thr3ads.net - Xen devel - [PATCH v4 0/2] Implement VFP context switch for arm32 [Jun 2013]

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Julien Grall

2013-Jun-17 13:47 UTC

[PATCH v4 0/2] Implement VFP context switch for arm32

Hello,

This is the fourth version of this patch series.

I have only implemented the VFP context switch support for arm32 and add dummy
function to avoid avoid compilation breakage on arm64.

For all the changes see each patch.

Cheers,

Julien Grall (2):
  xen/arm: don''t enable VFP on XEN during the boot
  xen/arm32: implement VFP context switch

 xen/arch/arm/Rules.mk           |    2 +-
 xen/arch/arm/arm32/Makefile     |    1 +
 xen/arch/arm/arm32/vfp.c        |   95 +++++++++++++++++++++++++++++++++++++++
 xen/arch/arm/arm64/Makefile     |    1 +
 xen/arch/arm/arm64/vfp.c        |   13 ++++++
 xen/arch/arm/domain.c           |    7 ++-
 xen/arch/arm/setup.c            |    3 --
 xen/arch/arm/smpboot.c          |    2 -
 xen/include/asm-arm/arm32/vfp.h |   41 +++++++++++++++++
 xen/include/asm-arm/arm64/vfp.h |   16 +++++++
 xen/include/asm-arm/cpregs.h    |    9 ++++
 xen/include/asm-arm/domain.h    |    4 ++
 xen/include/asm-arm/vfp.h       |   42 +++++------------
 13 files changed, 198 insertions(+), 38 deletions(-)
 create mode 100644 xen/arch/arm/arm32/vfp.c
 create mode 100644 xen/arch/arm/arm64/vfp.c
 create mode 100644 xen/include/asm-arm/arm32/vfp.h
 create mode 100644 xen/include/asm-arm/arm64/vfp.h

-- 
1.7.10.4

Julien Grall

2013-Jun-17 13:47 UTC

head link

[PATCH v4 1/2] xen/arm: don''t enable VFP on XEN during the boot

We can safely remove VFP support in XEN because:
    - the guest will enable VFP support when a process requires it
    - XEN doesn''t use VFP

Signed-off-by: Julien Grall <julien.grall@linaro.org>

---
Changes in v2:
    - Remove asm/vfp.h and all the inclusions of this header
---
 xen/arch/arm/Rules.mk     |    2 +-
 xen/arch/arm/setup.c      |    3 ---
 xen/arch/arm/smpboot.c    |    2 --
 xen/include/asm-arm/vfp.h |   43 -------------------------------------------
 4 files changed, 1 insertion(+), 49 deletions(-)
 delete mode 100644 xen/include/asm-arm/vfp.h

diff --git a/xen/arch/arm/Rules.mk b/xen/arch/arm/Rules.mk
index 422ed04..a18e7fd 100644
--- a/xen/arch/arm/Rules.mk
+++ b/xen/arch/arm/Rules.mk
@@ -22,7 +22,7 @@ arm := y
 ifeq ($(TARGET_SUBARCH),arm32)
 # Prevent floating-point variables from creeping into Xen.
 CFLAGS += -msoft-float
-CFLAGS += -mcpu=cortex-a15 -mfpu=vfpv3 -mfloat-abi=softfp
+CFLAGS += -mcpu=cortex-a15
 arm32 := y
 arm64 := n
 endif
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index da2a734..b192d15 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -38,7 +38,6 @@
 #include <asm/page.h>
 #include <asm/current.h>
 #include <asm/setup.h>
-#include <asm/vfp.h>
 #include <asm/early_printk.h>
 #include <asm/gic.h>
 #include <asm/cpufeature.h>
@@ -457,8 +456,6 @@ void __init start_xen(unsigned long boot_phys_offset,
 
     setup_virt_paging();
 
