[PATCH] arm64: Work around broken GCC handling of "S" constraint

[PATCH] arm64: Work around broken GCC handling of "S" constraint

[Marc Zyngier]

GCC 4.9 seems to have a problem with the "S" asm constraint
when the symbol lives in the same compilation unit, and pretends
the constraint is impossible:

$ cat x.c
void *foo(void)
{
	static int x;
	int *addr;
	asm("adrp %0, %1" : "=r" (addr) : "S" (&x));
	return addr;
}

$ ~/Work/gcc-linaro-aarch64-linux-gnu-4.9-2014.09_linux/bin/aarch64-linux-gnu-gcc -S -x c -O2 x.c
x.c: In function ‘foo’:
x.c:5:2: error: impossible constraint in ‘asm’
  asm("adrp %0, %1" : "=r" (addr) : "S" (&x));
  ^

Boo. Following revisions of the compiler work just fine, though.

We can fallback to the "i" constraint in that case, which
*seems* to do the right thing. Hopefully we will be able to
remove this at some point, but in the meantime this gets us going.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/Makefile              | 9 +++++++++
 arch/arm64/include/asm/kvm_asm.h | 8 +++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 5789c2d18d43..c4ee8e64ad1a 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -44,12 +44,21 @@ cc_has_k_constraint := $(call try-run,echo				\
 		return 0;						\
 	}' | $(CC) -S -x c -o "$$TMP" -,,-DCONFIG_CC_HAS_K_CONSTRAINT=1)
 
+cc_has_broken_s_constraint := $(call try-run,echo			\
+	'void *foo(void) {						\
+		static int x;						\
+		int *addr;						\
+		asm("adrp %0, %1" : "=r" (addr) : "S" (&x));		\
+		return addr;						\
+	}' | $(CC) -S -x c -c -O2 -o "$$TMP" -,,-DCONFIG_CC_HAS_BROKEN_S_CONSTRAINT=1)
+
 ifeq ($(CONFIG_BROKEN_GAS_INST),y)
 $(warning Detected assembler with broken .inst; disassembly will be unreliable)
 endif
 
 KBUILD_CFLAGS	+= -mgeneral-regs-only	\
 		   $(compat_vdso) $(cc_has_k_constraint)
+KBUILD_CFLAGS	+= $(cc_has_broken_s_constraint)
 KBUILD_CFLAGS	+= $(call cc-disable-warning, psabi)
 KBUILD_AFLAGS	+= $(compat_vdso)
 
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 7ccf770c53d9..fa8e886998a3 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -199,6 +199,12 @@ extern void __vgic_v3_init_lrs(void);
 
 extern u32 __kvm_get_mdcr_el2(void);
 
+#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
+#define SYM_CONSTRAINT	"i"
+#else
+#define SYM_CONSTRAINT	"S"
+#endif
+
 /*
  * Obtain the PC-relative address of a kernel symbol
  * s: symbol
@@ -215,7 +221,7 @@ extern u32 __kvm_get_mdcr_el2(void);
 		typeof(s) *addr;					\
 		asm("adrp	%0, %1\n"				\
 		    "add	%0, %0, :lo12:%1\n"			\
-		    : "=r" (addr) : "S" (&s));				\
+		    : "=r" (addr) : SYM_CONSTRAINT (&s));		\
 		addr;							\
 	})
 
-- 
2.29.2

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[PATCH] arm64: Work around broken GCC handling of "S" constraint

[Marc Zyngier]

GCC 4.9 seems to have a problem with the "S" asm constraint
when the symbol lives in the same compilation unit, and pretends
the constraint is impossible:

$ cat x.c
void *foo(void)
{
	static int x;
	int *addr;
	asm("adrp %0, %1" : "=r" (addr) : "S" (&x));
	return addr;
}

$ ~/Work/gcc-linaro-aarch64-linux-gnu-4.9-2014.09_linux/bin/aarch64-linux-gnu-gcc -S -x c -O2 x.c
x.c: In function ‘foo’:
x.c:5:2: error: impossible constraint in ‘asm’
  asm("adrp %0, %1" : "=r" (addr) : "S" (&x));
  ^

Boo. Following revisions of the compiler work just fine, though.

