Commit b8d776928a

Alex Rønne Petersen <alex@alexrp.com>
2025-10-18 01:56:20
std: make all MIPS inline asm safe for MIPS I
MIPS I has load hazards so we need to insert nops in a few places. This is not a problem for MIPS II and later. While doing this, I also touched up all the inline asm to use ABI register aliases and a consistent formatting convention. Also fixed a few places that didn't properly check if the syscall return value should be negated.
1 parent f3da54f
Changed files (5)
lib/std/os/linux/mips.zig
@@ -5,10 +5,10 @@ const SYS = std.os.linux.SYS;
 pub fn syscall0(number: SYS) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ subu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ subu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
         : .{ .r1 = true, .r3 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .r13 = true, .r14 = true, .r15 = true, .r24 = true, .r25 = true, .hi = true, .lo = true, .memory = true });
@@ -16,17 +16,15 @@ pub fn syscall0(number: SYS) u32 {
 
 pub fn syscall_pipe(fd: *[2]i32) u32 {
     return asm volatile (
-        \\ .set noat
-        \\ .set noreorder
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ nop
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 2f
+        \\ subu $v0, $zero, $v0
         \\ b 2f
-        \\ subu $2, $0, $2
-        \\ 1:
-        \\ sw $2, 0($4)
-        \\ sw $3, 4($4)
-        \\ 2:
+        \\1:
+        \\ sw $v0, 0($a0)
+        \\ sw $v1, 4($a0)
+        \\2:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(SYS.pipe)),
           [fd] "{$4}" (fd),
@@ -36,10 +34,10 @@ pub fn syscall_pipe(fd: *[2]i32) u32 {
 pub fn syscall1(number: SYS, arg1: u32) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ subu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ subu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -49,10 +47,10 @@ pub fn syscall1(number: SYS, arg1: u32) u32 {
 pub fn syscall2(number: SYS, arg1: u32, arg2: u32) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ subu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ subu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -63,10 +61,10 @@ pub fn syscall2(number: SYS, arg1: u32, arg2: u32) u32 {
 pub fn syscall3(number: SYS, arg1: u32, arg2: u32, arg3: u32) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ subu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ subu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -78,10 +76,10 @@ pub fn syscall3(number: SYS, arg1: u32, arg2: u32, arg3: u32) u32 {
 pub fn syscall4(number: SYS, arg1: u32, arg2: u32, arg3: u32, arg4: u32) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ subu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ subu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -91,17 +89,19 @@ pub fn syscall4(number: SYS, arg1: u32, arg2: u32, arg3: u32, arg4: u32) u32 {
         : .{ .r1 = true, .r3 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .r13 = true, .r14 = true, .r15 = true, .r24 = true, .r25 = true, .hi = true, .lo = true, .memory = true });
 }
 
+// NOTE: The o32 calling convention requires the callee to reserve 16 bytes for
+// the first four arguments even though they're passed in $a0-$a3.
+
 pub fn syscall5(number: SYS, arg1: u32, arg2: u32, arg3: u32, arg4: u32, arg5: u32) u32 {
     return asm volatile (
-        \\ .set noat
         \\ subu $sp, $sp, 24
         \\ sw %[arg5], 16($sp)
         \\ syscall
         \\ addu $sp, $sp, 24
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ subu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ subu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -112,9 +112,6 @@ pub fn syscall5(number: SYS, arg1: u32, arg2: u32, arg3: u32, arg4: u32, arg5: u
         : .{ .r1 = true, .r3 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .r13 = true, .r14 = true, .r15 = true, .r24 = true, .r25 = true, .hi = true, .lo = true, .memory = true });
 }
 
-// NOTE: The o32 calling convention requires the callee to reserve 16 bytes for
-// the first four arguments even though they're passed in $a0-$a3.
-
 pub fn syscall6(
     number: SYS,
     arg1: u32,
@@ -125,16 +122,15 @@ pub fn syscall6(
     arg6: u32,
 ) u32 {
     return asm volatile (
-        \\ .set noat
         \\ subu $sp, $sp, 24
         \\ sw %[arg5], 16($sp)
         \\ sw %[arg6], 20($sp)
         \\ syscall
         \\ addu $sp, $sp, 24
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ subu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ subu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -157,17 +153,16 @@ pub fn syscall7(
     arg7: u32,
 ) u32 {
     return asm volatile (
-        \\ .set noat
         \\ subu $sp, $sp, 32
         \\ sw %[arg5], 16($sp)
         \\ sw %[arg6], 20($sp)
         \\ sw %[arg7], 24($sp)
         \\ syscall
         \\ addu $sp, $sp, 32
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ subu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ subu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -182,52 +177,51 @@ pub fn syscall7(
 
