Commit 46409b7e authored by Andreas Schwab's avatar Andreas Schwab Committed by Greg Kroah-Hartman

m68k: Define asmlinkage_protect

commit 8474ba74193d302e8340dddd1e16c85cc4b98caf 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: default avatarAndreas Schwab <schwab@linux-m68k.org>
Signed-off-by: default avatarGeert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 339cb27f
......@@ -4,4 +4,34 @@
#define __ALIGN .align 4
#define __ALIGN_STR ".align 4"
/*
* Make sure the compiler doesn't do anything stupid with the
* arguments on the stack - they are owned by the *caller*, not
* the callee. This just fools gcc into not spilling into them,
* and keeps it from doing tailcall recursion and/or using the
* stack slots for temporaries, since they are live and "used"
* all the way to the end of the function.
*/
#define asmlinkage_protect(n, ret, args...) \
__asmlinkage_protect##n(ret, ##args)
#define __asmlinkage_protect_n(ret, args...) \
__asm__ __volatile__ ("" : "=r" (ret) : "0" (ret), ##args)
#define __asmlinkage_protect0(ret) \
__asmlinkage_protect_n(ret)
#define __asmlinkage_protect1(ret, arg1) \
__asmlinkage_protect_n(ret, "m" (arg1))
#define __asmlinkage_protect2(ret, arg1, arg2) \
__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2))
#define __asmlinkage_protect3(ret, arg1, arg2, arg3) \
__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3))
#define __asmlinkage_protect4(ret, arg1, arg2, arg3, arg4) \
__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
"m" (arg4))
#define __asmlinkage_protect5(ret, arg1, arg2, arg3, arg4, arg5) \
__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
"m" (arg4), "m" (arg5))
#define __asmlinkage_protect6(ret, arg1, arg2, arg3, arg4, arg5, arg6) \
__asmlinkage_protect_n(ret, "m" (arg1), "m" (arg2), "m" (arg3), \
"m" (arg4), "m" (arg5), "m" (arg6))
#endif
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