From 247147654fe5cd11cf15d8dff91440405ea57040 Mon Sep 17 00:00:00 2001
From: Simon Hosie <simon.hosie@arm.com>
Date: Wed, 12 Apr 2017 15:44:21 -0700
Subject: [PATCH 2/2] Inflate using wider loads and stores
In inflate_fast() the output pointer always has plenty of room to write. This
means that so long as the target is capable, wide un-aligned loads and stores
can be used to transfer several bytes at once. When the reference distance is
too short simply unroll the data a little to increase the distance.
Change-Id: I59854eb25d2b1e43561c8a2afaf9175bf10cf674
---
contrib/arm/chunkcopy.h | 279 ++++++++++++++++++++++++++++++++++++++++++++++++
contrib/arm/inffast.c | 96 +++++++----------
contrib/arm/inflate.c | 22 ++--
3 files changed, 335 insertions(+), 62 deletions(-)
create mode 100644 contrib/arm/chunkcopy.h
diff --git a/contrib/arm/chunkcopy.h b/contrib/arm/chunkcopy.h
new file mode 100644
index 00000000..2d6fd6f9
--- /dev/null
+++ b/contrib/arm/chunkcopy.h
@@ -0,0 +1,279 @@
+/* chunkcopy.h -- fast copies and sets
+ * Copyright (C) 2017 ARM, Inc.
+ * For conditions of distribution and use, see copyright notice in zlib.h
+ */
+
+#ifndef CHUNKCOPY_H
+#define CHUNKCOPY_H
+
+#include "zutil.h"
+#include <arm_neon.h>
+
+#if __STDC_VERSION__ >= 199901L
+#define Z_RESTRICT restrict
+#else
+#define Z_RESTRICT
+#endif
+
+typedef uint8x16_t chunkcopy_chunk_t;
+#define CHUNKCOPY_CHUNK_SIZE sizeof(chunkcopy_chunk_t)
+
+/*
+ Ask the compiler to perform a wide, unaligned load with an machine
+ instruction appropriate for the chunkcopy_chunk_t type.
+ */
+static inline chunkcopy_chunk_t loadchunk(const unsigned char FAR *s) {
+ chunkcopy_chunk_t c;
+ __builtin_memcpy(&c, s, sizeof(c));
+ return c;
+}
+
+/*
+ Ask the compiler to perform a wide, unaligned store with an machine
+ instruction appropriate for the chunkcopy_chunk_t type.
+ */
+static inline void storechunk(unsigned char FAR *d, chunkcopy_chunk_t c) {
+ __builtin_memcpy(d, &c, sizeof(c));
+}
+
+/*
+ Perform a memcpy-like operation, but assume that length is non-zero and that
+ it's OK to overwrite at least CHUNKCOPY_CHUNK_SIZE bytes of output even if
+ the length is shorter than this.
+
+ It also guarantees that it will properly unroll the data if the distance
+ between `out` and `from` is at least CHUNKCOPY_CHUNK_SIZE, which we rely on
+ in chunkcopy_relaxed().
+
+ Aside from better memory bus utilisation, this means that short copies
+ (CHUNKCOPY_CHUNK_SIZE bytes or fewer) will fall straight through the loop
+ without iteration, which will hopefully make the branch prediction more
+ reliable.
+ */
+static inline unsigned char FAR *chunkcopy_core(unsigned char FAR *out,
+ const unsigned char FAR *from,
+ unsigned len) {
+ int bump = (--len % CHUNKCOPY_CHUNK_SIZE) + 1;
+ storechunk(out, loadchunk(from));
+ out += bump;
+ from += bump;
+ len /= CHUNKCOPY_CHUNK_SIZE;
+ while (len-- > 0) {
+ storechunk(out, loadchunk(from));
+ out += CHUNKCOPY_CHUNK_SIZE;
+ from += CHUNKCOPY_CHUNK_SIZE;
+ }
+ return out;
+}
+
+/*
+ Like chunkcopy_core, but avoid writing beyond of legal output.
+
+ Accepts an additional pointer to the end of safe output. A generic safe
+ copy would use (out + len), but it's normally the case that the end of the
+ output buffer is beyond the end of the current copy, and this can still be
+ exploited.
+ */
+static inline unsigned char FAR *chunkcopy_core_safe(unsigned char FAR *out,
+ const unsigned char FAR * from,
+ unsigned len,
+ unsigned char FAR *limit) {
+ Assert(out + len <= limit, "chunk copy exceeds safety limit");
+ if (limit - out < CHUNKCOPY_CHUNK_SIZE) {
+ const unsigned char FAR * Z_RESTRICT rfrom = from;
+ if (len & 8) { __builtin_memcpy(out, rfrom, 8); out += 8; rfrom += 8; }
+ if (len & 4) { __builtin_memcpy(out, rfrom, 4); out += 4; rfrom += 4; }
+ if (len & 2) { __builtin_memcpy(out, rfrom, 2); out += 2; rfrom += 2; }
+ if (len & 1) { *out++ = *rfrom++; }
+ return out;
+ }
+ return chunkcopy_core(out, from, len);
+}
+
+/*
+ Perform short copies until distance can be rewritten as being at least
+ CHUNKCOPY_CHUNK_SIZE.
