In banked-sr.c, we use a top-level '__asm__(".arch_extension virt")'
statement to allow compilation of a multi-CPU kernel for ARMv6
and older ARMv7-A that don't normally support access to the banked
registers.
This is considered to be a programming error by the gcc developers
and will no longer work in gcc-8, where we now get a build error:
/tmp/cc4Qy7GR.s:34: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_usr'
/tmp/cc4Qy7GR.s:41: Error: Banked registers are not available with this architecture. -- `mrs r3,ELR_hyp'
/tmp/cc4Qy7GR.s:55: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_svc'
/tmp/cc4Qy7GR.s:62: Error: Banked registers are not available with this architecture. -- `mrs r3,LR_svc'
/tmp/cc4Qy7GR.s:69: Error: Banked registers are not available with this architecture. -- `mrs r3,SPSR_svc'
/tmp/cc4Qy7GR.s:76: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_abt'
Passign the '-march-armv7ve' flag to gcc works, and is ok here, because
we know the functions won't ever be called on pre-ARMv7VE machines.
Unfortunately, older compiler versions (4.8 and earlier) do not understand
that flag, so we still need to keep the asm around.
Backporting to stable kernels (4.6+) is needed to allow those to be built
with future compilers as well.
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84129
Fixes: 33280b4cd1dc ("ARM: KVM: Add banked registers save/restore")
Cc: [email protected]
Signed-off-by: Arnd Bergmann <[email protected]>
---
arch/arm/kvm/hyp/Makefile | 5 +++++
arch/arm/kvm/hyp/banked-sr.c | 4 ++++
2 files changed, 9 insertions(+)
diff --git a/arch/arm/kvm/hyp/Makefile b/arch/arm/kvm/hyp/Makefile
index 5638ce0c9524..63d6b404d88e 100644
--- a/arch/arm/kvm/hyp/Makefile
+++ b/arch/arm/kvm/hyp/Makefile
@@ -7,6 +7,8 @@ ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING
KVM=../../../../virt/kvm
+CFLAGS_ARMV7VE :=$(call cc-option, -march=armv7ve)
+
obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/vgic-v2-sr.o
obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/vgic-v3-sr.o
obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/timer-sr.o
@@ -15,7 +17,10 @@ obj-$(CONFIG_KVM_ARM_HOST) += tlb.o
obj-$(CONFIG_KVM_ARM_HOST) += cp15-sr.o
obj-$(CONFIG_KVM_ARM_HOST) += vfp.o
obj-$(CONFIG_KVM_ARM_HOST) += banked-sr.o
+CFLAGS_banked-sr.o += $(CFLAGS_ARMV7VE)
+
obj-$(CONFIG_KVM_ARM_HOST) += entry.o
obj-$(CONFIG_KVM_ARM_HOST) += hyp-entry.o
obj-$(CONFIG_KVM_ARM_HOST) += switch.o
+CFLAGS_switch.o += $(CFLAGS_ARMV7VE)
obj-$(CONFIG_KVM_ARM_HOST) += s2-setup.o
diff --git a/arch/arm/kvm/hyp/banked-sr.c b/arch/arm/kvm/hyp/banked-sr.c
index 111bda8cdebd..be4b8b0a40ad 100644
--- a/arch/arm/kvm/hyp/banked-sr.c
+++ b/arch/arm/kvm/hyp/banked-sr.c
@@ -20,6 +20,10 @@
#include <asm/kvm_hyp.h>
+/*
+ * gcc before 4.9 doesn't understand -march=armv7ve, so we have to
+ * trick the assembler.
+ */
__asm__(".arch_extension virt");
void __hyp_text __banked_save_state(struct kvm_cpu_context *ctxt)
--
2.9.0
We use a hack in xscale-cp0.c to allow building it for ARMv4 while
also using ARMv5TE and iWMMXt specific inline assembly, by
adding a top-level asm statement.
Unfortunately that hack no longer works with gcc-8, since it will
revert back to the normal architecture. The recommended way of
handling this is to use __attribute__((target("armv5te"))) on the
functions that need it, or #pragma GCC target("arch=armv5te").
