1 .. SPDX-License-Identifier: GPL-2.0-only 1 .. SPDX-License-Identifier: GPL-2.0-only
2 2
3 ============ 3 ============
4 UAPI Checker 4 UAPI Checker
5 ============ 5 ============
6 6
7 The UAPI checker (``scripts/check-uapi.sh``) i 7 The UAPI checker (``scripts/check-uapi.sh``) is a shell script which
8 checks UAPI header files for userspace backwar 8 checks UAPI header files for userspace backwards-compatibility across
9 the git tree. 9 the git tree.
10 10
11 Options 11 Options
12 ======= 12 =======
13 13
14 This section will describe the options with wh 14 This section will describe the options with which ``check-uapi.sh``
15 can be run. 15 can be run.
16 16
17 Usage:: 17 Usage::
18 18
19 check-uapi.sh [-b BASE_REF] [-p PAST_REF] 19 check-uapi.sh [-b BASE_REF] [-p PAST_REF] [-j N] [-l ERROR_LOG] [-i] [-q] [-v]
20 20
21 Available options:: 21 Available options::
22 22
23 -b BASE_REF Base git reference to use f 23 -b BASE_REF Base git reference to use for comparison. If unspecified or empty,
24 will use any dirty changes 24 will use any dirty changes in tree to UAPI files. If there are no
25 dirty changes, HEAD will be 25 dirty changes, HEAD will be used.
26 -p PAST_REF Compare BASE_REF to PAST_RE 26 -p PAST_REF Compare BASE_REF to PAST_REF (e.g. -p v6.1). If unspecified or empty,
27 will use BASE_REF^1. Must b 27 will use BASE_REF^1. Must be an ancestor of BASE_REF. Only headers
28 that exist on PAST_REF will 28 that exist on PAST_REF will be checked for compatibility.
29 -j JOBS Number of checks to run in 29 -j JOBS Number of checks to run in parallel (default: number of CPU cores).
30 -l ERROR_LOG Write error log to file (de 30 -l ERROR_LOG Write error log to file (default: no error log is generated).
31 -i Ignore ambiguous changes th 31 -i Ignore ambiguous changes that may or may not break UAPI compatibility.
32 -q Quiet operation. 32 -q Quiet operation.
33 -v Verbose operation (print mo 33 -v Verbose operation (print more information about each header being checked).
34 34
35 Environmental args:: 35 Environmental args::
36 36
37 ABIDIFF Custom path to abidiff binary 37 ABIDIFF Custom path to abidiff binary
38 CC C compiler (default is "gcc") 38 CC C compiler (default is "gcc")
39 ARCH Target architecture of C compiler 39 ARCH Target architecture of C compiler (default is host arch)
40 40
41 Exit codes:: 41 Exit codes::
42 42
43 0) Success 43 0) Success
44 1) ABI difference detected 44 1) ABI difference detected
45 2) Prerequisite not met 45 2) Prerequisite not met
46 46
47 Examples 47 Examples
48 ======== 48 ========
49 49
50 Basic Usage 50 Basic Usage
51 ----------- 51 -----------
52 52
53 First, let's try making a change to a UAPI hea 53 First, let's try making a change to a UAPI header file that obviously
54 won't break userspace:: 54 won't break userspace::
55 55
56 cat << 'EOF' | patch -l -p1 56 cat << 'EOF' | patch -l -p1
57 --- a/include/uapi/linux/acct.h 57 --- a/include/uapi/linux/acct.h
58 +++ b/include/uapi/linux/acct.h 58 +++ b/include/uapi/linux/acct.h
59 @@ -21,7 +21,9 @@ 59 @@ -21,7 +21,9 @@
60 #include <asm/param.h> 60 #include <asm/param.h>
61 #include <asm/byteorder.h> 61 #include <asm/byteorder.h>
62 62
63 -/* 63 -/*
64 +#define FOO 64 +#define FOO
65 + 65 +
66 +/* 66 +/*
67 * comp_t is a 16-bit "floating" point n 67 * comp_t is a 16-bit "floating" point number with a 3-bit base 8
68 * exponent and a 13-bit fraction. 68 * exponent and a 13-bit fraction.
