Merge bitcoin/bitcoin#22930: build: remove glibc back compat

76630cbfb9247a78c7760aa8dca62c6b599a0c7c doc: add glibc to dependencies.md (fanquake)
a907704e7f0f1989e70b9b073c25b740e9d5003d compat: remove glibc_compat.cpp (fanquake)
62e45da94537ffaecc51441896242ef5123106a5 build: remove glibc-back-compat from build system (fanquake)
2ef0accefc1653ea0845683db8256dddf3b55e04 remove --enable-glibc-back-compat from CI and docs (fanquake)

Pull request description:

  This removes our glibc backwards compatibility code (glibcxx sanity checks remain), which is [no-longer used for release builds](https://github.com/bitcoin/bitcoin/pull/22405).

  With these changes our minimum required glibc remains at 2.17, as Guix builds [are done with `--disable-thread-local`](https://github.com/bitcoin/bitcoin/blob/d2dd1697cee9d6d0f13f9cb351bce84eaa4a72b4/contrib/guix/libexec/build.sh#L242).

  Guix builds:
  ```bash
  d9024376ac06b836800b942fcbe8a6454866ded652e41c43d605255f840e8183  guix-build-76630cbfb924/output/aarch64-linux-gnu/SHA256SUMS.part
  bea9607f111b7a501e2410e59ccfca6f83ea075edb299d2f9b878860a4f1ad50  guix-build-76630cbfb924/output/aarch64-linux-gnu/bitcoin-76630cbfb924-aarch64-linux-gnu-debug.tar.gz
  b41d7eaec5b598f146ead32a40c0e2281d22138c02a7000fb154fe8ff341ab9d  guix-build-76630cbfb924/output/aarch64-linux-gnu/bitcoin-76630cbfb924-aarch64-linux-gnu.tar.gz
  9ec0e1b2cd4ca55d5c12354325d7c4552333f1bad7e620db247eb24e15500210  guix-build-76630cbfb924/output/arm-linux-gnueabihf/SHA256SUMS.part
  dbb3e92a3b7d6460e0d5319f49c91eb65593d8604807c1b3084c9d657b198271  guix-build-76630cbfb924/output/arm-linux-gnueabihf/bitcoin-76630cbfb924-arm-linux-gnueabihf-debug.tar.gz
  ff2fa70b01f92b9fba9f0216deebc3e511d84ff93a7316f6766a405160a20483  guix-build-76630cbfb924/output/arm-linux-gnueabihf/bitcoin-76630cbfb924-arm-linux-gnueabihf.tar.gz
  486586b4f3e81855a52e5410127b92f6dde9d1eede2720de260b13552a4b4823  guix-build-76630cbfb924/output/dist-archive/bitcoin-76630cbfb924.tar.gz
  466ccc848c39c0ca85c4575c2bfcd1bc7aba2caa5ba8a42147cce60be5120bf6  guix-build-76630cbfb924/output/powerpc64-linux-gnu/SHA256SUMS.part
  4c739da127df3738e993dcef48ec8f005b7d7938060197c718e771cdd18c2087  guix-build-76630cbfb924/output/powerpc64-linux-gnu/bitcoin-76630cbfb924-powerpc64-linux-gnu-debug.tar.gz
  2294fc23c170d63fc03085d56ba8653e3cf0cff15c8bd5680faa7b7552e1db07  guix-build-76630cbfb924/output/powerpc64-linux-gnu/bitcoin-76630cbfb924-powerpc64-linux-gnu.tar.gz
  7be025478c51a1ba7884a7c2f090a1311651fc218d706051b1830cbc4e82ee4d  guix-build-76630cbfb924/output/powerpc64le-linux-gnu/SHA256SUMS.part
  30600ad6d9bfe70b68a2a4bedc733b56b26232a45d4491b1a6fa30b76cd3f690  guix-build-76630cbfb924/output/powerpc64le-linux-gnu/bitcoin-76630cbfb924-powerpc64le-linux-gnu-debug.tar.gz