We can fallback to the "i" constraint in that case, which
*seems* to do the right thing. Hopefully we will be able to
remove this at some point, but in the meantime this gets us going.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/Makefile              | 9 +++++++++
 arch/arm64/include/asm/kvm_asm.h | 8 +++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 5789c2d18d43..c4ee8e64ad1a 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -44,12 +44,21 @@ cc_has_k_constraint := $(call try-run,echo				\
 		return 0;						\
 	}' | $(CC) -S -x c -o "$$TMP" -,,-DCONFIG_CC_HAS_K_CONSTRAINT=1)
 
+cc_has_broken_s_constraint := $(call try-run,echo			\
+	'void *foo(void) {						\
+		static int x;						\
+		int *addr;						\
+		asm("adrp %0, %1" : "=r" (addr) : "S" (&x));		\
+		return addr;						\
+	}' | $(CC) -S -x c -c -O2 -o "$$TMP" -,,-DCONFIG_CC_HAS_BROKEN_S_CONSTRAINT=1)
+
 ifeq ($(CONFIG_BROKEN_GAS_INST),y)
 $(warning Detected assembler with broken .inst; disassembly will be unreliable)
 endif
 
 KBUILD_CFLAGS	+= -mgeneral-regs-only	\
 		   $(compat_vdso) $(cc_has_k_constraint)
+KBUILD_CFLAGS	+= $(cc_has_broken_s_constraint)
 KBUILD_CFLAGS	+= $(call cc-disable-warning, psabi)
 KBUILD_AFLAGS	+= $(compat_vdso)
 
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 7ccf770c53d9..fa8e886998a3 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -199,6 +199,12 @@ extern void __vgic_v3_init_lrs(void);
 
 extern u32 __kvm_get_mdcr_el2(void);
 
+#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
+#define SYM_CONSTRAINT	"i"
+#else
+#define SYM_CONSTRAINT	"S"
+#endif
+
 /*
  * Obtain the PC-relative address of a kernel symbol
  * s: symbol
@@ -215,7 +221,7 @@ extern u32 __kvm_get_mdcr_el2(void);
 		typeof(s) *addr;					\
 		asm("adrp	%0, %1\n"				\
 		    "add	%0, %0, :lo12:%1\n"			\
-		    : "=r" (addr) : "S" (&s));				\
+		    : "=r" (addr) : SYM_CONSTRAINT (&s));		\
 		addr;							\
 	})
 
-- 
2.29.2


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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Ard Biesheuvel]

On Mon, 7 Dec 2020 at 16:43, Marc Zyngier <maz@kernel.org> wrote:
>
> GCC 4.9 seems to have a problem with the "S" asm constraint
> when the symbol lives in the same compilation unit, and pretends
> the constraint is impossible:
>
> $ cat x.c
> void *foo(void)
> {
>         static int x;
>         int *addr;
>         asm("adrp %0, %1" : "=r" (addr) : "S" (&x));
>         return addr;
> }
>
> $ ~/Work/gcc-linaro-aarch64-linux-gnu-4.9-2014.09_linux/bin/aarch64-linux-gnu-gcc -S -x c -O2 x.c
> x.c: In function ‘foo’:
> x.c:5:2: error: impossible constraint in ‘asm’
>   asm("adrp %0, %1" : "=r" (addr) : "S" (&x));
>   ^
>
> Boo. Following revisions of the compiler work just fine, though.
>
> We can fallback to the "i" constraint in that case, which
> *seems* to do the right thing. Hopefully we will be able to
> remove this at some point, but in the meantime this gets us going.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>

> ---
>  arch/arm64/Makefile              | 9 +++++++++
>  arch/arm64/include/asm/kvm_asm.h | 8 +++++++-
>  2 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 5789c2d18d43..c4ee8e64ad1a 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -44,12 +44,21 @@ cc_has_k_constraint := $(call try-run,echo                          \
>                 return 0;                                               \
>         }' | $(CC) -S -x c -o "$$TMP" -,,-DCONFIG_CC_HAS_K_CONSTRAINT=1)
>
> +cc_has_broken_s_constraint := $(call try-run,echo                      \
> +       'void *foo(void) {                                              \
> +               static int x;                                           \
> +               int *addr;                                              \
> +               asm("adrp %0, %1" : "=r" (addr) : "S" (&x));            \
> +               return addr;                                            \
> +       }' | $(CC) -S -x c -c -O2 -o "$$TMP" -,,-DCONFIG_CC_HAS_BROKEN_S_CONSTRAINT=1)
> +
>  ifeq ($(CONFIG_BROKEN_GAS_INST),y)
>  $(warning Detected assembler with broken .inst; disassembly will be unreliable)
>  endif
>
>  KBUILD_CFLAGS  += -mgeneral-regs-only  \
>                    $(compat_vdso) $(cc_has_k_constraint)
> +KBUILD_CFLAGS  += $(cc_has_broken_s_constraint)
>  KBUILD_CFLAGS  += $(call cc-disable-warning, psabi)
>  KBUILD_AFLAGS  += $(compat_vdso)
>
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 7ccf770c53d9..fa8e886998a3 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -199,6 +199,12 @@ extern void __vgic_v3_init_lrs(void);
>
>  extern u32 __kvm_get_mdcr_el2(void);
>
> +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
> +#define SYM_CONSTRAINT "i"
> +#else
> +#define SYM_CONSTRAINT "S"
> +#endif
> +