69 * comp2_t is 24-bit with 5-bit base 2 e 69 * comp2_t is 24-bit with 5-bit base 2 exponent and 20 bit fraction
70 diff --git a/include/uapi/linux/bpf.h b/in 70 diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
71 EOF 71 EOF
72 72
73 Now, let's use the script to validate:: 73 Now, let's use the script to validate::
74 74
75 % ./scripts/check-uapi.sh 75 % ./scripts/check-uapi.sh
76 Installing user-facing UAPI headers from d 76 Installing user-facing UAPI headers from dirty tree... OK
77 Installing user-facing UAPI headers from H 77 Installing user-facing UAPI headers from HEAD... OK
78 Checking changes to UAPI headers between H 78 Checking changes to UAPI headers between HEAD and dirty tree...
79 All 912 UAPI headers compatible with x86 a 79 All 912 UAPI headers compatible with x86 appear to be backwards compatible
80 80
81 Let's add another change that *might* break us 81 Let's add another change that *might* break userspace::
82 82
83 cat << 'EOF' | patch -l -p1 83 cat << 'EOF' | patch -l -p1
84 --- a/include/uapi/linux/bpf.h 84 --- a/include/uapi/linux/bpf.h
85 +++ b/include/uapi/linux/bpf.h 85 +++ b/include/uapi/linux/bpf.h
86 @@ -74,7 +74,7 @@ struct bpf_insn { 86 @@ -74,7 +74,7 @@ struct bpf_insn {
87 __u8 dst_reg:4; /* dest re 87 __u8 dst_reg:4; /* dest register */
88 __u8 src_reg:4; /* source 88 __u8 src_reg:4; /* source register */
89 __s16 off; /* signed 89 __s16 off; /* signed offset */
90 - __s32 imm; /* signed 90 - __s32 imm; /* signed immediate constant */
91 + __u32 imm; /* unsigne 91 + __u32 imm; /* unsigned immediate constant */
92 }; 92 };
93 93
94 /* Key of an a BPF_MAP_TYPE_LPM_TRIE entr 94 /* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */
95 EOF 95 EOF
96 96
97 The script will catch this:: 97 The script will catch this::
98 98
99 % ./scripts/check-uapi.sh 99 % ./scripts/check-uapi.sh
100 Installing user-facing UAPI headers from d 100 Installing user-facing UAPI headers from dirty tree... OK
101 Installing user-facing UAPI headers from H 101 Installing user-facing UAPI headers from HEAD... OK
102 Checking changes to UAPI headers between H 102 Checking changes to UAPI headers between HEAD and dirty tree...
103 ==== ABI differences detected in include/l 103 ==== ABI differences detected in include/linux/bpf.h from HEAD -> dirty tree ====
104 [C] 'struct bpf_insn' changed: 104 [C] 'struct bpf_insn' changed:
105 type size hasn't changed 105 type size hasn't changed
106 1 data member change: 106 1 data member change:
107 type of '__s32 imm' changed: 107 type of '__s32 imm' changed:
108 typedef name changed from __s32 108 typedef name changed from __s32 to __u32 at int-ll64.h:27:1
109 underlying type 'int' changed: 109 underlying type 'int' changed:
110 type name changed from 'int' t 110 type name changed from 'int' to 'unsigned int'
111 type size hasn't changed 111 type size hasn't changed
112 ========================================== 112 ==================================================================================
113 113
114 error - 1/912 UAPI headers compatible with 114 error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible
115 115
116 In this case, the script is reporting the type 116 In this case, the script is reporting the type change because it could
117 break a userspace program that passes in a neg 117 break a userspace program that passes in a negative number. Now, let's
118 say you know that no userspace program could p 118 say you know that no userspace program could possibly be using a negative
119 value in ``imm``, so changing to an unsigned t 119 value in ``imm``, so changing to an unsigned type there shouldn't hurt
120 anything. You can pass the ``-i`` flag to the 120 anything. You can pass the ``-i`` flag to the script to ignore changes
121 in which the userspace backwards compatibility 121 in which the userspace backwards compatibility is ambiguous::
