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m68k: Define asmlinkage_protect

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commit 8474ba7419 upstream.

Make sure the compiler does not modify arguments of syscall functions.
This can happen if the compiler generates a tailcall to another
function.  For example, without asmlinkage_protect sys_openat is compiled
into this function:

sys_openat:
	clr.l %d0
	move.w 18(%sp),%d0
	move.l %d0,16(%sp)
	jbra do_sys_open

Note how the fourth argument is modified in place, modifying the register
%d4 that gets restored from this stack slot when the function returns to
user-space.  The caller may expect the register to be unmodified across
system calls.

Signed-off-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
This commit is contained in:
Andreas Schwab 2015-09-23 23:12:09 +02:00 • committed by Luis Henriques
commit 5ae1b59c00
1 changed files with 30 additions and 0 deletions
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