Could we just check GCC_VERSION here?

>  /*
>   * Obtain the PC-relative address of a kernel symbol
>   * s: symbol
> @@ -215,7 +221,7 @@ extern u32 __kvm_get_mdcr_el2(void);
>                 typeof(s) *addr;                                        \
>                 asm("adrp       %0, %1\n"                               \
>                     "add        %0, %0, :lo12:%1\n"                     \
> -                   : "=r" (addr) : "S" (&s));                          \
> +                   : "=r" (addr) : SYM_CONSTRAINT (&s));               \
>                 addr;                                                   \
>         })
>
> --
> 2.29.2
>
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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Ard Biesheuvel]

On Mon, 7 Dec 2020 at 16:43, Marc Zyngier <maz@kernel.org> wrote:
>
> GCC 4.9 seems to have a problem with the "S" asm constraint
> when the symbol lives in the same compilation unit, and pretends
> the constraint is impossible:
>
> $ cat x.c
> void *foo(void)
> {
>         static int x;
>         int *addr;
>         asm("adrp %0, %1" : "=r" (addr) : "S" (&x));
>         return addr;
> }
>
> $ ~/Work/gcc-linaro-aarch64-linux-gnu-4.9-2014.09_linux/bin/aarch64-linux-gnu-gcc -S -x c -O2 x.c
> x.c: In function ‘foo’:
> x.c:5:2: error: impossible constraint in ‘asm’
>   asm("adrp %0, %1" : "=r" (addr) : "S" (&x));
>   ^
>
> Boo. Following revisions of the compiler work just fine, though.
>
> We can fallback to the "i" constraint in that case, which
> *seems* to do the right thing. Hopefully we will be able to
> remove this at some point, but in the meantime this gets us going.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>

> ---
>  arch/arm64/Makefile              | 9 +++++++++
>  arch/arm64/include/asm/kvm_asm.h | 8 +++++++-
>  2 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> index 5789c2d18d43..c4ee8e64ad1a 100644
> --- a/arch/arm64/Makefile
> +++ b/arch/arm64/Makefile
> @@ -44,12 +44,21 @@ cc_has_k_constraint := $(call try-run,echo                          \
>                 return 0;                                               \
>         }' | $(CC) -S -x c -o "$$TMP" -,,-DCONFIG_CC_HAS_K_CONSTRAINT=1)
>
> +cc_has_broken_s_constraint := $(call try-run,echo                      \
> +       'void *foo(void) {                                              \
> +               static int x;                                           \
> +               int *addr;                                              \
> +               asm("adrp %0, %1" : "=r" (addr) : "S" (&x));            \
> +               return addr;                                            \
> +       }' | $(CC) -S -x c -c -O2 -o "$$TMP" -,,-DCONFIG_CC_HAS_BROKEN_S_CONSTRAINT=1)
> +
>  ifeq ($(CONFIG_BROKEN_GAS_INST),y)
>  $(warning Detected assembler with broken .inst; disassembly will be unreliable)
>  endif
>
>  KBUILD_CFLAGS  += -mgeneral-regs-only  \
>                    $(compat_vdso) $(cc_has_k_constraint)
> +KBUILD_CFLAGS  += $(cc_has_broken_s_constraint)
>  KBUILD_CFLAGS  += $(call cc-disable-warning, psabi)
>  KBUILD_AFLAGS  += $(compat_vdso)
>
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 7ccf770c53d9..fa8e886998a3 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -199,6 +199,12 @@ extern void __vgic_v3_init_lrs(void);
>
>  extern u32 __kvm_get_mdcr_el2(void);
>
> +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
> +#define SYM_CONSTRAINT "i"
> +#else
> +#define SYM_CONSTRAINT "S"
> +#endif
> +

Could we just check GCC_VERSION here?

