From ff9a184cfb6542bef98aff1789481284e122a4b3 Mon Sep 17 00:00:00 2001 From: Will Deacon <will.deacon@arm.com> Date: Mon, 23 Apr 2012 15:42:16 +0100 Subject: [PATCH] ARM: 7400/1: vfp: clear fpscr length and stride bits on entry to sig handler The ARM PCS mandates that the length and stride bits of the fpscr are cleared on entry to and return from a public interface. Although signal handlers run asynchronously with respect to the interrupted function, the handler itself expects to run as though it has been called like a normal function. This patch updates the state mirroring the VFP hardware before entry to a signal handler so that it adheres to the PCS. Furthermore, we disable VFP to ensure that we trap on any floating point operation performed by the signal handler and synchronise the hardware appropriately. A check is inserted after the signal handler to avoid redundant flushing if VFP was not used. Reported-by: Peter Maydell <peter.maydell@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> --- arch/arm/vfp/vfpmodule.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c index 05872d92fca2..bc683b8219b5 100644 --- a/arch/arm/vfp/vfpmodule.c +++ b/arch/arm/vfp/vfpmodule.c @@ -564,6 +564,21 @@ int vfp_preserve_user_clear_hwstate(struct user_vfp __user *ufp, if (err) return -EFAULT; + + /* Ensure that VFP is disabled. */ + vfp_flush_hwstate(thread); + + /* + * As per the PCS, clear the length and stride bits for function + * entry. + */ + hwstate->fpscr &= ~(FPSCR_LENGTH_MASK | FPSCR_STRIDE_MASK); + + /* + * Disable VFP in the hwstate so that we can detect if it gets + * used. + */ + hwstate->fpexc &= ~FPEXC_EN; return 0; } @@ -576,7 +591,12 @@ int vfp_restore_user_hwstate(struct user_vfp __user *ufp, unsigned long fpexc; int err = 0; - vfp_flush_hwstate(thread); + /* + * If VFP has been used, then disable it to avoid corrupting + * the new thread state. + */ + if (hwstate->fpexc & FPEXC_EN) + vfp_flush_hwstate(thread); /* * Copy the floating point registers. There can be unused -- 2.20.1