[PATCH 06/10] powerpc: remove GCC version check for UPD_CONSTR

Now that GCC 5.1 is the minimum supported version, we can drop this
workaround for older versions of GCC. This adversely affected clang,
too.

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <redacted>
Cc: Segher Boessenkool <redacted>
Cc: Christophe Leroy <redacted>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
 arch/powerpc/include/asm/asm-const.h | 10 ----------
 1 file changed, 10 deletions(-)

diff --git a/arch/powerpc/include/asm/asm-const.h b/arch/powerpc/include/asm/asm-const.h
index 0ce2368bd20f..dbfa5e1e3198 100644
--- a/arch/powerpc/include/asm/asm-const.h
+++ b/arch/powerpc/include/asm/asm-const.h

@@ -12,16 +12,6 @@
 #  define ASM_CONST(x)		__ASM_CONST(x)
 #endif
 
-/*
- * Inline assembly memory constraint
- *
- * GCC 4.9 doesn't properly handle pre update memory constraint "m<>"
- *
- */
-#if defined(GCC_VERSION) && GCC_VERSION < 50000
-#define UPD_CONSTR ""
-#else
 #define UPD_CONSTR "<>"
-#endif
 
 #endif /* _ASM_POWERPC_ASM_CONST_H */

-- 
2.33.0.309.g3052b89438-goog

On 9/10/2021 4:40 PM, Nick Desaulniers wrote:

The only reason this exists is because of commit 592bbe9c505d 
("powerpc/uaccess: Don't use "m<>" constraint with GCC 4.9"). It is 
probably just worth sinking "<>" into all of the callsites and removing
UPD_CONSTR.

  
  #endif /* _ASM_POWERPC_ASM_CONST_H */

Nathan Chancellor [off-list ref] writes:

On 9/10/2021 4:40 PM, Nick Desaulniers wrote:

quoted

Now that GCC 5.1 is the minimum supported version, we can drop this
workaround for older versions of GCC. This adversely affected clang,
too.

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <redacted>
Cc: Segher Boessenkool <redacted>
Cc: Christophe Leroy <redacted>
Cc: linuxppc-dev@lists.ozlabs.org
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
---
  arch/powerpc/include/asm/asm-const.h | 10 ----------
  1 file changed, 10 deletions(-)

diff --git a/arch/powerpc/include/asm/asm-const.h b/arch/powerpc/include/asm/asm-const.h
index 0ce2368bd20f..dbfa5e1e3198 100644
--- a/arch/powerpc/include/asm/asm-const.h
+++ b/arch/powerpc/include/asm/asm-const.h

@@ -12,16 +12,6 @@
  #  define ASM_CONST(x)		__ASM_CONST(x)
  #endif
  
-/*
- * Inline assembly memory constraint
- *
- * GCC 4.9 doesn't properly handle pre update memory constraint "m<>"
- *
- */
-#if defined(GCC_VERSION) && GCC_VERSION < 50000
-#define UPD_CONSTR ""
-#else
  #define UPD_CONSTR "<>"
-#endif

The only reason this exists is because of commit 592bbe9c505d 
("powerpc/uaccess: Don't use "m<>" constraint with GCC 4.9"). It is 
probably just worth sinking "<>" into all of the callsites and removing
UPD_CONSTR.

Yeah that would be great if you're doing a v2. Or we can do it as a
follow-up.

cheers

Le 11/09/2021 à 01:40, Nick Desaulniers a écrit :

Now that GCC 5.1 is the minimum supported version, we can drop this
workaround for older versions of GCC. This adversely affected clang,
too.

Why do you say that GCC 5.1 is the minimum supported ?

As far as I can see, the minimum supported is still 4.9, see 
https://github.com/torvalds/linux/blob/master/Documentation/process/changes.rst

There is no point in keeping UPD_CONSTR if it becomes invariant. You 
should just replace all instances of UPD_CONSTR with <> and drop 
UPD_CONSTR completely.

Christophe