Either of those work with gcc-8, but not earlier versions, and
it seems worse to combine that with the old hack.
Instead, this adds the .arch statement to each inline assembler
statement that needs it individually. That is also slightly uglier
than the previous hack, but it works with all compiler versions
and documents better why we need the override in the first place.
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84129
Signed-off-by: Arnd Bergmann <[email protected]>
---
arch/arm/kernel/xscale-cp0.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/arm/kernel/xscale-cp0.c b/arch/arm/kernel/xscale-cp0.c
index 77a2eef72115..e06a2f6dac4f 100644
--- a/arch/arm/kernel/xscale-cp0.c
+++ b/arch/arm/kernel/xscale-cp0.c
@@ -17,11 +17,10 @@
#include <asm/thread_notify.h>
#include <asm/cputype.h>
-asm(" .arch armv5te\n");
-
static inline void dsp_save_state(u32 *state)
{
__asm__ __volatile__ (
+ ".arch armv5te\n\t"
"mrrc p0, 0, %0, %1, c0\n"
: "=r" (state[0]), "=r" (state[1]));
}
@@ -29,6 +28,7 @@ static inline void dsp_save_state(u32 *state)
static inline void dsp_load_state(u32 *state)
{
__asm__ __volatile__ (
+ ".arch armv5te\n\t"
"mcrr p0, 0, %0, %1, c0\n"
: : "r" (state[0]), "r" (state[1]));
}
@@ -134,7 +134,8 @@ static int __init cpu_has_iwmmxt(void)
* tmrrc %0, %1, wR0
*/
__asm__ __volatile__ (
- "mcrr p0, 0, %2, %3, c0\n"
+ ".arch armv5te\n\t"
+ "mcrr p0, 0, %2, %3, c0\n\t"
"mrrc p0, 0, %0, %1, c0\n"
: "=r" (lo), "=r" (hi)
: "r" (0), "r" (0x100));
--
2.9.0
On 02/02/18 15:07, Arnd Bergmann wrote:
> In banked-sr.c, we use a top-level '__asm__(".arch_extension virt")'
> statement to allow compilation of a multi-CPU kernel for ARMv6
> and older ARMv7-A that don't normally support access to the banked
> registers.
>
> This is considered to be a programming error by the gcc developers
> and will no longer work in gcc-8, where we now get a build error:
>
> /tmp/cc4Qy7GR.s:34: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_usr'
> /tmp/cc4Qy7GR.s:41: Error: Banked registers are not available with this architecture. -- `mrs r3,ELR_hyp'
> /tmp/cc4Qy7GR.s:55: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_svc'
> /tmp/cc4Qy7GR.s:62: Error: Banked registers are not available with this architecture. -- `mrs r3,LR_svc'
> /tmp/cc4Qy7GR.s:69: Error: Banked registers are not available with this architecture. -- `mrs r3,SPSR_svc'
> /tmp/cc4Qy7GR.s:76: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_abt'
>
> Passign the '-march-armv7ve' flag to gcc works, and is ok here, because
> we know the functions won't ever be called on pre-ARMv7VE machines.
> Unfortunately, older compiler versions (4.8 and earlier) do not understand
> that flag, so we still need to keep the asm around.
>
> Backporting to stable kernels (4.6+) is needed to allow those to be built
> with future compilers as well.
Is "-Wa,arch=armv7-a+virt" (as we appear to do for a couple of files
already) viable as a possibly cleaner alternative, or is GCC itself now
policing the contents of inline asms?