-    enable_vfp();
-
     softirq_init();
 
     tasklet_subsys_init();
diff --git a/xen/arch/arm/smpboot.c b/xen/arch/arm/smpboot.c
index 8011987..c7421fc 100644
--- a/xen/arch/arm/smpboot.c
+++ b/xen/arch/arm/smpboot.c
@@ -28,7 +28,6 @@
 #include <xen/softirq.h>
 #include <xen/timer.h>
 #include <xen/irq.h>
-#include <asm/vfp.h>
 #include <asm/gic.h>
 
 cpumask_t cpu_online_map;
@@ -153,7 +152,6 @@ void __cpuinit start_secondary(unsigned long
boot_phys_offset,
     setup_virt_paging();
 
     mmu_init_secondary_cpu();
-    enable_vfp();
 
     gic_init_secondary_cpu();
 
diff --git a/xen/include/asm-arm/vfp.h b/xen/include/asm-arm/vfp.h
deleted file mode 100644
index b800816..0000000
--- a/xen/include/asm-arm/vfp.h
+++ /dev/null
@@ -1,43 +0,0 @@
-#ifndef __ARM_VFP_H_
-#define __ARM_VFP_H_
-
-#include <xen/types.h>
-
-
-#ifdef CONFIG_ARM_32
-
-#define FPEXC_EN (1u << 30)
-
-/* Save and restore FP state.
- * Ought to be using the new vmrs/vmsr names, but older binutils has a
- * bug where it only allows them to target fpscr (and not, say, fpexc). */
-#define READ_FP(reg) ({                                 \
-    uint32_t val;                                       \
-    asm volatile ("fmrx %0, fp" #reg : "=r" (val));     \
-    val; })
-
-#define WRITE_FP(reg, val) do {                         \
-    asm volatile ("fmxr fp" #reg ", %0" : : "r"
(val)); \
-} while (0)
-
-/* Start-of-day: Turn on VFP */
-static inline void enable_vfp(void)
-{
-    WRITE_FP(exc, READ_FP(exc) | FPEXC_EN);
-}
-#else
-static inline void enable_vfp(void)
-{
-    /* Always enable on 64-bit */
-}
-#endif
-
-#endif
-/*
- * Local variables:
- * mode: C
- * c-file-style: "BSD"
- * c-basic-offset: 4
- * indent-tabs-mode: nil
- * End:
- */
-- 
1.7.10.4

Julien Grall

2013-Jun-17 13:47 UTC

head link

[PATCH v4 2/2] xen/arm32: implement VFP context switch

Add support for VFP context switch on arm32 and a dummy support for arm64

Signed-off-by: Julien Grall <julien.grall@linaro.org>

---
Changes in v4:
    - Use Q in assembly constraint

Changes in v3:
    - Add vfp_init to check if the processor supports VFP 3
    - Add clobber memory
    - Remove tmps
    - s/COFNIG_ARM64/CONFIG_ARM64/ in include/asm/arm.h

Changes in v2:
    - Fix all the small errors (type, lost headers...)
    - Add some comments
---
 xen/arch/arm/arm32/Makefile     |    1 +
 xen/arch/arm/arm32/vfp.c        |   95 +++++++++++++++++++++++++++++++++++++++
 xen/arch/arm/arm64/Makefile     |    1 +
 xen/arch/arm/arm64/vfp.c        |   13 ++++++
 xen/arch/arm/domain.c           |    7 ++-
 xen/include/asm-arm/arm32/vfp.h |   41 +++++++++++++++++
 xen/include/asm-arm/arm64/vfp.h |   16 +++++++
 xen/include/asm-arm/cpregs.h    |    9 ++++
 xen/include/asm-arm/domain.h    |    4 ++
 xen/include/asm-arm/vfp.h       |   25 +++++++++++
 10 files changed, 210 insertions(+), 2 deletions(-)
 create mode 100644 xen/arch/arm/arm32/vfp.c
 create mode 100644 xen/arch/arm/arm64/vfp.c
 create mode 100644 xen/include/asm-arm/arm32/vfp.h
 create mode 100644 xen/include/asm-arm/arm64/vfp.h
 create mode 100644 xen/include/asm-arm/vfp.h