>  /*
>   * Obtain the PC-relative address of a kernel symbol
>   * s: symbol
> @@ -215,7 +221,7 @@ extern u32 __kvm_get_mdcr_el2(void);
>                 typeof(s) *addr;                                        \
>                 asm("adrp       %0, %1\n"                               \
>                     "add        %0, %0, :lo12:%1\n"                     \
> -                   : "=r" (addr) : "S" (&s));                          \
> +                   : "=r" (addr) : SYM_CONSTRAINT (&s));               \
>                 addr;                                                   \
>         })
>
> --
> 2.29.2
>

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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Ard Biesheuvel]

(resend with David's email address fixed)

On Mon, 7 Dec 2020 at 18:17, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Mon, 7 Dec 2020 at 16:43, Marc Zyngier <maz@kernel.org> wrote:
> >
> > GCC 4.9 seems to have a problem with the "S" asm constraint
> > when the symbol lives in the same compilation unit, and pretends
> > the constraint is impossible:
> >
> > $ cat x.c
> > void *foo(void)
> > {
> >         static int x;
> >         int *addr;
> >         asm("adrp %0, %1" : "=r" (addr) : "S" (&x));
> >         return addr;
> > }
> >
> > $ ~/Work/gcc-linaro-aarch64-linux-gnu-4.9-2014.09_linux/bin/aarch64-linux-gnu-gcc -S -x c -O2 x.c
> > x.c: In function ‘foo’:
> > x.c:5:2: error: impossible constraint in ‘asm’
> >   asm("adrp %0, %1" : "=r" (addr) : "S" (&x));
> >   ^
> >
> > Boo. Following revisions of the compiler work just fine, though.
> >
> > We can fallback to the "i" constraint in that case, which
> > *seems* to do the right thing. Hopefully we will be able to
> > remove this at some point, but in the meantime this gets us going.
> >
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
>
> > ---
> >  arch/arm64/Makefile              | 9 +++++++++
> >  arch/arm64/include/asm/kvm_asm.h | 8 +++++++-
> >  2 files changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> > index 5789c2d18d43..c4ee8e64ad1a 100644
> > --- a/arch/arm64/Makefile
> > +++ b/arch/arm64/Makefile
> > @@ -44,12 +44,21 @@ cc_has_k_constraint := $(call try-run,echo                          \
> >                 return 0;                                               \
> >         }' | $(CC) -S -x c -o "$$TMP" -,,-DCONFIG_CC_HAS_K_CONSTRAINT=1)
> >
> > +cc_has_broken_s_constraint := $(call try-run,echo                      \
> > +       'void *foo(void) {                                              \
> > +               static int x;                                           \
> > +               int *addr;                                              \
> > +               asm("adrp %0, %1" : "=r" (addr) : "S" (&x));            \
> > +               return addr;                                            \
> > +       }' | $(CC) -S -x c -c -O2 -o "$$TMP" -,,-DCONFIG_CC_HAS_BROKEN_S_CONSTRAINT=1)
> > +
> >  ifeq ($(CONFIG_BROKEN_GAS_INST),y)
> >  $(warning Detected assembler with broken .inst; disassembly will be unreliable)
> >  endif
> >
> >  KBUILD_CFLAGS  += -mgeneral-regs-only  \
> >                    $(compat_vdso) $(cc_has_k_constraint)
> > +KBUILD_CFLAGS  += $(cc_has_broken_s_constraint)
> >  KBUILD_CFLAGS  += $(call cc-disable-warning, psabi)
> >  KBUILD_AFLAGS  += $(compat_vdso)
> >
> > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> > index 7ccf770c53d9..fa8e886998a3 100644
> > --- a/arch/arm64/include/asm/kvm_asm.h
> > +++ b/arch/arm64/include/asm/kvm_asm.h
> > @@ -199,6 +199,12 @@ extern void __vgic_v3_init_lrs(void);
> >
> >  extern u32 __kvm_get_mdcr_el2(void);
> >
> > +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
> > +#define SYM_CONSTRAINT "i"
> > +#else
> > +#define SYM_CONSTRAINT "S"
> > +#endif
> > +
>
> Could we just check GCC_VERSION here?
>
> >  /*
> >   * Obtain the PC-relative address of a kernel symbol
> >   * s: symbol
> > @@ -215,7 +221,7 @@ extern u32 __kvm_get_mdcr_el2(void);
> >                 typeof(s) *addr;                                        \
> >                 asm("adrp       %0, %1\n"                               \
> >                     "add        %0, %0, :lo12:%1\n"                     \
> > -                   : "=r" (addr) : "S" (&s));                          \
> > +                   : "=r" (addr) : SYM_CONSTRAINT (&s));               \
> >                 addr;                                                   \
> >         })
> >
> > --
> > 2.29.2
> >
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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Ard Biesheuvel]