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84129
> Fixes: 33280b4cd1dc ("ARM: KVM: Add banked registers save/restore")
> Cc: [email protected]
> Signed-off-by: Arnd Bergmann <[email protected]>
> ---
> arch/arm/kvm/hyp/Makefile | 5 +++++
> arch/arm/kvm/hyp/banked-sr.c | 4 ++++
> 2 files changed, 9 insertions(+)
>
> diff --git a/arch/arm/kvm/hyp/Makefile b/arch/arm/kvm/hyp/Makefile
> index 5638ce0c9524..63d6b404d88e 100644
> --- a/arch/arm/kvm/hyp/Makefile
> +++ b/arch/arm/kvm/hyp/Makefile
> @@ -7,6 +7,8 @@ ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING
>
> KVM=../../../../virt/kvm
>
> +CFLAGS_ARMV7VE :=$(call cc-option, -march=armv7ve)
> +
> obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/vgic-v2-sr.o
> obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/vgic-v3-sr.o
> obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/timer-sr.o
> @@ -15,7 +17,10 @@ obj-$(CONFIG_KVM_ARM_HOST) += tlb.o
> obj-$(CONFIG_KVM_ARM_HOST) += cp15-sr.o
> obj-$(CONFIG_KVM_ARM_HOST) += vfp.o
> obj-$(CONFIG_KVM_ARM_HOST) += banked-sr.o
> +CFLAGS_banked-sr.o += $(CFLAGS_ARMV7VE)
> +
> obj-$(CONFIG_KVM_ARM_HOST) += entry.o
> obj-$(CONFIG_KVM_ARM_HOST) += hyp-entry.o
> obj-$(CONFIG_KVM_ARM_HOST) += switch.o
> +CFLAGS_switch.o += $(CFLAGS_ARMV7VE)
> obj-$(CONFIG_KVM_ARM_HOST) += s2-setup.o
> diff --git a/arch/arm/kvm/hyp/banked-sr.c b/arch/arm/kvm/hyp/banked-sr.c
> index 111bda8cdebd..be4b8b0a40ad 100644
> --- a/arch/arm/kvm/hyp/banked-sr.c
> +++ b/arch/arm/kvm/hyp/banked-sr.c
> @@ -20,6 +20,10 @@
>
> #include <asm/kvm_hyp.h>
>
> +/*
> + * gcc before 4.9 doesn't understand -march=armv7ve, so we have to
> + * trick the assembler.
> + */
> __asm__(".arch_extension virt");
Would it be worth wrapping this in a preprocessor check for compilers
that won't understand the command-line flag? I believe LLVM tends to
choke on these global asm statements entirely, so minimising exposure
might be a good thing to do in general.
Robin.
>
> void __hyp_text __banked_save_state(struct kvm_cpu_context *ctxt)
>
On 02/02/18 15:55, Robin Murphy wrote:
> On 02/02/18 15:07, Arnd Bergmann wrote:
>> In banked-sr.c, we use a top-level '__asm__(".arch_extension virt")'
>> statement to allow compilation of a multi-CPU kernel for ARMv6
>> and older ARMv7-A that don't normally support access to the banked
>> registers.
>>
>> This is considered to be a programming error by the gcc developers
>> and will no longer work in gcc-8, where we now get a build error:
>>
>> /tmp/cc4Qy7GR.s:34: Error: Banked registers are not available with
>> this architecture. -- `mrs r3,SP_usr'
>> /tmp/cc4Qy7GR.s:41: Error: Banked registers are not available with
>> this architecture. -- `mrs r3,ELR_hyp'
>> /tmp/cc4Qy7GR.s:55: Error: Banked registers are not available with
>> this architecture. -- `mrs r3,SP_svc'
>> /tmp/cc4Qy7GR.s:62: Error: Banked registers are not available with
>> this architecture. -- `mrs r3,LR_svc'
>> /tmp/cc4Qy7GR.s:69: Error: Banked registers are not available with
>> this architecture. -- `mrs r3,SPSR_svc'
>> /tmp/cc4Qy7GR.s:76: Error: Banked registers are not available with
>> this architecture. -- `mrs r3,SP_abt'
>>
>> Passign the '-march-armv7ve' flag to gcc works, and is ok here, because
>> we know the functions won't ever be called on pre-ARMv7VE machines.
>> Unfortunately, older compiler versions (4.8 and earlier) do not
>> understand
>> that flag, so we still need to keep the asm around.
>>
>> Backporting to stable kernels (4.6+) is needed to allow those to be built
>> with future compilers as well.
