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aarch64: MTE compatible strrchr
Add support for MTE to strrchr. Regression tested with xcheck and benchmarked with glibc's benchtests on the Cortex-A53, Cortex-A72, and Neoverse N1. The existing implementation assumes that any access to the pages in which the string resides is safe. This assumption is not true when MTE is enabled. This patch updates the algorithm to ensure that accesses remain within the bounds of an MTE tag (16-byte chunks) and improves overall performance. Co-authored-by: Wilco Dijkstra <wilco.dijkstra@arm.com>
This commit is contained in:
Alex Butler
Szabolcs Nagy
parent
df06b0d90f
commit
79160c06c7
@ -24,142 +24,119 @@
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*
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* ARMv8-a, AArch64
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* Neon Available.
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* MTE compatible.
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*/
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/* Arguments and results. */
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#define srcin x0
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#define chrin w1
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#define result x0
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#define src x2
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#define tmp1 x3
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#define wtmp2 w4
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#define tmp3 x5
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#define src_match x6
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#define src_offset x7
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#define const_m1 x8
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#define tmp4 x9
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#define nul_match x10
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#define chr_match x11
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#define tmp x3
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#define wtmp w3
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#define synd x3
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#define shift x4
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#define src_match x4
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#define nul_match x5
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#define chr_match x6
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#define vrepchr v0
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#define vdata1 v1
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#define vdata2 v2
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#define vhas_nul1 v3
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#define vhas_nul2 v4
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#define vhas_chr1 v5
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#define vhas_chr2 v6
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#define vrepmask_0 v7
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#define vrepmask_c v16
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#define vend1 v17
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#define vend2 v18
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#define vdata v1
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#define vhas_nul v2
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#define vhas_chr v3
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#define vrepmask v4
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#define vrepmask2 v5
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#define vend v5
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#define dend d5
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/* Core algorithm.
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For each 32-byte hunk we calculate a 64-bit syndrome value, with
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two bits per byte (LSB is always in bits 0 and 1, for both big
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and little-endian systems). For each tuple, bit 0 is set iff
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the relevant byte matched the requested character; bit 1 is set
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iff the relevant byte matched the NUL end of string (we trigger
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off bit0 for the special case of looking for NUL). Since the bits
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in the syndrome reflect exactly the order in which things occur
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in the original string a count_trailing_zeros() operation will
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identify exactly which byte is causing the termination, and why. */
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For each 16-byte chunk we calculate a 64-bit syndrome value, with
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four bits per byte (LSB is always in bits 0 and 1, for both big
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and little-endian systems). For each tuple, bits 0-1 are set if
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the relevant byte matched the requested character; bits 2-3 are set
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if the relevant byte matched the NUL end of string. */
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ENTRY(strrchr)
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DELOUSE (0)
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cbz x1, L(null_search)
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/* Magic constant 0x40100401 to allow us to identify which lane
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matches the requested byte. Magic constant 0x80200802 used
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similarly for NUL termination. */
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mov wtmp2, #0x0401
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movk wtmp2, #0x4010, lsl #16
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bic src, srcin, 15
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dup vrepchr.16b, chrin
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bic src, srcin, #31 /* Work with aligned 32-byte hunks. */
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dup vrepmask_c.4s, wtmp2
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mov src_offset, #0
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ands tmp1, srcin, #31
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add vrepmask_0.4s, vrepmask_c.4s, vrepmask_c.4s /* equiv: lsl #1 */
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b.eq L(aligned)
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mov wtmp, 0x3003
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dup vrepmask.8h, wtmp
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tst srcin, 15
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beq L(loop1)
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/* Input string is not 32-byte aligned. Rather than forcing
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the padding bytes to a safe value, we calculate the syndrome
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for all the bytes, but then mask off those bits of the
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syndrome that are related to the padding. */
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ld1 {vdata1.16b, vdata2.16b}, [src], #32
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neg tmp1, tmp1
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cmeq vhas_nul1.16b, vdata1.16b, #0
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cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
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cmeq vhas_nul2.16b, vdata2.16b, #0
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cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
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and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
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and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
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and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
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and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
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addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b // 256->128
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addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
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addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b // 128->64
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addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b // 128->64
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mov nul_match, vhas_nul1.2d[0]
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lsl tmp1, tmp1, #1
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mov const_m1, #~0
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mov chr_match, vhas_chr1.2d[0]
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lsr tmp3, const_m1, tmp1
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ld1 {vdata.16b}, [src], 16
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cmeq vhas_nul.16b, vdata.16b, 0
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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mov wtmp, 0xf00f
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dup vrepmask2.8h, wtmp
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bit vhas_nul.16b, vhas_chr.16b, vrepmask.16b
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and vhas_nul.16b, vhas_nul.16b, vrepmask2.16b
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addp vend.16b, vhas_nul.16b, vhas_nul.16b
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lsl shift, srcin, 2
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fmov synd, dend
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lsr synd, synd, shift
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lsl synd, synd, shift
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ands nul_match, synd, 0xcccccccccccccccc
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bne L(tail)
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cbnz synd, L(loop2)
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bic nul_match, nul_match, tmp3 // Mask padding bits.