  70528805fae16b95d1df46011511ca1c2616fb89422c0164e30d02fa0193b6a1  guix-build-76630cbfb924/output/powerpc64le-linux-gnu/bitcoin-76630cbfb924-powerpc64le-linux-gnu.tar.gz
  20f4daaa095803e9c34ed8b119f948e3e61d03b4d5814e4b15ca285c2ba5a109  guix-build-76630cbfb924/output/riscv64-linux-gnu/SHA256SUMS.part
  6f969d6b6561ea87d1e54a3a643640da54e4e33d2470dbc607ad27f3a87a0f1d  guix-build-76630cbfb924/output/riscv64-linux-gnu/bitcoin-76630cbfb924-riscv64-linux-gnu-debug.tar.gz
  7c1e925d199d21781c96e9ee8d63d5eac995cbe2574ccedd81c0938531f694c1  guix-build-76630cbfb924/output/riscv64-linux-gnu/bitcoin-76630cbfb924-riscv64-linux-gnu.tar.gz
  d0f13a7a9fcd95669cbab3b637940c2014632405037959989768ec2ffa7fd861  guix-build-76630cbfb924/output/x86_64-apple-darwin18/SHA256SUMS.part
  ff23fbdd72fd42140bf11773866061cd5571b66d65bbd769b1345969d195b7ce  guix-build-76630cbfb924/output/x86_64-apple-darwin18/bitcoin-76630cbfb924-osx-unsigned.dmg
  1b51f4a7611b85d4f599291f42887643ddd59babfc6fb71284793123d8a6be33  guix-build-76630cbfb924/output/x86_64-apple-darwin18/bitcoin-76630cbfb924-osx-unsigned.tar.gz
  e0dc9be66c3dc9ba30c5224cf0499ef02b3b7e213081561a6d57d5cc76b3e9a7  guix-build-76630cbfb924/output/x86_64-apple-darwin18/bitcoin-76630cbfb924-osx64.tar.gz
  ae3fb0320a0f39dae48354fe74f3d071b16b33920b3b7b27244658439fdfbc93  guix-build-76630cbfb924/output/x86_64-linux-gnu/SHA256SUMS.part
  9545ccf26a930a3f876058bb0c4965e1320a354ee2d9ce27d95f8bdd2e8679a6  guix-build-76630cbfb924/output/x86_64-linux-gnu/bitcoin-76630cbfb924-x86_64-linux-gnu-debug.tar.gz
  4827206220eaa2b36ebb44b68035c6bda0cec0c2f1b27c08b8349f2f7b3f56d5  guix-build-76630cbfb924/output/x86_64-linux-gnu/bitcoin-76630cbfb924-x86_64-linux-gnu.tar.gz
  c2ad3ed62b2ac41a25a43e1c38869a588bf93853cae4502880adf0b66ce30369  guix-build-76630cbfb924/output/x86_64-w64-mingw32/SHA256SUMS.part
  a88ee3a0cb715d32cf12cb164d8fe4d9c4c810cc417426f3aacc4e7f08460271  guix-build-76630cbfb924/output/x86_64-w64-mingw32/bitcoin-76630cbfb924-win-unsigned.tar.gz
  7673ac8df641d185ea7a150ed27eeee9645168e126d186c6ae935eefdff9edae  guix-build-76630cbfb924/output/x86_64-w64-mingw32/bitcoin-76630cbfb924-win64-debug.zip
  b90d243d292d1b603d744639e5061917035bd8fba6acd0bb61f10479a200f5aa  guix-build-76630cbfb924/output/x86_64-w64-mingw32/bitcoin-76630cbfb924-win64-setup-unsigned.exe
  fe69d000da647e0fb7ab19252149be4b45af742223b4c37630200b1d5b43de33  guix-build-76630cbfb924/output/x86_64-w64-mingw32/bitcoin-76630cbfb924-win64.zip
  ```

ACKs for top commit:
  laanwj:
    Code review ACK 76630cbfb9247a78c7760aa8dca62c6b599a0c7c

Tree-SHA512: 6bd1e344f0f37cfb0017fb8b2b0eee41c6a043f23f8ccb2ad1d59e7f2a47f4b84fe431d7d059c409b63263a0af38be955961c4b2ba7b03538f77a0597abb7880

