From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Wed, 1 Feb 2012 14:03:12 +0000 Subject: [PATCH v3 2/2] ARM: vfp: clear fpscr length and stride bits on entry to sig handler In-Reply-To: <1328104992-8016-1-git-send-email-will.deacon@arm.com> References: <1328104992-8016-1-git-send-email-will.deacon@arm.com> Message-ID: <1328104992-8016-3-git-send-email-will.deacon@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 Signed-off-by: Will Deacon --- arch/arm/vfp/vfpmodule.c | 22 +++++++++++++++++++++- 1 files changed, 21 insertions(+), 1 deletions(-) diff --git a/arch/arm/vfp/vfpmodule.c b/arch/arm/vfp/vfpmodule.c index 3e35e35..49cf328 100644 --- a/arch/arm/vfp/vfpmodule.c +++ b/arch/arm/vfp/vfpmodule.c @@ -562,6 +562,21 @@ int vfp_preserve_user_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 before entry + * to the signal handler. + */ + hwstate->fpscr &= ~(FPSCR_LENGTH_MASK | FPSCR_STRIDE_MASK); + + /* + * Disable VFP in the hwstate so that we can detect if it was + * used by the signal handler. + */ + hwstate->fpexc &= ~FPEXC_EN; return 0; } @@ -574,7 +589,12 @@ 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 -- 1.7.4.1