10 *
11 * This module handles execution of a.out files which have been run through
12 * "gzip". This saves diskspace, but wastes cpu-cycles and VM.
13 *
14 * TODO:
15 * text-segments should be made R/O after being filled
16 * is the vm-stuff safe ?
17 * should handle the entire header of gzip'ed stuff.
18 * inflate isn't quite reentrant yet...
19 * error-handling is a mess...
20 * so is the rest...
21 * tidy up unnecesary includes
22 */
23
24#include <sys/param.h>
25#include <sys/exec.h>
26#include <sys/imgact.h>
27#include <sys/imgact_aout.h>
28#include <sys/kernel.h>
29#include <sys/lock.h>
30#include <sys/mman.h>
31#include <sys/mutex.h>
32#include <sys/proc.h>
33#include <sys/resourcevar.h>
34#include <sys/sysent.h>
35#include <sys/systm.h>
36#include <sys/vnode.h>
37#include <sys/inflate.h>
38
39#include <vm/vm.h>
40#include <vm/vm_param.h>
41#include <vm/pmap.h>
42#include <vm/vm_map.h>
43#include <vm/vm_kern.h>
44#include <vm/vm_extern.h>
45
46struct imgact_gzip {
47 struct image_params *ip;
48 struct exec a_out;
49 int error;
50 int gotheader;
51 int where;
52 u_char *inbuf;
53 u_long offset;
54 u_long output;
55 u_long len;
56 int idx;
57 u_long virtual_offset, file_offset, file_end, bss_size;
58};
59
60static int exec_gzip_imgact __P((struct image_params *imgp));
61static int NextByte __P((void *vp));
62static int do_aout_hdr __P((struct imgact_gzip *));
63static int Flush __P((void *vp, u_char *, u_long siz));
64
65static int
66exec_gzip_imgact(imgp)
67 struct image_params *imgp;
68{
69 int error, error2 = 0;
70 const u_char *p = (const u_char *) imgp->image_header;
71 struct imgact_gzip igz;
72 struct inflate infl;
73 struct vmspace *vmspace;
74
75 /* If these four are not OK, it isn't a gzip file */
76 if (p[0] != 0x1f)
77 return -1; /* 0 Simply magic */
78 if (p[1] != 0x8b)
79 return -1; /* 1 Simply magic */
80 if (p[2] != 0x08)
81 return -1; /* 2 Compression method */
82 if (p[9] != 0x03)
83 return -1; /* 9 OS compressed on */
84
85 /*
86 * If this one contains anything but a comment or a filename marker,
87 * we don't want to chew on it
88 */
89 if (p[3] & ~(0x18))
90 return ENOEXEC; /* 3 Flags */
91
92 /* These are of no use to us */
93 /* 4-7 Timestamp */
94 /* 8 Extra flags */
95
96 bzero(&igz, sizeof igz);
97 bzero(&infl, sizeof infl);
98 infl.gz_private = (void *) &igz;
99 infl.gz_input = NextByte;
100 infl.gz_output = Flush;
101
102 igz.ip = imgp;
103 igz.idx = 10;
104
105 if (p[3] & 0x08) { /* skip a filename */
106 while (p[igz.idx++])
107 if (igz.idx >= PAGE_SIZE)
108 return ENOEXEC;
109 }
110 if (p[3] & 0x10) { /* skip a comment */
111 while (p[igz.idx++])
112 if (igz.idx >= PAGE_SIZE)
113 return ENOEXEC;
114 }
115 igz.len = imgp->attr->va_size;
116
117 error = inflate(&infl);
118
119 /*
120 * The unzipped file may not even have been long enough to contain
121 * a header giving Flush() a chance to return error. Check for this.