 pub fn clone() callconv(.naked) u32 {
     // __clone(func, stack, flags, arg, ptid, tls, ctid)
-    //         3,    4,     5,     6,   7,    8,   9
+    //         a0,   a1,    a2,    a3,  +0,   +4,  +8
     //
     // syscall(SYS_clone, flags, stack, ptid, tls, ctid)
-    //         2          4,     5,     6,    7,   8
+    //         v0         a0,    a1,    a2,   a3,  +0
     asm volatile (
-        \\  # Save function pointer and argument pointer on new thread stack
-        \\  and $5, $5, -8
-        \\  subu $5, $5, 16
-        \\  sw $4, 0($5)
-        \\  sw $7, 4($5)
-        \\  # Shuffle (fn,sp,fl,arg,ptid,tls,ctid) to (fl,sp,ptid,tls,ctid)
-        \\  move $4, $6
-        \\  lw $6, 16($sp)
-        \\  lw $7, 20($sp)
-        \\  lw $9, 24($sp)
-        \\  subu $sp, $sp, 16
-        \\  sw $9, 16($sp)
-        \\  li $2, 4120 # SYS_clone
-        \\  syscall
-        \\  beq $7, $0, 1f
-        \\  nop
-        \\  addu $sp, $sp, 16
-        \\  jr $ra
-        \\  subu $2, $0, $2
-        \\1:
-        \\  beq $2, $0, 1f
-        \\  nop
-        \\  addu $sp, $sp, 16
-        \\  jr $ra
-        \\  nop
+        \\ # Save function pointer and argument pointer on new thread stack
+        \\ and $a1, $a1, -8
+        \\ subu $a1, $a1, 16
+        \\ sw $a0, 0($a1)
+        \\ sw $a3, 4($a1)
+        \\
+        \\ # Shuffle (fn,sp,fl,arg,ptid,tls,ctid) to (fl,sp,ptid,tls,ctid)
+        \\ move $a0, $a2
+        \\ lw $a2, 16($sp)
+        \\ lw $a3, 20($sp)
+        \\ lw $t1, 24($sp)
+        \\ subu $sp, $sp, 16
+        \\ sw $t1, 16($sp)
+        \\ li $v0, 4120 # SYS_clone
+        \\ syscall
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 2f
+        \\ subu $v0, $zero, $v0
+        \\ b 2f
         \\1:
+        \\ beq $v0, $zero, 3f
+        \\2:
+        \\ addu $sp, $sp, 16
+        \\ jr $ra
+        \\3:
     );
     if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
-        \\  .cfi_undefined $ra
+        \\ .cfi_undefined $ra
     );
     asm volatile (
-        \\  move $fp, $zero
-        \\  move $ra, $zero
+        \\ move $fp, $zero
+        \\ move $ra, $zero
         \\
-        \\  lw $25, 0($sp)
-        \\  lw $4, 4($sp)
-        \\  jalr $25
-        \\  nop
-        \\  move $4, $2
-        \\  li $2, 4001 # SYS_exit
-        \\  syscall
+        \\ lw $t9, 0($sp)
+        \\ lw $a0, 4($sp)
+        \\ jalr $t9
+        \\
+        \\ move $a0, $v0
+        \\ li $v0, 4001 # SYS_exit
+        \\ syscall
     );
 }
 
lib/std/os/linux/mips64.zig
@@ -5,10 +5,10 @@ const SYS = std.os.linux.SYS;
 pub fn syscall0(number: SYS) u64 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u64),
         : [number] "{$2}" (@intFromEnum(number)),
         : .{ .r1 = true, .r3 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .r13 = true, .r14 = true, .r15 = true, .r24 = true, .r25 = true, .hi = true, .lo = true, .memory = true });
@@ -16,17 +16,15 @@ pub fn syscall0(number: SYS) u64 {
 
