| Message ID | 1369924733-18701-3-git-send-email-julien.grall@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
On Thu, 2013-05-30 at 15:38 +0100, Julien Grall wrote: > 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> > --- > xen/arch/arm/Rules.mk | 2 +- > xen/arch/arm/setup.c | 2 -- > xen/arch/arm/smpboot.c | 1 - > xen/include/asm-arm/vfp.h | 28 ---------------------------- > 4 files changed, 1 insertion(+), 32 deletions(-) > > 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 ($(TARGET_SUBARCH),arm32) > # Prevent floating-point variables from creeping into Xen. > CFLAGS += -msoft-float > -CFLAGS += -mcpu=cortex-a15 -mfpu=vfpv3 -mfloat-abi=softfp > +CFLAGS += -mcpu=cortex-a15 Does removing this have the side effect that if we accidentally add a floating point operation to the hypervisor (very easy to do) it will now compile with h/w fp, unlike previously where it would generate a call to a non-existent library call and fail the build? Since using vfp inside the hypervisor would require more supporting code failing to build is quite useful.
On 05/30/2013 04:15 PM, Ian Campbell wrote: > On Thu, 2013-05-30 at 15:38 +0100, Julien Grall wrote: >> We can safely remove VFP support in XEN because: >> - the guest will enable VFP support when a process requires it >> - XEN doesn't use VFP >> >> Signed-off-by: Julien Grall <julien.grall@linaro.org> >> --- >> xen/arch/arm/Rules.mk | 2 +- >> xen/arch/arm/setup.c | 2 -- >> xen/arch/arm/smpboot.c | 1 - >> xen/include/asm-arm/vfp.h | 28 ---------------------------- >> 4 files changed, 1 insertion(+), 32 deletions(-) >> >> diff --git a/xen/arch/arm/Rules.mk b/xen/arch/arm/Rules.mk >> index 422ed04..a18e7fd 100644 >> --- a/xen/arch/arm/Rules.mk >> +++ b/xen/arch/arm/Rules.mk >> @@ -22,7 +22,7 @@ arm := y >> ifeq ($(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 > > Does removing this have the side effect that if we accidentally add a > floating point operation to the hypervisor (very easy to do) it will now > compile with h/w fp, unlike previously where it would generate a call to > a non-existent library call and fail the build? Yes. GCC will notify that VFP support is not enabled, except if we use directly mrc and mcr.
On Thu, 2013-05-30 at 16:38 +0100, Julien Grall wrote: > On 05/30/2013 04:15 PM, Ian Campbell wrote: > > > On Thu, 2013-05-30 at 15:38 +0100, Julien Grall wrote: > >> 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> > >> --- > >> xen/arch/arm/Rules.mk | 2 +- > >> xen/arch/arm/setup.c | 2 -- > >> xen/arch/arm/smpboot.c | 1 - > >> xen/include/asm-arm/vfp.h | 28 ---------------------------- > >> 4 files changed, 1 insertion(+), 32 deletions(-) > >> > >> 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 ($(TARGET_SUBARCH),arm32) > >> # Prevent floating-point variables from creeping into Xen. > >> CFLAGS += -msoft-float > >> -CFLAGS += -mcpu=cortex-a15 -mfpu=vfpv3 -mfloat-abi=softfp > >> +CFLAGS += -mcpu=cortex-a15 > > > > Does removing this have the side effect that if we accidentally add a > > floating point operation to the hypervisor (very easy to do) it will now > > compile with h/w fp, unlike previously where it would generate a call to > > a non-existent library call and fail the build? > > > Yes. GCC will notify that VFP support is not enabled, Great! > except if we use directly mrc and mcr. Lets not do that! Ian.
diff --git a/xen/arch/arm/Rules.mk b/xen/arch/arm/Rules.mk index 422ed04..a18e7fd 100644 --- a/xen/arch/arm/Rules.mk +++ b/xen/arch/arm/Rules.mk @@ -22,7 +22,7 @@ arm := y ifeq ($(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..2df091e 100644 --- a/xen/arch/arm/setup.c +++ b/xen/arch/arm/setup.c @@ -457,8 +457,6 @@ 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..67e20d0 100644 --- a/xen/arch/arm/smpboot.c +++ b/xen/arch/arm/smpboot.c @@ -153,7 +153,6 @@ 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 index 6ba3cd1..fcffdf2 100644 --- a/xen/include/asm-arm/vfp.h +++ b/xen/include/asm-arm/vfp.h @@ -11,34 +11,6 @@ # error "Unknown ARM variant" #endif -#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 - void vfp_save_state(struct vcpu *v); void vfp_restore_state(struct vcpu *v);
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> --- xen/arch/arm/Rules.mk | 2 +- xen/arch/arm/setup.c | 2 -- xen/arch/arm/smpboot.c | 1 - xen/include/asm-arm/vfp.h | 28 ---------------------------- 4 files changed, 1 insertion(+), 32 deletions(-)