instrumentation: Prevent inherited process metrics in chained commands

Shells may exec the final chained command instead of forking it,
preserving resource usage accumulated from earlier children.

When processMetrics is enabled, append a shell builtin to generated
command chains and scripts for Ninja, Makefiles, and FASTBuild to prevent
this optimization while preserving command exit status.

Source/cmFastbuildNormalTargetGenerator.cxx

@@ -33,6 +33,8 @@
 #include "cmGeneratorTarget.h"
 #include "cmGlobalCommonGenerator.h"
 #include "cmGlobalFastbuildGenerator.h"
+#include "cmInstrumentation.h"
+#include "cmInstrumentationQuery.h"
 #include "cmLinkLineComputer.h"
 #include "cmLinkLineDeviceComputer.h"
 #include "cmList.h"
@@ -1156,19 +1158,30 @@ void cmFastbuildNormalTargetGenerator::CollapseAllExecsIntoOneScriptfile(
   }
   LogMessage("Writing collapsed Execs to " + scriptFileName);
   auto const shell = cmGlobalFastbuildGenerator::GetExternalShellExecutable();
+  char const* suffix = "\n";
+#if !defined(_WIN32) && !defined(CMAKE_BOOTSTRAP)
+  cmInstrumentation* instrumentation =
+    this->GetLocalGenerator()->GetCMakeInstance()->GetInstrumentation();
+  if (instrumentation->HasOption(
+        cmInstrumentationQuery::Option::ProcessMetrics)) {
+    // Prevent shell exec optimization from passing accumulated child resource
+    // usage to the final instrumentation wrapper.
+    suffix = " && :\n";
+  }
+#endif
   for (auto const& exec : execs) {
     if (exec.ScriptFile.empty()) {
       scriptFile << cmSystemTools::ConvertToOutputPath(exec.ExecExecutable)
-                 << " " << exec.ExecArguments << '\n';
+                 << " " << exec.ExecArguments << suffix;
     } else {
 #if defined(_WIN32)
       scriptFile << "call "
                  << cmSystemTools::ConvertToWindowsOutputPath(exec.ScriptFile)
-                 << '\n';
+                 << suffix;
 #else
       scriptFile << cmSystemTools::ConvertToOutputPath(shell) << " "
                  << cmSystemTools::ConvertToOutputPath(exec.ScriptFile)
-                 << '\n';
+                 << suffix;
 #endif
     }
   }

Source/cmFastbuildTargetGenerator.cxx

@@ -21,6 +21,8 @@
 #include "cmGeneratorTarget.h"
 #include "cmGlobalCommonGenerator.h"
 #include "cmGlobalFastbuildGenerator.h"
+#include "cmInstrumentation.h"
+#include "cmInstrumentationQuery.h"
 #include "cmList.h"
 #include "cmListFileCache.h"
 #include "cmLocalCommonGenerator.h"
@@ -38,6 +40,7 @@
 #include "cmTarget.h"
 #include "cmTargetTypes.h"
 #include "cmValue.h"
+#include "cmake.h"
 
 #define FASTBUILD_DOLLAR_TAG "FASTBUILD_DOLLAR_TAG"
 
@@ -180,6 +183,15 @@ void cmFastbuildTargetGenerator::WriteScriptEpilog(cmsys::ofstream& file) const
           "echo Batch file failed at line %FAIL_LINE% "
           "with errorcode %ERRORLEVEL%\n"
           "exit /b %ERROR_CODE%";
+#elif !defined(CMAKE_BOOTSTRAP)
+  cmInstrumentation* instrumentation =
+    this->GetLocalGenerator()->GetCMakeInstance()->GetInstrumentation();
+  if (instrumentation->HasOption(
+        cmInstrumentationQuery::Option::ProcessMetrics)) {
+    // Prevent shell exec optimization from passing accumulated child resource
+    // usage to the final instrumentation wrapper.
+    file << ":\n";
+  }
 #endif
 }
 

Source/cmLocalNinjaGenerator.cxx

@@ -25,6 +25,8 @@
 #include "cmGeneratorTarget.h"
 #include "cmGlobalGenerator.h"
 #include "cmGlobalNinjaGenerator.h"
+#include "cmInstrumentation.h"
+#include "cmInstrumentationQuery.h"
 #include "cmList.h"
 #include "cmListFileCache.h"
 #include "cmLocalGenerator.h"
@@ -476,6 +478,13 @@ std::string cmLocalNinjaGenerator::WriteCommandScript(
             "echo Batch file failed at line %FAIL_LINE% "
             "with errorcode %ERRORLEVEL%\n"
             "exit /b %ERROR_CODE%";
+#elif !defined(CMAKE_BOOTSTRAP)
+  if (this->GetCMakeInstance()->GetInstrumentation()->HasOption(
+        cmInstrumentationQuery::Option::ProcessMetrics)) {
+    // Prevent shell exec optimization from passing accumulated child resource
+    // usage to the final instrumentation wrapper.
+    script << ":\n";
+  }
 #endif
 
   return scriptPath;
@@ -567,6 +576,14 @@ std::string cmLocalNinjaGenerator::BuildCommandLine(
     }
     cmd << *li;
   }
+#  ifndef CMAKE_BOOTSTRAP
+  if (this->GetCMakeInstance()->GetInstrumentation()->HasOption(
+        cmInstrumentationQuery::Option::ProcessMetrics)) {
+    // Prevent shell exec optimization from passing accumulated child resource
+    // usage to the final instrumentation wrapper.
+    cmd << " && :";
+  }
+#  endif
 #endif
   return cmd.str();
 }

