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xtensa: fix fast_syscall_spill_registers 

The original implementation could clobber registers under certain conditions.

The Xtensa processor architecture uses windowed registers and the original
implementation was using a4 as a temporary register, which under certain
conditions could be register a0 of the oldest window frame, and didn't always
restore the content correctly.

By moving the _spill_registers routine inside the fast system call, it frees
up one more register (the return address is not required anymore) for the
spill routine.

Signed-off-by: Chris Zankel <chris@zankel.net>
This commit is contained in:
Chris Zankel 2014-01-28 22:09:51 -08:00
parent 6b5a1f74e5
commit c0e50d4112
2 changed files with 1 additions and 3 deletions
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2
arch/xtensa/kernel/vectors.S
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@ -235,7 +235,7 @@ ENTRY(_DoubleExceptionVector)
/* Check for overflow/underflow exception, jump if overflow. */
_bbci.l a0, 6, _DoubleExceptionVector_WindowOverflow
bbci.l a0, 6, _DoubleExceptionVector_WindowOverflow
/*
* Restart window underflow exception.

2
arch/xtensa/kernel/xtensa_ksyms.c
View File

@ -122,9 +122,7 @@ EXPORT_SYMBOL(insw);
EXPORT_SYMBOL(insl);
extern long common_exception_return;
extern long _spill_registers;
EXPORT_SYMBOL(common_exception_return);
EXPORT_SYMBOL(_spill_registers);
#ifdef CONFIG_FUNCTION_TRACER
EXPORT_SYMBOL(_mcount);