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Old 02-22-2010, 09:38 AM
Bryan Wu
 
Default ARM: VFP: preserve the HW context when calling signal handlers

From: Imre Deak <imre.deak@nokia.com>

Signal handlers can use floating point, so prevent them to corrupt
the main thread's VFP context. So far there were two signal stack
frame formats defined based on the VFP implementation, but the user
struct used for ptrace covers all posibilities, so use it for the
signal stack too. This patch extends the user struct and leaves
its magic number the same, in the hope that user space code does
not depend on its size and can parse the original regs w/o
problems.

Support to save / restore the exception registers was added by
Will Deacon.

Signed-off-by: Imre Deak <imre.deak@nokia.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>
---
arch/arm/include/asm/ucontext.h | 19 +++-----
arch/arm/include/asm/user.h | 3 +
arch/arm/kernel/signal.c | 91 +++++++++++++++++++++++++++++++++++++--
3 files changed, 97 insertions(+), 16 deletions(-)

diff --git a/arch/arm/include/asm/ucontext.h b/arch/arm/include/asm/ucontext.h
index bf65e9f..1c3236b 100644
--- a/arch/arm/include/asm/ucontext.h
+++ b/arch/arm/include/asm/ucontext.h
@@ -59,23 +59,18 @@ struct iwmmxt_sigframe {
#endif /* CONFIG_IWMMXT */

#ifdef CONFIG_VFP
-#if __LINUX_ARM_ARCH__ < 6
-/* For ARM pre-v6, we use fstmiax and fldmiax. This adds one extra
- * word after the registers, and a word of padding at the end for
- * alignment. */
#define VFP_MAGIC 0x56465001
-#define VFP_STORAGE_SIZE 152
-#else
-#define VFP_MAGIC 0x56465002
-#define VFP_STORAGE_SIZE 144
-#endif

struct vfp_sigframe
{
unsigned long magic;
unsigned long size;
- union vfp_state storage;
-};
+ struct user_vfp ufp;
+} __attribute__((__aligned__(8)));
+
+/* 8 byte for magic and size, 272 byte for ufp */
+#define VFP_STORAGE_SIZE sizeof(struct vfp_sigframe)
+
#endif /* CONFIG_VFP */

/*
@@ -91,7 +86,7 @@ struct aux_sigframe {
#ifdef CONFIG_IWMMXT
struct iwmmxt_sigframe iwmmxt;
#endif
-#if 0 && defined CONFIG_VFP /* Not yet saved. */
+#ifdef CONFIG_VFP
struct vfp_sigframe vfp;
#endif
/* Something that isn't a valid magic number for any coprocessor. */
diff --git a/arch/arm/include/asm/user.h b/arch/arm/include/asm/user.h
index df95e05..ea7e44d 100644
--- a/arch/arm/include/asm/user.h
+++ b/arch/arm/include/asm/user.h
@@ -88,6 +88,9 @@ struct user{
struct user_vfp {
unsigned long long fpregs[32];
unsigned long fpscr;
+ unsigned long fpexc;
+ unsigned long fpinst;
+ unsigned long fpinst2;
};

#endif /* _ARM_USER_H */
diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index f6bc5d4..6dd5008 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -17,6 +17,7 @@
#include <asm/cacheflush.h>
#include <asm/ucontext.h>
#include <asm/unistd.h>
+#include <asm/vfp.h>

#include "ptrace.h"
#include "signal.h"
@@ -196,6 +197,88 @@ static int restore_iwmmxt_context(struct iwmmxt_sigframe *frame)

#endif

+#ifdef CONFIG_VFP
+
+static int preserve_vfp_context(struct vfp_sigframe __user *frame)
+{
+ struct thread_info *thread = current_thread_info();
+ struct vfp_hard_struct *h = &thread->vfpstate.hard;
+ const unsigned long magic = VFP_MAGIC;
+ const unsigned long size = VFP_STORAGE_SIZE;
+ int err = 0;
+
+ vfp_sync_state(thread);
+ __put_user_error(magic, &frame->magic, err);
+ __put_user_error(size, &frame->size, err);
+
+ /*
+ * Copy the floating point registers. There can be unused
+ * registers see asm/hwcap.h for details.
+ */
+ err |= __copy_to_user(&frame->ufp.fpregs, &h->fpregs,
+ sizeof(h->fpregs));
+ /*
+ * Copy the status and control register.
+ */
+ __put_user_error(h->fpscr, &frame->ufp.fpscr, err);
+
+ /*
+ * Copy the exception registers.
+ */
+ __put_user_error(h->fpexc, &frame->ufp.fpexc, err);
+ __put_user_error(h->fpinst, &frame->ufp.fpinst, err);
+ __put_user_error(h->fpinst2, &frame->ufp.fpinst2, err);
+
+ return err ? -EFAULT : 0;
+}
+
+static int restore_vfp_context(struct vfp_sigframe __user *frame)
+{
+ struct thread_info *thread = current_thread_info();
+ struct vfp_hard_struct *h = &thread->vfpstate.hard;
+ unsigned long magic;
+ unsigned long size;
+ unsigned long fpexc;
+ int err = 0;
+
+ vfp_sync_state(thread);
+ __get_user_error(magic, &frame->magic, err);
+ __get_user_error(size, &frame->size, err);
+
+ if (err)
+ return -EFAULT;
+ if (magic != VFP_MAGIC || size != VFP_STORAGE_SIZE)
+ return -EINVAL;
+
+ /*
+ * Copy the floating point registers. There can be unused
+ * registers see asm/hwcap.h for details.
+ */
+ err |= __copy_from_user(&h->fpregs, &frame->ufp.fpregs,
+ sizeof(h->fpregs));
+ /*
+ * Copy the status and control register.
+ */
+ __get_user_error(h->fpscr, &frame->ufp.fpscr, err);
+
+ /*
+ * Sanitise and restore the exception registers.
+ */
+ __get_user_error(fpexc, &frame->ufp.fpexc, err);
+ /* Ensure the VFP is enabled. */
+ fpexc |= FPEXC_EN;
+ /* Ensure FPINST2 is invalid and the exception flag is cleared. */
+ fpexc &= ~(FPEXC_EX | FPEXC_FP2V);
+ h->fpexc = fpexc;
+
+ __get_user_error(h->fpinst, &frame->ufp.fpinst, err);
+ __get_user_error(h->fpinst2, &frame->ufp.fpinst2, err);
+
+ return err ? -EFAULT : 0;
+}
+
+#endif
+
/*
* Do a signal return; undo the signal stack. These are aligned to 64-bit.
*/
@@ -254,8 +337,8 @@ static int restore_sigframe(struct pt_regs *regs, struct sigframe __user *sf)
err |= restore_iwmmxt_context(&aux->iwmmxt);
#endif
#ifdef CONFIG_VFP
-// if (err == 0)
-// err |= vfp_restore_state(&sf->aux.vfp);
+ if (err == 0)
+ err |= restore_vfp_context(&aux->vfp);
#endif

return err;
@@ -369,8 +452,8 @@ setup_sigframe(struct sigframe __user *sf, struct pt_regs *regs, sigset_t *set)
err |= preserve_iwmmxt_context(&aux->iwmmxt);
#endif
#ifdef CONFIG_VFP
-// if (err == 0)
-// err |= vfp_save_state(&sf->aux.vfp);
+ if (err == 0)
+ err |= preserve_vfp_context(&aux->vfp);
#endif
__put_user_error(0, &aux->end_magic, err);

--
1.6.3.3


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