diff --git a/xen/arch/arm/arm32/Makefile b/xen/arch/arm/arm32/Makefile
index aaf277a..b903803 100644
--- a/xen/arch/arm/arm32/Makefile
+++ b/xen/arch/arm/arm32/Makefile
@@ -6,5 +6,6 @@ obj-y += proc-ca15.o
 
 obj-y += traps.o
 obj-y += domain.o
+obj-y += vfp.o
 
 obj-$(EARLY_PRINTK) += debug.o
diff --git a/xen/arch/arm/arm32/vfp.c b/xen/arch/arm/arm32/vfp.c
new file mode 100644
index 0000000..6780131
--- /dev/null
+++ b/xen/arch/arm/arm32/vfp.c
@@ -0,0 +1,95 @@
+#include <xen/sched.h>
+#include <xen/init.h>
+#include <asm/processor.h>
+#include <asm/vfp.h>
+
+void vfp_save_state(struct vcpu *v)
+{
+    v->arch.vfp.fpexc = READ_CP32(FPEXC);
+
+    WRITE_CP32(v->arch.vfp.fpexc | FPEXC_EN, FPEXC);
+
+    v->arch.vfp.fpscr = READ_CP32(FPSCR);
+
+    if ( v->arch.vfp.fpexc & FPEXC_EX ) /* Check for sub-architecture */
+    {
+        v->arch.vfp.fpinst = READ_CP32(FPINST);
+
+        if ( v->arch.vfp.fpexc & FPEXC_FP2V )
+            v->arch.vfp.fpinst2 = READ_CP32(FPINST2);
+        /* Disable FPEXC_EX */
+        WRITE_CP32((v->arch.vfp.fpexc | FPEXC_EN) & ~FPEXC_EX, FPEXC);
+    }
+
+    /* Save {d0-d15} */
+    asm volatile("stc p11, cr0, %0, #32*4"
+                 : "=Q" (v->arch.vfp.fpregs1));
+
+    /* 32 x 64 bits registers? */
+    if ( (READ_CP32(MVFR0) & MVFR0_A_SIMD_MASK) == 2 )
+    {
+        /* Save {d16-d31} */
+        asm volatile("stcl p11, cr0, %0, #32*4"
+                     : "=Q" (v->arch.vfp.fpregs2));
+    }
+
+    WRITE_CP32(v->arch.vfp.fpexc & ~(FPEXC_EN), FPEXC);
+}
+
+void vfp_restore_state(struct vcpu *v)
+{
+    WRITE_CP32(READ_CP32(FPEXC) | FPEXC_EN, FPEXC);
+
+    /* Restore {d0-d15} */
+    asm volatile("ldc p11, cr0, %0, #32*4"
+                 : : "Q" (v->arch.vfp.fpregs1));
+
+    /* 32 x 64 bits registers? */
+    if ( (READ_CP32(MVFR0) & MVFR0_A_SIMD_MASK) == 2 ) /* 32 x 64 bits
registers */
+        /* Restore {d16-d31} */
+        asm volatile("ldcl p11, cr0, %0, #32*4"
+                     : : "Q" (v->arch.vfp.fpregs2));
+
+    if ( v->arch.vfp.fpexc & FPEXC_EX )
+    {
+        WRITE_CP32(v->arch.vfp.fpinst, FPINST);
+        if ( v->arch.vfp.fpexc & FPEXC_FP2V )
+            WRITE_CP32(v->arch.vfp.fpinst2, FPINST2);
+    }
+
+    WRITE_CP32(v->arch.vfp.fpscr, FPSCR);
+
+    WRITE_CP32(v->arch.vfp.fpexc, FPEXC);
+}
+
+static __init int vfp_init(void)
+{
+    unsigned int vfpsid;
+    unsigned int vfparch;
+
+    vfpsid = READ_CP32(FPSID);
+
+    printk("VFP implementer 0x%02x architecture %d part 0x%02x variant
0x%x "
+           "rev 0x%x\n",
+           (vfpsid & FPSID_IMPLEMENTER_MASK) >>
FPSID_IMPLEMENTER_BIT,
+           (vfpsid & FPSID_ARCH_MASK) >> FPSID_ARCH_BIT,
+           (vfpsid & FPSID_PART_MASK) >> FPSID_PART_BIT,
+           (vfpsid & FPSID_VARIANT_MASK) >> FPSID_VARIANT_BIT,
+           (vfpsid & FPSID_REV_MASK) >> FPSID_REV_BIT);
+
+    vfparch = (vfpsid & FPSID_ARCH_MASK) >> FPSID_ARCH_BIT;
+    if ( vfparch < 2 )
+        panic("Xen only support VFP 3\n");
+
+    return 0;
+}
+presmp_initcall(vfp_init);
+
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/arch/arm/arm64/Makefile b/xen/arch/arm/arm64/Makefile
index 9484548..e06a0a9 100644
--- a/xen/arch/arm/arm64/Makefile
+++ b/xen/arch/arm/arm64/Makefile
@@ -5,5 +5,6 @@ obj-y += mode_switch.o
 