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bic chr_match, chr_match, tmp3 // Mask padding bits.
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cbnz nul_match, L(tail)
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.p2align 5
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L(loop1):
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ld1 {vdata.16b}, [src], 16
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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cmhs vhas_nul.16b, vhas_chr.16b, vdata.16b
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umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov synd, dend
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cbz synd, L(loop1)
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L(loop):
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cmp chr_match, #0
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csel src_match, src, src_match, ne
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csel src_offset, chr_match, src_offset, ne
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L(aligned):
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ld1 {vdata1.16b, vdata2.16b}, [src], #32
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cmeq vhas_nul1.16b, vdata1.16b, #0
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cmeq vhas_chr1.16b, vdata1.16b, vrepchr.16b
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cmeq vhas_nul2.16b, vdata2.16b, #0
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cmeq vhas_chr2.16b, vdata2.16b, vrepchr.16b
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addp vend1.16b, vhas_nul1.16b, vhas_nul2.16b // 256->128
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and vhas_chr1.16b, vhas_chr1.16b, vrepmask_c.16b
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and vhas_chr2.16b, vhas_chr2.16b, vrepmask_c.16b
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addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr2.16b // 256->128
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addp vend1.16b, vend1.16b, vend1.16b // 128->64
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addp vhas_chr1.16b, vhas_chr1.16b, vhas_chr1.16b // 128->64
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mov nul_match, vend1.2d[0]
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mov chr_match, vhas_chr1.2d[0]
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cbz nul_match, L(loop)
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and vhas_nul1.16b, vhas_nul1.16b, vrepmask_0.16b
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and vhas_nul2.16b, vhas_nul2.16b, vrepmask_0.16b
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addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul2.16b
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addp vhas_nul1.16b, vhas_nul1.16b, vhas_nul1.16b
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mov nul_match, vhas_nul1.2d[0]
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cmeq vhas_nul.16b, vdata.16b, 0
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bit vhas_nul.16b, vhas_chr.16b, vrepmask.16b
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bic vhas_nul.8h, 0x0f, lsl 8
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addp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov synd, dend
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ands nul_match, synd, 0xcccccccccccccccc
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beq L(loop2)
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L(tail):
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/* Work out exactly where the string ends. */
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sub tmp4, nul_match, #1
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eor tmp4, tmp4, nul_match
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ands chr_match, chr_match, tmp4
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/* And pick the values corresponding to the last match. */
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csel src_match, src, src_match, ne
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csel src_offset, chr_match, src_offset, ne
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/* Count down from the top of the syndrome to find the last match. */
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clz tmp3, src_offset
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/* Src_match points beyond the word containing the match, so we can
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simply subtract half the bit-offset into the syndrome. Because
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we are counting down, we need to go back one more character. */
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add tmp3, tmp3, #2
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sub result, src_match, tmp3, lsr #1
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/* But if the syndrome shows no match was found, then return NULL. */
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cmp src_offset, #0
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sub nul_match, nul_match, 1
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and chr_match, synd, 0x3333333333333333
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ands chr_match, chr_match, nul_match
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sub result, src, 1
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clz tmp, chr_match
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sub result, result, tmp, lsr 2
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csel result, result, xzr, ne
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ret
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L(null_search):
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b __strchrnul
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.p2align 4
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L(loop2):
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cmp synd, 0
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csel src_match, src, src_match, ne
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csel chr_match, synd, chr_match, ne
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ld1 {vdata.16b}, [src], 16
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cmeq vhas_nul.16b, vdata.16b, 0
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cmeq vhas_chr.16b, vdata.16b, vrepchr.16b
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bit vhas_nul.16b, vhas_chr.16b, vrepmask.16b
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umaxp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov synd, dend
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tst synd, 0xcccccccccccccccc
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beq L(loop2)
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bic vhas_nul.8h, 0x0f, lsl 8
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addp vend.16b, vhas_nul.16b, vhas_nul.16b
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fmov synd, dend
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and nul_match, synd, 0xcccccccccccccccc
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sub nul_match, nul_match, 1
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and tmp, synd, 0x3333333333333333
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ands tmp, tmp, nul_match
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csel chr_match, tmp, chr_match, ne
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csel src_match, src, src_match, ne
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sub src_match, src_match, 1
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clz tmp, chr_match
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sub result, src_match, tmp, lsr 2
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ret
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END(strrchr)
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weak_alias (strrchr, rindex)
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