Fix endianness issues in absl/hash

3 files changed, 113 insertions, 0 deletions

diff --git a/debian/changelog b/debian/changelog
index 63e67f3d..664d5007 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,6 +1,7 @@
 abseil (0~20200923.3-1) UNRELEASED; urgency=medium
 
   * New upstream release.
+  * Correct endianness issues in hash functions.
 
  -- Benjamin Barenblat <bbaren@debian.org>  Thu, 04 Feb 2021 12:08:46 -0500
 
diff --git a/debian/patches/endian-hash.diff b/debian/patches/endian-hash.diff
new file mode 100644
index 00000000..01c1b6b0
--- /dev/null
+++ b/debian/patches/endian-hash.diff
@@ -0,0 +1,111 @@
+From: Benjamin Barenblat <bbaren@google.com>
+Subject: Remove endian-sensitivity from hash slow path
+Forwarded: yes
+Applied-Upstream: https://github.com/abseil/abseil-cpp/commit/9c6a50fdd80bb39fabd95faeda84f04062685ff3
+
+Prior to this commit, the Abseil hash fast path was endian-agnostic, but
+the slow path assumed a little-endian platform. Change the slow path to
+be endian-correct, ensuring that values produced by the fast and slow
+paths are equal even on big-endian systems.
+
+The author works at Google. Upstream applied this patch as Piper revision
+355424258 and exported it to GitHub; the Applied-Upstream URL above points to
+the exported commit.
+
+--- a/absl/hash/BUILD.bazel
++++ b/absl/hash/BUILD.bazel
+@@ -37,6 +37,7 @@ cc_library(name = "hash",
+     linkopts = ABSL_DEFAULT_LINKOPTS,
+     deps = [
+         ":city",
++        "//absl/base:config",
+         "//absl/base:core_headers",
+         "//absl/base:endian",
+         "//absl/container:fixed_array",
+--- a/absl/hash/CMakeLists.txt
++++ b/absl/hash/CMakeLists.txt
+@@ -25,6 +25,7 @@ absl_cc_library(NAME hash
+   COPTS
+     ${ABSL_DEFAULT_COPTS}
+   DEPS
++    absl::config
+     absl::core_headers
+     absl::endian
+     absl::fixed_array
+--- a/absl/hash/internal/hash.h
++++ b/absl/hash/internal/hash.h
+@@ -38,7 +38,8 @@
+ #include <utility>
+ #include <vector>
+ 
+-#include "absl/base/internal/endian.h"
++#include "absl/base/config.h"
++#include "absl/base/internal/unaligned_access.h"
+ #include "absl/base/port.h"
+ #include "absl/container/fixed_array.h"
+ #include "absl/meta/type_traits.h"
+@@ -804,26 +805,54 @@ class ABSL_DLL CityHashState
+                                                size_t len);
+ 
+   // Reads 9 to 16 bytes from p.
+-  // The first 8 bytes are in .first, the rest (zero padded) bytes are in
+-  // .second.
++  // The least significant 8 bytes are in .first, the rest (zero padded) bytes
++  // are in .second.
+   static std::pair<uint64_t, uint64_t> Read9To16(const unsigned char* p,
+                                                  size_t len) {
+-    uint64_t high = little_endian::Load64(p + len - 8);
+-    return {little_endian::Load64(p), high >> (128 - len * 8)};
++    uint64_t low_mem = absl::base_internal::UnalignedLoad64(p);
++    uint64_t high_mem = absl::base_internal::UnalignedLoad64(p + len - 8);
++#ifdef ABSL_IS_LITTLE_ENDIAN
++    uint64_t most_significant = high_mem;
++    uint64_t least_significant = low_mem;
++#else
++    uint64_t most_significant = low_mem;
++    uint64_t least_significant = high_mem;
++#endif
++    return {least_significant, most_significant >> (128 - len * 8)};
+   }
+ 
+   // Reads 4 to 8 bytes from p. Zero pads to fill uint64_t.
+   static uint64_t Read4To8(const unsigned char* p, size_t len) {
+-    return (static_cast<uint64_t>(little_endian::Load32(p + len - 4))
+-            << (len - 4) * 8) |
+-           little_endian::Load32(p);
++    uint32_t low_mem = absl::base_internal::UnalignedLoad32(p);
++    uint32_t high_mem = absl::base_internal::UnalignedLoad32(p + len - 4);
++#ifdef ABSL_IS_LITTLE_ENDIAN
++    uint32_t most_significant = high_mem;
++    uint32_t least_significant = low_mem;
++#else
++    uint32_t most_significant = low_mem;
++    uint32_t least_significant = high_mem;
++#endif
++    return (static_cast<uint64_t>(most_significant) << (len - 4) * 8) |
++           least_significant;
+   }
+ 
+   // Reads 1 to 3 bytes from p. Zero pads to fill uint32_t.
+   static uint32_t Read1To3(const unsigned char* p, size_t len) {
+-    return static_cast<uint32_t>((p[0]) |                         //
+-                                 (p[len / 2] << (len / 2 * 8)) |  //
+-                                 (p[len - 1] << ((len - 1) * 8)));
++    unsigned char mem0 = p[0];
++    unsigned char mem1 = p[len / 2];
++    unsigned char mem2 = p[len - 1];
++#ifdef ABSL_IS_LITTLE_ENDIAN
++    unsigned char significant2 = mem2;
++    unsigned char significant1 = mem1;
++    unsigned char significant0 = mem0;
++#else
++    unsigned char significant2 = mem0;
++    unsigned char significant1 = mem1;
++    unsigned char significant0 = mem2;
++#endif
++    return static_cast<uint32_t>(significant0 |                     //
++                                 (significant1 << (len / 2 * 8)) |  //
++                                 (significant2 << ((len - 1) * 8)));
+   }
+ 
+   ABSL_ATTRIBUTE_ALWAYS_INLINE static uint64_t Mix(uint64_t state, uint64_t v) {
diff --git a/debian/patches/series b/debian/patches/series
index 9c73d904..33ae234a 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -4,3 +4,4 @@ std-hash.diff
 latomic.diff
 cpu-frequency.diff
 nan-narrowing.diff
+endian-hash.diff