122 122
123 % ./scripts/check-uapi.sh -i 123 % ./scripts/check-uapi.sh -i
124 Installing user-facing UAPI headers from d 124 Installing user-facing UAPI headers from dirty tree... OK
125 Installing user-facing UAPI headers from H 125 Installing user-facing UAPI headers from HEAD... OK
126 Checking changes to UAPI headers between H 126 Checking changes to UAPI headers between HEAD and dirty tree...
127 All 912 UAPI headers compatible with x86 a 127 All 912 UAPI headers compatible with x86 appear to be backwards compatible
128 128
129 Now, let's make a similar change that *will* b 129 Now, let's make a similar change that *will* break userspace::
130 130
131 cat << 'EOF' | patch -l -p1 131 cat << 'EOF' | patch -l -p1
132 --- a/include/uapi/linux/bpf.h 132 --- a/include/uapi/linux/bpf.h
133 +++ b/include/uapi/linux/bpf.h 133 +++ b/include/uapi/linux/bpf.h
134 @@ -71,8 +71,8 @@ enum { 134 @@ -71,8 +71,8 @@ enum {
135 135
136 struct bpf_insn { 136 struct bpf_insn {
137 __u8 code; /* opcode 137 __u8 code; /* opcode */
138 - __u8 dst_reg:4; /* dest re 138 - __u8 dst_reg:4; /* dest register */
139 __u8 src_reg:4; /* source 139 __u8 src_reg:4; /* source register */
140 + __u8 dst_reg:4; /* dest re 140 + __u8 dst_reg:4; /* dest register */
141 __s16 off; /* signed 141 __s16 off; /* signed offset */
142 __s32 imm; /* signed 142 __s32 imm; /* signed immediate constant */
143 }; 143 };
144 EOF 144 EOF
145 145
146 Since we're re-ordering an existing struct mem 146 Since we're re-ordering an existing struct member, there's no ambiguity,
147 and the script will report the breakage even i 147 and the script will report the breakage even if you pass ``-i``::
148 148
149 % ./scripts/check-uapi.sh -i 149 % ./scripts/check-uapi.sh -i
150 Installing user-facing UAPI headers from d 150 Installing user-facing UAPI headers from dirty tree... OK
151 Installing user-facing UAPI headers from H 151 Installing user-facing UAPI headers from HEAD... OK
152 Checking changes to UAPI headers between H 152 Checking changes to UAPI headers between HEAD and dirty tree...
153 ==== ABI differences detected in include/l 153 ==== ABI differences detected in include/linux/bpf.h from HEAD -> dirty tree ====
154 [C] 'struct bpf_insn' changed: 154 [C] 'struct bpf_insn' changed:
155 type size hasn't changed 155 type size hasn't changed
156 2 data member changes: 156 2 data member changes:
157 '__u8 dst_reg' offset changed from 157 '__u8 dst_reg' offset changed from 8 to 12 (in bits) (by +4 bits)
158 '__u8 src_reg' offset changed from 158 '__u8 src_reg' offset changed from 12 to 8 (in bits) (by -4 bits)
159 ========================================== 159 ==================================================================================
160 160
161 error - 1/912 UAPI headers compatible with 161 error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible
162 162
163 Let's commit the breaking change, then commit 163 Let's commit the breaking change, then commit the innocuous change::
164 164
165 % git commit -m 'Breaking UAPI change' inc 165 % git commit -m 'Breaking UAPI change' include/uapi/linux/bpf.h
166 [detached HEAD f758e574663a] Breaking UAPI 166 [detached HEAD f758e574663a] Breaking UAPI change
167 1 file changed, 1 insertion(+), 1 deletio 167 1 file changed, 1 insertion(+), 1 deletion(-)
168 % git commit -m 'Innocuous UAPI change' in 168 % git commit -m 'Innocuous UAPI change' include/uapi/linux/acct.h
169 [detached HEAD 2e87df769081] Innocuous UAP 169 [detached HEAD 2e87df769081] Innocuous UAPI change
170 1 file changed, 3 insertions(+), 1 deleti 170 1 file changed, 3 insertions(+), 1 deletion(-)