+
+ This assumes that it's OK to overwrite at least the first
+ 2*CHUNKCOPY_CHUNK_SIZE bytes of output even if the copy is shorter than
+ this. This assumption holds within inflate_fast() which starts every
+ iteration with at least 258 bytes of output space available (258 being the
+ maximum length output from a single token; see inffast.c).
+ */
+static inline unsigned char FAR *chunkunroll_relaxed(unsigned char FAR *out,
+ unsigned FAR *dist,
+ unsigned FAR *len) {
+ const unsigned char FAR *from = out - *dist;
+ while (*dist < *len && *dist < CHUNKCOPY_CHUNK_SIZE) {
+ storechunk(out, loadchunk(from));
+ out += *dist;
+ *len -= *dist;
+ *dist += *dist;
+ }
+ return out;
+}
+
+
+static inline uint8x16_t chunkset_vld1q_dup_u8x8(const unsigned char FAR * Z_RESTRICT from) {
+#if defined(__clang__) || defined(__aarch64__)
+ return vreinterpretq_u8_u64(vld1q_dup_u64((void *)from));
+#else
+ /* 32-bit GCC uses an alignment hint for vld1q_dup_u64, even when given a
+ * void pointer, so here's an alternate implementation.
+ */
+ uint8x8_t h = vld1_u8(from);
+ return vcombine_u8(h, h);
+#endif
+}
+
+/*
+ Perform an overlapping copy which behaves as a memset() operation, but
+ supporting periods other than one, and assume that length is non-zero and
+ that it's OK to overwrite at least CHUNKCOPY_CHUNK_SIZE*3 bytes of output
+ even if the length is shorter than this.
+ */
+static inline unsigned char FAR *chunkset_core(unsigned char FAR *out,
+ unsigned period,
+ unsigned len) {
+ uint8x16_t f;
+ int bump = ((len - 1) % sizeof(f)) + 1;
+
+ switch (period) {
+ case 1:
+ f = vld1q_dup_u8(out - 1);
+ vst1q_u8(out, f);
+ out += bump;
+ len -= bump;
+ while (len > 0) {
+ vst1q_u8(out, f);
+ out += sizeof(f);
+ len -= sizeof(f);
+ }
+ return out;
+ case 2:
+ f = vreinterpretq_u8_u16(vld1q_dup_u16((void *)(out - 2)));
+ vst1q_u8(out, f);
+ out += bump;
+ len -= bump;
+ if (len > 0) {
+ f = vreinterpretq_u8_u16(vld1q_dup_u16((void *)(out - 2)));
+ do {
+ vst1q_u8(out, f);
+ out += sizeof(f);
+ len -= sizeof(f);
+ } while (len > 0);
+ }
+ return out;
+ case 4:
+ f = vreinterpretq_u8_u32(vld1q_dup_u32((void *)(out - 4)));
+ vst1q_u8(out, f);
+ out += bump;
+ len -= bump;
+ if (len > 0) {
+ f = vreinterpretq_u8_u32(vld1q_dup_u32((void *)(out - 4)));
+ do {
+ vst1q_u8(out, f);
+ out += sizeof(f);
+ len -= sizeof(f);
+ } while (len > 0);
+ }
+ return out;
+ case 8:
+ f = chunkset_vld1q_dup_u8x8(out - 8);
+ vst1q_u8(out, f);
+ out += bump;
+ len -= bump;
+ if (len > 0) {
+ f = chunkset_vld1q_dup_u8x8(out - 8);
+ do {
+ vst1q_u8(out, f);
+ out += sizeof(f);
+ len -= sizeof(f);
+ } while (len > 0);
+ }
+ return out;
+ }
+ out = chunkunroll_relaxed(out, &period, &len);
+ return chunkcopy_core(out, out - period, len);
+}
+
+/*
+ Perform a memcpy-like operation, but assume that length is non-zero and that
+ it's OK to overwrite at least CHUNKCOPY_CHUNK_SIZE bytes of output even if
+ the length is shorter than this.
+
+ Unlike chunkcopy_core() above, no guarantee is made regarding the behaviour
+ of overlapping buffers, regardless of the distance between the pointers.
+ This is reflected in the `restrict`-qualified pointers, allowing the
+ compiler to reorder loads and stores.