 obj-y += traps.o
 obj-y += domain.o
+obj-y += vfp.o
 
 obj-$(EARLY_PRINTK) += debug.o
diff --git a/xen/arch/arm/arm64/vfp.c b/xen/arch/arm/arm64/vfp.c
new file mode 100644
index 0000000..74e6a50
--- /dev/null
+++ b/xen/arch/arm/arm64/vfp.c
@@ -0,0 +1,13 @@
+#include <xen/sched.h>
+#include <asm/processor.h>
+#include <asm/vfp.h>
+
+void vfp_save_state(struct vcpu *v)
+{
+    /* TODO: implement it */
+}
+
+void vfp_restore_state(struct vcpu *v)
+{
+    /* TODO: implement it */
+}
diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index 4c434a1..f465ab7 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -27,6 +27,7 @@
 #include <asm/p2m.h>
 #include <asm/irq.h>
 #include <asm/cpufeature.h>
+#include <asm/vfp.h>
 
 #include <asm/gic.h>
 #include "vtimer.h"
@@ -117,7 +118,8 @@ static void ctxt_switch_from(struct vcpu *p)
 
     /* XXX MPU */
 
-    /* XXX VFP */
+    /* VFP */
+    vfp_save_state(p);
 
     /* VGIC */
     gic_save_state(p);
@@ -143,7 +145,8 @@ static void ctxt_switch_to(struct vcpu *n)
     /* VGIC */
     gic_restore_state(n);
 
-    /* XXX VFP */
+    /* VFP */
+    vfp_restore_state(n);
 
