From 972b5fde9a2d1b5517c15803fb437195e6663085 Mon Sep 17 00:00:00 2001
From: Rich Felker <dalias@aerifal.cx>
Date: Wed, 11 Mar 2020 18:50:21 -0400
Subject: [PATCH] revert mips (32-bit, o32) syscall asm clean-up due to
 regressions

exactly revert commit 604f8d3d8b08ee4f548de193050ef93a7753c2e0 which
was wrong; it caused a major regression on Linux versions prior to
2.6.36. old kernels did not properly preserve r2 across syscall
restart, and instead restarted with the instruction right before
syscall, imposing a contract that the previous instruction must load
r2 from an immediate or a register (or memory) not clobbered by the
syscall.
---
 arch/mips/syscall_arch.h | 63 ++++++++++++++++++++--------------------
 1 file changed, 31 insertions(+), 32 deletions(-)

diff --git a/arch/mips/syscall_arch.h b/arch/mips/syscall_arch.h
index f821e73f..a3812188 100644
--- a/arch/mips/syscall_arch.h
+++ b/arch/mips/syscall_arch.h
@@ -18,11 +18,10 @@
 static inline long __syscall0(long n)
 {
 	register long r7 __asm__("$7");
-	register long r2 __asm__("$2") = n;
+	register long r2 __asm__("$2");
 	__asm__ __volatile__ (
-		"syscall"
-		: "+r"(r2), "=r"(r7)
-		:
+		"addu $2,$0,%2 ; syscall"
+		: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7)
 		: SYSCALL_CLOBBERLIST, "$8", "$9", "$10");
 	return r7 ? -r2 : r2;
 }
@@ -31,11 +30,11 @@ static inline long __syscall1(long n, long a)
 {
 	register long r4 __asm__("$4") = a;
 	register long r7 __asm__("$7");
-	register long r2 __asm__("$2") = n;
+	register long r2 __asm__("$2");
 	__asm__ __volatile__ (
-		"syscall"
-		: "+r"(r2), "=r"(r7)
-		: "r"(r4)
+		"addu $2,$0,%2 ; syscall"
+		: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7),
+		  "r"(r4)
 		: SYSCALL_CLOBBERLIST, "$8", "$9", "$10");
 	return r7 ? -r2 : r2;
 }
@@ -45,11 +44,11 @@ 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");
-	register long r2 __asm__("$2") = n;
+	register long r2 __asm__("$2");
 	__asm__ __volatile__ (
-		"syscall"
-		: "+r"(r2), "=r"(r7)
-		: "r"(r4), "r"(r5)
+		"addu $2,$0,%2 ; syscall"
+		: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7),
+		  "r"(r4), "r"(r5)
 		: SYSCALL_CLOBBERLIST, "$8", "$9", "$10");
 	return r7 ? -r2 : r2;
 }
@@ -60,11 +59,11 @@ 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");
-	register long r2 __asm__("$2") = n;
+	register long r2 __asm__("$2");
 	__asm__ __volatile__ (
-		"syscall"
-		: "+r"(r2), "=r"(r7)
-		: "r"(r4), "r"(r5), "r"(r6)
+		"addu $2,$0,%2 ; syscall"
+		: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7),
+		  "r"(r4), "r"(r5), "r"(r6)
 		: SYSCALL_CLOBBERLIST, "$8", "$9", "$10");
 	return r7 ? -r2 : r2;
 }
@@ -75,11 +74,11 @@ 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;
-	register long r2 __asm__("$2") = n;
+	register long r2 __asm__("$2");
 	__asm__ __volatile__ (
-		"syscall"
-		: "+r"(r2), "+r"(r7)
-		: "r"(r4), "r"(r5), "r"(r6)
+		"addu $2,$0,%2 ; syscall"
+		: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7),
+		  "r"(r4), "r"(r5), "r"(r6)
 		: SYSCALL_CLOBBERLIST, "$8", "$9", "$10");
 	return r7 ? -r2 : r2;
 }
@@ -91,13 +90,13 @@ static inline long __syscall5(long n, long a, long b, long c, long d, long e)
 	register long r6 __asm__("$6") = c;
 	register long r7 __asm__("$7") = d;
 	register long r8 __asm__("$8") = e;
-	register long r2 __asm__("$2") = n;
+	register long r2 __asm__("$2");
 	__asm__ __volatile__ (
 		"subu $sp,$sp,32 ; sw $8,16($sp) ; "
-		"syscall ;"
+		"addu $2,$0,%3 ; syscall ;"
 		"addu $sp,$sp,32"
-		: "+r"(r2), "+r"(r7), "+r"(r8)
-		: "r"(r4), "r"(r5), "r"(r6)
+		: "=&r"(r2), "=r"(r7), "+r"(r8)
+		: "ir"(n), "0"(r2), "1"(r7), "r"(r4), "r"(r5), "r"(r6)
 		: SYSCALL_CLOBBERLIST, "$9", "$10");
 	return r7 ? -r2 : r2;
 }
@@ -110,13 +109,13 @@ static inline long __syscall6(long n, long a, long b, long c, long d, long e, lo
 	register long r7 __asm__("$7") = d;
 	register long r8 __asm__("$8") = e;
 	register long r9 __asm__("$9") = f;
-	register long r2 __asm__("$2") = n;
+	register long r2 __asm__("$2");
 	__asm__ __volatile__ (
 		"subu $sp,$sp,32 ; sw $8,16($sp) ; sw $9,20($sp) ; "
-		"syscall ;"
+		"addu $2,$0,%4 ; syscall ;"
 		"addu $sp,$sp,32"
-		: "+r"(r2), "+r"(r7), "+r"(r8), "+r"(r9)
-		: "r"(r4), "r"(r5), "r"(r6)
+		: "=&r"(r2), "=r"(r7), "+r"(r8), "+r"(r9)
+		: "ir"(n), "0"(r2), "1"(r7), "r"(r4), "r"(r5), "r"(r6)
 		: SYSCALL_CLOBBERLIST, "$10");
 	return r7 ? -r2 : r2;
 }
@@ -130,13 +129,13 @@ static inline long __syscall7(long n, long a, long b, long c, long d, long e, lo
 	register long r8 __asm__("$8") = e;
 	register long r9 __asm__("$9") = f;
 	register long r10 __asm__("$10") = g;
-	register long r2 __asm__("$2") = n;
+	register long r2 __asm__("$2");
 	__asm__ __volatile__ (
 		"subu $sp,$sp,32 ; sw $8,16($sp) ; sw $9,20($sp) ; sw $10,24($sp) ; "
-		"syscall ;"
+		"addu $2,$0,%5 ; syscall ;"
 		"addu $sp,$sp,32"
-		: "+r"(r2), "+r"(r7), "+r"(r8), "+r"(r9), "+r"(r10)
-		: "r"(r4), "r"(r5), "r"(r6)
+		: "=&r"(r2), "=r"(r7), "+r"(r8), "+r"(r9), "+r"(r10)
+		: "ir"(n), "0"(r2), "1"(r7), "r"(r4), "r"(r5), "r"(r6)
 		: SYSCALL_CLOBBERLIST);
 	return r7 ? -r2 : r2;
 }
-- 
2.25.1