Commit d4973c992203ed6fb761d3f3b871dd9849541b5a | zig

author	Alex Rønne Petersen <alex@alexrp.com> 2024-08-16 11:09:52+02:00
committer	Alex Rønne Petersen <alex@alexrp.com> 2024-08-18 07:27:23+02:00
log	d4973c992203ed6fb761d3f3b871dd9849541b5a
tree	8dc1a3f1b684ca5526ea78615fdd5f2c77a09ec5
parent	bcf41c859430301fe8117514b90e2610ae107276

std.os.linux: Fix syscall errno value handling for mips.

The kernel sets r7 to 0 (success) or -1 (error), and stores the result in r2.
When r7 is -1 and the result is positive, it needs to be negated to get the
errno value that higher-level code, such as errnoFromSyscall(), expects to see.

The old code was missing the check that r2 is positive, but was also doing the
r7 check incorrectly; since it can only be set to 0 or -1, the blez instruction
would always branch.

In practice, this fix is necessary for e.g. the ENOSYS error to be interpreted
correctly. This manifested as hitting an unreachable branch when calling
process_vm_readv() in std.debug.MemoryAccessor.

2 files changed, 35 insertions(+), 18 deletions(-)

lib
- std
  - os
    linux
    mips.zig
    mips64.zig

lib/std/os/linux/mips.zig+17-9

...	...	@@ -14,7 +14,8 @@ const timespec = linux.timespec;
14	14	pub fn syscall0(number: SYS) usize {
15	15	return asm volatile (
16	16	\\ syscall
17		\\ blez $7, 1f
	17	\\ beq $7, $zero, 1f
	18	\\ blez $2, 1f
18	19	\\ subu $2, $0, $2
19	20	\\ 1:
20	21	: [ret] "={$2}" (-> usize),
...	...	@@ -28,7 +29,7 @@ pub fn syscall_pipe(fd: *[2]i32) usize {
28	29	\\ .set noat
29	30	\\ .set noreorder
30	31	\\ syscall
31		\\ blez $7, 1f
	32	\\ beq $7, $zero, 1f
32	33	\\ nop
33	34	\\ b 2f
34	35	\\ subu $2, $0, $2
...	...	@@ -46,7 +47,8 @@ pub fn syscall_pipe(fd: *[2]i32) usize {
46	47	pub fn syscall1(number: SYS, arg1: usize) usize {
47	48	return asm volatile (
48	49	\\ syscall
49		\\ blez $7, 1f
	50	\\ beq $7, $zero, 1f
	51	\\ blez $2, 1f
50	52	\\ subu $2, $0, $2
51	53	\\ 1:
52	54	: [ret] "={$2}" (-> usize),
...	...	@@ -59,7 +61,8 @@ pub fn syscall1(number: SYS, arg1: usize) usize {
59	61	pub fn syscall2(number: SYS, arg1: usize, arg2: usize) usize {
60	62	return asm volatile (
61	63	\\ syscall
62		\\ blez $7, 1f
	64	\\ beq $7, $zero, 1f
	65	\\ blez $2, 1f
63	66	\\ subu $2, $0, $2
64	67	\\ 1:
65	68	: [ret] "={$2}" (-> usize),
...	...	@@ -73,7 +76,8 @@ pub fn syscall2(number: SYS, arg1: usize, arg2: usize) usize {
73	76	pub fn syscall3(number: SYS, arg1: usize, arg2: usize, arg3: usize) usize {
74	77	return asm volatile (
75	78	\\ syscall
76		\\ blez $7, 1f
	79	\\ beq $7, $zero, 1f
	80	\\ blez $2, 1f
77	81	\\ subu $2, $0, $2
78	82	\\ 1:
79	83	: [ret] "={$2}" (-> usize),
...	...	@@ -88,7 +92,8 @@ pub fn syscall3(number: SYS, arg1: usize, arg2: usize, arg3: usize) usize {
88	92	pub fn syscall4(number: SYS, arg1: usize, arg2: usize, arg3: usize, arg4: usize) usize {
89	93	return asm volatile (
90	94	\\ syscall
91		\\ blez $7, 1f
	95	\\ beq $7, $zero, 1f
	96	\\ blez $2, 1f
92	97	\\ subu $2, $0, $2
93	98	\\ 1:
94	99	: [ret] "={$2}" (-> usize),
...	...	@@ -108,7 +113,8 @@ pub fn syscall5(number: SYS, arg1: usize, arg2: usize, arg3: usize, arg4: usize,
108	113	\\ sw %[arg5], 16($sp)
109	114	\\ syscall
110	115	\\ addu $sp, $sp, 24
111		\\ blez $7, 1f
	116	\\ beq $7, $zero, 1f
	117	\\ blez $2, 1f
112	118	\\ subu $2, $0, $2
113	119	\\ 1:
114	120	: [ret] "={$2}" (-> usize),
...	...	@@ -141,7 +147,8 @@ pub fn syscall6(
141	147	\\ sw %[arg6], 20($sp)
142	148	\\ syscall
143	149	\\ addu $sp, $sp, 24
144		\\ blez $7, 1f
	150	\\ beq $7, $zero, 1f
	151	\\ blez $2, 1f
145	152	\\ subu $2, $0, $2
146	153	\\ 1:
147	154	: [ret] "={$2}" (-> usize),
...	...	@@ -174,7 +181,8 @@ pub fn syscall7(
174	181	\\ sw %[arg7], 24($sp)
175	182	\\ syscall
176	183	\\ addu $sp, $sp, 32
177		\\ blez $7, 1f
	184	\\ beq $7, $zero, 1f
	185	\\ blez $2, 1f
178	186	\\ subu $2, $0, $2
179	187	\\ 1:
180	188	: [ret] "={$2}" (-> usize),