     /* XXX MPU */
 
diff --git a/xen/include/asm-arm/arm32/vfp.h b/xen/include/asm-arm/arm32/vfp.h
new file mode 100644
index 0000000..bade3bc
--- /dev/null
+++ b/xen/include/asm-arm/arm32/vfp.h
@@ -0,0 +1,41 @@
+#ifndef _ARM_ARM32_VFP_H
+#define _ARM_ARM32_VFP_H
+
+#define FPEXC_EX                (1u << 31)
+#define FPEXC_EN                (1u << 30)
+#define FPEXC_FP2V              (1u << 28)
+
+#define MVFR0_A_SIMD_MASK       (0xf << 0)
+
+
+#define FPSID_IMPLEMENTER_BIT   (24)
+#define FPSID_IMPLEMENTER_MASK  (0xff << FPSID_IMPLEMENTER_BIT)
+#define FPSID_ARCH_BIT          (16)
+#define FPSID_ARCH_MASK         (0xf << FPSID_ARCH_BIT)
+#define FPSID_PART_BIT          (8)
+#define FPSID_PART_MASK         (0xff << FPSID_PART_BIT)
+#define FPSID_VARIANT_BIT       (4)
+#define FPSID_VARIANT_MASK      (0xf << FPSID_VARIANT_BIT)
+#define FPSID_REV_BIT           (0)
+#define FPSID_REV_MASK          (0xf << FPSID_REV_BIT)
+
+struct vfp_state
+{
+    uint64_t fpregs1[16]; /* {d0-d15} */
+    uint64_t fpregs2[16]; /* {d16-d31} */
+    uint32_t fpexc;
+    uint32_t fpscr;
+    /* VFP implementation specific state */
+    uint32_t fpinst;
+    uint32_t fpinst2;
+};
+
+#endif /* _ARM_ARM32_VFP_H */
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/include/asm-arm/arm64/vfp.h b/xen/include/asm-arm/arm64/vfp.h
new file mode 100644
index 0000000..3733d2c
--- /dev/null
+++ b/xen/include/asm-arm/arm64/vfp.h
@@ -0,0 +1,16 @@
+#ifndef _ARM_ARM64_VFP_H
+#define _ARM_ARM64_VFP_H
+
+struct vfp_state
+{
+};
+
+#endif /* _ARM_ARM64_VFP_H */
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
diff --git a/xen/include/asm-arm/cpregs.h b/xen/include/asm-arm/cpregs.h
index f08d59a..122dd1a 100644
--- a/xen/include/asm-arm/cpregs.h
+++ b/xen/include/asm-arm/cpregs.h
@@ -60,6 +60,15 @@
  * arguments, which are cp,opc1,crn,crm,opc2.
  */
 
+/* Coprocessor 10 */
+
+#define FPSID           p10,7,c0,c0,0   /* Floating-Point System ID Register */
+#define FPSCR           p10,7,c1,c0,0   /* Floating-Point Status and Control
Register */
+#define MVFR0           p10,7,c7,c0,0   /* Media and VFP Feature Register 0 */
+#define FPEXC           p10,7,c8,c0,0   /* Floating-Point Exception Control
Register */
+#define FPINST          p10,7,c9,c0,0   /* Floating-Point Instruction Register
*/
+#define FPINST2         p10,7,c10,c0,0  /* Floating-point Instruction Register
2 */
+
 /* Coprocessor 14 */
 
 /* CP14 CR0: */
diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
index cb251cc..339b6e6 100644
--- a/xen/include/asm-arm/domain.h
+++ b/xen/include/asm-arm/domain.h
@@ -6,6 +6,7 @@
 #include <xen/sched.h>
 #include <asm/page.h>
 #include <asm/p2m.h>
+#include <asm/vfp.h>
 #include <public/hvm/params.h>
 
 /* Represents state corresponding to a block of 32 interrupts */
@@ -188,6 +189,9 @@ struct arch_vcpu
     uint32_t joscr, jmcr;
 #endif
 
+    /* Float-pointer */
+    struct vfp_state vfp;
+
     /* CP 15 */
     uint32_t csselr;
 
diff --git a/xen/include/asm-arm/vfp.h b/xen/include/asm-arm/vfp.h
new file mode 100644
index 0000000..5f10fe5
--- /dev/null
+++ b/xen/include/asm-arm/vfp.h
@@ -0,0 +1,25 @@
+#ifndef _ASM_VFP_H
+#define _ASM_VFP_H
+
+#include <xen/sched.h>
+
+#if defined(CONFIG_ARM_32)
+# include <asm/arm32/vfp.h>
+#elif defined(CONFIG_ARM_64)
+# include <asm/arm64/vfp.h>
+#else
+# error "Unknown ARM variant"
+#endif
+
+void vfp_save_state(struct vcpu *v);
+void vfp_restore_state(struct vcpu *v);
+
+#endif /* _ASM_VFP_H */
+/*
+ * Local variables:
+ * mode: C
+ * c-file-style: "BSD"
+ * c-basic-offset: 4
+ * indent-tabs-mode: nil
+ * End:
+ */
-- 
1.7.10.4