 pub fn syscall_pipe(fd: *[2]i32) u64 {
     return asm volatile (
-        \\ .set noat
-        \\ .set noreorder
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ nop
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 2f
+        \\ dsubu $v0, $zero, $v0
         \\ b 2f
-        \\ subu $2, $0, $2
-        \\ 1:
-        \\ sw $2, 0($4)
-        \\ sw $3, 4($4)
-        \\ 2:
+        \\1:
+        \\ sw $v0, 0($a0)
+        \\ sw $v1, 4($a0)
+        \\2:
         : [ret] "={$2}" (-> u64),
         : [number] "{$2}" (@intFromEnum(SYS.pipe)),
           [fd] "{$4}" (fd),
@@ -36,11 +34,10 @@ pub fn syscall_pipe(fd: *[2]i32) u64 {
 pub fn syscall1(number: SYS, arg1: u64) u64 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ nop
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u64),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -50,10 +47,10 @@ pub fn syscall1(number: SYS, arg1: u64) u64 {
 pub fn syscall2(number: SYS, arg1: u64, arg2: u64) u64 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u64),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -64,10 +61,10 @@ pub fn syscall2(number: SYS, arg1: u64, arg2: u64) u64 {
 pub fn syscall3(number: SYS, arg1: u64, arg2: u64, arg3: u64) u64 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u64),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -79,10 +76,10 @@ pub fn syscall3(number: SYS, arg1: u64, arg2: u64, arg3: u64) u64 {
 pub fn syscall4(number: SYS, arg1: u64, arg2: u64, arg3: u64, arg4: u64) u64 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u64),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -95,10 +92,10 @@ pub fn syscall4(number: SYS, arg1: u64, arg2: u64, arg3: u64, arg4: u64) u64 {
 pub fn syscall5(number: SYS, arg1: u64, arg2: u64, arg3: u64, arg4: u64, arg5: u64) u64 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u64),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -120,10 +117,10 @@ pub fn syscall6(
 ) u64 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u64),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -147,10 +144,10 @@ pub fn syscall7(
 ) u64 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u64),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -165,33 +162,33 @@ pub fn syscall7(
 
 pub fn clone() callconv(.naked) u64 {
     // __clone(func, stack, flags, arg, ptid, tls, ctid)
-    //         3,    4,     5,     6,   7,    8,   9
+    //         a0,   a1,    a2,    a3,  a4,   a5,  a6
     //
     // syscall(SYS_clone, flags, stack, ptid, tls, ctid)
-    //         2          4,     5,     6,    7,   8
+    //         v0         a0,    a1,    a2,   a3,  a4
     asm volatile (
         \\ # Save function pointer and argument pointer on new thread stack
-        \\ and $5, $5, -16
-        \\ dsubu $5, $5, 16
-        \\ sd $4, 0($5)
-        \\ sd $7, 8($5)
+        \\ and $a1, $a1, -16
+        \\ dsubu $a1, $a1, 16
+        \\ sd $a0, 0($a1)
+        \\ sd $a3, 8($a1)
+        \\
         \\ # Shuffle (fn,sp,fl,arg,ptid,tls,ctid) to (fl,sp,ptid,tls,ctid)
-        \\ move $4, $6
-        \\ move $6, $8
-        \\ move $7, $9
-        \\ move $8, $10
-        \\ li $2, 5055 # SYS_clone
+        \\ move $a0, $a2
+        \\ move $a2, $a4
+        \\ move $a3, $a5
+        \\ move $a4, $a6
+        \\ li $v0, 5055 # SYS_clone
         \\ syscall
-        \\ beq $7, $0, 1f
-        \\ nop
-        \\ jr $ra
-        \\ dsubu $2, $0, $2
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 2f
+        \\ dsubu $v0, $zero, $v0
+        \\ b 2f
         \\1:
-        \\ beq $2, $0, 1f
-        \\ nop
+        \\ beq $v0, $zero, 3f
+        \\2:
         \\ jr $ra
-        \\ nop
-        \\1:
+        \\3:
     );
     if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
         \\ .cfi_undefined $ra
@@ -200,12 +197,12 @@ pub fn clone() callconv(.naked) u64 {
         \\ move $fp, $zero
         \\ move $ra, $zero
         \\
-        \\ ld $25, 0($sp)
-        \\ ld $4, 8($sp)
-        \\ jalr $25
-        \\ nop
-        \\ move $4, $2
-        \\ li $2, 5058 # SYS_exit
+        \\ ld $t9, 0($sp)
+        \\ ld $a0, 8($sp)
+        \\ jalr $t9
+        \\
+        \\ move $a0, $v0
+        \\ li $v0, 5058 # SYS_exit
         \\ syscall
     );
 }
lib/std/os/linux/mipsn32.zig
@@ -7,10 +7,10 @@ const SYS = std.os.linux.SYS;
 pub fn syscall0(number: SYS) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
         : .{ .r1 = true, .r3 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .r13 = true, .r14 = true, .r15 = true, .r24 = true, .r25 = true, .hi = true, .lo = true, .memory = true });
@@ -18,17 +18,15 @@ pub fn syscall0(number: SYS) u32 {
 