>
> Is "-Wa,arch=armv7-a+virt" (as we appear to do for a couple of files
> already) viable as a possibly cleaner alternative, or is GCC itself now
> policing the contents of inline asms?
In fact, looking at the binutils history, any version capable of
assembling this file should understand that (modulo my typo), so
hopefully it ought to be feasible to replace these global asms with
assembler flags entirely.
Robin.
>> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84129
>> Fixes: 33280b4cd1dc ("ARM: KVM: Add banked registers save/restore")
>> Cc: [email protected]
>> Signed-off-by: Arnd Bergmann <[email protected]>
>> ---
>> arch/arm/kvm/hyp/Makefile | 5 +++++
>> arch/arm/kvm/hyp/banked-sr.c | 4 ++++
>> 2 files changed, 9 insertions(+)
>>
>> diff --git a/arch/arm/kvm/hyp/Makefile b/arch/arm/kvm/hyp/Makefile
>> index 5638ce0c9524..63d6b404d88e 100644
>> --- a/arch/arm/kvm/hyp/Makefile
>> +++ b/arch/arm/kvm/hyp/Makefile
>> @@ -7,6 +7,8 @@ ccflags-y += -fno-stack-protector
>> -DDISABLE_BRANCH_PROFILING
>> KVM=../../../../virt/kvm
>> +CFLAGS_ARMV7VE :=$(call cc-option, -march=armv7ve)
>> +
>> obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/vgic-v2-sr.o
>> obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/vgic-v3-sr.o
>> obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/timer-sr.o
>> @@ -15,7 +17,10 @@ obj-$(CONFIG_KVM_ARM_HOST) += tlb.o
>> obj-$(CONFIG_KVM_ARM_HOST) += cp15-sr.o
>> obj-$(CONFIG_KVM_ARM_HOST) += vfp.o
>> obj-$(CONFIG_KVM_ARM_HOST) += banked-sr.o
>> +CFLAGS_banked-sr.o += $(CFLAGS_ARMV7VE)
>> +
>> obj-$(CONFIG_KVM_ARM_HOST) += entry.o
>> obj-$(CONFIG_KVM_ARM_HOST) += hyp-entry.o
>> obj-$(CONFIG_KVM_ARM_HOST) += switch.o
>> +CFLAGS_switch.o += $(CFLAGS_ARMV7VE)
>> obj-$(CONFIG_KVM_ARM_HOST) += s2-setup.o
>> diff --git a/arch/arm/kvm/hyp/banked-sr.c b/arch/arm/kvm/hyp/banked-sr.c
>> index 111bda8cdebd..be4b8b0a40ad 100644
>> --- a/arch/arm/kvm/hyp/banked-sr.c
>> +++ b/arch/arm/kvm/hyp/banked-sr.c
>> @@ -20,6 +20,10 @@
>> #include <asm/kvm_hyp.h>
>> +/*
>> + * gcc before 4.9 doesn't understand -march=armv7ve, so we have to
>> + * trick the assembler.
>> + */
>> __asm__(".arch_extension virt");
>
> Would it be worth wrapping this in a preprocessor check for compilers
> that won't understand the command-line flag? I believe LLVM tends to
> choke on these global asm statements entirely, so minimising exposure
> might be a good thing to do in general.
>
> Robin.
>
>> void __hyp_text __banked_save_state(struct kvm_cpu_context *ctxt)
>>
>
> _______________________________________________
> linux-arm-kernel mailing list
> [email protected]
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Fri, Feb 2, 2018 at 5:23 PM, Robin Murphy <[email protected]> wrote:
> On 02/02/18 15:55, Robin Murphy wrote:
>>
>> On 02/02/18 15:07, Arnd Bergmann wrote:
>>>
>>> In banked-sr.c, we use a top-level '__asm__(".arch_extension virt")'
>>> statement to allow compilation of a multi-CPU kernel for ARMv6
>>> and older ARMv7-A that don't normally support access to the banked
>>> registers.