(resend with David's email address fixed)

On Mon, 7 Dec 2020 at 18:17, Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Mon, 7 Dec 2020 at 16:43, Marc Zyngier <maz@kernel.org> wrote:
> >
> > GCC 4.9 seems to have a problem with the "S" asm constraint
> > when the symbol lives in the same compilation unit, and pretends
> > the constraint is impossible:
> >
> > $ cat x.c
> > void *foo(void)
> > {
> >         static int x;
> >         int *addr;
> >         asm("adrp %0, %1" : "=r" (addr) : "S" (&x));
> >         return addr;
> > }
> >
> > $ ~/Work/gcc-linaro-aarch64-linux-gnu-4.9-2014.09_linux/bin/aarch64-linux-gnu-gcc -S -x c -O2 x.c
> > x.c: In function ‘foo’:
> > x.c:5:2: error: impossible constraint in ‘asm’
> >   asm("adrp %0, %1" : "=r" (addr) : "S" (&x));
> >   ^
> >
> > Boo. Following revisions of the compiler work just fine, though.
> >
> > We can fallback to the "i" constraint in that case, which
> > *seems* to do the right thing. Hopefully we will be able to
> > remove this at some point, but in the meantime this gets us going.
> >
> > Signed-off-by: Marc Zyngier <maz@kernel.org>
>
> > ---
> >  arch/arm64/Makefile              | 9 +++++++++
> >  arch/arm64/include/asm/kvm_asm.h | 8 +++++++-
> >  2 files changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> > index 5789c2d18d43..c4ee8e64ad1a 100644
> > --- a/arch/arm64/Makefile
> > +++ b/arch/arm64/Makefile
> > @@ -44,12 +44,21 @@ cc_has_k_constraint := $(call try-run,echo                          \
> >                 return 0;                                               \
> >         }' | $(CC) -S -x c -o "$$TMP" -,,-DCONFIG_CC_HAS_K_CONSTRAINT=1)
> >
> > +cc_has_broken_s_constraint := $(call try-run,echo                      \
> > +       'void *foo(void) {                                              \
> > +               static int x;                                           \
> > +               int *addr;                                              \
> > +               asm("adrp %0, %1" : "=r" (addr) : "S" (&x));            \
> > +               return addr;                                            \
> > +       }' | $(CC) -S -x c -c -O2 -o "$$TMP" -,,-DCONFIG_CC_HAS_BROKEN_S_CONSTRAINT=1)
> > +
> >  ifeq ($(CONFIG_BROKEN_GAS_INST),y)
> >  $(warning Detected assembler with broken .inst; disassembly will be unreliable)
> >  endif
> >
> >  KBUILD_CFLAGS  += -mgeneral-regs-only  \
> >                    $(compat_vdso) $(cc_has_k_constraint)
> > +KBUILD_CFLAGS  += $(cc_has_broken_s_constraint)
> >  KBUILD_CFLAGS  += $(call cc-disable-warning, psabi)
> >  KBUILD_AFLAGS  += $(compat_vdso)
> >
> > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> > index 7ccf770c53d9..fa8e886998a3 100644
> > --- a/arch/arm64/include/asm/kvm_asm.h
> > +++ b/arch/arm64/include/asm/kvm_asm.h
> > @@ -199,6 +199,12 @@ extern void __vgic_v3_init_lrs(void);
> >
> >  extern u32 __kvm_get_mdcr_el2(void);
> >
> > +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
> > +#define SYM_CONSTRAINT "i"
> > +#else
> > +#define SYM_CONSTRAINT "S"
> > +#endif
> > +
>
> Could we just check GCC_VERSION here?
>
> >  /*
> >   * Obtain the PC-relative address of a kernel symbol
> >   * s: symbol
> > @@ -215,7 +221,7 @@ extern u32 __kvm_get_mdcr_el2(void);
> >                 typeof(s) *addr;                                        \
> >                 asm("adrp       %0, %1\n"                               \
> >                     "add        %0, %0, :lo12:%1\n"                     \
> > -                   : "=r" (addr) : "S" (&s));                          \
> > +                   : "=r" (addr) : SYM_CONSTRAINT (&s));               \
> >                 addr;                                                   \
> >         })
> >
> > --
> > 2.29.2
> >