Ian Campbell

2013-Jun-28 11:40 UTC

head link

Re: [PATCH v4 0/2] Implement VFP context switch for arm32

On Mon, 2013-06-17 at 14:47 +0100, Julien Grall wrote:> Hello,
> 
> This is the fourth version of this patch series.
> 
> I have only implemented the VFP context switch support for arm32 and add
dummy
> function to avoid avoid compilation breakage on arm64.
After speaking with Stefano we''ve decided that since this
didn''t
actually address the SMP issue you were chasing and since we are now so
close to the 4.3 release (this is partly my fault for being tardy with
applying the patch, sorry) we will hold off on this change until 4.4
development opens. Shouldn''t be long now before we branch...

Ian.
> 
> For all the changes see each patch.
> 
> Cheers,
> 
> Julien Grall (2):
>   xen/arm: don''t enable VFP on XEN during the boot
>   xen/arm32: implement VFP context switch
> 
>  xen/arch/arm/Rules.mk           |    2 +-
>  xen/arch/arm/arm32/Makefile     |    1 +
>  xen/arch/arm/arm32/vfp.c        |   95
+++++++++++++++++++++++++++++++++++++++
>  xen/arch/arm/arm64/Makefile     |    1 +
>  xen/arch/arm/arm64/vfp.c        |   13 ++++++
>  xen/arch/arm/domain.c           |    7 ++-
>  xen/arch/arm/setup.c            |    3 --
>  xen/arch/arm/smpboot.c          |    2 -
>  xen/include/asm-arm/arm32/vfp.h |   41 +++++++++++++++++
>  xen/include/asm-arm/arm64/vfp.h |   16 +++++++
>  xen/include/asm-arm/cpregs.h    |    9 ++++
>  xen/include/asm-arm/domain.h    |    4 ++
>  xen/include/asm-arm/vfp.h       |   42 +++++------------
>  13 files changed, 198 insertions(+), 38 deletions(-)
>  create mode 100644 xen/arch/arm/arm32/vfp.c
>  create mode 100644 xen/arch/arm/arm64/vfp.c
>  create mode 100644 xen/include/asm-arm/arm32/vfp.h
>  create mode 100644 xen/include/asm-arm/arm64/vfp.h
>

Ian Campbell

2013-Jul-04 10:40 UTC

head link

Re: [PATCH v4 0/2] Implement VFP context switch for arm32

On Mon, 2013-06-17 at 14:47 +0100, Julien Grall wrote:> Hello,
> 
> This is the fourth version of this patch series.
> 
> I have only implemented the VFP context switch support for arm32 and add
dummy
> function to avoid avoid compilation breakage on arm64.
> 
> For all the changes see each patch.
> 
> Cheers,
> 
> Julien Grall (2):
>   xen/arm: don''t enable VFP on XEN during the boot
>   xen/arm32: implement VFP context switch
Acked both and applied to staging.

Ian Campbell

2013-Jul-06 20:45 UTC

head link

Re: [PATCH v4 2/2] xen/arm32: implement VFP context switch

On Mon, 2013-06-17 at 14:47 +0100, Julien Grall wrote:> Add support for VFP context switch on arm32 and a dummy support for arm64
> 
> Signed-off-by: Julien Grall <julien.grall@linaro.org>
This patch is causing failures for me with the gcc 4.6.3 cross compiler
which I use and with gcc-linaro-arm-linux-gnueabihf-4.7-2013.04-20130415

vfp.c: In function ''vfp_restore_state'':
vfp.c:45:27: error: memory input 0 is not directly addressable
vfp.c:51:31: error: memory input 0 is not directly addressable

For some reason this didn''t happen during my pre-commit build tests (or
I somehow missed it), and the test system seems happy with it (no
regression reported). But it does seem to fail on the same system (with
the same compiler) I used for those pre-commit tests now.

