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Linux/arch/arm/vdso/vdsomunge.c

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  1 /*
  2  * Copyright 2015 Mentor Graphics Corporation.
  3  *
  4  * This program is free software; you can redistribute it and/or
  5  * modify it under the terms of the GNU General Public License
  6  * as published by the Free Software Foundation; version 2 of the
  7  * License.
  8  *
  9  * This program is distributed in the hope that it will be useful, but
 10  * WITHOUT ANY WARRANTY; without even the implied warranty of
 11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 12  * General Public License for more details.
 13  *
 14  * You should have received a copy of the GNU General Public License
 15  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 16  *
 17  *
 18  * vdsomunge - Host program which produces a shared object
 19  * architecturally specified to be usable by both soft- and hard-float
 20  * programs.
 21  *
 22  * The Procedure Call Standard for the ARM Architecture (ARM IHI
 23  * 0042E) says:
 24  *
 25  *      6.4.1 VFP and Base Standard Compatibility
 26  *
 27  *      Code compiled for the VFP calling standard is compatible with
 28  *      the base standard (and vice-versa) if no floating-point or
 29  *      containerized vector arguments or results are used.
 30  *
 31  * And ELF for the ARM Architecture (ARM IHI 0044E) (Table 4-2) says:
 32  *
 33  *      If both EF_ARM_ABI_FLOAT_XXXX bits are clear, conformance to the
 34  *      base procedure-call standard is implied.
 35  *
 36  * The VDSO is built with -msoft-float, as with the rest of the ARM
 37  * kernel, and uses no floating point arguments or results.  The build
 38  * process will produce a shared object that may or may not have the
 39  * EF_ARM_ABI_FLOAT_SOFT flag set (it seems to depend on the binutils
 40  * version; binutils starting with 2.24 appears to set it).  The
 41  * EF_ARM_ABI_FLOAT_HARD flag should definitely not be set, and this
 42  * program will error out if it is.
 43  *
 44  * If the soft-float flag is set, this program clears it.  That's all
 45  * it does.
 46  */
 47 
 48 #include <elf.h>
 49 #include <errno.h>
 50 #include <fcntl.h>
 51 #include <stdarg.h>
 52 #include <stdbool.h>
 53 #include <stdio.h>
 54 #include <stdlib.h>
 55 #include <string.h>
 56 #include <sys/mman.h>
 57 #include <sys/stat.h>
 58 #include <sys/types.h>
 59 #include <unistd.h>
 60 
 61 #define swab16(x) \
 62         ((((x) & 0x00ff) << 8) | \
 63          (((x) & 0xff00) >> 8))
 64 
 65 #define swab32(x) \
 66         ((((x) & 0x000000ff) << 24) | \
 67          (((x) & 0x0000ff00) <<  8) | \
 68          (((x) & 0x00ff0000) >>  8) | \
 69          (((x) & 0xff000000) >> 24))
 70 
 71 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 72 #define HOST_ORDER ELFDATA2LSB
 73 #elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 74 #define HOST_ORDER ELFDATA2MSB
 75 #endif
 76 
 77 /* Some of the ELF constants we'd like to use were added to <elf.h>
 78  * relatively recently.
 79  */
 80 #ifndef EF_ARM_EABI_VER5
 81 #define EF_ARM_EABI_VER5 0x05000000
 82 #endif
 83 
 84 #ifndef EF_ARM_ABI_FLOAT_SOFT
 85 #define EF_ARM_ABI_FLOAT_SOFT 0x200
 86 #endif
 87 
 88 #ifndef EF_ARM_ABI_FLOAT_HARD
 89 #define EF_ARM_ABI_FLOAT_HARD 0x400
 90 #endif
 91 
 92 static int failed;
 93 static const char *argv0;
 94 static const char *outfile;
 95 
 96 static void fail(const char *fmt, ...)