171 171
172 Now, let's run the script again with no argume 172 Now, let's run the script again with no arguments::
173 173
174 % ./scripts/check-uapi.sh 174 % ./scripts/check-uapi.sh
175 Installing user-facing UAPI headers from H 175 Installing user-facing UAPI headers from HEAD... OK
176 Installing user-facing UAPI headers from H 176 Installing user-facing UAPI headers from HEAD^1... OK
177 Checking changes to UAPI headers between H 177 Checking changes to UAPI headers between HEAD^1 and HEAD...
178 All 912 UAPI headers compatible with x86 a 178 All 912 UAPI headers compatible with x86 appear to be backwards compatible
179 179
180 It doesn't catch any breaking change because, 180 It doesn't catch any breaking change because, by default, it only
181 compares ``HEAD`` to ``HEAD^1``. The breaking 181 compares ``HEAD`` to ``HEAD^1``. The breaking change was committed on
182 ``HEAD~2``. If we wanted the search scope to g 182 ``HEAD~2``. If we wanted the search scope to go back further, we'd have to
183 use the ``-p`` option to pass a different past 183 use the ``-p`` option to pass a different past reference. In this case,
184 let's pass ``-p HEAD~2`` to the script so it c 184 let's pass ``-p HEAD~2`` to the script so it checks UAPI changes between
185 ``HEAD~2`` and ``HEAD``:: 185 ``HEAD~2`` and ``HEAD``::
186 186
187 % ./scripts/check-uapi.sh -p HEAD~2 187 % ./scripts/check-uapi.sh -p HEAD~2
188 Installing user-facing UAPI headers from H 188 Installing user-facing UAPI headers from HEAD... OK
189 Installing user-facing UAPI headers from H 189 Installing user-facing UAPI headers from HEAD~2... OK
190 Checking changes to UAPI headers between H 190 Checking changes to UAPI headers between HEAD~2 and HEAD...
191 ==== ABI differences detected in include/l 191 ==== ABI differences detected in include/linux/bpf.h from HEAD~2 -> HEAD ====
192 [C] 'struct bpf_insn' changed: 192 [C] 'struct bpf_insn' changed:
193 type size hasn't changed 193 type size hasn't changed
194 2 data member changes: 194 2 data member changes:
195 '__u8 dst_reg' offset changed from 195 '__u8 dst_reg' offset changed from 8 to 12 (in bits) (by +4 bits)
196 '__u8 src_reg' offset changed from 196 '__u8 src_reg' offset changed from 12 to 8 (in bits) (by -4 bits)
197 ========================================== 197 ==============================================================================
198 198
199 error - 1/912 UAPI headers compatible with 199 error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible
200 200
201 Alternatively, we could have also run with ``- 201 Alternatively, we could have also run with ``-b HEAD~``. This would set the
202 base reference to ``HEAD~`` so then the script 202 base reference to ``HEAD~`` so then the script would compare it to ``HEAD~^1``.
203 203
204 Architecture-specific Headers 204 Architecture-specific Headers
205 ----------------------------- 205 -----------------------------
206 206
207 Consider this change:: 207 Consider this change::
208 208
209 cat << 'EOF' | patch -l -p1 209 cat << 'EOF' | patch -l -p1
210 --- a/arch/arm64/include/uapi/asm/sigconte 210 --- a/arch/arm64/include/uapi/asm/sigcontext.h
211 +++ b/arch/arm64/include/uapi/asm/sigconte 211 +++ b/arch/arm64/include/uapi/asm/sigcontext.h
212 @@ -70,6 +70,7 @@ struct sigcontext { 212 @@ -70,6 +70,7 @@ struct sigcontext {
213 struct _aarch64_ctx { 213 struct _aarch64_ctx {
214 __u32 magic; 214 __u32 magic;
215 __u32 size; 215 __u32 size;
216 + __u32 new_var; 216 + __u32 new_var;
217 }; 217 };
218 218
219 #define FPSIMD_MAGIC 0x46508001 219 #define FPSIMD_MAGIC 0x46508001
220 EOF 220 EOF
221 221
222 This is a change to an arm64-specific UAPI hea 222 This is a change to an arm64-specific UAPI header file. In this example, I'm
223 running the script from an x86 machine with an 223 running the script from an x86 machine with an x86 compiler, so, by default,
224 the script only checks x86-compatible UAPI hea 224 the script only checks x86-compatible UAPI header files::
225 225
226 % ./scripts/check-uapi.sh 226 % ./scripts/check-uapi.sh
227 Installing user-facing UAPI headers from d 227 Installing user-facing UAPI headers from dirty tree... OK
228 Installing user-facing UAPI headers from H 228 Installing user-facing UAPI headers from HEAD... OK
229 No changes to UAPI headers were applied be 229 No changes to UAPI headers were applied between HEAD and dirty tree
230 230
231 With an x86 compiler, we can't check header fi 231 With an x86 compiler, we can't check header files in ``arch/arm64``, so the
232 script doesn't even try. 232 script doesn't even try.
