context.S

@@ -29 +29 @@
 #include <abi/asmtool.h>
 #include <arch/context_struct.h>
+#include <arch/vreg.h>
 
 .text
@@ -50 +51 @@
         movq %r14, CONTEXT_OFFSET_R14(%rdi)
         movq %r15, CONTEXT_OFFSET_R15(%rdi)
+
+        movq vreg_ptr, %rsi
+        movq %fs:VREG_TP(%rsi), %rsi
+        movq %rsi, CONTEXT_OFFSET_TP(%rdi)
         
         xorl %eax, %eax       # context_save returns 1
@@ -72 +77 @@
         movq CONTEXT_OFFSET_SP(%rdi), %rsp   # ctx->sp -> %rsp
         
-        movq CONTEXT_OFFSET_PC(%rdi), %rdx 
-        
+        movq CONTEXT_OFFSET_PC(%rdi), %rdx
         movq %rdx, (%rsp)
+
+        movq CONTEXT_OFFSET_TP(%rdi), %rcx 
+        movq vreg_ptr, %rsi
+        movq %rcx, %fs:VREG_TP(%rsi)
         
         xorl %eax, %eax       # context_restore returns 0