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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Marc Zyngier]

On 2020-12-07 17:19, Ard Biesheuvel wrote:
> (resend with David's email address fixed)

Irk. Thanks for that.

>> > +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
>> > +#define SYM_CONSTRAINT "i"
>> > +#else
>> > +#define SYM_CONSTRAINT "S"
>> > +#endif
>> > +
>> 
>> Could we just check GCC_VERSION here?

I guess we could. But I haven't investigated which exact range of
compiler is broken (GCC 6.3 seems fixed, but that's the oldest
I have apart from the offending 4.9).

         M.
-- 
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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Marc Zyngier]

On 2020-12-07 17:19, Ard Biesheuvel wrote:
> (resend with David's email address fixed)

Irk. Thanks for that.

>> > +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
>> > +#define SYM_CONSTRAINT "i"
>> > +#else
>> > +#define SYM_CONSTRAINT "S"
>> > +#endif
>> > +
>> 
>> Could we just check GCC_VERSION here?

I guess we could. But I haven't investigated which exact range of
compiler is broken (GCC 6.3 seems fixed, but that's the oldest
I have apart from the offending 4.9).

         M.
-- 
Jazz is not dead. It just smells funny...

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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Ard Biesheuvel]

On Mon, 7 Dec 2020 at 18:41, Marc Zyngier <maz@kernel.org> wrote:
>
> On 2020-12-07 17:19, Ard Biesheuvel wrote:
> > (resend with David's email address fixed)
>
> Irk. Thanks for that.
>
> >> > +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
> >> > +#define SYM_CONSTRAINT "i"
> >> > +#else
> >> > +#define SYM_CONSTRAINT "S"
> >> > +#endif
> >> > +
> >>
> >> Could we just check GCC_VERSION here?
>
> I guess we could. But I haven't investigated which exact range of
> compiler is broken (GCC 6.3 seems fixed, but that's the oldest
> I have apart from the offending 4.9).
>

I tried 5.4 on godbolt, and it seems happy. And the failure will be
obvious, so we can afford to get it slightly wrong and refine it
later.
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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Ard Biesheuvel]

On Mon, 7 Dec 2020 at 18:41, Marc Zyngier <maz@kernel.org> wrote:
>
> On 2020-12-07 17:19, Ard Biesheuvel wrote:
> > (resend with David's email address fixed)
>
> Irk. Thanks for that.
>
> >> > +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
> >> > +#define SYM_CONSTRAINT "i"
> >> > +#else
> >> > +#define SYM_CONSTRAINT "S"
> >> > +#endif
> >> > +
> >>
> >> Could we just check GCC_VERSION here?
>
> I guess we could. But I haven't investigated which exact range of
> compiler is broken (GCC 6.3 seems fixed, but that's the oldest
> I have apart from the offending 4.9).
>

I tried 5.4 on godbolt, and it seems happy. And the failure will be
obvious, so we can afford to get it slightly wrong and refine it
later.

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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Robin Murphy]

On 2020-12-07 17:47, Ard Biesheuvel wrote:
> On Mon, 7 Dec 2020 at 18:41, Marc Zyngier <maz@kernel.org> wrote:
>>
>> On 2020-12-07 17:19, Ard Biesheuvel wrote:
>>> (resend with David's email address fixed)
>>
>> Irk. Thanks for that.
>>
>>>>> +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
>>>>> +#define SYM_CONSTRAINT "i"
>>>>> +#else
>>>>> +#define SYM_CONSTRAINT "S"
>>>>> +#endif
>>>>> +
>>>>
>>>> Could we just check GCC_VERSION here?
>>
>> I guess we could. But I haven't investigated which exact range of
>> compiler is broken (GCC 6.3 seems fixed, but that's the oldest
>> I have apart from the offending 4.9).
>>
> 
> I tried 5.4 on godbolt, and it seems happy. And the failure will be
> obvious, so we can afford to get it slightly wrong and refine it
> later.

