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Commit e88d2468 authored by David S. Miller's avatar David S. Miller
Browse files

sparc: Stash orig_i0 into %g6 instead of %g2 



As per the comments added by this commit, %g2 turns out to not be a
usable place to save away orig_i0 for syscall restart handling.

In fact all of %g2, %g3, %g4, and %g5 are assumed to be saved across
a system call by various bits of code in glibc.

%g1 can't be used because that holds the syscall number, which would
need to be saved and restored for syscall restart handling too, and
that would only compound our problems :-)

This leaves us with %g6 and %g7 which are for "system use".  %g7 is
used as the "thread register" by glibc, but %g6 is used as a compiler
and assembler temporary scratch register.  And in no instance is %g6
used to hold a value across a system call.

Therefore %g6 is safe for storing away orig_i0, at least for now.

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1d299bc7

arch/sparc/kernel/signal32.c

+1 −1
Original line number Diff line number Diff line
@@ -837,7 +837,7 @@ void do_signal32(sigset_t *oldset, struct pt_regs * regs) 
	if (pt_regs_is_syscall(regs) &&

	    (regs->tstate & (TSTATE_XCARRY | TSTATE_ICARRY))) {

		restart_syscall = 1;

		orig_i0 = regs->u_regs[UREG_G2];

		orig_i0 = regs->u_regs[UREG_G6];

	}



	if (signr > 0) {

arch/sparc/kernel/signal_32.c

+15 −5
Original line number Diff line number Diff line
@@ -523,12 +523,22 @@ static void do_signal(struct pt_regs *regs, unsigned long orig_i0) 
	 * register for GDB to save and restore in order to get

	 * orig_i0 correct for syscall restarts when debugging.

	 *

	 * However, we luckily can use the fact that several registers

	 * are volatile across system calls.  One such register is

	 * %g2, so use that as a place to save away orig_i0.

	 * Although it should be the case that most of the global

	 * registers are volatile across a system call, glibc already

	 * depends upon that fact that we preserve them.  So we can't

	 * just use any global register to save away the orig_i0 value.

	 *

	 * In particular %g2, %g3, %g4, and %g5 are all assumed to be

	 * preserved across a system call trap by various pieces of

	 * code in glibc.

	 *

	 * %g7 is used as the "thread register".   %g6 is not used in

	 * any fixed manner.  %g6 is used as a scratch register and

	 * a compiler temporary, but it's value is never used across

	 * a system call.  Therefore %g6 is usable for orig_i0 storage.

	 */

	if (pt_regs_is_syscall(regs) && (regs->psr & PSR_C))

		regs->u_regs[UREG_G2] = orig_i0;

		regs->u_regs[UREG_G6] = orig_i0;



	if (test_thread_flag(TIF_RESTORE_SIGMASK))

		oldset = &current->saved_sigmask;
@@ -544,7 +554,7 @@ static void do_signal(struct pt_regs *regs, unsigned long orig_i0) 
	restart_syscall = 0;

	if (pt_regs_is_syscall(regs) && (regs->psr & PSR_C)) {

		restart_syscall = 1;

		orig_i0 = regs->u_regs[UREG_G2];

		orig_i0 = regs->u_regs[UREG_G6];

	}

arch/sparc/kernel/signal_64.c

+15 −5
Original line number Diff line number Diff line
@@ -533,13 +533,23 @@ static void do_signal(struct pt_regs *regs, unsigned long orig_i0) 
	 * register for GDB to save and restore in order to get

	 * orig_i0 correct for syscall restarts when debugging.

	 *

	 * However, we luckily can use the fact that several registers

	 * are volatile across system calls.  One such register is

	 * %g2, so use that as a place to save away orig_i0.

	 * Although it should be the case that most of the global

	 * registers are volatile across a system call, glibc already

	 * depends upon that fact that we preserve them.  So we can't

	 * just use any global register to save away the orig_i0 value.

	 *

	 * In particular %g2, %g3, %g4, and %g5 are all assumed to be

	 * preserved across a system call trap by various pieces of

	 * code in glibc.

	 *

	 * %g7 is used as the "thread register".   %g6 is not used in

	 * any fixed manner.  %g6 is used as a scratch register and

	 * a compiler temporary, but it's value is never used across

	 * a system call.  Therefore %g6 is usable for orig_i0 storage.

	 */

	if (pt_regs_is_syscall(regs) &&

	    (regs->tstate & (TSTATE_XCARRY | TSTATE_ICARRY)))

		regs->u_regs[UREG_G2] = orig_i0;

		regs->u_regs[UREG_G6] = orig_i0;



	if (current_thread_info()->status & TS_RESTORE_SIGMASK)

		oldset = &current->saved_sigmask;
@@ -560,7 +570,7 @@ static void do_signal(struct pt_regs *regs, unsigned long orig_i0) 
	if (pt_regs_is_syscall(regs) &&

	    (regs->tstate & (TSTATE_XCARRY | TSTATE_ICARRY))) {

		restart_syscall = 1;

		orig_i0 = regs->u_regs[UREG_G2];

		orig_i0 = regs->u_regs[UREG_G6];

	}



	if (signr > 0) {