[PATCHv3] mips: Do not include hi and lo in clobber list for R6

[PATCHv3] mips: Do not include hi and lo in clobber list for R6

[Romain Naour]

From [1]
"GCC 10 (PR 91233) won't silently allow registers that are not architecturally
available to be present in the clobber list anymore, resulting in build failure
for mips*r6 targets in form of:
...
.../sysdep.h:146:2: error: the register ‘lo’ cannot be clobbered in ‘asm’ for the current target
  146 |  __asm__ volatile (      \
      |  ^~~~~~~

This is because base R6 ISA doesn't define hi and lo registers w/o DSP extension.
This patch provides the alternative clobber list for r6 targets that won't include
those registers."

Since kernel 5.4 and mips support for generic vDSO [2], the kernel fail to build
for mips r6 cpus with gcc 10 for the same reason as glibc.

[1] https://sourceware.org/git/?p=glibc.git;a=commit;h=020b2a97bb15f807c0482f0faee2184ed05bcad8
[2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=24640f233b466051ad3a5d2786d2951e43026c9d

Signed-off-by: Romain Naour <romain.naour@gmail.com>
---
v3 Avoid duplicate code (Maciej W. Rozycki)
v2 use MIPS_ISA_REV instead of __mips_isa_rev (Alexander Lobakin)
---
 arch/mips/include/asm/vdso/gettimeofday.h | 30 +++++++++++++++++++----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/arch/mips/include/asm/vdso/gettimeofday.h b/arch/mips/include/asm/vdso/gettimeofday.h
index c63ddcaea54c..93008551282e 100644
--- a/arch/mips/include/asm/vdso/gettimeofday.h
+++ b/arch/mips/include/asm/vdso/gettimeofday.h
@@ -35,7 +35,11 @@ static __always_inline long gettimeofday_fallback(
 	: "=r" (ret), "=r" (error)
 	: "r" (tv), "r" (tz), "r" (nr)
 	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
-	  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
+	  "$14", "$15", "$24", "$25",
+#if MIPS_ISA_REV < 6
+	  "hi", "lo",
+#endif
+          "memory");
 
 	return error ? -ret : ret;
 }
@@ -59,7 +63,11 @@ static __always_inline long clock_gettime_fallback(
 	: "=r" (ret), "=r" (error)
 	: "r" (clkid), "r" (ts), "r" (nr)
 	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
-	  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
+	  "$14", "$15", "$24", "$25",
+#if MIPS_ISA_REV < 6
+	  "hi", "lo",
+#endif
+	  "memory");
 
 	return error ? -ret : ret;
 }
@@ -83,7 +91,11 @@ static __always_inline int clock_getres_fallback(
 	: "=r" (ret), "=r" (error)
 	: "r" (clkid), "r" (ts), "r" (nr)
 	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
-	  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
+	  "$14", "$15", "$24", "$25",
+#if MIPS_ISA_REV < 6
+	  "hi", "lo",
+#endif
+	  "memory");
 
 	return error ? -ret : ret;
 }
@@ -105,7 +117,11 @@ static __always_inline long clock_gettime32_fallback(
 	: "=r" (ret), "=r" (error)
 	: "r" (clkid), "r" (ts), "r" (nr)
 	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
-	  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
+	  "$14", "$15", "$24", "$25",
+#if MIPS_ISA_REV < 6
+	  "hi", "lo",
+#endif
+	  "memory");
 
 	return error ? -ret : ret;
 }
@@ -125,7 +141,11 @@ static __always_inline int clock_getres32_fallback(
 	: "=r" (ret), "=r" (error)
 	: "r" (clkid), "r" (ts), "r" (nr)
 	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
-	  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
+	  "$14", "$15", "$24", "$25",
+#if MIPS_ISA_REV < 6
+	  "hi", "lo",
+#endif
+	  "memory");
 
 	return error ? -ret : ret;
 }
-- 
2.25.4

Re: [PATCHv3] mips: Do not include hi and lo in clobber list for R6

[Maciej W. Rozycki]

On Sat, 1 Aug 2020, Romain Naour wrote:

> v3 Avoid duplicate code (Maciej W. Rozycki)
> v2 use MIPS_ISA_REV instead of __mips_isa_rev (Alexander Lobakin)
> ---
>  arch/mips/include/asm/vdso/gettimeofday.h | 30 +++++++++++++++++++----
>  1 file changed, 25 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/mips/include/asm/vdso/gettimeofday.h b/arch/mips/include/asm/vdso/gettimeofday.h
> index c63ddcaea54c..93008551282e 100644
> --- a/arch/mips/include/asm/vdso/gettimeofday.h
> +++ b/arch/mips/include/asm/vdso/gettimeofday.h
> @@ -35,7 +35,11 @@ static __always_inline long gettimeofday_fallback(
>  	: "=r" (ret), "=r" (error)
>  	: "r" (tv), "r" (tz), "r" (nr)
>  	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
> -	  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
> +	  "$14", "$15", "$24", "$25",
> +#if MIPS_ISA_REV < 6
> +	  "hi", "lo",
> +#endif
> +          "memory");

 Can you please use a helper macro, say GCC_REGS_HI_LO, moving the details 
into a separate header, just as I suggested with examples given?  My very 
point was to avoid `#if MIPS_ISA_REV < 6' sprinkled throughout code.

 Also I note all the clobbers are the same across all the syscalls used 
here, so another possibility is to have a macro like VDSO_SYSCALL_CLOBBERS 
defined in a single place according to the architecture level, and then 
just use it throughout avoiding code duplication.

  Maciej