FWIW the Linaro 14.11, 15.02 and 15.05 releases of GCC 4.9.3 seem to 
build rc7 without complaint. The only thing older that I have to hand is 
Ubuntu's GCC 4.8.4, which Kbuild chokes on entirely now.

Robin.
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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Robin Murphy]

On 2020-12-07 17:47, Ard Biesheuvel wrote:
> On Mon, 7 Dec 2020 at 18:41, Marc Zyngier <maz@kernel.org> wrote:
>>
>> On 2020-12-07 17:19, Ard Biesheuvel wrote:
>>> (resend with David's email address fixed)
>>
>> Irk. Thanks for that.
>>
>>>>> +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
>>>>> +#define SYM_CONSTRAINT "i"
>>>>> +#else
>>>>> +#define SYM_CONSTRAINT "S"
>>>>> +#endif
>>>>> +
>>>>
>>>> Could we just check GCC_VERSION here?
>>
>> I guess we could. But I haven't investigated which exact range of
>> compiler is broken (GCC 6.3 seems fixed, but that's the oldest
>> I have apart from the offending 4.9).
>>
> 
> I tried 5.4 on godbolt, and it seems happy. And the failure will be
> obvious, so we can afford to get it slightly wrong and refine it
> later.

FWIW the Linaro 14.11, 15.02 and 15.05 releases of GCC 4.9.3 seem to 
build rc7 without complaint. The only thing older that I have to hand is 
Ubuntu's GCC 4.8.4, which Kbuild chokes on entirely now.

Robin.

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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Marc Zyngier]

Hi Robin,

On Mon, 07 Dec 2020 18:42:23 +0000,
Robin Murphy <robin.murphy@arm.com> wrote:
> 
> On 2020-12-07 17:47, Ard Biesheuvel wrote:
> > On Mon, 7 Dec 2020 at 18:41, Marc Zyngier <maz@kernel.org> wrote:
> >> 
> >> On 2020-12-07 17:19, Ard Biesheuvel wrote:
> >>> (resend with David's email address fixed)
> >> 
> >> Irk. Thanks for that.
> >> 
> >>>>> +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
> >>>>> +#define SYM_CONSTRAINT "i"
> >>>>> +#else
> >>>>> +#define SYM_CONSTRAINT "S"
> >>>>> +#endif
> >>>>> +
> >>>> 
> >>>> Could we just check GCC_VERSION here?
> >> 
> >> I guess we could. But I haven't investigated which exact range of
> >> compiler is broken (GCC 6.3 seems fixed, but that's the oldest
> >> I have apart from the offending 4.9).
> >> 
> > 
> > I tried 5.4 on godbolt, and it seems happy. And the failure will be
> > obvious, so we can afford to get it slightly wrong and refine it
> > later.
> 
> FWIW the Linaro 14.11, 15.02 and 15.05 releases of GCC 4.9.3 seem to
> build rc7 without complaint. The only thing older that I have to hand
> is Ubuntu's GCC 4.8.4, which Kbuild chokes on entirely now.

Can you try kvmarm/next? David's PSCI relay is breaking badly here.

Thanks,

	M.

-- 
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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Marc Zyngier]

Hi Robin,

On Mon, 07 Dec 2020 18:42:23 +0000,
Robin Murphy <robin.murphy@arm.com> wrote:
> 
> On 2020-12-07 17:47, Ard Biesheuvel wrote:
> > On Mon, 7 Dec 2020 at 18:41, Marc Zyngier <maz@kernel.org> wrote:
> >> 
> >> On 2020-12-07 17:19, Ard Biesheuvel wrote:
> >>> (resend with David's email address fixed)
> >> 
> >> Irk. Thanks for that.
> >> 
> >>>>> +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
> >>>>> +#define SYM_CONSTRAINT "i"
> >>>>> +#else
> >>>>> +#define SYM_CONSTRAINT "S"
> >>>>> +#endif
> >>>>> +
> >>>> 
> >>>> Could we just check GCC_VERSION here?
> >> 
> >> I guess we could. But I haven't investigated which exact range of
> >> compiler is broken (GCC 6.3 seems fixed, but that's the oldest
> >> I have apart from the offending 4.9).
> >> 
> > 
> > I tried 5.4 on godbolt, and it seems happy. And the failure will be
> > obvious, so we can afford to get it slightly wrong and refine it
> > later.
> 
> FWIW the Linaro 14.11, 15.02 and 15.05 releases of GCC 4.9.3 seem to
> build rc7 without complaint. The only thing older that I have to hand
> is Ubuntu's GCC 4.8.4, which Kbuild chokes on entirely now.