 pub fn syscall_pipe(fd: *[2]i32) u32 {
     return asm volatile (
-        \\ .set noat
-        \\ .set noreorder
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ nop
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 2f
+        \\ dsubu $v0, $zero, $v0
         \\ b 2f
-        \\ subu $2, $0, $2
-        \\ 1:
-        \\ sw $2, 0($4)
-        \\ sw $3, 4($4)
-        \\ 2:
+        \\1:
+        \\ sw $v0, 0($a0)
+        \\ sw $v1, 4($a0)
+        \\2:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(SYS.pipe)),
           [fd] "{$4}" (fd),
@@ -38,11 +36,10 @@ pub fn syscall_pipe(fd: *[2]i32) u32 {
 pub fn syscall1(number: SYS, arg1: u32) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ nop
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -52,10 +49,10 @@ pub fn syscall1(number: SYS, arg1: u32) u32 {
 pub fn syscall2(number: SYS, arg1: u32, arg2: u32) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -66,10 +63,10 @@ pub fn syscall2(number: SYS, arg1: u32, arg2: u32) u32 {
 pub fn syscall3(number: SYS, arg1: u32, arg2: u32, arg3: u32) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -81,10 +78,10 @@ pub fn syscall3(number: SYS, arg1: u32, arg2: u32, arg3: u32) u32 {
 pub fn syscall4(number: SYS, arg1: u32, arg2: u32, arg3: u32, arg4: u32) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -97,10 +94,10 @@ pub fn syscall4(number: SYS, arg1: u32, arg2: u32, arg3: u32, arg4: u32) u32 {
 pub fn syscall5(number: SYS, arg1: u32, arg2: u32, arg3: u32, arg4: u32, arg5: u32) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -122,10 +119,10 @@ pub fn syscall6(
 ) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -149,10 +146,10 @@ pub fn syscall7(
 ) u32 {
     return asm volatile (
         \\ syscall
-        \\ beq $7, $zero, 1f
-        \\ blez $2, 1f
-        \\ dsubu $2, $0, $2
-        \\ 1:
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 1f
+        \\ dsubu $v0, $zero, $v0
+        \\1:
         : [ret] "={$2}" (-> u32),
         : [number] "{$2}" (@intFromEnum(number)),
           [arg1] "{$4}" (arg1),
@@ -167,33 +164,33 @@ pub fn syscall7(
 