8 files changed, 9 insertions, 97 deletions

diff --git a/ci/test/00_setup_env_arm.sh b/ci/test/00_setup_env_arm.sh
index 93f8017d98..f18052fe37 100755
--- a/ci/test/00_setup_env_arm.sh
+++ b/ci/test/00_setup_env_arm.sh
@@ -25,4 +25,4 @@ export RUN_FUNCTIONAL_TESTS=false
 export GOAL="install"
 # -Wno-psabi is to disable ABI warnings: "note: parameter passing for argument of type ... changed in GCC 7.1"
 # This could be removed once the ABI change warning does not show up by default
-export BITCOIN_CONFIG="--enable-glibc-back-compat --enable-reduce-exports CXXFLAGS=-Wno-psabi"
+export BITCOIN_CONFIG="--enable-reduce-exports CXXFLAGS=-Wno-psabi"
diff --git a/ci/test/00_setup_env_native_nowallet.sh b/ci/test/00_setup_env_native_nowallet.sh
index d167c9198a..5edc6ae2da 100755
--- a/ci/test/00_setup_env_native_nowallet.sh
+++ b/ci/test/00_setup_env_native_nowallet.sh
@@ -11,4 +11,4 @@ export DOCKER_NAME_TAG=ubuntu:18.04  # Use bionic to have one config run the tes
 export PACKAGES="python3-zmq clang-5.0 llvm-5.0"  # Use clang-5 to test C++17 compatibility, see doc/dependencies.md
 export DEP_OPTS="NO_WALLET=1"
 export GOAL="install"
-export BITCOIN_CONFIG="--enable-glibc-back-compat --enable-reduce-exports CC=clang-5.0 CXX=clang++-5.0"
+export BITCOIN_CONFIG="--enable-reduce-exports CC=clang-5.0 CXX=clang++-5.0"
diff --git a/ci/test/00_setup_env_native_qt5.sh b/ci/test/00_setup_env_native_qt5.sh
index b3e967c898..7d73f2d0b2 100755
--- a/ci/test/00_setup_env_native_qt5.sh
+++ b/ci/test/00_setup_env_native_qt5.sh
@@ -15,5 +15,5 @@ export RUN_UNIT_TESTS_SEQUENTIAL="true"
 export RUN_UNIT_TESTS="false"
 export GOAL="install"
 export PREVIOUS_RELEASES_TO_DOWNLOAD="v0.15.2 v0.16.3 v0.17.2 v0.18.1 v0.19.1 v0.20.1"
-export BITCOIN_CONFIG="--enable-zmq --with-libs=no --with-gui=qt5 --enable-glibc-back-compat --enable-reduce-exports
+export BITCOIN_CONFIG="--enable-zmq --with-libs=no --with-gui=qt5 --enable-reduce-exports
 --enable-debug --disable-fuzz-binary  CFLAGS=\"-g0 -O2 -funsigned-char\" CXXFLAGS=\"-g0 -O2 -funsigned-char\""
diff --git a/configure.ac b/configure.ac
index e50d53f6dd..be5df8fde3 100644
--- a/configure.ac
+++ b/configure.ac
@@ -240,15 +240,9 @@ AC_ARG_ENABLE([lcov-branch-coverage],
   [use_lcov_branch=yes],
   [use_lcov_branch=no])
 
-AC_ARG_ENABLE([glibc-back-compat],
-  [AS_HELP_STRING([--enable-glibc-back-compat],
-  [enable backwards compatibility with glibc])],
-  [use_glibc_compat=$enableval],
-  [use_glibc_compat=no])
-
 AC_ARG_ENABLE([threadlocal],
   [AS_HELP_STRING([--enable-threadlocal],
-  [enable features that depend on the c++ thread_local keyword (currently just thread names in debug logs). (default is to enabled if there is platform support and glibc-back-compat is not enabled)])],
+  [enable features that depend on the c++ thread_local keyword (currently just thread names in debug logs). (default is to enable if there is platform support)])],
   [use_thread_local=$enableval],
   [use_thread_local=auto])
 
@@ -863,17 +857,7 @@ if test x$ac_cv_sys_large_files != x &&
   CPPFLAGS="$CPPFLAGS -D_LARGE_FILES=$ac_cv_sys_large_files"
 fi
 
-if test x$use_glibc_compat != xno; then
-  AX_CHECK_LINK_FLAG([[-Wl,--wrap=__divmoddi4]], [COMPAT_LDFLAGS="$COMPAT_LDFLAGS -Wl,--wrap=__divmoddi4"])
-  AX_CHECK_LINK_FLAG([[-Wl,--wrap=log2f]], [COMPAT_LDFLAGS="$COMPAT_LDFLAGS -Wl,--wrap=log2f"])
-  case $host in
-    powerpc64* | ppc64*)
-      AX_CHECK_LINK_FLAG([[-Wl,--no-tls-get-addr-optimize]], [COMPAT_LDFLAGS="$COMPAT_LDFLAGS -Wl,--no-tls-get-addr-optimize"])
-    ;;
-  esac
-else
-  AC_SEARCH_LIBS([clock_gettime],[rt])
-fi
+AC_SEARCH_LIBS([clock_gettime],[rt])
 