>>>
>>> This is considered to be a programming error by the gcc developers
>>> and will no longer work in gcc-8, where we now get a build error:
>>>
>>> /tmp/cc4Qy7GR.s:34: Error: Banked registers are not available with this
>>> architecture. -- `mrs r3,SP_usr'
>>> /tmp/cc4Qy7GR.s:41: Error: Banked registers are not available with this
>>> architecture. -- `mrs r3,ELR_hyp'
>>> /tmp/cc4Qy7GR.s:55: Error: Banked registers are not available with this
>>> architecture. -- `mrs r3,SP_svc'
>>> /tmp/cc4Qy7GR.s:62: Error: Banked registers are not available with this
>>> architecture. -- `mrs r3,LR_svc'
>>> /tmp/cc4Qy7GR.s:69: Error: Banked registers are not available with this
>>> architecture. -- `mrs r3,SPSR_svc'
>>> /tmp/cc4Qy7GR.s:76: Error: Banked registers are not available with this
>>> architecture. -- `mrs r3,SP_abt'
>>>
>>> Passign the '-march-armv7ve' flag to gcc works, and is ok here, because
>>> we know the functions won't ever be called on pre-ARMv7VE machines.
>>> Unfortunately, older compiler versions (4.8 and earlier) do not
>>> understand
>>> that flag, so we still need to keep the asm around.
>>>
>>> Backporting to stable kernels (4.6+) is needed to allow those to be built
>>> with future compilers as well.
>>
>>
>> Is "-Wa,arch=armv7-a+virt" (as we appear to do for a couple of files
>> already) viable as a possibly cleaner alternative, or is GCC itself now
>> policing the contents of inline asms?
>
>
> In fact, looking at the binutils history, any version capable of assembling
> this file should understand that (modulo my typo), so hopefully it ought to
> be feasible to replace these global asms with assembler flags entirely.
No, this only works for .S files, not .c, since gcc starts the output with
an explicit .arch setting that overrides the command line. I think this
was done intentionally to prevent such a hack from working, and have
more reliable checks on the validity of the assembler instruction in
inline asm statements (which we try to circumvent here).
Arnd
On 02/02/18 16:29, Arnd Bergmann wrote:
> On Fri, Feb 2, 2018 at 5:23 PM, Robin Murphy <[email protected]> wrote:
>> On 02/02/18 15:55, Robin Murphy wrote:
>>>
>>> On 02/02/18 15:07, Arnd Bergmann wrote:
>>>>
>>>> In banked-sr.c, we use a top-level '__asm__(".arch_extension virt")'
>>>> statement to allow compilation of a multi-CPU kernel for ARMv6
>>>> and older ARMv7-A that don't normally support access to the banked
>>>> registers.
>>>>
>>>> This is considered to be a programming error by the gcc developers
>>>> and will no longer work in gcc-8, where we now get a build error:
>>>>
>>>> /tmp/cc4Qy7GR.s:34: Error: Banked registers are not available with this
>>>> architecture. -- `mrs r3,SP_usr'
>>>> /tmp/cc4Qy7GR.s:41: Error: Banked registers are not available with this
>>>> architecture. -- `mrs r3,ELR_hyp'
>>>> /tmp/cc4Qy7GR.s:55: Error: Banked registers are not available with this
>>>> architecture. -- `mrs r3,SP_svc'
>>>> /tmp/cc4Qy7GR.s:62: Error: Banked registers are not available with this
>>>> architecture. -- `mrs r3,LR_svc'
>>>> /tmp/cc4Qy7GR.s:69: Error: Banked registers are not available with this
>>>> architecture. -- `mrs r3,SPSR_svc'
>>>> /tmp/cc4Qy7GR.s:76: Error: Banked registers are not available with this
>>>> architecture. -- `mrs r3,SP_abt'
>>>>
>>>> Passign the '-march-armv7ve' flag to gcc works, and is ok here, because
>>>> we know the functions won't ever be called on pre-ARMv7VE machines.
>>>> Unfortunately, older compiler versions (4.8 and earlier) do not
>>>> understand
>>>> that flag, so we still need to keep the asm around.
>>>>
>>>> Backporting to stable kernels (4.6+) is needed to allow those to be built
>>>> with future compilers as well.
