Re: [PATCH] lib/bch: Remove VLA usage

From: kbuild test robot
Date: Thu May 31 2018 - 07:50:56 EST

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In reply to: Kees Cook: "Re: [PATCH] lib/bch: Remove VLA usage"
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Hi Kees,

I love your patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v4.17-rc7 next-20180530]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url: https://github.com/0day-ci/linux/commits/Kees-Cook/lib-bch-Remove-VLA-usage/20180531-055540
reproduce:
# apt-get install sparse
make ARCH=x86_64 allmodconfig
make C=1 CF=-D__CHECK_ENDIAN__

sparse warnings: (new ones prefixed by >>)

>> lib/bch.c:237:26: sparse: restricted __be32 degrades to integer

vim +237 lib/bch.c

437aa565 Ivan Djelic 2011-03-11 171
437aa565 Ivan Djelic 2011-03-11 172 /**
437aa565 Ivan Djelic 2011-03-11 173 * encode_bch - calculate BCH ecc parity of data
437aa565 Ivan Djelic 2011-03-11 174 * @bch: BCH control structure
437aa565 Ivan Djelic 2011-03-11 175 * @data: data to encode
437aa565 Ivan Djelic 2011-03-11 176 * @len: data length in bytes
437aa565 Ivan Djelic 2011-03-11 177 * @ecc: ecc parity data, must be initialized by caller
437aa565 Ivan Djelic 2011-03-11 178 *
437aa565 Ivan Djelic 2011-03-11 179 * The @ecc parity array is used both as input and output parameter, in order to
437aa565 Ivan Djelic 2011-03-11 180 * allow incremental computations. It should be of the size indicated by member
437aa565 Ivan Djelic 2011-03-11 181 * @ecc_bytes of @bch, and should be initialized to 0 before the first call.
437aa565 Ivan Djelic 2011-03-11 182 *
437aa565 Ivan Djelic 2011-03-11 183 * The exact number of computed ecc parity bits is given by member @ecc_bits of
437aa565 Ivan Djelic 2011-03-11 184 * @bch; it may be less than m*t for large values of t.
437aa565 Ivan Djelic 2011-03-11 185 */
437aa565 Ivan Djelic 2011-03-11 186 void encode_bch(struct bch_control *bch, const uint8_t *data,
437aa565 Ivan Djelic 2011-03-11 187 unsigned int len, uint8_t *ecc)
437aa565 Ivan Djelic 2011-03-11 188 {
437aa565 Ivan Djelic 2011-03-11 189 const unsigned int l = BCH_ECC_WORDS(bch)-1;
437aa565 Ivan Djelic 2011-03-11 190 unsigned int i, mlen;
437aa565 Ivan Djelic 2011-03-11 191 unsigned long m;
da5dc7be Kees Cook 2018-05-29 192 uint32_t w;
437aa565 Ivan Djelic 2011-03-11 193 const uint32_t * const tab0 = bch->mod8_tab;
437aa565 Ivan Djelic 2011-03-11 194 const uint32_t * const tab1 = tab0 + 256*(l+1);
437aa565 Ivan Djelic 2011-03-11 195 const uint32_t * const tab2 = tab1 + 256*(l+1);
437aa565 Ivan Djelic 2011-03-11 196 const uint32_t * const tab3 = tab2 + 256*(l+1);
437aa565 Ivan Djelic 2011-03-11 197 const uint32_t *pdata, *p0, *p1, *p2, *p3;
437aa565 Ivan Djelic 2011-03-11 198
437aa565 Ivan Djelic 2011-03-11 199 if (ecc) {
437aa565 Ivan Djelic 2011-03-11 200 /* load ecc parity bytes into internal 32-bit buffer */
437aa565 Ivan Djelic 2011-03-11 201 load_ecc8(bch, bch->ecc_buf, ecc);
437aa565 Ivan Djelic 2011-03-11 202 } else {
da5dc7be Kees Cook 2018-05-29 203 memset(bch->ecc_work, 0, bch->ecc_bytes);
437aa565 Ivan Djelic 2011-03-11 204 }
437aa565 Ivan Djelic 2011-03-11 205
437aa565 Ivan Djelic 2011-03-11 206 /* process first unaligned data bytes */
437aa565 Ivan Djelic 2011-03-11 207 m = ((unsigned long)data) & 3;
437aa565 Ivan Djelic 2011-03-11 208 if (m) {
437aa565 Ivan Djelic 2011-03-11 209 mlen = (len < (4-m)) ? len : 4-m;
437aa565 Ivan Djelic 2011-03-11 210 encode_bch_unaligned(bch, data, mlen, bch->ecc_buf);
437aa565 Ivan Djelic 2011-03-11 211 data += mlen;
