[PATCH v4] mips: Do not include hi and lo in clobber list for R6

[Sudip Mukherjee]

From: Romain Naour <romain.naour@xxxxxxxxx>

>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] '24640f233b46 ("mips: Add support for generic vDSO")'

Signed-off-by: Romain Naour <romain.naour@xxxxxxxxx>
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@xxxxxxxxx>
---

v4: [sudip] added macro VDSO_SYSCALL_CLOBBERS and fix checkpatch errors with commit message.
v3 Avoid duplicate code (Maciej W. Rozycki)
v2 use MIPS_ISA_REV instead of __mips_isa_rev (Alexander Lobakin)

I have reused the original patch by Romain and have retained his s-o-b
and author name as he is the original author of this patch. I have just
added the macro. Build tested with gcc-10.3.1 and gcc-9.3.0.

 arch/mips/include/asm/vdso/gettimeofday.h | 26 ++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/arch/mips/include/asm/vdso/gettimeofday.h b/arch/mips/include/asm/vdso/gettimeofday.h
index 2203e2d0ae2a..44a45f3fa4b0 100644
--- a/arch/mips/include/asm/vdso/gettimeofday.h
+++ b/arch/mips/include/asm/vdso/gettimeofday.h
@@ -20,6 +20,12 @@
 
 #define VDSO_HAS_CLOCK_GETRES		1
 
+#if MIPS_ISA_REV < 6
+#define VDSO_SYSCALL_CLOBBERS "hi", "lo",
+#else
+#define VDSO_SYSCALL_CLOBBERS
+#endif
+
 static __always_inline long gettimeofday_fallback(
 				struct __kernel_old_timeval *_tv,
 				struct timezone *_tz)
@@ -35,7 +41,9 @@ 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",
+	  VDSO_SYSCALL_CLOBBERS
+	  "memory");
 
 	return error ? -ret : ret;
 }
@@ -59,7 +67,9 @@ 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",
+	  VDSO_SYSCALL_CLOBBERS
+	  "memory");
 
 	return error ? -ret : ret;
 }
@@ -83,7 +93,9 @@ 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",
+	  VDSO_SYSCALL_CLOBBERS
+	  "memory");
 
 	return error ? -ret : ret;
 }
@@ -105,7 +117,9 @@ 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",
+	  VDSO_SYSCALL_CLOBBERS
+	  "memory");
 
 	return error ? -ret : ret;
 }
@@ -125,7 +139,9 @@ 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",
+	  VDSO_SYSCALL_CLOBBERS
+	  "memory");
 
 	return error ? -ret : ret;
 }
-- 
2.30.2