lib/std/os/linux/mips64.zig+18-9

...	...	@@ -14,7 +14,8 @@ const timespec = linux.timespec;
14	14	pub fn syscall0(number: SYS) usize {
15	15	return asm volatile (
16	16	\\ syscall
17		\\ blez $7, 1f
	17	\\ beq $7, $zero, 1f
	18	\\ blez $2, 1f
18	19	\\ dsubu $2, $0, $2
19	20	\\ 1:
20	21	: [ret] "={$2}" (-> usize),
...	...	@@ -28,7 +29,7 @@ pub fn syscall_pipe(fd: *[2]i32) usize {
28	29	\\ .set noat
29	30	\\ .set noreorder
30	31	\\ syscall
31		\\ blez $7, 1f
	32	\\ beq $7, $zero, 1f
32	33	\\ nop
33	34	\\ b 2f
34	35	\\ subu $2, $0, $2
...	...	@@ -46,7 +47,9 @@ pub fn syscall_pipe(fd: *[2]i32) usize {
46	47	pub fn syscall1(number: SYS, arg1: usize) usize {
47	48	return asm volatile (
48	49	\\ syscall
49		\\ blez $7, 1f
	50	\\ beq $7, $zero, 1f
	51	\\ blez $2, 1f
	52	\\ nop
50	53	\\ dsubu $2, $0, $2
51	54	\\ 1:
52	55	: [ret] "={$2}" (-> usize),
...	...	@@ -59,7 +62,8 @@ pub fn syscall1(number: SYS, arg1: usize) usize {
59	62	pub fn syscall2(number: SYS, arg1: usize, arg2: usize) usize {
60	63	return asm volatile (
61	64	\\ syscall
62		\\ blez $7, 1f
	65	\\ beq $7, $zero, 1f
	66	\\ blez $2, 1f
63	67	\\ dsubu $2, $0, $2
64	68	\\ 1:
65	69	: [ret] "={$2}" (-> usize),
...	...	@@ -73,7 +77,8 @@ pub fn syscall2(number: SYS, arg1: usize, arg2: usize) usize {
73	77	pub fn syscall3(number: SYS, arg1: usize, arg2: usize, arg3: usize) usize {
74	78	return asm volatile (
75	79	\\ syscall
76		\\ blez $7, 1f
	80	\\ beq $7, $zero, 1f
	81	\\ blez $2, 1f
77	82	\\ dsubu $2, $0, $2
78	83	\\ 1:
79	84	: [ret] "={$2}" (-> usize),
...	...	@@ -88,7 +93,8 @@ pub fn syscall3(number: SYS, arg1: usize, arg2: usize, arg3: usize) usize {
88	93	pub fn syscall4(number: SYS, arg1: usize, arg2: usize, arg3: usize, arg4: usize) usize {
89	94	return asm volatile (
90	95	\\ syscall
91		\\ blez $7, 1f
	96	\\ beq $7, $zero, 1f
	97	\\ blez $2, 1f
92	98	\\ dsubu $2, $0, $2
93	99	\\ 1:
94	100	: [ret] "={$2}" (-> usize),
...	...	@@ -104,7 +110,8 @@ pub fn syscall4(number: SYS, arg1: usize, arg2: usize, arg3: usize, arg4: usize)
104	110	pub fn syscall5(number: SYS, arg1: usize, arg2: usize, arg3: usize, arg4: usize, arg5: usize) usize {
105	111	return asm volatile (
106	112	\\ syscall
107		\\ blez $7, 1f
	113	\\ beq $7, $zero, 1f
	114	\\ blez $2, 1f
108	115	\\ dsubu $2, $0, $2
109	116	\\ 1:
110	117	: [ret] "={$2}" (-> usize),
...	...	@@ -129,7 +136,8 @@ pub fn syscall6(
129	136	) usize {
130	137	return asm volatile (
131	138	\\ syscall
132		\\ blez $7, 1f
	139	\\ beq $7, $zero, 1f
	140	\\ blez $2, 1f
133	141	\\ dsubu $2, $0, $2
134	142	\\ 1:
135	143	: [ret] "={$2}" (-> usize),
...	...	@@ -156,7 +164,8 @@ pub fn syscall7(
156	164	) usize {
157	165	return asm volatile (
158	166	\\ syscall
159		\\ blez $7, 1f
	167	\\ beq $7, $zero, 1f
	168	\\ blez $2, 1f
160	169	\\ dsubu $2, $0, $2
161	170	\\ 1:
162	171	: [ret] "={$2}" (-> usize),