Commit 8d6eb13c725f409270fc34c104da4c206b70c376 | zig

author	Chris Burgess <cgburgess10@gmail.com> 2026-10-21 21:02:25+00:00
committer	Alex Rønne Petersen <alex@alexrp.com> 2026-10-22 09:50:49+02:00
log	8d6eb13c725f409270fc34c104da4c206b70c376
tree	afea18956410cfe3462b26b1ba9f7b3f65764ba2
parent	6817928c37bfc3cd84da87de18c74a06b3960ee2

std.os.linux.aarch64: declare SVE registers as syscall clobbers

The kernel zeroes P0-P15 and the bits of Z0-Z31 above 128 on syscall. Only
declare them when SVE is enabled, since LLVM treats a Z clobber as clobbering
the overlapping V register, which would add spills to code built without SVE.

closes https://codeberg.org/ziglang/zig/issues/37321

1 files changed, 61 insertions(+), 7 deletions(-)

lib
- std
  - os
    linux
    aarch64.zig

lib/std/os/linux/aarch64.zig+61-7

...	@@ -4,13 +4,67 @@ const SYS = std.os.linux.SYS;	...	@@ -4,13 +4,67 @@ const SYS = std.os.linux.SYS;
4		4
5	pub const syscall_arg_t = u64;	5	pub const syscall_arg_t = u64;
6		6
		7	/// Declared only with SVE, since a Z clobber also clobbers the V register within it.
		8	const clobbers: std.lang.assembly.Clobbers = if (builtin.zig_backend != .stage2_aarch64 and
		9	builtin.cpu.has(.aarch64, .sve)) .{
		10	.memory = true,
		11	.p0 = true,
		12	.p1 = true,
		13	.p2 = true,
		14	.p3 = true,
		15	.p4 = true,
		16	.p5 = true,
		17	.p6 = true,
		18	.p7 = true,
		19	.p8 = true,
		20	.p9 = true,
		21	.p10 = true,
		22	.p11 = true,
		23	.p12 = true,
		24	.p13 = true,
		25	.p14 = true,
		26	.p15 = true,
		27	.z0 = true,
		28	.z1 = true,
		29	.z2 = true,
		30	.z3 = true,
		31	.z4 = true,
		32	.z5 = true,
		33	.z6 = true,
		34	.z7 = true,
		35	.z8 = true,
		36	.z9 = true,
		37	.z10 = true,
		38	.z11 = true,
		39	.z12 = true,
		40	.z13 = true,
		41	.z14 = true,
		42	.z15 = true,
		43	.z16 = true,
		44	.z17 = true,
		45	.z18 = true,
		46	.z19 = true,
		47	.z20 = true,
		48	.z21 = true,
		49	.z22 = true,
		50	.z23 = true,
		51	.z24 = true,
		52	.z25 = true,
		53	.z26 = true,
		54	.z27 = true,
		55	.z28 = true,
		56	.z29 = true,
		57	.z30 = true,
		58	.z31 = true,
		59	} else .{ .memory = true };
		60
7	pub fn syscall0(	61	pub fn syscall0(
8	number: SYS,	62	number: SYS,
9	) u64 {	63	) u64 {
10	return asm volatile ("svc #0"	64	return asm volatile ("svc #0"
11	: [ret] "={x0}" (-> u64),	65	: [ret] "={x0}" (-> u64),
12	: [number] "{x8}" (@backingInt(number)),	66	: [number] "{x8}" (@backingInt(number)),
13	: .{ .memory = true });	67	: clobbers);
14	}	68	}
15		69
16	pub fn syscall1(	70	pub fn syscall1(
...	@@ -21,7 +75,7 @@ pub fn syscall1(	...	@@ -21,7 +75,7 @@ pub fn syscall1(
21	: [ret] "={x0}" (-> u64),	75	: [ret] "={x0}" (-> u64),
22	: [number] "{x8}" (@backingInt(number)),	76	: [number] "{x8}" (@backingInt(number)),
23	[arg1] "{x0}" (arg1),	77	[arg1] "{x0}" (arg1),
24	: .{ .memory = true });	78	: clobbers);
25	}	79	}
26		80
27	pub fn syscall2(	81	pub fn syscall2(
...	@@ -34,7 +88,7 @@ pub fn syscall2(	...	@@ -34,7 +88,7 @@ pub fn syscall2(
34	: [number] "{x8}" (@backingInt(number)),	88	: [number] "{x8}" (@backingInt(number)),
35	[arg1] "{x0}" (arg1),	89	[arg1] "{x0}" (arg1),
36	[arg2] "{x1}" (arg2),	90	[arg2] "{x1}" (arg2),
37	: .{ .memory = true });	91	: clobbers);
38	}	92	}
39		93
40	pub fn syscall3(	94	pub fn syscall3(
...	@@ -49,7 +103,7 @@ pub fn syscall3(	...	@@ -49,7 +103,7 @@ pub fn syscall3(
49	[arg1] "{x0}" (arg1),	103	[arg1] "{x0}" (arg1),
50	[arg2] "{x1}" (arg2),	104	[arg2] "{x1}" (arg2),
51	[arg3] "{x2}" (arg3),	105	[arg3] "{x2}" (arg3),
52	: .{ .memory = true });	106	: clobbers);
53	}	107	}
54		108
55	pub fn syscall4(	109	pub fn syscall4(
...	@@ -66,7 +120,7 @@ pub fn syscall4(	...	@@ -66,7 +120,7 @@ pub fn syscall4(
66	[arg2] "{x1}" (arg2),	120	[arg2] "{x1}" (arg2),
67	[arg3] "{x2}" (arg3),	121	[arg3] "{x2}" (arg3),
68	[arg4] "{x3}" (arg4),	122	[arg4] "{x3}" (arg4),
69	: .{ .memory = true });	123	: clobbers);
70	}	124	}
71		125
72	pub fn syscall5(	126	pub fn syscall5(
...	@@ -85,7 +139,7 @@ pub fn syscall5(	...	@@ -85,7 +139,7 @@ pub fn syscall5(
85	[arg3] "{x2}" (arg3),	139	[arg3] "{x2}" (arg3),
86	[arg4] "{x3}" (arg4),	140	[arg4] "{x3}" (arg4),
87	[arg5] "{x4}" (arg5),	141	[arg5] "{x4}" (arg5),
88	: .{ .memory = true });	142	: clobbers);
89	}	143	}
90		144
91	pub fn syscall6(	145	pub fn syscall6(
...	@@ -106,7 +160,7 @@ pub fn syscall6(	...	@@ -106,7 +160,7 @@ pub fn syscall6(
106	[arg4] "{x3}" (arg4),	160	[arg4] "{x3}" (arg4),
107	[arg5] "{x4}" (arg5),	161	[arg5] "{x4}" (arg5),
108	[arg6] "{x5}" (arg6),	162	[arg6] "{x5}" (arg6),
109	: .{ .memory = true });	163	: clobbers);
110	}	164	}
111		165
112	pub fn clone() callconv(.naked) u64 {	166	pub fn clone() callconv(.naked) u64 {