122 */
123 if ( !igz.gotheader )
124 return ENOEXEC;
125
126 if ( !error ) {
127 vmspace = imgp->proc->p_vmspace;
128 error = vm_map_protect(&vmspace->vm_map,
129 (vm_offset_t) vmspace->vm_taddr,
130 (vm_offset_t) (vmspace->vm_taddr +
131 (vmspace->vm_tsize << PAGE_SHIFT)) ,
132 VM_PROT_READ|VM_PROT_EXECUTE,0);
133 }
134
135 if (igz.inbuf) {
136 error2 =
137 vm_map_remove(kernel_map, (vm_offset_t) igz.inbuf,
138 (vm_offset_t) igz.inbuf + PAGE_SIZE);
139 }
140 if (igz.error || error || error2) {
141 printf("Output=%lu ", igz.output);
142 printf("Inflate_error=%d igz.error=%d error2=%d where=%d\n",
143 error, igz.error, error2, igz.where);
144 }
145 if (igz.error)
146 return igz.error;
147 if (error)
148 return ENOEXEC;
149 if (error2)
150 return error2;
151 return 0;
152}
153
154static int
155do_aout_hdr(struct imgact_gzip * gz)
156{
157 int error;
158 struct vmspace *vmspace;
159 vm_offset_t vmaddr;
160
161 /*
162 * Set file/virtual offset based on a.out variant. We do two cases:
163 * host byte order and network byte order (for NetBSD compatibility)
164 */
165 switch ((int) (gz->a_out.a_magic & 0xffff)) {
166 case ZMAGIC:
167 gz->virtual_offset = 0;
168 if (gz->a_out.a_text) {
169 gz->file_offset = PAGE_SIZE;
170 } else {
171 /* Bill's "screwball mode" */
172 gz->file_offset = 0;
173 }
174 break;
175 case QMAGIC:
176 gz->virtual_offset = PAGE_SIZE;
177 gz->file_offset = 0;
178 break;
179 default:
180 /* NetBSD compatibility */
181 switch ((int) (ntohl(gz->a_out.a_magic) & 0xffff)) {
182 case ZMAGIC:
183 case QMAGIC:
184 gz->virtual_offset = PAGE_SIZE;
185 gz->file_offset = 0;
186 break;
187 default:
188 gz->where = __LINE__;
189 return (-1);
190 }
191 }
192
193 gz->bss_size = roundup(gz->a_out.a_bss, PAGE_SIZE);
194
195 /*
196 * Check various fields in header for validity/bounds.
197 */
198 if ( /* entry point must lay with text region */
199 gz->a_out.a_entry < gz->virtual_offset ||
200 gz->a_out.a_entry >= gz->virtual_offset + gz->a_out.a_text ||
201
202 /* text and data size must each be page rounded */
203 gz->a_out.a_text & PAGE_MASK || gz->a_out.a_data & PAGE_MASK) {
204 gz->where = __LINE__;
205 return (-1);
206 }
207 /*
208 * text/data/bss must not exceed limits
209 */
210 mtx_assert(&Giant, MA_OWNED);
211 if ( /* text can't exceed maximum text size */
| 10 *
11 * This module handles execution of a.out files which have been run through
12 * "gzip". This saves diskspace, but wastes cpu-cycles and VM.
13 *
14 * TODO:
15 * text-segments should be made R/O after being filled
16 * is the vm-stuff safe ?
17 * should handle the entire header of gzip'ed stuff.
18 * inflate isn't quite reentrant yet...
19 * error-handling is a mess...
20 * so is the rest...
21 * tidy up unnecesary includes
22 */
23
24#include <sys/param.h>
25#include <sys/exec.h>
26#include <sys/imgact.h>
27#include <sys/imgact_aout.h>
28#include <sys/kernel.h>
29#include <sys/lock.h>
30#include <sys/mman.h>
31#include <sys/mutex.h>
32#include <sys/proc.h>
33#include <sys/resourcevar.h>
34#include <sys/sysent.h>
35#include <sys/systm.h>
36#include <sys/vnode.h>
37#include <sys/inflate.h>
38
39#include <vm/vm.h>
40#include <vm/vm_param.h>
41#include <vm/pmap.h>
42#include <vm/vm_map.h>
43#include <vm/vm_kern.h>
44#include <vm/vm_extern.h>
45
46struct imgact_gzip {
47 struct image_params *ip;
48 struct exec a_out;
49 int error;
50 int gotheader;
51 int where;
52 u_char *inbuf;
53 u_long offset;
54 u_long output;
55 u_long len;
56 int idx;
57 u_long virtual_offset, file_offset, file_end, bss_size;