233 233
234 If we want to check the header file, we'll hav 234 If we want to check the header file, we'll have to use an arm64 compiler and
235 set ``ARCH`` accordingly:: 235 set ``ARCH`` accordingly::
236 236
237 % CC=aarch64-linux-gnu-gcc ARCH=arm64 ./sc 237 % CC=aarch64-linux-gnu-gcc ARCH=arm64 ./scripts/check-uapi.sh
238 Installing user-facing UAPI headers from d 238 Installing user-facing UAPI headers from dirty tree... OK
239 Installing user-facing UAPI headers from H 239 Installing user-facing UAPI headers from HEAD... OK
240 Checking changes to UAPI headers between H 240 Checking changes to UAPI headers between HEAD and dirty tree...
241 ==== ABI differences detected in include/a 241 ==== ABI differences detected in include/asm/sigcontext.h from HEAD -> dirty tree ====
242 [C] 'struct _aarch64_ctx' changed: 242 [C] 'struct _aarch64_ctx' changed:
243 type size changed from 64 to 96 (in 243 type size changed from 64 to 96 (in bits)
244 1 data member insertion: 244 1 data member insertion:
245 '__u32 new_var', at offset 64 (in 245 '__u32 new_var', at offset 64 (in bits) at sigcontext.h:73:1
246 -- snip -- 246 -- snip --
247 [C] 'struct zt_context' changed: 247 [C] 'struct zt_context' changed:
248 type size changed from 128 to 160 (i 248 type size changed from 128 to 160 (in bits)
249 2 data member changes (1 filtered): 249 2 data member changes (1 filtered):
250 '__u16 nregs' offset changed from 250 '__u16 nregs' offset changed from 64 to 96 (in bits) (by +32 bits)
251 '__u16 __reserved[3]' offset chang 251 '__u16 __reserved[3]' offset changed from 80 to 112 (in bits) (by +32 bits)
252 ========================================== 252 =======================================================================================
253 253
254 error - 1/884 UAPI headers compatible with 254 error - 1/884 UAPI headers compatible with arm64 appear _not_ to be backwards compatible
255 255
256 We can see with ``ARCH`` and ``CC`` set proper 256 We can see with ``ARCH`` and ``CC`` set properly for the file, the ABI
257 change is reported properly. Also notice that 257 change is reported properly. Also notice that the total number of UAPI
258 header files checked by the script changes. Th 258 header files checked by the script changes. This is because the number
259 of headers installed for arm64 platforms is di 259 of headers installed for arm64 platforms is different than x86.
260 260
261 Cross-Dependency Breakages 261 Cross-Dependency Breakages
262 -------------------------- 262 --------------------------
263 263
264 Consider this change:: 264 Consider this change::
265 265
266 cat << 'EOF' | patch -l -p1 266 cat << 'EOF' | patch -l -p1
267 --- a/include/uapi/linux/types.h 267 --- a/include/uapi/linux/types.h
268 +++ b/include/uapi/linux/types.h 268 +++ b/include/uapi/linux/types.h
269 @@ -52,7 +52,7 @@ typedef __u32 __bitwise 269 @@ -52,7 +52,7 @@ typedef __u32 __bitwise __wsum;
270 #define __aligned_be64 __be64 __attribute 270 #define __aligned_be64 __be64 __attribute__((aligned(8)))
271 #define __aligned_le64 __le64 __attribute 271 #define __aligned_le64 __le64 __attribute__((aligned(8)))
272 272
273 -typedef unsigned __bitwise __poll_t; 273 -typedef unsigned __bitwise __poll_t;
274 +typedef unsigned short __bitwise __poll_t 274 +typedef unsigned short __bitwise __poll_t;
275 275
276 #endif /* __ASSEMBLY__ */ 276 #endif /* __ASSEMBLY__ */
277 #endif /* _UAPI_LINUX_TYPES_H */ 277 #endif /* _UAPI_LINUX_TYPES_H */
278 EOF 278 EOF
279 279
280 Here, we're changing a ``typedef`` in ``types. 280 Here, we're changing a ``typedef`` in ``types.h``. This doesn't break
281 a UAPI in ``types.h``, but other UAPIs in the 281 a UAPI in ``types.h``, but other UAPIs in the tree may break due to
282 this change:: 282 this change::
283 283
284 % ./scripts/check-uapi.sh 284 % ./scripts/check-uapi.sh
285 Installing user-facing UAPI headers from d 285 Installing user-facing UAPI headers from dirty tree... OK
286 Installing user-facing UAPI headers from H 286 Installing user-facing UAPI headers from HEAD... OK
287 Checking changes to UAPI headers between H 287 Checking changes to UAPI headers between HEAD and dirty tree...
288 ==== ABI differences detected in include/l 288 ==== ABI differences detected in include/linux/eventpoll.h from HEAD -> dirty tree ====
289 [C] 'struct epoll_event' changed: 289 [C] 'struct epoll_event' changed:
290 type size changed from 96 to 80 (in 290 type size changed from 96 to 80 (in bits)
291 2 data member changes: 291 2 data member changes:
292 type of '__poll_t events' changed: 292 type of '__poll_t events' changed:
293 underlying type 'unsigned int' c 293 underlying type 'unsigned int' changed:
294 type name changed from 'unsign 294 type name changed from 'unsigned int' to 'unsigned short int'
295 type size changed from 32 to 1 295 type size changed from 32 to 16 (in bits)
296 '__u64 data' offset changed from 3 296 '__u64 data' offset changed from 32 to 16 (in bits) (by -16 bits)
297 ========================================== 297 ========================================================================================
298 include/linux/eventpoll.h did not change b 298 include/linux/eventpoll.h did not change between HEAD and dirty tree...
