1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
|
From f3ed8bfe8a82af1870ddc8696ed4cc1d5aa6b441 Mon Sep 17 00:00:00 2001
From: Rich Felker <dalias@aerifal.cx>
Date: Mon, 5 Aug 2019 18:41:47 -0400
Subject: fix x87 stack imbalance in corner cases of i386 math asm
commit 31c5fb80b9eae86f801be4f46025bc6532a554c5 introduced underflow
code paths for the i386 math asm, along with checks on the fpu status
word to skip the underflow-generation instructions if the underflow
flag was already raised. unfortunately, at least one such path, in
log1p, returned with 2 items on the x87 stack rather than just 1 item
for the return value. this is a violation of the ABI's calling
convention, and could cause subsequent floating point code to produce
NANs due to x87 stack overflow. if floating point results are used in
flow control, this can lead to runaway wrong code execution.
rather than reviewing each "underflow already raised" code path for
correctness, remove them all. they're likely slower than just
performing the underflow code unconditionally, and significantly more
complex.
all of this code should be ripped out and replaced by C source files
with inline asm. doing so would preclude this kind of error by having
the compiler perform all x87 stack register allocation and stack
manipulation, and would produce comparable or better code. however
such a change is a much larger project.
---
src/math/i386/asin.s | 10 ++--------
src/math/i386/atan.s | 7 ++-----
src/math/i386/atan2.s | 5 +----
src/math/i386/atan2f.s | 5 +----
src/math/i386/atanf.s | 7 ++-----
src/math/i386/exp.s | 10 ++--------
src/math/i386/log1p.s | 7 ++-----
src/math/i386/log1pf.s | 7 ++-----
8 files changed, 14 insertions(+), 44 deletions(-)
diff --git a/src/math/i386/asin.s b/src/math/i386/asin.s
index a9f691bf..920d967a 100644
--- a/src/math/i386/asin.s
+++ b/src/math/i386/asin.s
@@ -7,13 +7,10 @@ asinf:
cmp $0x01000000,%eax
jae 1f
# subnormal x, return x with underflow
- fnstsw %ax
- and $16,%ax
- jnz 2f
fld %st(0)
fmul %st(1)
fstps 4(%esp)
-2: ret
+ ret
.global asinl
.type asinl,@function
@@ -30,11 +27,8 @@ asin:
cmp $0x00200000,%eax
jae 1f
# subnormal x, return x with underflow
- fnstsw %ax
- and $16,%ax
- jnz 2f
fsts 4(%esp)
-2: ret
+ ret
1: fld %st(0)
fld1
fsub %st(0),%st(1)
diff --git a/src/math/i386/atan.s b/src/math/i386/atan.s
index d73137b2..a26feae1 100644
--- a/src/math/i386/atan.s
+++ b/src/math/i386/atan.s
@@ -10,8 +10,5 @@ atan:
fpatan
ret
# subnormal x, return x with underflow
-1: fnstsw %ax
- and $16,%ax
- jnz 2f
- fsts 4(%esp)
-2: ret
+1: fsts 4(%esp)
+ ret
diff --git a/src/math/i386/atan2.s b/src/math/i386/atan2.s
index a7d2979b..1fa0524d 100644
--- a/src/math/i386/atan2.s
+++ b/src/math/i386/atan2.s
@@ -10,8 +10,5 @@ atan2:
cmp $0x00200000,%eax
jae 1f
# subnormal x, return x with underflow
- fnstsw %ax
- and $16,%ax
- jnz 1f
fsts 4(%esp)
-1: ret
+ ret
diff --git a/src/math/i386/atan2f.s b/src/math/i386/atan2f.s
index 14b88ce5..0b264726 100644
--- a/src/math/i386/atan2f.s
+++ b/src/math/i386/atan2f.s
@@ -10,10 +10,7 @@ atan2f:
cmp $0x01000000,%eax
jae 1f
# subnormal x, return x with underflow
- fnstsw %ax
- and $16,%ax
- jnz 1f
fld %st(0)
fmul %st(1)
fstps 4(%esp)
-1: ret
+ ret
diff --git a/src/math/i386/atanf.s b/src/math/i386/atanf.s
index 8caddefa..893beac5 100644
--- a/src/math/i386/atanf.s
+++ b/src/math/i386/atanf.s
@@ -10,10 +10,7 @@ atanf:
fpatan
ret
# subnormal x, return x with underflow
-1: fnstsw %ax
- and $16,%ax
- jnz 2f
- fld %st(0)
+1: fld %st(0)
fmul %st(1)
fstps 4(%esp)
-2: ret
+ ret
diff --git a/src/math/i386/exp.s b/src/math/i386/exp.s
index c7aa5b6e..df87c497 100644
--- a/src/math/i386/exp.s
+++ b/src/math/i386/exp.s
@@ -7,13 +7,10 @@ expm1f:
cmp $0x01000000,%eax
jae 1f
# subnormal x, return x with underflow
- fnstsw %ax
- and $16,%ax
- jnz 2f
fld %st(0)
fmul %st(1)
fstps 4(%esp)
-2: ret
+ ret
.global expm1l
.type expm1l,@function
@@ -30,11 +27,8 @@ expm1:
cmp $0x00200000,%eax
jae 1f
# subnormal x, return x with underflow
- fnstsw %ax
- and $16,%ax
- jnz 2f
fsts 4(%esp)
-2: ret
+ ret
1: fldl2e
fmulp
mov $0xc2820000,%eax
diff --git a/src/math/i386/log1p.s b/src/math/i386/log1p.s
index 6b6929c7..354f391a 100644
--- a/src/math/i386/log1p.s
+++ b/src/math/i386/log1p.s
@@ -16,9 +16,6 @@ log1p:
fyl2x
ret
# subnormal x, return x with underflow
-2: fnstsw %ax
- and $16,%ax
- jnz 1f
- fsts 4(%esp)
+2: fsts 4(%esp)
fstp %st(1)
-1: ret
+ ret
diff --git a/src/math/i386/log1pf.s b/src/math/i386/log1pf.s
index c0bcd30f..4d3484cd 100644
--- a/src/math/i386/log1pf.s
+++ b/src/math/i386/log1pf.s
@@ -16,10 +16,7 @@ log1pf:
fyl2x
ret
# subnormal x, return x with underflow
-2: fnstsw %ax
- and $16,%ax
- jnz 1f
- fxch
+2: fxch
fmul %st(1)
fstps 4(%esp)
-1: ret
+ ret
--
cgit v1.2.1
|