Source/cmLocalUnixMakefileGenerator3.cxx

@@ -29,6 +29,7 @@
 #include "cmGlobalGenerator.h"
 #include "cmGlobalUnixMakefileGenerator3.h"
 #include "cmInstrumentation.h"
+#include "cmInstrumentationQuery.h"
 #include "cmList.h"
 #include "cmListFileCache.h"
 #include "cmLocalGenerator.h"
@@ -631,7 +632,24 @@ void cmLocalUnixMakefileGenerator3::WriteMakeRule(
 
   if (!commands.empty()) {
     // Write the list of commands.
-    os << cmWrap("\t", commands, "", "\n") << '\n';
+    bool protectProcessMetrics = false;
+#if !defined(_WIN32) && !defined(CMAKE_BOOTSTRAP)
+    if (this->GetCMakeInstance()->GetInstrumentation()->HasOption(
+          cmInstrumentationQuery::Option::ProcessMetrics)) {
+      // Prevent shell exec optimization from passing accumulated child
+      // resource usage to the final instrumentation wrapper.
+      protectProcessMetrics = true;
+    }
+#endif
+    for (std::string const& command : commands) {
+      os << '\t' << command;
+      // Preserve the instrumentation daemon's explicit exec command.
+      if (protectProcessMetrics && !command.empty() &&
+          !cmHasLiteralPrefix(command, "exec ")) {
+        os << " && :";
+      }
+      os << '\n';
+    }
   }
   if (symbolic && !this->IsWatcomWMake()) {
     os << ".PHONY : " << tgt << '\n';

Tests/RunCMake/Instrumentation/check-data-dir.cmake

@@ -8,6 +8,8 @@ if (NOT snippets)
 endif()
 
 set(FOUND_SNIPPETS "")
+unset(process_metrics_chain_head_rss)
+unset(process_metrics_chain_tail_rss)
 foreach(snippet IN LISTS snippets)
   get_filename_component(filename "${snippet}" NAME)
 
@@ -42,7 +44,13 @@ foreach(snippet IN LISTS snippets)
     if (filename MATCHES "^custom-")
       string(JSON outputs ERROR_VARIABLE noOutputs GET "${contents}" outputs)
       if (outputs MATCHES "process_metrics_custom\.stamp")
-        set(process_metrics_case "memory")
+        string(JSON command GET "${contents}" command)
+        if (command MATCHES "process_metrics_memory\\.py")
+          set(process_metrics_case "memory")
+          string(JSON process_metrics_chain_head_rss GET "${process_metrics}" maxRSS)
+        else()
+          string(JSON process_metrics_chain_tail_rss GET "${process_metrics}" maxRSS)
+        endif()
       elseif (outputs MATCHES "process_metrics_cpu_custom\.stamp")
         set(process_metrics_case "cpu")
       endif()
@@ -254,6 +262,16 @@ foreach(snippet IN LISTS snippets)
 
 endforeach()
 
+# The final chained command must not inherit the preceding command's memory peak.
+# (SunOS does not populate maxRSS, so both commands report zero.)
+if (ARGS_PROCESS_METRICS_QUERY AND ARGS_BUILD AND NOT CMAKE_HOST_SYSTEM_NAME STREQUAL "SunOS")
+  if (NOT DEFINED process_metrics_chain_head_rss OR NOT DEFINED process_metrics_chain_tail_rss)
+    add_error("Missing process metrics for one or both chained commands")
+  elseif (process_metrics_chain_head_rss EQUAL process_metrics_chain_tail_rss)
+    add_error("Chained commands reported identical maxRSS: ${process_metrics_chain_tail_rss} KiB")
+  endif()
+endif()
+
 # Verify that listed snippets match expected roles
 set(EXPECTED_SNIPPETS configure generate)
 if (ARGS_BUILD OR ARGS_BUILD_MAKE_PROGRAM)

Tests/RunCMake/Instrumentation/project/CMakeLists.txt

@@ -30,6 +30,8 @@ if (PROCESS_METRICS_QUERY)
     COMMAND ${Python_EXECUTABLE}
             ${CMAKE_CURRENT_LIST_DIR}/process_metrics_memory.py
             ${CMAKE_CURRENT_BINARY_DIR}/process_metrics_custom.stamp
+    # The last command must not inherit the preceding command's memory peak.
+    COMMAND ${CMAKE_COMMAND} -E true
     VERBATIM
   )
   add_custom_command(