>>>
>>>
>>> Is "-Wa,arch=armv7-a+virt" (as we appear to do for a couple of files
>>> already) viable as a possibly cleaner alternative, or is GCC itself now
>>> policing the contents of inline asms?
>>
>>
>> In fact, looking at the binutils history, any version capable of assembling
>> this file should understand that (modulo my typo), so hopefully it ought to
>> be feasible to replace these global asms with assembler flags entirely.
>
> No, this only works for .S files, not .c, since gcc starts the output with
> an explicit .arch setting that overrides the command line. I think this
> was done intentionally to prevent such a hack from working, and have
> more reliable checks on the validity of the assembler instruction in
> inline asm statements (which we try to circumvent here).
Ah, I see, that is unfortunate. Thanks for clarifying.
Robin.
On Fri, 2 Feb 2018, Arnd Bergmann wrote:
> We use a hack in xscale-cp0.c to allow building it for ARMv4 while
> also using ARMv5TE and iWMMXt specific inline assembly, by
> adding a top-level asm statement.
>
> Unfortunately that hack no longer works with gcc-8, since it will
> revert back to the normal architecture. The recommended way of
> handling this is to use __attribute__((target("armv5te"))) on the
> functions that need it, or #pragma GCC target("arch=armv5te").
> Either of those work with gcc-8, but not earlier versions, and
> it seems worse to combine that with the old hack.
>
> Instead, this adds the .arch statement to each inline assembler
> statement that needs it individually. That is also slightly uglier
> than the previous hack, but it works with all compiler versions
> and documents better why we need the override in the first place.
>
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84129
> Signed-off-by: Arnd Bergmann <[email protected]>
Acked-by: Nicolas Pitre <[email protected]>
> ---
> arch/arm/kernel/xscale-cp0.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/kernel/xscale-cp0.c b/arch/arm/kernel/xscale-cp0.c
> index 77a2eef72115..e06a2f6dac4f 100644
> --- a/arch/arm/kernel/xscale-cp0.c
> +++ b/arch/arm/kernel/xscale-cp0.c
> @@ -17,11 +17,10 @@
> #include <asm/thread_notify.h>
> #include <asm/cputype.h>
>
> -asm(" .arch armv5te\n");
> -
> static inline void dsp_save_state(u32 *state)
> {
> __asm__ __volatile__ (
> + ".arch armv5te\n\t"
> "mrrc p0, 0, %0, %1, c0\n"
> : "=r" (state[0]), "=r" (state[1]));
> }
> @@ -29,6 +28,7 @@ static inline void dsp_save_state(u32 *state)
> static inline void dsp_load_state(u32 *state)
> {
> __asm__ __volatile__ (
> + ".arch armv5te\n\t"
> "mcrr p0, 0, %0, %1, c0\n"
> : : "r" (state[0]), "r" (state[1]));
> }
> @@ -134,7 +134,8 @@ static int __init cpu_has_iwmmxt(void)
> * tmrrc %0, %1, wR0
> */
> __asm__ __volatile__ (
> - "mcrr p0, 0, %2, %3, c0\n"
> + ".arch armv5te\n\t"
> + "mcrr p0, 0, %2, %3, c0\n\t"
> "mrrc p0, 0, %0, %1, c0\n"
> : "=r" (lo), "=r" (hi)
> : "r" (0), "r" (0x100));
> --
> 2.9.0
>
>
Hi Arnd,
On Fri, Feb 02, 2018 at 04:07:34PM +0100, Arnd Bergmann wrote:
> In banked-sr.c, we use a top-level '__asm__(".arch_extension virt")'
> statement to allow compilation of a multi-CPU kernel for ARMv6
> and older ARMv7-A that don't normally support access to the banked
> registers.