 97 {
 98         va_list ap;
 99 
100         failed = 1;
101         fprintf(stderr, "%s: ", argv0);
102         va_start(ap, fmt);
103         vfprintf(stderr, fmt, ap);
104         va_end(ap);
105         exit(EXIT_FAILURE);
106 }
107 
108 static void cleanup(void)
109 {
110         if (failed && outfile != NULL)
111                 unlink(outfile);
112 }
113 
114 static Elf32_Word read_elf_word(Elf32_Word word, bool swap)
115 {
116         return swap ? swab32(word) : word;
117 }
118 
119 static Elf32_Half read_elf_half(Elf32_Half half, bool swap)
120 {
121         return swap ? swab16(half) : half;
122 }
123 
124 static void write_elf_word(Elf32_Word val, Elf32_Word *dst, bool swap)
125 {
126         *dst = swap ? swab32(val) : val;
127 }
128 
129 int main(int argc, char **argv)
130 {
131         const Elf32_Ehdr *inhdr;
132         bool clear_soft_float;
133         const char *infile;
134         Elf32_Word e_flags;
135         const void *inbuf;
136         struct stat stat;
137         void *outbuf;
138         bool swap;
139         int outfd;
140         int infd;
141 
142         atexit(cleanup);
143         argv0 = argv[0];
144 
145         if (argc != 3)
146                 fail("Usage: %s [infile] [outfile]\n", argv[0]);
147 
148         infile = argv[1];
149         outfile = argv[2];
150 
151         infd = open(infile, O_RDONLY);
152         if (infd < 0)
153                 fail("Cannot open %s: %s\n", infile, strerror(errno));
154 
155         if (fstat(infd, &stat) != 0)
156                 fail("Failed stat for %s: %s\n", infile, strerror(errno));
157 
158         inbuf = mmap(NULL, stat.st_size, PROT_READ, MAP_PRIVATE, infd, 0);
159         if (inbuf == MAP_FAILED)
160                 fail("Failed to map %s: %s\n", infile, strerror(errno));
161 
162         close(infd);
163 
164         inhdr = inbuf;
165 
166         if (memcmp(&inhdr->e_ident, ELFMAG, SELFMAG) != 0)
167                 fail("Not an ELF file\n");
168 
169         if (inhdr->e_ident[EI_CLASS] != ELFCLASS32)
170                 fail("Unsupported ELF class\n");
171 
172         swap = inhdr->e_ident[EI_DATA] != HOST_ORDER;
173 
174         if (read_elf_half(inhdr->e_type, swap) != ET_DYN)
175                 fail("Not a shared object\n");
176 
177         if (read_elf_half(inhdr->e_machine, swap) != EM_ARM)
178                 fail("Unsupported architecture %#x\n", inhdr->e_machine);
179 
180         e_flags = read_elf_word(inhdr->e_flags, swap);
181 
182         if (EF_ARM_EABI_VERSION(e_flags) != EF_ARM_EABI_VER5) {
183                 fail("Unsupported EABI version %#x\n",
184                      EF_ARM_EABI_VERSION(e_flags));
185         }
186 
187         if (e_flags & EF_ARM_ABI_FLOAT_HARD)
188                 fail("Unexpected hard-float flag set in e_flags\n");
189 
190         clear_soft_float = !!(e_flags & EF_ARM_ABI_FLOAT_SOFT);
191 
192         outfd = open(outfile, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
193         if (outfd < 0)
194                 fail("Cannot open %s: %s\n", outfile, strerror(errno));
195 
196         if (ftruncate(outfd, stat.st_size) != 0)
197                 fail("Cannot truncate %s: %s\n", outfile, strerror(errno));
198 
199         outbuf = mmap(NULL, stat.st_size, PROT_READ | PROT_WRITE, MAP_SHARED,
200                       outfd, 0);
201         if (outbuf == MAP_FAILED)
202                 fail("Failed to map %s: %s\n", outfile, strerror(errno));
203 
204         close(outfd);
205 
206         memcpy(outbuf, inbuf, stat.st_size);
207 
208         if (clear_soft_float) {
209                 Elf32_Ehdr *outhdr;
210 
211                 outhdr = outbuf;
212                 e_flags &= ~EF_ARM_ABI_FLOAT_SOFT;
213                 write_elf_word(e_flags, &outhdr->e_flags, swap);
214         }
215 
216         if (msync(outbuf, stat.st_size, MS_SYNC) != 0)
217                 fail("Failed to sync %s: %s\n", outfile, strerror(errno));
218 
219         return EXIT_SUCCESS;
220 }
221 

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