 if test "x$enable_gprof" = xyes; then
     dnl -pg is incompatible with -pie. Since hardening and profiling together doesn't make sense,
@@ -1065,7 +1049,7 @@ AC_COMPILE_IFELSE([AC_LANG_SOURCE([
 dnl thread_local is currently disabled when building with glibc back compat.
 dnl Our minimum supported glibc is 2.17, however support for thread_local
 dnl did not arrive in glibc until 2.18.
-if test "x$use_thread_local" = xyes || { test "x$use_thread_local" = xauto && test "x$use_glibc_compat" = xno; }; then
+if test "x$use_thread_local" = xyes || test "x$use_thread_local" = xauto; then
   TEMP_LDFLAGS="$LDFLAGS"
   LDFLAGS="$TEMP_LDFLAGS $PTHREAD_CFLAGS"
   AC_MSG_CHECKING([for thread_local support])
@@ -1806,7 +1790,6 @@ AM_CONDITIONAL([ENABLE_BENCH],[test x$use_bench = xyes])
 AM_CONDITIONAL([USE_QRCODE], [test x$use_qr = xyes])
 AM_CONDITIONAL([USE_LCOV],[test x$use_lcov = xyes])
 AM_CONDITIONAL([USE_LIBEVENT],[test x$use_libevent = xyes])
-AM_CONDITIONAL([GLIBC_BACK_COMPAT],[test x$use_glibc_compat = xyes])
 AM_CONDITIONAL([HARDEN],[test x$use_hardening = xyes])
 AM_CONDITIONAL([ENABLE_SSE42],[test x$enable_sse42 = xyes])
 AM_CONDITIONAL([ENABLE_SSE41],[test x$enable_sse41 = xyes])
@@ -1849,7 +1832,6 @@ AC_SUBST(DEBUG_CPPFLAGS)
 AC_SUBST(WARN_CXXFLAGS)
 AC_SUBST(NOWARN_CXXFLAGS)
 AC_SUBST(DEBUG_CXXFLAGS)
-AC_SUBST(COMPAT_LDFLAGS)
 AC_SUBST(ERROR_CXXFLAGS)
 AC_SUBST(GPROF_CXXFLAGS)
 AC_SUBST(GPROF_LDFLAGS)
diff --git a/doc/build-unix.md b/doc/build-unix.md
index 44b6ad5968..02c36eea7c 100644
--- a/doc/build-unix.md
+++ b/doc/build-unix.md
@@ -348,7 +348,7 @@ To build executables for ARM:
     make HOST=arm-linux-gnueabihf NO_QT=1
     cd ..
     ./autogen.sh
-    CONFIG_SITE=$PWD/depends/arm-linux-gnueabihf/share/config.site ./configure --enable-glibc-back-compat --enable-reduce-exports LDFLAGS=-static-libstdc++
+    CONFIG_SITE=$PWD/depends/arm-linux-gnueabihf/share/config.site ./configure --enable-reduce-exports LDFLAGS=-static-libstdc++
     make
 
 
diff --git a/doc/dependencies.md b/doc/dependencies.md
index b7634718e8..abdbeee3ce 100644
--- a/doc/dependencies.md
+++ b/doc/dependencies.md
@@ -12,6 +12,7 @@ These are the dependencies currently used by Bitcoin Core. You can find instruct
 | fontconfig | [2.12.1](https://www.freedesktop.org/software/fontconfig/release/) |  | No | Yes |  |
 | FreeType | [2.7.1](https://download.savannah.gnu.org/releases/freetype) |  | No |  | [Yes](https://github.com/bitcoin/bitcoin/blob/master/depends/packages/qt.mk) (Android only) |
 | GCC |  | [7+](https://gcc.gnu.org/) (C++17 support) |  |  |  |
+| glibc | | [2.17](https://www.gnu.org/software/libc/) |  |  |  |  |
 | HarfBuzz-NG |  |  |  |  | [Yes](https://github.com/bitcoin/bitcoin/blob/master/depends/packages/qt.mk) |
 | libevent | [2.1.12-stable](https://github.com/libevent/libevent/releases) | [2.0.21](https://github.com/bitcoin/bitcoin/pull/18676) | No |  |  |
 | libnatpmp | git commit [4536032...](https://github.com/miniupnp/libnatpmp/tree/4536032ae32268a45c073a4d5e91bbab4534773a) |  | No |  |  |
diff --git a/src/Makefile.am b/src/Makefile.am
index eea98c7f22..52c8b85357 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -571,7 +571,7 @@ libbitcoin_common_a_SOURCES = \
 
