Changeset 296426ad in mainline for kernel/arch/amd64/src/asm_utils.S

Timestamp:

2007-11-16T16:17:18Z (18 years ago)

Author:

Jakub Jermar <jakub@…>

Branches:

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

Children:

9c2fb97

Parents:

e686744c

Message:

Support for 6 syscalls arguments on amd64.

File:

• kernel/arch/amd64/src/asm_utils.S (modified) (2 diffs)

kernel/arch/amd64/src/asm_utils.S

@@ -221 +221 @@
 
         /*
-         * Choose between version with error code and version without error code.
-         * Both versions have to be of the same size. amd64 assembly is, however,
-         * a little bit tricky. For instance, subq $0x80, %rsp and subq $0x78, %rsp
-         * can result in two instructions with different op-code lengths.
+         * Choose between version with error code and version without error
+         * code. Both versions have to be of the same size. amd64 assembly is,
+         * however, a little bit tricky. For instance, subq $0x80, %rsp and
+         * subq $0x78, %rsp can result in two instructions with different
+         * op-code lengths.
          * Therefore we align the interrupt handlers.
          */
@@ -270 +271 @@
 h_end:
 
-        
+## Low-level syscall handler
+# 
+# Registers on entry:
+#
+# @param rcx            Userspace return address.
+# @param r11            Userspace RLFAGS.
+#
+# @param rax            Syscall number.
+# @param rdi            1st syscall argument.
+# @param rsi            2nd syscall argument.
+# @param rdx            3rd syscall argument.
+# @param r10            4th syscall argument. Used instead of RCX because the
+#                       SYSCALL instruction clobbers it.
+# @param r8             5th syscall argument.
+# @param r9             6th syscall argument.
+#
+# @return               Return value is in rax.
+#
 syscall_entry:
-        # Switch to hidden gs   
-        swapgs
-        # %gs:0 now points to pointer to stack page
-        mov %gs:0, %r10     # We have a ptr to stack page in r10
-        addq $PAGE_SIZE-16, %r10 # We need some space to store old %sp
-        
-        movq %rsp, 0(%r10)  # Save old stack pointer to stack
-        movq %r10, %rsp     # Change to new stack
-        pushq %rcx          # Return address
-        pushq %r11          # Save flags
-
-        # Switch back to remain consistent
-        swapgs 
-
+        swapgs                  # Switch to hidden gs   
+        # 
+        # %gs:0                 Scratch space for this thread's user RSP
+        # %gs:8                 Address to be used as this thread's kernel RSP
+        #
+        movq %rsp, %gs:0        # Save this thread's user RSP
+        movq %gs:8, %rsp        # Set this thread's kernel RSP
+        swapgs                  # Switch back to remain consistent
         sti
-        movq %r9, %rcx      # Exchange last parameter as a third
-        
+        
+        pushq %rcx
+        pushq %r11
+
+        movq %r10, %rcx         # Copy the 4th argument where it is expected 
+        pushq %rax
         call syscall_handler
-        cli                 # We will be touching stack pointer
+        addq $8, %rsp
                 
         popq %r11
         popq %rcx
-        movq 0(%rsp), %rsp
+
+        cli
+        swapgs
+        movq %gs:0, %rsp        # Restore the user RSP
+        swapgs
+
         sysretq
-                
-                
+
 .data
 .global interrupt_handler_size