>
> This is considered to be a programming error by the gcc developers
> and will no longer work in gcc-8, where we now get a build error:
>
> /tmp/cc4Qy7GR.s:34: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_usr'
> /tmp/cc4Qy7GR.s:41: Error: Banked registers are not available with this architecture. -- `mrs r3,ELR_hyp'
> /tmp/cc4Qy7GR.s:55: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_svc'
> /tmp/cc4Qy7GR.s:62: Error: Banked registers are not available with this architecture. -- `mrs r3,LR_svc'
> /tmp/cc4Qy7GR.s:69: Error: Banked registers are not available with this architecture. -- `mrs r3,SPSR_svc'
> /tmp/cc4Qy7GR.s:76: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_abt'
>
> Passign the '-march-armv7ve' flag to gcc works, and is ok here, because
> we know the functions won't ever be called on pre-ARMv7VE machines.
> Unfortunately, older compiler versions (4.8 and earlier) do not understand
> that flag, so we still need to keep the asm around.
Does "not understand" mean "ignores" or do we get an error?
>
> Backporting to stable kernels (4.6+) is needed to allow those to be built
> with future compilers as well.
This builds on the toolchains I have on my machine, so:
Acked-by: Christoffer Dall <[email protected]>
Are you applying this via a tree with other fixes or would you like me
to carry it in the kvmarm tree?
Thanks,
-Christoffer
>
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84129
> Fixes: 33280b4cd1dc ("ARM: KVM: Add banked registers save/restore")
> Cc: [email protected]
> Signed-off-by: Arnd Bergmann <[email protected]>
> ---
> arch/arm/kvm/hyp/Makefile | 5 +++++
> arch/arm/kvm/hyp/banked-sr.c | 4 ++++
> 2 files changed, 9 insertions(+)
>
> diff --git a/arch/arm/kvm/hyp/Makefile b/arch/arm/kvm/hyp/Makefile
> index 5638ce0c9524..63d6b404d88e 100644
> --- a/arch/arm/kvm/hyp/Makefile
> +++ b/arch/arm/kvm/hyp/Makefile
> @@ -7,6 +7,8 @@ ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING
>
> KVM=../../../../virt/kvm
>
> +CFLAGS_ARMV7VE :=$(call cc-option, -march=armv7ve)
> +
> obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/vgic-v2-sr.o
> obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/vgic-v3-sr.o
> obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/timer-sr.o
> @@ -15,7 +17,10 @@ obj-$(CONFIG_KVM_ARM_HOST) += tlb.o
> obj-$(CONFIG_KVM_ARM_HOST) += cp15-sr.o
> obj-$(CONFIG_KVM_ARM_HOST) += vfp.o
> obj-$(CONFIG_KVM_ARM_HOST) += banked-sr.o
> +CFLAGS_banked-sr.o += $(CFLAGS_ARMV7VE)
> +
> obj-$(CONFIG_KVM_ARM_HOST) += entry.o
> obj-$(CONFIG_KVM_ARM_HOST) += hyp-entry.o
> obj-$(CONFIG_KVM_ARM_HOST) += switch.o
> +CFLAGS_switch.o += $(CFLAGS_ARMV7VE)
> obj-$(CONFIG_KVM_ARM_HOST) += s2-setup.o
> diff --git a/arch/arm/kvm/hyp/banked-sr.c b/arch/arm/kvm/hyp/banked-sr.c
> index 111bda8cdebd..be4b8b0a40ad 100644
> --- a/arch/arm/kvm/hyp/banked-sr.c
> +++ b/arch/arm/kvm/hyp/banked-sr.c
> @@ -20,6 +20,10 @@
>
> #include <asm/kvm_hyp.h>
>
> +/*
> + * gcc before 4.9 doesn't understand -march=armv7ve, so we have to
> + * trick the assembler.
> + */
> __asm__(".arch_extension virt");
>
> void __hyp_text __banked_save_state(struct kvm_cpu_context *ctxt)
> --
> 2.9.0
>
On Sun, Feb 4, 2018 at 7:45 PM, Christoffer Dall
<[email protected]> wrote:
> Hi Arnd,
>
> On Fri, Feb 02, 2018 at 04:07:34PM +0100, Arnd Bergmann wrote:
>> In banked-sr.c, we use a top-level '__asm__(".arch_extension virt")'
>> statement to allow compilation of a multi-CPU kernel for ARMv6
>> and older ARMv7-A that don't normally support access to the banked
>> registers.
