diff --git a/lib/std/os/linux/powerpc.zig b/lib/std/os/linux/powerpc.zig
index c8e03a1b04..a77ecab16b 100644
--- a/lib/std/os/linux/powerpc.zig
+++ b/lib/std/os/linux/powerpc.zig
@@ -15,84 +15,125 @@ const sockaddr = linux.sockaddr;
 const timespec = linux.timespec;
 
 pub fn syscall0(number: SYS) usize {
+    // r0 is both an input register and a clobber. musl and glibc achieve this with
+    // a "+" constraint, which isn't supported in Zig, so instead we separately list
+    // r0 as both an input and an output. (Listing it as an input and a clobber would
+    // cause the C backend to emit invalid code; see #25209.)
+    var r0_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
         : [number] "{r0}" (@intFromEnum(number)),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn syscall1(number: SYS, arg1: usize) usize {
+    // r0 is both an input and a clobber.
+    var r0_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
         : [number] "{r0}" (@intFromEnum(number)),
           [arg1] "{r3}" (arg1),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn syscall2(number: SYS, arg1: usize, arg2: usize) usize {
+    // These registers are both inputs and clobbers.
+    var r0_out: usize = undefined;
+    var r4_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
+          [r4_out] "={r4}" (r4_out),
         : [number] "{r0}" (@intFromEnum(number)),
           [arg1] "{r3}" (arg1),
           [arg2] "{r4}" (arg2),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn syscall3(number: SYS, arg1: usize, arg2: usize, arg3: usize) usize {
+    // These registers are both inputs and clobbers.
+    var r0_out: usize = undefined;
+    var r4_out: usize = undefined;
+    var r5_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
+          [r4_out] "={r4}" (r4_out),
+          [r5_out] "={r5}" (r5_out),
         : [number] "{r0}" (@intFromEnum(number)),
           [arg1] "{r3}" (arg1),
           [arg2] "{r4}" (arg2),
           [arg3] "{r5}" (arg3),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn syscall4(number: SYS, arg1: usize, arg2: usize, arg3: usize, arg4: usize) usize {
+    // These registers are both inputs and clobbers.
+    var r0_out: usize = undefined;
+    var r4_out: usize = undefined;
+    var r5_out: usize = undefined;
+    var r6_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
+          [r4_out] "={r4}" (r4_out),
+          [r5_out] "={r5}" (r5_out),
+          [r6_out] "={r6}" (r6_out),
         : [number] "{r0}" (@intFromEnum(number)),
           [arg1] "{r3}" (arg1),
           [arg2] "{r4}" (arg2),
           [arg3] "{r5}" (arg3),
           [arg4] "{r6}" (arg4),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn syscall5(number: SYS, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) usize {
+    // These registers are both inputs and clobbers.
+    var r0_out: usize = undefined;
+    var r4_out: usize = undefined;
+    var r5_out: usize = undefined;
+    var r6_out: usize = undefined;
+    var r7_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
+          [r4_out] "={r4}" (r4_out),
+          [r5_out] "={r5}" (r5_out),
+          [r6_out] "={r6}" (r6_out),
+          [r7_out] "={r7}" (r7_out),
         : [number] "{r0}" (@intFromEnum(number)),
           [arg1] "{r3}" (arg1),
           [arg2] "{r4}" (arg2),
           [arg3] "{r5}" (arg3),
           [arg4] "{r6}" (arg4),
           [arg5] "{r7}" (arg5),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn syscall6(
@@ -104,12 +145,25 @@ pub fn syscall6(
     arg5: usize,
     arg6: usize,
 ) usize {
+    // These registers are both inputs and clobbers.
+    var r0_out: usize = undefined;
+    var r4_out: usize = undefined;
+    var r5_out: usize = undefined;
+    var r6_out: usize = undefined;
+    var r7_out: usize = undefined;
+    var r8_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
+          [r4_out] "={r4}" (r4_out),
+          [r5_out] "={r5}" (r5_out),
+          [r6_out] "={r6}" (r6_out),
+          [r7_out] "={r7}" (r7_out),
+          [r8_out] "={r8}" (r8_out),
         : [number] "{r0}" (@intFromEnum(number)),
           [arg1] "{r3}" (arg1),
           [arg2] "{r4}" (arg2),
@@ -117,7 +171,7 @@ pub fn syscall6(
           [arg4] "{r6}" (arg4),
           [arg5] "{r7}" (arg5),
           [arg6] "{r8}" (arg6),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn clone() callconv(.naked) usize {
diff --git a/lib/std/os/linux/powerpc64.zig b/lib/std/os/linux/powerpc64.zig
index ff07ac9180..1e42dc88c8 100644
--- a/lib/std/os/linux/powerpc64.zig
+++ b/lib/std/os/linux/powerpc64.zig
@@ -15,84 +15,125 @@ const sockaddr = linux.sockaddr;
 const timespec = linux.timespec;
 