+ */
+static inline unsigned char FAR *chunkcopy_relaxed(unsigned char FAR * Z_RESTRICT out,
+ const unsigned char FAR * Z_RESTRICT from,
+ unsigned len) {
+ return chunkcopy_core(out, from, len);
+}
+
+/*
+ Like chunkcopy_relaxed, but avoid writing beyond of legal output.
+
+ Unlike chunkcopy_core_safe() above, no guarantee is made regarding the
+ behaviour of overlapping buffers, regardless of the distance between the
+ pointers. This is reflected in the `restrict`-qualified pointers, allowing
+ the compiler to reorder loads and stores.
+
+ Accepts an additional pointer to the end of safe output. A generic safe
+ copy would use (out + len), but it's normally the case that the end of the
+ output buffer is beyond the end of the current copy, and this can still be
+ exploited.
+ */
+static inline unsigned char FAR *chunkcopy_safe(unsigned char FAR *out,
+ const unsigned char FAR * Z_RESTRICT from,
+ unsigned len,
+ unsigned char FAR *limit) {
+ Assert(out + len <= limit, "chunk copy exceeds safety limit");
+ return chunkcopy_core_safe(out, from, len, limit);
+}
+
+/*
+ Perform chunky copy within the same buffer, where the source and destination
+ may potentially overlap.
+
+ Assumes that len > 0 on entry, and that it's safe to write at least
+ CHUNKCOPY_CHUNK_SIZE*3 bytes to the output.
+ */
+static inline unsigned char FAR *chunkcopy_lapped_relaxed(unsigned char FAR *out,
+ unsigned dist,
+ unsigned len) {
+ if (dist < len && dist < CHUNKCOPY_CHUNK_SIZE) {
+ return chunkset_core(out, dist, len);
+ }
+ return chunkcopy_core(out, out - dist, len);
+}
+
+/*
+ Behave like chunkcopy_lapped_relaxed, but avoid writing beyond of legal output.
+
+ Accepts an additional pointer to the end of safe output. A generic safe
+ copy would use (out + len), but it's normally the case that the end of the
+ output buffer is beyond the end of the current copy, and this can still be
+ exploited.
+ */
+static inline unsigned char FAR *chunkcopy_lapped_safe(unsigned char FAR *out,
+ unsigned dist,
+ unsigned len,
+ unsigned char FAR *limit) {
+ Assert(out + len <= limit, "chunk copy exceeds safety limit");
+ if (limit - out < CHUNKCOPY_CHUNK_SIZE * 3) {
+ /* TODO: try harder to optimise this */
+ while (len-- > 0) {
+ *out = *(out - dist);
+ out++;
+ }
+ return out;
+ }
+ return chunkcopy_lapped_relaxed(out, dist, len);
+}
+
+#undef Z_RESTRICT
+
+#endif /* CHUNKCOPY_H */
diff --git a/contrib/arm/inffast.c b/contrib/arm/inffast.c
index 0dbd1dbc..f7f50071 100644
--- a/contrib/arm/inffast.c
+++ b/contrib/arm/inffast.c
@@ -7,6 +7,7 @@
#include "inftrees.h"
#include "inflate.h"
#include "inffast.h"
+#include "chunkcopy.h"
#ifdef ASMINF
# pragma message("Assembler code may have bugs -- use at your own risk")
@@ -57,6 +58,7 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
unsigned char FAR *out; /* local strm->next_out */
unsigned char FAR *beg; /* inflate()'s initial strm->next_out */
unsigned char FAR *end; /* while out < end, enough space available */
+ unsigned char FAR *limit; /* safety limit for chunky copies */
#ifdef INFLATE_STRICT
unsigned dmax; /* maximum distance from zlib header */
#endif
@@ -84,12 +86,13 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
out = strm->next_out;
beg = out - (start - strm->avail_out);
end = out + (strm->avail_out - 257);
+ limit = out + strm->avail_out;
#ifdef INFLATE_STRICT
dmax = state->dmax;
#endif
wsize = state->wsize;
whave = state->whave;
- wnext = state->wnext;
+ wnext = (state->wnext == 0 && whave >= wsize) ? wsize : state->wnext;
window = state->window;
hold = state->hold;
bits = state->bits;
@@ -197,70 +200,51 @@ unsigned start; /* inflate()'s starting value for strm->avail_out */
#endif
}
from = window;
- if (wnext == 0) { /* very common case */
- from += wsize - op;
- if (op < len) { /* some from window */
- len -= op;
- do {
- *out++ = *from++;
- } while (--op);
- from = out - dist; /* rest from output */
- }
+ if (wnext >= op) { /* contiguous in window */
+ from += wnext - op;
}
- else if (wnext < op) { /* wrap around window */
- from += wsize + wnext - op;
+ else { /* wrap around window */
op -= wnext;
+ from += wsize - op;
if (op < len) { /* some from end of window */
len -= op;
- do {
- *out++ = *from++;
- } while (--op);
- from = window;
- if (wnext < len) { /* some from start of window */
- op = wnext;
- len -= op;
- do {
- *out++ = *from++;
- } while (--op);
- from = out - dist; /* rest from output */
- }
+ out = chunkcopy_safe(out, from, op, limit);
+ from = window; /* more from start of window */
+ op = wnext;
+ /* This (rare) case can create a situation where
+ the first chunkcopy below must be checked.