 pub fn clone() callconv(.naked) u32 {
     // __clone(func, stack, flags, arg, ptid, tls, ctid)
-    //         3,    4,     5,     6,   7,    8,   9
+    //         a0,   a1,    a2,    a3,  a4,   a5,  a6
     //
     // syscall(SYS_clone, flags, stack, ptid, tls, ctid)
-    //         2          4,     5,     6,    7,   8
+    //         v0         a0,    a1,    a2,   a3,  a4
     asm volatile (
         \\ # Save function pointer and argument pointer on new thread stack
-        \\ and $5, $5, -16
-        \\ dsubu $5, $5, 16
-        \\ sd $4, 0($5)
-        \\ sd $7, 8($5)
+        \\ and $a1, $a1, -16
+        \\ dsubu $a1, $a1, 16
+        \\ sd $a0, 0($a1)
+        \\ sd $a3, 8($a1)
+        \\
         \\ # Shuffle (fn,sp,fl,arg,ptid,tls,ctid) to (fl,sp,ptid,tls,ctid)
-        \\ move $4, $6
-        \\ move $6, $8
-        \\ move $7, $9
-        \\ move $8, $10
-        \\ li $2, 5055 # SYS_clone
+        \\ move $a0, $a2
+        \\ move $a2, $a4
+        \\ move $a3, $a5
+        \\ move $a4, $a6
+        \\ li $v0, 5055 # SYS_clone
         \\ syscall
-        \\ beq $7, $0, 1f
-        \\ nop
-        \\ jr $ra
-        \\ dsubu $2, $0, $2
+        \\ beq $a3, $zero, 1f
+        \\ blez $v0, 2f
+        \\ dsubu $v0, $zero, $v0
+        \\ b 2f
         \\1:
-        \\ beq $2, $0, 1f
-        \\ nop
+        \\ beq $v0, $zero, 3f
+        \\2:
         \\ jr $ra
-        \\ nop
-        \\1:
+        \\3:
     );
     if (builtin.unwind_tables != .none or !builtin.strip_debug_info) asm volatile (
         \\ .cfi_undefined $ra
@@ -202,12 +199,12 @@ pub fn clone() callconv(.naked) u32 {
         \\ move $fp, $zero
         \\ move $ra, $zero
         \\
-        \\ ld $25, 0($sp)
-        \\ ld $4, 8($sp)
-        \\ jalr $25
-        \\ nop
-        \\ move $4, $2
-        \\ li $2, 5058 # SYS_exit
+        \\ ld $t9, 0($sp)
+        \\ ld $a0, 8($sp)
+        \\ jalr $t9
+        \\
+        \\ move $a0, $v0
+        \\ li $v0, 5058 # SYS_exit
         \\ syscall
     );
 }
lib/std/pie.zig
@@ -121,8 +121,9 @@ inline fn getDynamicSymbol() [*]const elf.Dyn {
                 \\ .hidden _DYNAMIC
                 \\ bal 1f
                 \\ .gpword _DYNAMIC
-                \\ 1:
+                \\1:
                 \\ lw %[ret], 0($ra)
+                \\ nop
                 \\ addu %[ret], %[ret], $gp
                 : [ret] "=r" (-> [*]const elf.Dyn),
                 :
@@ -133,7 +134,7 @@ inline fn getDynamicSymbol() [*]const elf.Dyn {
                 \\ .balign 8
                 \\ bal 1f
                 \\ .gpdword _DYNAMIC
-                \\ 1:
+                \\1:
                 \\ ld %[ret], 0($ra)
                 \\ daddu %[ret], %[ret], $gp
                 : [ret] "=r" (-> [*]const elf.Dyn),
lib/std/start.zig
@@ -325,24 +325,26 @@ fn _start() callconv(.naked) noreturn {
             \\ jsr (%%pc, %%a0)
             ,
             .mips, .mipsel =>
-            \\ move $fp, $0
+            \\ move $fp, $zero
             \\ bal 1f
             \\ .gpword .
             \\ .gpword %[posixCallMainAndExit]
-            \\ 1:
+            \\1:
             // The `gp` register on MIPS serves a similar purpose to `r2` (ToC pointer) on PPC64.
             \\ lw $gp, 0($ra)
+            \\ nop
             \\ subu $gp, $ra, $gp
-            \\ lw $25, 4($ra)
-            \\ addu $25, $25, $gp
-            \\ move $ra, $0
+            \\ lw $t9, 4($ra)
+            \\ nop
+            \\ addu $t9, $t9, $gp
+            \\ move $ra, $zero
             \\ move $a0, $sp
             \\ and $sp, -8
             \\ subu $sp, $sp, 16
-            \\ jalr $25
+            \\ jalr $t9
             ,
             .mips64, .mips64el =>
-            \\ move $fp, $0
+            \\ move $fp, $zero
             // This is needed because early MIPS versions don't support misaligned loads. Without
             // this directive, the hidden `nop` inserted to fill the delay slot after `bal` would
             // cause the two doublewords to be aligned to 4 bytes instead of 8.
@@ -350,17 +352,17 @@ fn _start() callconv(.naked) noreturn {
             \\ bal 1f
             \\ .gpdword .
             \\ .gpdword %[posixCallMainAndExit]
-            \\ 1:
+            \\1:
             // The `gp` register on MIPS serves a similar purpose to `r2` (ToC pointer) on PPC64.
             \\ ld $gp, 0($ra)
             \\ dsubu $gp, $ra, $gp
-            \\ ld $25, 8($ra)
-            \\ daddu $25, $25, $gp
-            \\ move $ra, $0
+            \\ ld $t9, 8($ra)
+            \\ daddu $t9, $t9, $gp
+            \\ move $ra, $zero
             \\ move $a0, $sp
             \\ and $sp, -16
             \\ dsubu $sp, $sp, 16
-            \\ jalr $25
+            \\ jalr $t9
             ,
             .powerpc, .powerpcle =>
             // Set up the initial stack frame, and clear the back chain pointer.