58};
59
60static int exec_gzip_imgact __P((struct image_params *imgp));
61static int NextByte __P((void *vp));
62static int do_aout_hdr __P((struct imgact_gzip *));
63static int Flush __P((void *vp, u_char *, u_long siz));
64
65static int
66exec_gzip_imgact(imgp)
67 struct image_params *imgp;
68{
69 int error, error2 = 0;
70 const u_char *p = (const u_char *) imgp->image_header;
71 struct imgact_gzip igz;
72 struct inflate infl;
73 struct vmspace *vmspace;
74
75 /* If these four are not OK, it isn't a gzip file */
76 if (p[0] != 0x1f)
77 return -1; /* 0 Simply magic */
78 if (p[1] != 0x8b)
79 return -1; /* 1 Simply magic */
80 if (p[2] != 0x08)
81 return -1; /* 2 Compression method */
82 if (p[9] != 0x03)
83 return -1; /* 9 OS compressed on */
84
85 /*
86 * If this one contains anything but a comment or a filename marker,
87 * we don't want to chew on it
88 */
89 if (p[3] & ~(0x18))
90 return ENOEXEC; /* 3 Flags */
91
92 /* These are of no use to us */
93 /* 4-7 Timestamp */
94 /* 8 Extra flags */
95
96 bzero(&igz, sizeof igz);
97 bzero(&infl, sizeof infl);
98 infl.gz_private = (void *) &igz;
99 infl.gz_input = NextByte;
100 infl.gz_output = Flush;
101
102 igz.ip = imgp;
103 igz.idx = 10;
104
105 if (p[3] & 0x08) { /* skip a filename */
106 while (p[igz.idx++])
107 if (igz.idx >= PAGE_SIZE)
108 return ENOEXEC;
109 }
110 if (p[3] & 0x10) { /* skip a comment */
111 while (p[igz.idx++])
112 if (igz.idx >= PAGE_SIZE)
113 return ENOEXEC;
114 }
115 igz.len = imgp->attr->va_size;
116
117 error = inflate(&infl);
118
119 /*
120 * The unzipped file may not even have been long enough to contain
121 * a header giving Flush() a chance to return error. Check for this.
122 */
123 if ( !igz.gotheader )
124 return ENOEXEC;
125
126 if ( !error ) {
127 vmspace = imgp->proc->p_vmspace;
128 error = vm_map_protect(&vmspace->vm_map,
129 (vm_offset_t) vmspace->vm_taddr,
130 (vm_offset_t) (vmspace->vm_taddr +
131 (vmspace->vm_tsize << PAGE_SHIFT)) ,
132 VM_PROT_READ|VM_PROT_EXECUTE,0);
133 }
134
135 if (igz.inbuf) {
136 error2 =
137 vm_map_remove(kernel_map, (vm_offset_t) igz.inbuf,
138 (vm_offset_t) igz.inbuf + PAGE_SIZE);
139 }
140 if (igz.error || error || error2) {
141 printf("Output=%lu ", igz.output);
142 printf("Inflate_error=%d igz.error=%d error2=%d where=%d\n",
143 error, igz.error, error2, igz.where);
144 }
145 if (igz.error)
146 return igz.error;
147 if (error)
148 return ENOEXEC;
149 if (error2)
150 return error2;
151 return 0;
152}
153
154static int
155do_aout_hdr(struct imgact_gzip * gz)
156{
157 int error;
158 struct vmspace *vmspace;
159 vm_offset_t vmaddr;
160
161 /*
162 * Set file/virtual offset based on a.out variant. We do two cases:
163 * host byte order and network byte order (for NetBSD compatibility)
164 */
165 switch ((int) (gz->a_out.a_magic & 0xffff)) {
166 case ZMAGIC:
167 gz->virtual_offset = 0;
168 if (gz->a_out.a_text) {
169 gz->file_offset = PAGE_SIZE;
170 } else {
171 /* Bill's "screwball mode" */
172 gz->file_offset = 0;
173 }
174 break;
175 case QMAGIC:
176 gz->virtual_offset = PAGE_SIZE;
177 gz->file_offset = 0;
178 break;
179 default:
180 /* NetBSD compatibility */
181 switch ((int) (ntohl(gz->a_out.a_magic) & 0xffff)) {
182 case ZMAGIC:
183 case QMAGIC:
184 gz->virtual_offset = PAGE_SIZE;
185 gz->file_offset = 0;
186 break;
187 default:
188 gz->where = __LINE__;
189 return (-1);
190 }
191 }
192
193 gz->bss_size = roundup(gz->a_out.a_bss, PAGE_SIZE);
194
195 /*
196 * Check various fields in header for validity/bounds.