299 It's possible a change to one of the heade 299 It's possible a change to one of the headers it includes caused this error:
300 #include <linux/fcntl.h> 300 #include <linux/fcntl.h>
301 #include <linux/types.h> 301 #include <linux/types.h>
302 302
303 Note that the script noticed the failing heade 303 Note that the script noticed the failing header file did not change,
304 so it assumes one of its includes must have ca 304 so it assumes one of its includes must have caused the breakage. Indeed,
305 we can see ``linux/types.h`` is used from ``ev 305 we can see ``linux/types.h`` is used from ``eventpoll.h``.
306 306
307 UAPI Header Removals 307 UAPI Header Removals
308 -------------------- 308 --------------------
309 309
310 Consider this change:: 310 Consider this change::
311 311
312 cat << 'EOF' | patch -l -p1 312 cat << 'EOF' | patch -l -p1
313 diff --git a/include/uapi/asm-generic/Kbui 313 diff --git a/include/uapi/asm-generic/Kbuild b/include/uapi/asm-generic/Kbuild
314 index ebb180aac74e..a9c88b0a8b3b 100644 314 index ebb180aac74e..a9c88b0a8b3b 100644
315 --- a/include/uapi/asm-generic/Kbuild 315 --- a/include/uapi/asm-generic/Kbuild
316 +++ b/include/uapi/asm-generic/Kbuild 316 +++ b/include/uapi/asm-generic/Kbuild
317 @@ -31,6 +31,6 @@ mandatory-y += stat.h 317 @@ -31,6 +31,6 @@ mandatory-y += stat.h
318 mandatory-y += statfs.h 318 mandatory-y += statfs.h
319 mandatory-y += swab.h 319 mandatory-y += swab.h
320 mandatory-y += termbits.h 320 mandatory-y += termbits.h
321 -mandatory-y += termios.h 321 -mandatory-y += termios.h
322 +#mandatory-y += termios.h 322 +#mandatory-y += termios.h
323 mandatory-y += types.h 323 mandatory-y += types.h
324 mandatory-y += unistd.h 324 mandatory-y += unistd.h
325 EOF 325 EOF
326 326
327 This script removes a UAPI header file from th 327 This script removes a UAPI header file from the install list. Let's run
328 the script:: 328 the script::
329 329
330 % ./scripts/check-uapi.sh 330 % ./scripts/check-uapi.sh
331 Installing user-facing UAPI headers from d 331 Installing user-facing UAPI headers from dirty tree... OK
332 Installing user-facing UAPI headers from H 332 Installing user-facing UAPI headers from HEAD... OK
333 Checking changes to UAPI headers between H 333 Checking changes to UAPI headers between HEAD and dirty tree...
334 ==== UAPI header include/asm/termios.h was 334 ==== UAPI header include/asm/termios.h was removed between HEAD and dirty tree ====
335 335
336 error - 1/912 UAPI headers compatible with 336 error - 1/912 UAPI headers compatible with x86 appear _not_ to be backwards compatible
337 337
338 Removing a UAPI header is considered a breakin 338 Removing a UAPI header is considered a breaking change, and the script
339 will flag it as such. 339 will flag it as such.
340 340
341 Checking Historic UAPI Compatibility 341 Checking Historic UAPI Compatibility
342 ------------------------------------ 342 ------------------------------------
343 343
344 You can use the ``-b`` and ``-p`` options to e 344 You can use the ``-b`` and ``-p`` options to examine different chunks of your
345 git tree. For example, to check all changed UA 345 git tree. For example, to check all changed UAPI header files between tags
346 v6.0 and v6.1, you'd run:: 346 v6.0 and v6.1, you'd run::
347 347
348 % ./scripts/check-uapi.sh -b v6.1 -p v6.0 348 % ./scripts/check-uapi.sh -b v6.1 -p v6.0