+ */
}
}
- else { /* contiguous in window */
- from += wnext - op;
- if (op < len) { /* some from window */
- len -= op;
- do {
- *out++ = *from++;
- } while (--op);
- from = out - dist; /* rest from output */
- }
- }
- while (len > 2) {
- *out++ = *from++;
- *out++ = *from++;
- *out++ = *from++;
- len -= 3;
- }
- if (len) {
- *out++ = *from++;
- if (len > 1)
- *out++ = *from++;
+ if (op < len) { /* still need some from output */
+ out = chunkcopy_safe(out, from, op, limit);
+ len -= op;
+ /* When dist is small the amount of data that can be
+ copied from the window is also small, and progress
+ towards the dangerous end of the output buffer is
+ also small. This means that for trivial memsets and
+ for chunkunroll_relaxed() a safety check is
+ unnecessary. However, these conditions may not be
+ entered at all, and in that case it's possible that
+ the main copy is near the end.
+ */
+ out = chunkunroll_relaxed(out, &dist, &len);
+ out = chunkcopy_safe(out, out - dist, len, limit);
+ } else {
+ /* from points to window, so there is no risk of
+ overlapping pointers requiring memset-like behaviour
+ */
+ out = chunkcopy_safe(out, from, len, limit);
}
}
else {
- from = out - dist; /* copy direct from output */
- do { /* minimum length is three */
- *out++ = *from++;
- *out++ = *from++;
- *out++ = *from++;
- len -= 3;
- } while (len > 2);
- if (len) {
- *out++ = *from++;
- if (len > 1)
- *out++ = *from++;
- }
+ /* Whole reference is in range of current output. No
+ range checks are necessary because we start with room
+ for at least 258 bytes of output, so unroll and roundoff
+ operations can write beyond `out+len` so long as they
+ stay within 258 bytes of `out`.
+ */
+ out = chunkcopy_lapped_relaxed(out, dist, len);
}
}
else if ((op & 64) == 0) { /* 2nd level distance code */
diff --git a/contrib/arm/inflate.c b/contrib/arm/inflate.c
index ac333e8c..e40322c3 100644
--- a/contrib/arm/inflate.c
+++ b/contrib/arm/inflate.c
@@ -84,6 +84,7 @@
#include "inftrees.h"
#include "inflate.h"
#include "inffast.h"
+#include "contrib/arm/chunkcopy.h"
#ifdef MAKEFIXED
# ifndef BUILDFIXED
@@ -405,10 +406,20 @@ unsigned copy;
/* if it hasn't been done already, allocate space for the window */
if (state->window == Z_NULL) {
+ unsigned wsize = 1U << state->wbits;
state->window = (unsigned char FAR *)
- ZALLOC(strm, 1U << state->wbits,
+ ZALLOC(strm, wsize + CHUNKCOPY_CHUNK_SIZE,
sizeof(unsigned char));
if (state->window == Z_NULL) return 1;
+#ifdef INFLATE_CLEAR_UNUSED_UNDEFINED
+ /* Copies from the overflow portion of this buffer are undefined and
+ may cause analysis tools to raise a warning if we don't initialize
+ it. However, this undefined data overwrites other undefined data
+ and is subsequently either overwritten or left deliberately
+ undefined at the end of decode; so there's really no point.
+ */
+ memset(state->window + wsize, 0, CHUNKCOPY_CHUNK_SIZE);
+#endif
}
/* if window not in use yet, initialize */
@@ -1175,17 +1186,16 @@ int flush;
else
from = state->window + (state->wnext - copy);
if (copy > state->length) copy = state->length;
+ if (copy > left) copy = left;
+ put = chunkcopy_safe(put, from, copy, put + left);
}
else { /* copy from output */
- from = put - state->offset;
copy = state->length;
+ if (copy > left) copy = left;
+ put = chunkcopy_lapped_safe(put, state->offset, copy, put + left);
}
- if (copy > left) copy = left;
left -= copy;
state->length -= copy;
- do {
- *put++ = *from++;
- } while (--copy);
if (state->length == 0) state->mode = LEN;
break;
case LIT: