Commit 3cc91ba1495c486ff37ba0073b1d35301b25e2db | 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 20:36:32+02:00
log	3cc91ba1495c486ff37ba0073b1d35301b25e2db
tree	4c86b2d6b44fc176eeba660becad020f98198b05
parent	d20b0a4ad5992a24be45ebe78533691a5848dd5b
signature	Signed by SSH key SHA256:7B/LJ7bpR1eX8aCXSr4mtd5M45VMPKcx9zY8e95b5QM

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	4
5	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	61	pub fn syscall0(
8	62	number: SYS,
9	63	) u64 {
10	64	return asm volatile ("svc #0"
11	65	: [ret] "={x0}" (-> u64),
12	66	: [number] "{x8}" (@backingInt(number)),
13		: .{ .memory = true });
	67	: clobbers);
14	68	}
15	69
16	70	pub fn syscall1(
...	...	@@ -21,7 +75,7 @@ pub fn syscall1(
21	75	: [ret] "={x0}" (-> u64),
22	76	: [number] "{x8}" (@backingInt(number)),
23	77	[arg1] "{x0}" (arg1),
24		: .{ .memory = true });
	78	: clobbers);
25	79	}
26	80
27	81	pub fn syscall2(
...	...	@@ -34,7 +88,7 @@ pub fn syscall2(
34	88	: [number] "{x8}" (@backingInt(number)),
35	89	[arg1] "{x0}" (arg1),
36	90	[arg2] "{x1}" (arg2),
37		: .{ .memory = true });
	91	: clobbers);
38	92	}
39	93
40	94	pub fn syscall3(
...	...	@@ -49,7 +103,7 @@ pub fn syscall3(
49	103	[arg1] "{x0}" (arg1),
50	104	[arg2] "{x1}" (arg2),
51	105	[arg3] "{x2}" (arg3),
52		: .{ .memory = true });
	106	: clobbers);
53	107	}
54	108
55	109	pub fn syscall4(
...	...	@@ -66,7 +120,7 @@ pub fn syscall4(
66	120	[arg2] "{x1}" (arg2),
67	121	[arg3] "{x2}" (arg3),
68	122	[arg4] "{x3}" (arg4),
69		: .{ .memory = true });
	123	: clobbers);
70	124	}
71	125
72	126	pub fn syscall5(
...	...	@@ -85,7 +139,7 @@ pub fn syscall5(
85	139	[arg3] "{x2}" (arg3),
86	140	[arg4] "{x3}" (arg4),
87	141	[arg5] "{x4}" (arg5),
88		: .{ .memory = true });
	142	: clobbers);
89	143	}
90	144
91	145	pub fn syscall6(
...	...	@@ -106,7 +160,7 @@ pub fn syscall6(
106	160	[arg4] "{x3}" (arg4),
107	161	[arg5] "{x4}" (arg5),
108	162	[arg6] "{x5}" (arg6),
109		: .{ .memory = true });
	163	: clobbers);
110	164	}
111	165
112	166	pub fn clone() callconv(.naked) u64 {