349 Installing user-facing UAPI headers from v 349 Installing user-facing UAPI headers from v6.1... OK
350 Installing user-facing UAPI headers from v 350 Installing user-facing UAPI headers from v6.0... OK
351 Checking changes to UAPI headers between v 351 Checking changes to UAPI headers between v6.0 and v6.1...
352 352
353 --- snip --- 353 --- snip ---
354 error - 37/907 UAPI headers compatible wit 354 error - 37/907 UAPI headers compatible with x86 appear _not_ to be backwards compatible
355 355
356 Note: Before v5.3, a header file needed by the 356 Note: Before v5.3, a header file needed by the script is not present,
357 so the script is unable to check changes befor 357 so the script is unable to check changes before then.
358 358
359 You'll notice that the script detected many UA 359 You'll notice that the script detected many UAPI changes that are not
360 backwards compatible. Knowing that kernel UAPI 360 backwards compatible. Knowing that kernel UAPIs are supposed to be stable
361 forever, this is an alarming result. This brin 361 forever, this is an alarming result. This brings us to the next section:
362 caveats. 362 caveats.
363 363
364 Caveats 364 Caveats
365 ======= 365 =======
366 366
367 The UAPI checker makes no assumptions about th 367 The UAPI checker makes no assumptions about the author's intention, so some
368 types of changes may be flagged even though th 368 types of changes may be flagged even though they intentionally break UAPI.
369 369
370 Removals For Refactoring or Deprecation 370 Removals For Refactoring or Deprecation
371 --------------------------------------- 371 ---------------------------------------
372 372
373 Sometimes drivers for very old hardware are re 373 Sometimes drivers for very old hardware are removed, such as in this example::
374 374
375 % ./scripts/check-uapi.sh -b ba47652ba655 375 % ./scripts/check-uapi.sh -b ba47652ba655
376 Installing user-facing UAPI headers from b 376 Installing user-facing UAPI headers from ba47652ba655... OK
377 Installing user-facing UAPI headers from b 377 Installing user-facing UAPI headers from ba47652ba655^1... OK
378 Checking changes to UAPI headers between b 378 Checking changes to UAPI headers between ba47652ba655^1 and ba47652ba655...
379 ==== UAPI header include/linux/meye.h was 379 ==== UAPI header include/linux/meye.h was removed between ba47652ba655^1 and ba47652ba655 ====
380 380
381 error - 1/910 UAPI headers compatible with 381 error - 1/910 UAPI headers compatible with x86 appear _not_ to be backwards compatible
382 382
383 The script will always flag removals (even if 383 The script will always flag removals (even if they're intentional).
384 384
385 Struct Expansions 385 Struct Expansions
386 ----------------- 386 -----------------
387 387
388 Depending on how a structure is handled in ker 388 Depending on how a structure is handled in kernelspace, a change which
389 expands a struct could be non-breaking. 389 expands a struct could be non-breaking.
390 390
391 If a struct is used as the argument to an ioct 391 If a struct is used as the argument to an ioctl, then the kernel driver
392 must be able to handle ioctl commands of any s 392 must be able to handle ioctl commands of any size. Beyond that, you need
393 to be careful when copying data from the user. 393 to be careful when copying data from the user. Say, for example, that
394 ``struct foo`` is changed like this:: 394 ``struct foo`` is changed like this::
395 395
396 struct foo { 396 struct foo {
397 __u64 a; /* added in version 1 */ 397 __u64 a; /* added in version 1 */
398 + __u32 b; /* added in version 2 */ 398 + __u32 b; /* added in version 2 */
399 + __u32 c; /* added in version 2 */ 399 + __u32 c; /* added in version 2 */
400 } 400 }
401 401
402 By default, the script will flag this kind of 402 By default, the script will flag this kind of change for further review::
403 403
404 [C] 'struct foo' changed: 404 [C] 'struct foo' changed:
405 type size changed from 64 to 128 (in bit 405 type size changed from 64 to 128 (in bits)
406 2 data member insertions: 406 2 data member insertions:
407 '__u32 b', at offset 64 (in bits) 407 '__u32 b', at offset 64 (in bits)
408 '__u32 c', at offset 96 (in bits) 408 '__u32 c', at offset 96 (in bits)
409 409
410 However, it is possible that this change was m 410 However, it is possible that this change was made safely.
411 411
412 If a userspace program was built with version 412 If a userspace program was built with version 1, it will think
413 ``sizeof(struct foo)`` is 8. That size will be 413 ``sizeof(struct foo)`` is 8. That size will be encoded in the
414 ioctl value that gets sent to the kernel. If t 414 ioctl value that gets sent to the kernel. If the kernel is built
415 with version 2, it will think the ``sizeof(str 415 with version 2, it will think the ``sizeof(struct foo)`` is 16.