>>
>> This is considered to be a programming error by the gcc developers
>> and will no longer work in gcc-8, where we now get a build error:
>>
>> /tmp/cc4Qy7GR.s:34: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_usr'
>> /tmp/cc4Qy7GR.s:41: Error: Banked registers are not available with this architecture. -- `mrs r3,ELR_hyp'
>> /tmp/cc4Qy7GR.s:55: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_svc'
>> /tmp/cc4Qy7GR.s:62: Error: Banked registers are not available with this architecture. -- `mrs r3,LR_svc'
>> /tmp/cc4Qy7GR.s:69: Error: Banked registers are not available with this architecture. -- `mrs r3,SPSR_svc'
>> /tmp/cc4Qy7GR.s:76: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_abt'
>>
>> Passign the '-march-armv7ve' flag to gcc works, and is ok here, because
>> we know the functions won't ever be called on pre-ARMv7VE machines.
>> Unfortunately, older compiler versions (4.8 and earlier) do not understand
>> that flag, so we still need to keep the asm around.
>
> Does "not understand" mean "ignores" or do we get an error?
We get an error, which is why I used the $(call cc-option) Makefile
helper to check if the compiler supports it.
>> Backporting to stable kernels (4.6+) is needed to allow those to be built
>> with future compilers as well.
>
> This builds on the toolchains I have on my machine, so:
>
> Acked-by: Christoffer Dall <[email protected]>
>
> Are you applying this via a tree with other fixes or would you like me
> to carry it in the kvmarm tree?
Please pick it up in your tree.
Thanks,
Arnd
On Sun, Feb 04, 2018 at 09:57:49PM +0100, Arnd Bergmann wrote:
> On Sun, Feb 4, 2018 at 7:45 PM, Christoffer Dall
> <[email protected]> wrote:
> > Hi Arnd,
> >
> > On Fri, Feb 02, 2018 at 04:07:34PM +0100, Arnd Bergmann wrote:
> >> In banked-sr.c, we use a top-level '__asm__(".arch_extension virt")'
> >> statement to allow compilation of a multi-CPU kernel for ARMv6
> >> and older ARMv7-A that don't normally support access to the banked
> >> registers.
> >>
> >> This is considered to be a programming error by the gcc developers
> >> and will no longer work in gcc-8, where we now get a build error:
> >>
> >> /tmp/cc4Qy7GR.s:34: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_usr'
> >> /tmp/cc4Qy7GR.s:41: Error: Banked registers are not available with this architecture. -- `mrs r3,ELR_hyp'
> >> /tmp/cc4Qy7GR.s:55: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_svc'
> >> /tmp/cc4Qy7GR.s:62: Error: Banked registers are not available with this architecture. -- `mrs r3,LR_svc'
> >> /tmp/cc4Qy7GR.s:69: Error: Banked registers are not available with this architecture. -- `mrs r3,SPSR_svc'
> >> /tmp/cc4Qy7GR.s:76: Error: Banked registers are not available with this architecture. -- `mrs r3,SP_abt'
> >>
> >> Passign the '-march-armv7ve' flag to gcc works, and is ok here, because
> >> we know the functions won't ever be called on pre-ARMv7VE machines.
> >> Unfortunately, older compiler versions (4.8 and earlier) do not understand
> >> that flag, so we still need to keep the asm around.
> >
> > Does "not understand" mean "ignores" or do we get an error?
>
> We get an error, which is why I used the $(call cc-option) Makefile
> helper to check if the compiler supports it.
>
Right.
> >> Backporting to stable kernels (4.6+) is needed to allow those to be built
> >> with future compilers as well.
> >
> > This builds on the toolchains I have on my machine, so:
> >
> > Acked-by: Christoffer Dall <[email protected]>
> >
> > Are you applying this via a tree with other fixes or would you like me
> > to carry it in the kvmarm tree?
>
> Please pick it up in your tree.
>
Will do.
Thanks,
-Christoffer