197 */
198 if ( /* entry point must lay with text region */
199 gz->a_out.a_entry < gz->virtual_offset ||
200 gz->a_out.a_entry >= gz->virtual_offset + gz->a_out.a_text ||
201
202 /* text and data size must each be page rounded */
203 gz->a_out.a_text & PAGE_MASK || gz->a_out.a_data & PAGE_MASK) {
204 gz->where = __LINE__;
205 return (-1);
206 }
207 /*
208 * text/data/bss must not exceed limits
209 */
210 mtx_assert(&Giant, MA_OWNED);
211 if ( /* text can't exceed maximum text size */
|
213
214 /* data + bss can't exceed rlimit */
215 gz->a_out.a_data + gz->bss_size >
216 gz->ip->proc->p_rlimit[RLIMIT_DATA].rlim_cur) {
217 gz->where = __LINE__;
218 return (ENOMEM);
219 }
220 /* Find out how far we should go */
221 gz->file_end = gz->file_offset + gz->a_out.a_text + gz->a_out.a_data;
222
223 /* copy in arguments and/or environment from old process */
224 error = exec_extract_strings(gz->ip);
225 if (error) {
226 gz->where = __LINE__;
227 return (error);
228 }
229 /*
230 * Destroy old process VM and create a new one (with a new stack)
231 */
232 exec_new_vmspace(gz->ip);
233
234 vmspace = gz->ip->proc->p_vmspace;
235
236 vmaddr = gz->virtual_offset;
237
238 error = vm_mmap(&vmspace->vm_map,
239 &vmaddr,
240 gz->a_out.a_text + gz->a_out.a_data,
241 VM_PROT_ALL, VM_PROT_ALL, MAP_ANON | MAP_FIXED,
242 0,
243 0);
244
245 if (error) {
246 gz->where = __LINE__;
247 return (error);
248 }
249
250 if (gz->bss_size != 0) {
251 /*
252 * Allocate demand-zeroed area for uninitialized data.
253 * "bss" = 'block started by symbol' - named after the
254 * IBM 7090 instruction of the same name.
255 */
256 vmaddr = gz->virtual_offset + gz->a_out.a_text +
257 gz->a_out.a_data;
258 error = vm_map_find(&vmspace->vm_map,
259 NULL,
260 0,
261 &vmaddr,
262 gz->bss_size,
263 FALSE, VM_PROT_ALL, VM_PROT_ALL, 0);
264 if (error) {
265 gz->where = __LINE__;
266 return (error);
267 }
268 }
269 /* Fill in process VM information */
270 vmspace->vm_tsize = gz->a_out.a_text >> PAGE_SHIFT;
271 vmspace->vm_dsize = (gz->a_out.a_data + gz->bss_size) >> PAGE_SHIFT;
272 vmspace->vm_taddr = (caddr_t) (uintptr_t) gz->virtual_offset;
273 vmspace->vm_daddr = (caddr_t) (uintptr_t)
274 (gz->virtual_offset + gz->a_out.a_text);
275
276 /* Fill in image_params */
277 gz->ip->interpreted = 0;
278 gz->ip->entry_addr = gz->a_out.a_entry;
279
280 gz->ip->proc->p_sysent = &aout_sysvec;
281
282 return 0;
283}
284
285static int
286NextByte(void *vp)
287{
288 int error;
289 struct imgact_gzip *igz = (struct imgact_gzip *) vp;
290
291 if (igz->idx >= igz->len) {
292 igz->where = __LINE__;
293 return GZ_EOF;
294 }
295 if (igz->inbuf && igz->idx < (igz->offset + PAGE_SIZE)) {
296 return igz->inbuf[(igz->idx++) - igz->offset];
297 }
298 if (igz->inbuf) {
299 error = vm_map_remove(kernel_map, (vm_offset_t) igz->inbuf,
300 (vm_offset_t) igz->inbuf + PAGE_SIZE);
301 if (error) {
302 igz->where = __LINE__;
303 igz->error = error;
304 return GZ_EOF;
305 }
306 }
307 igz->offset = igz->idx & ~PAGE_MASK;
308
309 error = vm_mmap(kernel_map, /* map */
310 (vm_offset_t *) & igz->inbuf, /* address */