 pub fn syscall0(number: SYS) usize {
+    // r0 is both an input register and a clobber. musl and glibc achieve this with
+    // a "+" constraint, which isn't supported in Zig, so instead we separately list
+    // r0 as both an input and an output. (Listing it as an input and a clobber would
+    // cause the C backend to emit invalid code; see #25209.)
+    var r0_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
         : [number] "{r0}" (@intFromEnum(number)),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn syscall1(number: SYS, arg1: usize) usize {
+    // r0 is both an input and a clobber.
+    var r0_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
         : [number] "{r0}" (@intFromEnum(number)),
           [arg1] "{r3}" (arg1),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn syscall2(number: SYS, arg1: usize, arg2: usize) usize {
+    // These registers are both inputs and clobbers.
+    var r0_out: usize = undefined;
+    var r4_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
+          [r4_out] "={r4}" (r4_out),
         : [number] "{r0}" (@intFromEnum(number)),
           [arg1] "{r3}" (arg1),
           [arg2] "{r4}" (arg2),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn syscall3(number: SYS, arg1: usize, arg2: usize, arg3: usize) usize {
+    // These registers are both inputs and clobbers.
+    var r0_out: usize = undefined;
+    var r4_out: usize = undefined;
+    var r5_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
+          [r4_out] "={r4}" (r4_out),
+          [r5_out] "={r5}" (r5_out),
         : [number] "{r0}" (@intFromEnum(number)),
           [arg1] "{r3}" (arg1),
           [arg2] "{r4}" (arg2),
           [arg3] "{r5}" (arg3),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn syscall4(number: SYS, arg1: usize, arg2: usize, arg3: usize, arg4: usize) usize {
+    // These registers are both inputs and clobbers.
+    var r0_out: usize = undefined;
+    var r4_out: usize = undefined;
+    var r5_out: usize = undefined;
+    var r6_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
+          [r4_out] "={r4}" (r4_out),
+          [r5_out] "={r5}" (r5_out),
+          [r6_out] "={r6}" (r6_out),
         : [number] "{r0}" (@intFromEnum(number)),
           [arg1] "{r3}" (arg1),
           [arg2] "{r4}" (arg2),
           [arg3] "{r5}" (arg3),
           [arg4] "{r6}" (arg4),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn syscall5(number: SYS, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) usize {
+    // These registers are both inputs and clobbers.
+    var r0_out: usize = undefined;
+    var r4_out: usize = undefined;
+    var r5_out: usize = undefined;
+    var r6_out: usize = undefined;
+    var r7_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
+          [r4_out] "={r4}" (r4_out),
+          [r5_out] "={r5}" (r5_out),
+          [r6_out] "={r6}" (r6_out),
+          [r7_out] "={r7}" (r7_out),
         : [number] "{r0}" (@intFromEnum(number)),
           [arg1] "{r3}" (arg1),
           [arg2] "{r4}" (arg2),
           [arg3] "{r5}" (arg3),
           [arg4] "{r6}" (arg4),
           [arg5] "{r7}" (arg5),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn syscall6(
@@ -104,12 +145,25 @@ pub fn syscall6(
     arg5: usize,
     arg6: usize,
 ) usize {
+    // These registers are both inputs and clobbers.
+    var r0_out: usize = undefined;
+    var r4_out: usize = undefined;
+    var r5_out: usize = undefined;
+    var r6_out: usize = undefined;
+    var r7_out: usize = undefined;
+    var r8_out: usize = undefined;
     return asm volatile (
         \\ sc
         \\ bns+ 1f
         \\ neg 3, 3
         \\ 1:
         : [ret] "={r3}" (-> usize),
+          [r0_out] "={r0}" (r0_out),
+          [r4_out] "={r4}" (r4_out),
+          [r5_out] "={r5}" (r5_out),
+          [r6_out] "={r6}" (r6_out),
+          [r7_out] "={r7}" (r7_out),
+          [r8_out] "={r8}" (r8_out),
         : [number] "{r0}" (@intFromEnum(number)),
           [arg1] "{r3}" (arg1),
           [arg2] "{r4}" (arg2),
@@ -117,7 +171,7 @@ pub fn syscall6(
           [arg4] "{r6}" (arg4),
           [arg5] "{r7}" (arg5),
           [arg6] "{r8}" (arg6),
-        : .{ .memory = true, .cr0 = true, .r0 = true, .r4 = true, .r5 = true, .r6 = true, .r7 = true, .r8 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
+        : .{ .memory = true, .cr0 = true, .r9 = true, .r10 = true, .r11 = true, .r12 = true, .ctr = true, .xer = true });
 }
 
 pub fn clone() callconv(.naked) usize {