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xtensa: save current register frame in fast_syscall_spill_registers_fixup

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We need it saved because it contains a3 where we track which register
windows we still need to spill, and fixup handler may call C exception
handlers. Also fix comments.

Cc: stable@vger.kernel.org
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
This commit is contained in:
Max Filippov 2013-10-30 16:18:25 +04:00
parent e2fd1374c7
commit 3251f1e27a
1 changed files with 12 additions and 0 deletions
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12
arch/xtensa/kernel/entry.S
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@ -1117,6 +1117,13 @@ ENDPROC(fast_syscall_spill_registers)
* We basically restore WINDOWBASE and WINDOWSTART to the condition when
* we entered the spill routine and jump to the user exception handler.
*
* Note that we only need to restore the bits in windowstart that have not
* been spilled yet by the _spill_register routine. Luckily, a3 contains a
* rotated windowstart with only those bits set for frames that haven't been
* spilled yet. Because a3 is rotated such that bit 0 represents the register
* frame for the current windowbase - 1, we need to rotate a3 left by the
* value of the current windowbase + 1 and move it to windowstart.
*
* a0: value of depc, original value in depc
* a2: trashed, original value in EXC_TABLE_DOUBLE_SAVE
* a3: exctable, original value in excsave1
@ -1131,10 +1138,15 @@ ENTRY(fast_syscall_spill_registers_fixup)
/* We need to make sure the current registers (a0-a3) are preserved.
* To do this, we simply set the bit for the current window frame
* in WS, so that the exception handlers save them to the task stack.
*
* Note: we use a3 to set the windowbase, so we take a special care
* of it, saving it in the original _spill_registers frame across
* the exception handler call.
*/
xsr a3, excsave1 # get spill-mask
slli a3, a3, 1 # shift left by one
addi a3, a3, 1 # set the bit for the current window frame
slli a2, a3, 32-WSBITS
src a2, a3, a2 # a2 = xxwww1yyxxxwww1yy......