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author | David S. Miller <davem@davemloft.net> | 2011-11-16 00:57:00 +0400 |
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committer | David S. Miller <davem@davemloft.net> | 2011-11-16 00:57:00 +0400 |
commit | e88d2468718b0789b4c33da2f7e1cef2a1eee279 (patch) | |
tree | beb5a9eff292f1faa05eb9b96b7f1bd7815da131 /arch | |
parent | 1d299bc7732c34d85bd43ac1a8745f5a2fed2078 (diff) | |
download | linux-e88d2468718b0789b4c33da2f7e1cef2a1eee279.tar.xz |
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: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'arch')
-rw-r--r-- | arch/sparc/kernel/signal32.c | 2 | ||||
-rw-r--r-- | arch/sparc/kernel/signal_32.c | 20 | ||||
-rw-r--r-- | arch/sparc/kernel/signal_64.c | 20 |
3 files changed, 31 insertions, 11 deletions
diff --git a/arch/sparc/kernel/signal32.c b/arch/sparc/kernel/signal32.c index 2e86fd1ddc7b..023b8860dc97 100644 --- a/arch/sparc/kernel/signal32.c +++ b/arch/sparc/kernel/signal32.c @@ -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) { diff --git a/arch/sparc/kernel/signal_32.c b/arch/sparc/kernel/signal_32.c index 7dfaff64cd6b..d54c6e53aba0 100644 --- a/arch/sparc/kernel/signal_32.c +++ b/arch/sparc/kernel/signal_32.c @@ -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 = ¤t->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]; } diff --git a/arch/sparc/kernel/signal_64.c b/arch/sparc/kernel/signal_64.c index 1ddf0dedb929..f0836cd0e2f2 100644 --- a/arch/sparc/kernel/signal_64.c +++ b/arch/sparc/kernel/signal_64.c @@ -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 = ¤t->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) { |