Changeset 425 for trunk/hal/tsar_mips32/core/hal_kentry.S

Timestamp:

Jan 29, 2018, 5:57:57 PM (6 years ago)

Author:

alain

Message:

bloup

File:

• trunk/hal/tsar_mips32/core/hal_kentry.S (modified) (6 diffs)

trunk/hal/tsar_mips32/core/hal_kentry.S

@@ -119 +119 @@
 #------------------------------------------------------------------------------------
 # This code is executed when the core is already in kernel mode,
-# after a syscall, to handle an interrupt.
+# after a syscall, to handle an interrupt, or to handle a non-fatal exception.
 # - save current c2_mode in $26.
 # - set MMU OFF.
@@ -286 +286 @@
     
 #------------------------------------------------------------------------------------
-# This code calls the relevant Interrupt / Exception / Syscall handler,
-# depending on XCODE in CP0_CR.
-# In case of syscall or exception, it set the "uzone" pointer in thread descriptor,
-# that is used by the hal_do_syscall() & hal_do_exception() functions.
-# WARNING: This "uzone" pointer is NOT modified in case of interrupt,
-# because syscalls can be interrupted, and we want preserve this pointer.
-
+# This code handle the uzone pointers stack, and calls the relevant 
+# Interrupt / Exception / Syscall handler, depending on XCODE in CP0_CR.
+# Both the hal_do_syscall() and the hal_do_exception() functions use
+# the values saved in the "uzone", but a syscall can be interrupted 
+# by an interrupt, or by a non-fatal exception. Therefore, we need 
+# to handle a two-slots "stack of uzones", implemented in the kernel stack,
+# using the two "current_uzone" and "previous_uzone" pointers in thread descriptor. 
+# - at kernel_entry, we copy the "current_uzone" pointer to the "previous_uzone"
+#   slot, and copy the "$29" stack pointer to the "current_uzone" slot.
+# - at kernel_exit, we simply restore the "previous_uzone" value to the
+#   "current_uzone" slot.
+# For a syscall, the hal_do_syscall() function increment the uzone[EPC]
+# slot and set the return value in the uzone[V0] slot before returning.
+
+    # update "current_uzone" and "previous_uzone" pointers
+        mfc0    $4,     $4,   2             # $4 <= pointer on thread desc
+    lw      $5,     8($4)               # $5 <= current uzone pointer trom thread
+    sw      $29,    8($4)               # current uzone pointer <= $29
+    sw      $5,    12($4)               # previous uzone pointer <= current
+
+    # analyse XCODE to call relevant handler
         mfc0    $17,    $13                 # $17 <= CR
-        andi    $17,    $17,   0x3F         # $17 <= XCODE
+        andi    $17,    $17,  0x3F          # $17 <= XCODE
         ori         $8,     $0,   0x20
     beq     $8,     $17,  cause_sys     # go to syscall handler
@@ -302 +316 @@
 
 cause_excp:
-        mfc0    $4,     $4,   2             # get pointer on thread desc
-    sw      $29,    8($4)               # update uzone pointer in thread desc
+
         jal     hal_do_exception            # call exception handler
         nop
@@ -310 +323 @@
 
 cause_sys:
-        mfc0    $4,     $4,   2             # get pointer on thread desc
-    sw      $29,    8($4)               # update uzone pointer in thread desc
+
         jal     hal_do_syscall              # call syscall handler                 
     nop
@@ -318 +330 @@
         
 cause_int:
+
         jal     hal_do_interrupt            # call interrupt handler
     nop
@@ -330 +343 @@
 
 kentry_exit:
+
+    # restore "current_uzone" pointer
+        mfc0    $4,      $4,   2            # $4 <= pointer on thread desc
+    lw      $5,   12($4)                # $5 <= previous uzone pointer from thread
+    sw      $5,    8($4)                # current uzone pointer <= previous
 
 #----------------------