311 PAGE_SIZE, /* size */
312 VM_PROT_READ, /* protection */
313 VM_PROT_READ, /* max protection */
314 0, /* flags */
315 (caddr_t) igz->ip->vp, /* vnode */
316 igz->offset); /* offset */
317 if (error) {
318 igz->where = __LINE__;
319 igz->error = error;
320 return GZ_EOF;
321 }
322 return igz->inbuf[(igz->idx++) - igz->offset];
323}
324
325static int
326Flush(void *vp, u_char * ptr, u_long siz)
327{
328 struct imgact_gzip *gz = (struct imgact_gzip *) vp;
329 u_char *p = ptr, *q;
330 int i;
331
332 /* First, find a a.out-header */
333 if (gz->output < sizeof gz->a_out) {
334 q = (u_char *) & gz->a_out;
335 i = min(siz, sizeof gz->a_out - gz->output);
336 bcopy(p, q + gz->output, i);
337 gz->output += i;
338 p += i;
339 siz -= i;
340 if (gz->output == sizeof gz->a_out) {
341 gz->gotheader = 1;
342 i = do_aout_hdr(gz);
343 if (i == -1) {
344 if (!gz->where)
345 gz->where = __LINE__;
346 gz->error = ENOEXEC;
347 return ENOEXEC;
348 } else if (i) {
349 gz->where = __LINE__;
350 gz->error = i;
351 return ENOEXEC;
352 }
353 if (gz->file_offset == 0) {
354 q = (u_char *) (uintptr_t) gz->virtual_offset;
355 copyout(&gz->a_out, q, sizeof gz->a_out);
356 }
357 }
358 }
359 /* Skip over zero-padded first PAGE if needed */
360 if (gz->output < gz->file_offset &&
361 gz->output + siz > gz->file_offset) {
362 i = min(siz, gz->file_offset - gz->output);
363 gz->output += i;
364 p += i;
365 siz -= i;
366 }
367 if (gz->output >= gz->file_offset && gz->output < gz->file_end) {
368 i = min(siz, gz->file_end - gz->output);
369 q = (u_char *) (uintptr_t)
370 (gz->virtual_offset + gz->output - gz->file_offset);
371 copyout(p, q, i);
372 gz->output += i;
373 p += i;
374 siz -= i;
375 }
376 gz->output += siz;
377 return 0;
378}
379
380
381/*
382 * Tell kern_execve.c about it, with a little help from the linker.
383 */
384static struct execsw gzip_execsw = {exec_gzip_imgact, "gzip"};
385EXEC_SET(execgzip, gzip_execsw);
| 213
214 /* data + bss can't exceed rlimit */
215 gz->a_out.a_data + gz->bss_size >
216 gz->ip->proc->p_rlimit[RLIMIT_DATA].rlim_cur) {
217 gz->where = __LINE__;
218 return (ENOMEM);
219 }
220 /* Find out how far we should go */
221 gz->file_end = gz->file_offset + gz->a_out.a_text + gz->a_out.a_data;
222
223 /* copy in arguments and/or environment from old process */
224 error = exec_extract_strings(gz->ip);
225 if (error) {
226 gz->where = __LINE__;
227 return (error);
228 }
229 /*
230 * Destroy old process VM and create a new one (with a new stack)
231 */
232 exec_new_vmspace(gz->ip);
233
234 vmspace = gz->ip->proc->p_vmspace;
235
236 vmaddr = gz->virtual_offset;
237
238 error = vm_mmap(&vmspace->vm_map,
239 &vmaddr,
240 gz->a_out.a_text + gz->a_out.a_data,
241 VM_PROT_ALL, VM_PROT_ALL, MAP_ANON | MAP_FIXED,
242 0,
243 0);
244
245 if (error) {
246 gz->where = __LINE__;
247 return (error);
248 }
249
250 if (gz->bss_size != 0) {
251 /*
252 * Allocate demand-zeroed area for uninitialized data.
253 * "bss" = 'block started by symbol' - named after the
254 * IBM 7090 instruction of the same name.