Which compiler do you use?

I notice that Linux does its VFP context switch in a .S file, I wonder
if this sort of issue is why?

Ian.

Ian Campbell

2013-Jul-07 06:03 UTC

head link

Re: [PATCH v4 2/2] xen/arm32: implement VFP context switch

On Mon, 2013-06-17 at 14:47 +0100, Julien Grall wrote:> Add support for VFP context switch on arm32 and a dummy support for arm64
> 
> Signed-off-by: Julien Grall <julien.grall@linaro.org>
This patch is causing failures for me with the gcc 4.6.3 cross compiler
which I use and with gcc-linaro-arm-linux-gnueabihf-4.7-2013.04-20130415

vfp.c: In function ''vfp_restore_state'':
vfp.c:45:27: error: memory input 0 is not directly addressable
vfp.c:51:31: error: memory input 0 is not directly addressable

For some reason this didn''t happen during my pre-commit build tests (or
I somehow missed it), and the test system seems happy with it (no
regression reported). But it does seem to fail on the same system (with
the same compiler) I used for those pre-commit tests now.

Which compiler do you use?

I notice that Linux does its VFP context switch in a .S file, I wonder
if this sort of issue is why?

Ian.

Julien Grall

2013-Jul-07 16:02 UTC

head link

Re: [PATCH v4 2/2] xen/arm32: implement VFP context switch

On 6 July 2013 21:45, Ian Campbell <ian.campbell@citrix.com>
wrote:> On Mon, 2013-06-17 at 14:47 +0100, Julien Grall wrote:
>> Add support for VFP context switch on arm32 and a dummy support for
arm64
>>
>> Signed-off-by: Julien Grall <julien.grall@linaro.org>
>
> This patch is causing failures for me with the gcc 4.6.3 cross compiler
> which I use and with gcc-linaro-arm-linux-gnueabihf-4.7-2013.04-20130415
>
> vfp.c: In function ''vfp_restore_state'':
> vfp.c:45:27: error: memory input 0 is not directly addressable
> vfp.c:51:31: error: memory input 0 is not directly addressable
>
> For some reason this didn''t happen during my pre-commit build
tests (or
> I somehow missed it), and the test system seems happy with it (no
> regression reported). But it does seem to fail on the same system (with
> the same compiler) I used for those pre-commit tests now.
>
> Which compiler do you use?
I''m using gcc 4.8.1.
> I notice that Linux does its VFP context switch in a .S file, I wonder
> if this sort of issue is why?
Except if I missed something in the documentation, the constraint
''Q''([1])
doesn''t produce the same assembly code on gcc 4.8.1 and gcc 4.6.3.

asm volatile("ldr r0, %0" : : "Q" (v));

- gcc 4.6.3 : ldr r0, [r1, #0]
- gcc 4.8.1 : ldr r0, [r1]

That''s an issue for the VFP context switch, because I need to have
[rd] otherwise gcc will complain because the assembly instruction
has both pre-index and post-index.

[1]
http://gcc.gnu.org/onlinedocs/gcc-4.8.1/gcc/Machine-Constraints.html#Machine-Constraints

--
Julien Grall

Xen devel - Jun 2013 - [PATCH v4 0/2] Implement VFP context switch for arm32

[PATCH v4 0/2] Implement VFP context switch for arm32

[PATCH v4 1/2] xen/arm: don''t enable VFP on XEN during the boot

[PATCH v4 2/2] xen/arm32: implement VFP context switch

Re: [PATCH v4 0/2] Implement VFP context switch for arm32

Re: [PATCH v4 0/2] Implement VFP context switch for arm32

Re: [PATCH v4 2/2] xen/arm32: implement VFP context switch

Re: [PATCH v4 2/2] xen/arm32: implement VFP context switch

Re: [PATCH v4 2/2] xen/arm32: implement VFP context switch