437aa565 Ivan Djelic 2011-03-11 212 len -= mlen;
437aa565 Ivan Djelic 2011-03-11 213 }
437aa565 Ivan Djelic 2011-03-11 214
437aa565 Ivan Djelic 2011-03-11 215 /* process 32-bit aligned data words */
437aa565 Ivan Djelic 2011-03-11 216 pdata = (uint32_t *)data;
437aa565 Ivan Djelic 2011-03-11 217 mlen = len/4;
437aa565 Ivan Djelic 2011-03-11 218 data += 4*mlen;
437aa565 Ivan Djelic 2011-03-11 219 len -= 4*mlen;
da5dc7be Kees Cook 2018-05-29 220 memcpy(bch->ecc_work, bch->ecc_buf, bch->ecc_bytes);
437aa565 Ivan Djelic 2011-03-11 221
437aa565 Ivan Djelic 2011-03-11 222 /*
437aa565 Ivan Djelic 2011-03-11 223 * split each 32-bit word into 4 polynomials of weight 8 as follows:
437aa565 Ivan Djelic 2011-03-11 224 *
437aa565 Ivan Djelic 2011-03-11 225 * 31 ...24 23 ...16 15 ... 8 7 ... 0
437aa565 Ivan Djelic 2011-03-11 226 * xxxxxxxx yyyyyyyy zzzzzzzz tttttttt
437aa565 Ivan Djelic 2011-03-11 227 * tttttttt mod g = r0 (precomputed)
437aa565 Ivan Djelic 2011-03-11 228 * zzzzzzzz 00000000 mod g = r1 (precomputed)
437aa565 Ivan Djelic 2011-03-11 229 * yyyyyyyy 00000000 00000000 mod g = r2 (precomputed)
437aa565 Ivan Djelic 2011-03-11 230 * xxxxxxxx 00000000 00000000 00000000 mod g = r3 (precomputed)
437aa565 Ivan Djelic 2011-03-11 231 * xxxxxxxx yyyyyyyy zzzzzzzz tttttttt mod g = r0^r1^r2^r3
437aa565 Ivan Djelic 2011-03-11 232 */
437aa565 Ivan Djelic 2011-03-11 233 while (mlen--) {
da5dc7be Kees Cook 2018-05-29 234 uint32_t *r = bch->ecc_work;
da5dc7be Kees Cook 2018-05-29 235
437aa565 Ivan Djelic 2011-03-11 236 /* input data is read in big-endian format */
437aa565 Ivan Djelic 2011-03-11 @237 w = r[0]^cpu_to_be32(*pdata++);
437aa565 Ivan Djelic 2011-03-11 238 p0 = tab0 + (l+1)*((w >> 0) & 0xff);
437aa565 Ivan Djelic 2011-03-11 239 p1 = tab1 + (l+1)*((w >> 8) & 0xff);
437aa565 Ivan Djelic 2011-03-11 240 p2 = tab2 + (l+1)*((w >> 16) & 0xff);
437aa565 Ivan Djelic 2011-03-11 241 p3 = tab3 + (l+1)*((w >> 24) & 0xff);
437aa565 Ivan Djelic 2011-03-11 242
437aa565 Ivan Djelic 2011-03-11 243 for (i = 0; i < l; i++)
437aa565 Ivan Djelic 2011-03-11 244 r[i] = r[i+1]^p0[i]^p1[i]^p2[i]^p3[i];
437aa565 Ivan Djelic 2011-03-11 245
437aa565 Ivan Djelic 2011-03-11 246 r[l] = p0[l]^p1[l]^p2[l]^p3[l];
437aa565 Ivan Djelic 2011-03-11 247 }
da5dc7be Kees Cook 2018-05-29 248 memcpy(bch->ecc_buf, bch->ecc_work, bch->ecc_bytes);
437aa565 Ivan Djelic 2011-03-11 249
437aa565 Ivan Djelic 2011-03-11 250 /* process last unaligned bytes */
437aa565 Ivan Djelic 2011-03-11 251 if (len)
437aa565 Ivan Djelic 2011-03-11 252 encode_bch_unaligned(bch, data, len, bch->ecc_buf);
437aa565 Ivan Djelic 2011-03-11 253
437aa565 Ivan Djelic 2011-03-11 254 /* store ecc parity bytes into original parity buffer */
437aa565 Ivan Djelic 2011-03-11 255 if (ecc)
437aa565 Ivan Djelic 2011-03-11 256 store_ecc8(bch, ecc, bch->ecc_buf);
437aa565 Ivan Djelic 2011-03-11 257 }
437aa565 Ivan Djelic 2011-03-11 258 EXPORT_SYMBOL_GPL(encode_bch);
437aa565 Ivan Djelic 2011-03-11 259

:::::: The code at line 237 was first introduced by commit
:::::: 437aa565e2656776a7104aaacd792fe789ea8b2d lib: add shared BCH ECC library

:::::: TO: Ivan Djelic <ivan.djelic@xxxxxxxxxx>
:::::: CC: David Woodhouse <David.Woodhouse@xxxxxxxxx>

---
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Next message: Eric W. Biederman: "Re: [PATCH] autofs: small cleanup in autofs_getpath()"
Previous message: Benjamin Tissoires: "[PATCH] HID: core: allow concurrent registration of drivers"
In reply to: Kees Cook: "Re: [PATCH] lib/bch: Remove VLA usage"
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