Merge bitcoin/bitcoin#31901: contrib: Add deterministic-unittest-coverage

fa99c3b544 test: Exclude SeedStartup from coverage counts (MarcoFalke)
fa579d663d contrib: Add deterministic-unittest-coverage (MarcoFalke)
fa3940b1cb contrib: deterministic-fuzz-coverage fixups (MarcoFalke)
faf905b9b6 doc: Remove unused -fPIC (MarcoFalke)
fa1e0a7228 gitignore: target/ (MarcoFalke)

Pull request description:

  The `contrib/devtools/test_deterministic_coverage.sh` script is problematic:

  * It is written in bash. This can lead to issues when running with the ancient bash version shipped by macOS by default, or can lead to other compatibility issues, such as https://github.com/bitcoin/bitcoin/pull/31588#discussion_r1946784827. Also, pipefail isn't set, so IO errors may be silently ignored.
  * It is based on gcov. This can lead to issues, such as https://github.com/bitcoin/bitcoin/pull/31588#pullrequestreview-2602169248 (possibly due to prefix-map), or https://github.com/bitcoin/bitcoin/pull/31588#issuecomment-2646395385 (gcovr processing error), or https://github.com/bitcoin/bitcoin/pull/31588#pullrequestreview-2605954001 (gcovr assertion error).
  * The script is severely outdated, with the last update to `NON_DETERMINISTIC_TESTS` being in the prior decade.

  Instead of patching around all issues one-by-one, just provide a fresh rewrite, based on the recently added `deterministic-fuzz-coverage` tool based on clang, llvm-cov, and llvm-profdata. (Initial feedback indicates that this is a more promising attempt: https://github.com/bitcoin/bitcoin/pull/31588#issuecomment-2649356408 and https://github.com/bitcoin/bitcoin/pull/31588#issuecomment-2649354598).

  The new tool also sets `RANDOM_CTX_SEED=21` as suggested by hodlinator in https://github.com/bitcoin/bitcoin/pull/31588#issuecomment-2650784726.

ACKs for top commit:
  Prabhat1308:
    Concept ACK [`fa99c3b`](fa99c3b544)
  hodlinator:
    re-ACK fa99c3b544
  brunoerg:
    light ACK fa99c3b544
  dergoegge:
    tACK fa99c3b544
  janb84:
    Concept ACK [fa99c3b](fa99c3b544)

Tree-SHA512: 491d5e6413d929395a5c7caea54817bdc1a0e00562c9728a374d4e92f2e2017dba4a770ecdb2e7317e049df9fdeb390d83c90dff9aa5709f97aa3f6a0e70cdb4

src/test/fuzz/fuzz.cpp

@@ -7,6 +7,7 @@
 #include <netaddress.h>
 #include <netbase.h>
 #include <test/fuzz/util/check_globals.h>
+#include <test/util/coverage.h>
 #include <test/util/random.h>
 #include <test/util/setup_common.h>
 #include <util/check.h>
@@ -89,25 +90,6 @@ const std::function<std::string()> G_TEST_GET_FULL_NAME{[]{
     return std::string{g_fuzz_target};
 }};
 
-#if defined(__clang__) && defined(__linux__)
-extern "C" void __llvm_profile_reset_counters(void) __attribute__((weak));
-extern "C" void __gcov_reset(void) __attribute__((weak));
-
-void ResetCoverageCounters()
-{
-    if (__llvm_profile_reset_counters) {
-        __llvm_profile_reset_counters();
-    }
-
-    if (__gcov_reset) {
-        __gcov_reset();
-    }
-}
-#else
-void ResetCoverageCounters() {}
-#endif
-
-
 static void initialize()
 {
     // By default, make the RNG deterministic with a fixed seed. This will affect all

src/test/util/CMakeLists.txt

@@ -5,6 +5,7 @@
 add_library(test_util STATIC EXCLUDE_FROM_ALL
   blockfilter.cpp
   coins.cpp
+  coverage.cpp
   index.cpp
   json.cpp
   logging.cpp

src/test/util/coverage.cpp

@@ -0,0 +1,23 @@
+// Copyright (c) 2025-present The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <test/util/coverage.h>
+
+#if defined(__clang__) && defined(__linux__)
+extern "C" void __llvm_profile_reset_counters(void) __attribute__((weak));
+extern "C" void __gcov_reset(void) __attribute__((weak));
+
+void ResetCoverageCounters()
+{
+    if (__llvm_profile_reset_counters) {
+        __llvm_profile_reset_counters();
+    }
+
+    if (__gcov_reset) {
+        __gcov_reset();
+    }
+}
+#else
+void ResetCoverageCounters() {}
+#endif

src/test/util/coverage.h

@@ -0,0 +1,10 @@
+// Copyright (c) 2025-present The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_TEST_UTIL_COVERAGE_H
+#define BITCOIN_TEST_UTIL_COVERAGE_H
+
+void ResetCoverageCounters();
+
+#endif // BITCOIN_TEST_UTIL_COVERAGE_H

src/test/util/setup_common.cpp

@@ -37,6 +37,7 @@
 #include <scheduler.h>
 #include <script/sigcache.h>
 #include <streams.h>
+#include <test/util/coverage.h>
 #include <test/util/net.h>
 #include <test/util/random.h>
 #include <test/util/txmempool.h>
@@ -80,6 +81,7 @@ static const bool g_rng_temp_path_init{[] {
     Assert(!g_used_g_prng);
     (void)g_rng_temp_path.rand64();
     g_used_g_prng = false;
+    ResetCoverageCounters(); // The seed strengthen in SeedStartup is not deterministic, so exclude it from coverage counts
     return true;
 }()};