fix mips struct stat dev_t members for big endian

the mips version of this structure on the kernel side wrongly has
32-bit type rather than 64-bit type. fortunately there is adjacent
padding to bring it up to 64 bits, and on little-endian, this allows
us to treat the adjacent kernel st_dev and st_pad0[0] as as single
64-bit dev_t. however, on big endian, such treatment results in the
upper and lower 32-bit parts of the dev_t value being swapped. for the
purpose of just comparing st_dev values this did not break anything,
but it precluded actually processing the device numbers as major/minor
values.

since the broken kernel behavior that needs to be worked around is
isolated to one arch, I put the workarounds in syscall_arch.h rather
than adding a stat fixup path in the common code. on little endian
mips, the added code optimizes out completely.

the changes necessary were incompatible with the way the __asm_syscall
macro was factored so I just removed it and flattened the individual
__syscallN functions. this arguably makes the code easier to read and
understand, anyway.

arch/mips/syscall_arch.h

@@ -7,29 +7,44 @@ long (__syscall)(long, ...);
 
 #define SYSCALL_RLIM_INFINITY (-1UL/2)
 
-#ifndef __clang__
+#if _MIPSEL || __MIPSEL || __MIPSEL__
+#define __stat_fix(st) ((st),(void)0)
+#else
+#include <sys/stat.h>
+static inline void __stat_fix(long p)
+{
+	struct stat *st = (struct stat *)p;
+	st->st_dev >>= 32;
+	st->st_rdev >>= 32;
+}
+#endif
 
-#define __asm_syscall(...) do { \
+#ifndef __clang__
-	register long r2 __asm__("$2"); \
-	__asm__ __volatile__ ( \
-	"addu $2,$0,%2 ; syscall" \
-	: "=&r"(r2), "=r"(r7) : "ir"(n), __VA_ARGS__, "0"(r2), "1"(r7) \
-	: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13", \
-	  "$14", "$15", "$24", "$25", "hi", "lo", "memory"); \
-	return r7 ? -r2 : r2; \
-	} while (0)
 
 static inline long __syscall0(long n)
 {
 	register long r7 __asm__("$7");
-	__asm_syscall("i"(0));
+	register long r2 __asm__("$2");
+	__asm__ __volatile__ (
+		"addu $2,$0,%2 ; syscall"
+		: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7)
+		: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
+		  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
+	return r7 ? -r2 : r2;
 }
 
 static inline long __syscall1(long n, long a)
 {
 	register long r4 __asm__("$4") = a;
 	register long r7 __asm__("$7");
-	__asm_syscall("r"(r4));
+	register long r2 __asm__("$2");
+	__asm__ __volatile__ (
+		"addu $2,$0,%2 ; syscall"
+		: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7),
+		  "r"(r4)
+		: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
+		  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
+	return r7 ? -r2 : r2;
 }
 
 static inline long __syscall2(long n, long a, long b)
@@ -37,7 +52,16 @@ static inline long __syscall2(long n, long a, long b)
 	register long r4 __asm__("$4") = a;
 	register long r5 __asm__("$5") = b;
 	register long r7 __asm__("$7");
-	__asm_syscall("r"(r4), "r"(r5));
+	register long r2 __asm__("$2");
+	__asm__ __volatile__ (
+		"addu $2,$0,%2 ; syscall"
+		: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7),
+		  "r"(r4), "r"(r5)
+		: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
+		  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
+	if (r7) return -r2;
+	if (n == SYS_stat64 || n == SYS_fstat64 || n == SYS_lstat64) __stat_fix(b);
+	return r2;
 }
 
 static inline long __syscall3(long n, long a, long b, long c)
@@ -46,7 +70,16 @@ static inline long __syscall3(long n, long a, long b, long c)
 	register long r5 __asm__("$5") = b;
 	register long r6 __asm__("$6") = c;
 	register long r7 __asm__("$7");
-	__asm_syscall("r"(r4), "r"(r5), "r"(r6));
+	register long r2 __asm__("$2");
+	__asm__ __volatile__ (
+		"addu $2,$0,%2 ; syscall"
+		: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7),
+		  "r"(r4), "r"(r5), "r"(r6)
+		: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
+		  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
+	if (r7) return -r2;
+	if (n == SYS_stat64 || n == SYS_fstat64 || n == SYS_lstat64) __stat_fix(b);
+	return r2;
 }
 
 static inline long __syscall4(long n, long a, long b, long c, long d)
@@ -55,7 +88,17 @@ static inline long __syscall4(long n, long a, long b, long c, long d)
 	register long r5 __asm__("$5") = b;
 	register long r6 __asm__("$6") = c;
 	register long r7 __asm__("$7") = d;
-	__asm_syscall("r"(r4), "r"(r5), "r"(r6));
+	register long r2 __asm__("$2");
+	__asm__ __volatile__ (
+		"addu $2,$0,%2 ; syscall"
+		: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7),
+		  "r"(r4), "r"(r5), "r"(r6)
+		: "$1", "$3", "$8", "$9", "$10", "$11", "$12", "$13",
+		  "$14", "$15", "$24", "$25", "hi", "lo", "memory");
+	if (r7) return -r2;
+	if (n == SYS_stat64 || n == SYS_fstat64 || n == SYS_lstat64) __stat_fix(b);
+	if (n == SYS_fstatat) __stat_fix(c);
+	return r2;
 }
 
 #else
@@ -72,27 +115,45 @@ static inline long __syscall1(long n, long a)
 
 static inline long __syscall2(long n, long a, long b)
 {
-	return (__syscall)(n, a, b);
+	long r2 = (__syscall)(n, a, b);
+	if (r2 > -4096UL) return -r2;
+	if (n == SYS_stat64 || n == SYS_fstat64 || n == SYS_lstat64) __stat_fix(b);
+	return r2;
 }
 
 static inline long __syscall3(long n, long a, long b, long c)
 {
-	return (__syscall)(n, a, b, c);
+	long r2 = (__syscall)(n, a, b, c);
+	if (r2 > -4096UL) return -r2;
+	if (n == SYS_stat64 || n == SYS_fstat64 || n == SYS_lstat64) __stat_fix(b);
+	return r2;
 }
 
 static inline long __syscall4(long n, long a, long b, long c, long d)
 {
-	return (__syscall)(n, a, b, c, d);
+	long r2 = (__syscall)(n, a, b, c, d);
+	if (r2 > -4096UL) return -r2;
+	if (n == SYS_stat64 || n == SYS_fstat64 || n == SYS_lstat64) __stat_fix(b);
+	if (n == SYS_fstatat) __stat_fix(c);
+	return r2;
 }
 
 #endif
 
 static inline long __syscall5(long n, long a, long b, long c, long d, long e)
 {
-	return (__syscall)(n, a, b, c, d, e);
+	long r2 = (__syscall)(n, a, b, c, d, e);
+	if (r2 > -4096UL) return -r2;
+	if (n == SYS_stat64 || n == SYS_fstat64 || n == SYS_lstat64) __stat_fix(b);
+	if (n == SYS_fstatat) __stat_fix(c);
+	return r2;
 }
 
 static inline long __syscall6(long n, long a, long b, long c, long d, long e, long f)
 {
-	return (__syscall)(n, a, b, c, d, e, f);
+	long r2 = (__syscall)(n, a, b, c, d, e, f);
+	if (r2 > -4096UL) return -r2;
+	if (n == SYS_stat64 || n == SYS_fstat64 || n == SYS_lstat64) __stat_fix(b);
+	if (n == SYS_fstatat) __stat_fix(c);
+	return r2;
 }