416 416
417 The kernel can use the ``_IOC_SIZE`` macro to 417 The kernel can use the ``_IOC_SIZE`` macro to get the size encoded
418 in the ioctl code that the user passed in and 418 in the ioctl code that the user passed in and then use
419 ``copy_struct_from_user()`` to safely copy the 419 ``copy_struct_from_user()`` to safely copy the value::
420 420
421 int handle_ioctl(unsigned long cmd, unsign 421 int handle_ioctl(unsigned long cmd, unsigned long arg)
422 { 422 {
423 switch _IOC_NR(cmd) { 423 switch _IOC_NR(cmd) {
424 0x01: { 424 0x01: {
425 struct foo my_cmd; /* size 16 in 425 struct foo my_cmd; /* size 16 in the kernel */
426 426
427 ret = copy_struct_from_user(&my_cm 427 ret = copy_struct_from_user(&my_cmd, arg, sizeof(struct foo), _IOC_SIZE(cmd));
428 ... 428 ...
429 429
430 ``copy_struct_from_user`` will zero the struct 430 ``copy_struct_from_user`` will zero the struct in the kernel and then copy
431 only the bytes passed in from the user (leavin 431 only the bytes passed in from the user (leaving new members zeroized).
432 If the user passed in a larger struct, the ext 432 If the user passed in a larger struct, the extra members are ignored.
433 433
434 If you know this situation is accounted for in 434 If you know this situation is accounted for in the kernel code, you can
435 pass ``-i`` to the script, and struct expansio 435 pass ``-i`` to the script, and struct expansions like this will be ignored.
436 436
437 Flex Array Migration 437 Flex Array Migration
438 -------------------- 438 --------------------
439 439
440 While the script handles expansion into an exi 440 While the script handles expansion into an existing flex array, it does
441 still flag initial migration to flex arrays fr 441 still flag initial migration to flex arrays from 1-element fake flex
442 arrays. For example:: 442 arrays. For example::
443 443
444 struct foo { 444 struct foo {
445 __u32 x; 445 __u32 x;
446 - __u32 flex[1]; /* fake flex */ 446 - __u32 flex[1]; /* fake flex */
447 + __u32 flex[]; /* real flex */ 447 + __u32 flex[]; /* real flex */
448 }; 448 };
449 449
450 This change would be flagged by the script:: 450 This change would be flagged by the script::
451 451
452 [C] 'struct foo' changed: 452 [C] 'struct foo' changed:
453 type size changed from 64 to 32 (in bits 453 type size changed from 64 to 32 (in bits)
454 1 data member change: 454 1 data member change:
455 type of '__u32 flex[1]' changed: 455 type of '__u32 flex[1]' changed:
456 type name changed from '__u32[1]' to 456 type name changed from '__u32[1]' to '__u32[]'
457 array type size changed from 32 to ' 457 array type size changed from 32 to 'unknown'
458 array type subrange 1 changed length 458 array type subrange 1 changed length from 1 to 'unknown'
459 459
460 At this time, there's no way to filter these t 460 At this time, there's no way to filter these types of changes, so be
461 aware of this possible false positive. 461 aware of this possible false positive.
462 462
463 Summary 463 Summary
464 ------- 464 -------
465 465
466 While many types of false positives are filter 466 While many types of false positives are filtered out by the script,
467 it's possible there are some cases where the s 467 it's possible there are some cases where the script flags a change
468 which does not break UAPI. It's also possible 468 which does not break UAPI. It's also possible a change which *does*
469 break userspace would not be flagged by this s 469 break userspace would not be flagged by this script. While the script
470 has been run on much of the kernel history, th 470 has been run on much of the kernel history, there could still be corner
471 cases that are not accounted for. 471 cases that are not accounted for.
472 472
473 The intention is for this script to be used as 473 The intention is for this script to be used as a quick check for
474 maintainers or automated tooling, not as the e 474 maintainers or automated tooling, not as the end-all authority on
475 patch compatibility. It's best to remember: us 475 patch compatibility. It's best to remember: use your best judgment
476 (and ideally a unit test in userspace) to make 476 (and ideally a unit test in userspace) to make sure your UAPI changes
477 are backwards-compatible! 477 are backwards-compatible!
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