 # util: shared between all executables.
 # This library *must* be included to make sure that the glibc
-# backward-compatibility objects and their sanity checks are linked.
+# sanity checks are linked.
 libbitcoin_util_a_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
 libbitcoin_util_a_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
 libbitcoin_util_a_SOURCES = \
@@ -619,11 +619,6 @@ if USE_LIBEVENT
 libbitcoin_util_a_SOURCES += util/url.cpp
 endif
 
-if GLIBC_BACK_COMPAT
-libbitcoin_util_a_SOURCES += compat/glibc_compat.cpp
-AM_LDFLAGS += $(COMPAT_LDFLAGS)
-endif
-
 # cli: shared between bitcoin-cli and bitcoin-qt
 libbitcoin_cli_a_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES)
 libbitcoin_cli_a_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)
@@ -751,10 +746,6 @@ if BUILD_BITCOIN_LIBS
 include_HEADERS = script/bitcoinconsensus.h
 libbitcoinconsensus_la_SOURCES = support/cleanse.cpp $(crypto_libbitcoin_crypto_base_a_SOURCES) $(libbitcoin_consensus_a_SOURCES)
 
-if GLIBC_BACK_COMPAT
-  libbitcoinconsensus_la_SOURCES += compat/glibc_compat.cpp
-endif
-
 libbitcoinconsensus_la_LDFLAGS = $(AM_LDFLAGS) -no-undefined $(RELDFLAGS)
 libbitcoinconsensus_la_LIBADD = $(LIBSECP256K1)
 libbitcoinconsensus_la_CPPFLAGS = $(AM_CPPFLAGS) -I$(builddir)/obj -I$(srcdir)/secp256k1/include -DBUILD_BITCOIN_INTERNAL
diff --git a/src/compat/glibc_compat.cpp b/src/compat/glibc_compat.cpp
deleted file mode 100644
index ff581d4a9e..0000000000
--- a/src/compat/glibc_compat.cpp
+++ /dev/null
@@ -1,62 +0,0 @@
-// Copyright (c) 2009-2020 The Bitcoin Core developers
-// Distributed under the MIT software license, see the accompanying
-// file COPYING or http://www.opensource.org/licenses/mit-license.php.
-
-#if defined(HAVE_CONFIG_H)
-#include <config/bitcoin-config.h>
-#endif
-
-#include <cstddef>
-#include <cstdint>
-
-#if defined(__i386__) || defined(__arm__)
-
-extern "C" int64_t __udivmoddi4(uint64_t u, uint64_t v, uint64_t* rp);
-
-extern "C" int64_t __wrap___divmoddi4(int64_t u, int64_t v, int64_t* rp)
-{
-    int32_t c1 = 0, c2 = 0;
-    int64_t uu = u, vv = v;
-    int64_t w;
-    int64_t r;
-
-    if (uu < 0) {
-        c1 = ~c1, c2 = ~c2, uu = -uu;
-    }
-    if (vv < 0) {
-        c1 = ~c1, vv = -vv;
-    }
-
-    w = __udivmoddi4(uu, vv, (uint64_t*)&r);
-    if (c1)
-        w = -w;
-    if (c2)
-        r = -r;
-
-    *rp = r;
-    return w;
-}
-#endif
-
-extern "C" float log2f_old(float x);
-#ifdef __i386__
-__asm(".symver log2f_old,log2f@GLIBC_2.1");
-#elif defined(__amd64__)
-__asm(".symver log2f_old,log2f@GLIBC_2.2.5");
-#elif defined(__arm__)
-__asm(".symver log2f_old,log2f@GLIBC_2.4");
-#elif defined(__aarch64__)
-__asm(".symver log2f_old,log2f@GLIBC_2.17");
-#elif defined(__powerpc64__)
-#  ifdef WORDS_BIGENDIAN
-__asm(".symver log2f_old,log2f@GLIBC_2.3");
-#  else
-__asm(".symver log2f_old,log2f@GLIBC_2.17");
-#  endif
-#elif defined(__riscv)
-__asm(".symver log2f_old,log2f@GLIBC_2.27");
-#endif
-extern "C" float __wrap_log2f(float x)
-{
-    return log2f_old(x);
-}