255 */
256 vmaddr = gz->virtual_offset + gz->a_out.a_text +
257 gz->a_out.a_data;
258 error = vm_map_find(&vmspace->vm_map,
259 NULL,
260 0,
261 &vmaddr,
262 gz->bss_size,
263 FALSE, VM_PROT_ALL, VM_PROT_ALL, 0);
264 if (error) {
265 gz->where = __LINE__;
266 return (error);
267 }
268 }
269 /* Fill in process VM information */
270 vmspace->vm_tsize = gz->a_out.a_text >> PAGE_SHIFT;
271 vmspace->vm_dsize = (gz->a_out.a_data + gz->bss_size) >> PAGE_SHIFT;
272 vmspace->vm_taddr = (caddr_t) (uintptr_t) gz->virtual_offset;
273 vmspace->vm_daddr = (caddr_t) (uintptr_t)
274 (gz->virtual_offset + gz->a_out.a_text);
275
276 /* Fill in image_params */
277 gz->ip->interpreted = 0;
278 gz->ip->entry_addr = gz->a_out.a_entry;
279
280 gz->ip->proc->p_sysent = &aout_sysvec;
281
282 return 0;
283}
284
285static int
286NextByte(void *vp)
287{
288 int error;
289 struct imgact_gzip *igz = (struct imgact_gzip *) vp;
290
291 if (igz->idx >= igz->len) {
292 igz->where = __LINE__;
293 return GZ_EOF;
294 }
295 if (igz->inbuf && igz->idx < (igz->offset + PAGE_SIZE)) {
296 return igz->inbuf[(igz->idx++) - igz->offset];
297 }
298 if (igz->inbuf) {
299 error = vm_map_remove(kernel_map, (vm_offset_t) igz->inbuf,
300 (vm_offset_t) igz->inbuf + PAGE_SIZE);
301 if (error) {
302 igz->where = __LINE__;
303 igz->error = error;
304 return GZ_EOF;
305 }
306 }
307 igz->offset = igz->idx & ~PAGE_MASK;
308
309 error = vm_mmap(kernel_map, /* map */
310 (vm_offset_t *) & igz->inbuf, /* address */
311 PAGE_SIZE, /* size */
312 VM_PROT_READ, /* protection */
313 VM_PROT_READ, /* max protection */
314 0, /* flags */
315 (caddr_t) igz->ip->vp, /* vnode */
316 igz->offset); /* offset */
317 if (error) {
318 igz->where = __LINE__;
319 igz->error = error;
320 return GZ_EOF;
321 }
322 return igz->inbuf[(igz->idx++) - igz->offset];
323}
324
325static int
326Flush(void *vp, u_char * ptr, u_long siz)
327{
328 struct imgact_gzip *gz = (struct imgact_gzip *) vp;
329 u_char *p = ptr, *q;
330 int i;
331
332 /* First, find a a.out-header */
333 if (gz->output < sizeof gz->a_out) {
334 q = (u_char *) & gz->a_out;
335 i = min(siz, sizeof gz->a_out - gz->output);
336 bcopy(p, q + gz->output, i);
337 gz->output += i;
338 p += i;
339 siz -= i;
340 if (gz->output == sizeof gz->a_out) {
341 gz->gotheader = 1;
342 i = do_aout_hdr(gz);
343 if (i == -1) {
344 if (!gz->where)
345 gz->where = __LINE__;
346 gz->error = ENOEXEC;
347 return ENOEXEC;
348 } else if (i) {
349 gz->where = __LINE__;
350 gz->error = i;
351 return ENOEXEC;
352 }
353 if (gz->file_offset == 0) {
354 q = (u_char *) (uintptr_t) gz->virtual_offset;
355 copyout(&gz->a_out, q, sizeof gz->a_out);
356 }
357 }
358 }
359 /* Skip over zero-padded first PAGE if needed */
360 if (gz->output < gz->file_offset &&
361 gz->output + siz > gz->file_offset) {
362 i = min(siz, gz->file_offset - gz->output);
363 gz->output += i;
364 p += i;
365 siz -= i;
366 }
367 if (gz->output >= gz->file_offset && gz->output < gz->file_end) {
368 i = min(siz, gz->file_end - gz->output);
369 q = (u_char *) (uintptr_t)
370 (gz->virtual_offset + gz->output - gz->file_offset);
371 copyout(p, q, i);
372 gz->output += i;
373 p += i;
374 siz -= i;
375 }
376 gz->output += siz;
377 return 0;
378}
379
380
381/*
382 * Tell kern_execve.c about it, with a little help from the linker.
383 */
384static struct execsw gzip_execsw = {exec_gzip_imgact, "gzip"};
385EXEC_SET(execgzip, gzip_execsw);
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