Can you try kvmarm/next? David's PSCI relay is breaking badly here.

Thanks,

	M.

-- 
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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Robin Murphy]

On 2020-12-07 19:04, Marc Zyngier wrote:
> Hi Robin,
> 
> On Mon, 07 Dec 2020 18:42:23 +0000,
> Robin Murphy <robin.murphy@arm.com> wrote:
>>
>> On 2020-12-07 17:47, Ard Biesheuvel wrote:
>>> On Mon, 7 Dec 2020 at 18:41, Marc Zyngier <maz@kernel.org> wrote:
>>>>
>>>> On 2020-12-07 17:19, Ard Biesheuvel wrote:
>>>>> (resend with David's email address fixed)
>>>>
>>>> Irk. Thanks for that.
>>>>
>>>>>>> +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
>>>>>>> +#define SYM_CONSTRAINT "i"
>>>>>>> +#else
>>>>>>> +#define SYM_CONSTRAINT "S"
>>>>>>> +#endif
>>>>>>> +
>>>>>>
>>>>>> Could we just check GCC_VERSION here?
>>>>
>>>> I guess we could. But I haven't investigated which exact range of
>>>> compiler is broken (GCC 6.3 seems fixed, but that's the oldest
>>>> I have apart from the offending 4.9).
>>>>
>>>
>>> I tried 5.4 on godbolt, and it seems happy. And the failure will be
>>> obvious, so we can afford to get it slightly wrong and refine it
>>> later.
>>
>> FWIW the Linaro 14.11, 15.02 and 15.05 releases of GCC 4.9.3 seem to
>> build rc7 without complaint. The only thing older that I have to hand
>> is Ubuntu's GCC 4.8.4, which Kbuild chokes on entirely now.
> 
> Can you try kvmarm/next? David's PSCI relay is breaking badly here.

Ah, gotcha... Yes, they're all falling over on that :(

The 15.08 release of 5.1.1 is happy though, so Ard's probably right 
about generalising it to 4.x.

Cheers,
Robin.
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Re: [PATCH] arm64: Work around broken GCC handling of "S" constraint

[Robin Murphy]

On 2020-12-07 19:04, Marc Zyngier wrote:
> Hi Robin,
> 
> On Mon, 07 Dec 2020 18:42:23 +0000,
> Robin Murphy <robin.murphy@arm.com> wrote:
>>
>> On 2020-12-07 17:47, Ard Biesheuvel wrote:
>>> On Mon, 7 Dec 2020 at 18:41, Marc Zyngier <maz@kernel.org> wrote:
>>>>
>>>> On 2020-12-07 17:19, Ard Biesheuvel wrote:
>>>>> (resend with David's email address fixed)
>>>>
>>>> Irk. Thanks for that.
>>>>
>>>>>>> +#ifdef CONFIG_CC_HAS_BROKEN_S_CONSTRAINT
>>>>>>> +#define SYM_CONSTRAINT "i"
>>>>>>> +#else
>>>>>>> +#define SYM_CONSTRAINT "S"
>>>>>>> +#endif
>>>>>>> +
>>>>>>
>>>>>> Could we just check GCC_VERSION here?
>>>>
>>>> I guess we could. But I haven't investigated which exact range of
>>>> compiler is broken (GCC 6.3 seems fixed, but that's the oldest
>>>> I have apart from the offending 4.9).
>>>>
>>>
>>> I tried 5.4 on godbolt, and it seems happy. And the failure will be
>>> obvious, so we can afford to get it slightly wrong and refine it
>>> later.
>>
>> FWIW the Linaro 14.11, 15.02 and 15.05 releases of GCC 4.9.3 seem to
>> build rc7 without complaint. The only thing older that I have to hand
>> is Ubuntu's GCC 4.8.4, which Kbuild chokes on entirely now.
> 
> Can you try kvmarm/next? David's PSCI relay is breaking badly here.

Ah, gotcha... Yes, they're all falling over on that :(

The 15.08 release of 5.1.1 is happy though, so Ard's probably right 
about generalising it to 4.x.

Cheers,
Robin.

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