Ninja,Makefile: Unify command line limit logic

Move the logic to cmSystemTools to be shared among the generators.
Revise the implementation and add comments justifying each possible
source for a limit.

Source/cmGlobalNinjaGenerator.cxx

@@ -246,7 +246,7 @@ void cmGlobalNinjaGenerator::WriteBuild(
   bool useResponseFile = false;
   if (cmdLineLimit < 0 ||
       (cmdLineLimit > 0 &&
-       (args.size() + buildstr.size() + assignments.size()) >
+       (args.size() + buildstr.size() + assignments.size() + 1000) >
          static_cast<size_t>(cmdLineLimit))) {
     variable_assignments.str(std::string());
     cmGlobalNinjaGenerator::WriteVariable(variable_assignments, "RSP_FILE",

Source/cmMakefileTargetGenerator.cxx

@@ -30,10 +30,6 @@
 #include "cm_auto_ptr.hxx"
 #include "cmake.h"
 
-#ifndef _WIN32
-#include <unistd.h>
-#endif
-
 cmMakefileTargetGenerator::cmMakefileTargetGenerator(cmGeneratorTarget* target)
   : cmCommonTargetGenerator(target)
   , OSXBundleGenerator(CM_NULLPTR)
@@ -1492,15 +1488,6 @@ void cmMakefileTargetGenerator::CreateLinkScript(
   makefile_depends.push_back(linkScriptName);
 }
 
-static size_t calculateCommandLineLengthLimit()
-{
-#if defined(_SC_ARG_MAX)
-  return ((size_t)sysconf(_SC_ARG_MAX)) - 1000;
-#else
-  return 0;
-#endif
-}
-
 bool cmMakefileTargetGenerator::CheckUseResponseFileForObjects(
   std::string const& l) const
 {
@@ -1514,7 +1501,7 @@ bool cmMakefileTargetGenerator::CheckUseResponseFileForObjects(
   }
 
   // Check for a system limit.
-  if (size_t const limit = calculateCommandLineLengthLimit()) {
+  if (size_t const limit = cmSystemTools::CalculateCommandLineLengthLimit()) {
     // Compute the total length of our list of object files with room
     // for argument separation and quoting.  This does not convert paths
     // relative to CMAKE_CURRENT_BINARY_DIR like the final list will be, so the

Source/cmNinjaNormalTargetGenerator.cxx

@@ -5,11 +5,9 @@
 #include <algorithm>
 #include <assert.h>
 #include <iterator>
-#include <limits>
 #include <map>
 #include <set>
 #include <sstream>
-#include <stddef.h>
 
 #include "cmAlgorithms.h"
 #include "cmCustomCommand.h"
@@ -35,10 +33,6 @@
 #include "cm_auto_ptr.hxx"
 #include "cmake.h"
 
-#ifndef _WIN32
-#include <unistd.h>
-#endif
-
 cmNinjaNormalTargetGenerator::cmNinjaNormalTargetGenerator(
   cmGeneratorTarget* target)
   : cmNinjaTargetGenerator(target)
@@ -546,36 +540,6 @@ std::vector<std::string> cmNinjaNormalTargetGenerator::ComputeLinkCmd()
   return std::vector<std::string>();
 }
 
-static int calculateCommandLineLengthLimit(int linkRuleLength)
-{
-  static int const limits[] = {
-#ifdef _WIN32
-    8000,
-#endif
-#if defined(__linux)
-    // #define MAX_ARG_STRLEN (PAGE_SIZE * 32) in Linux's binfmts.h
-    ((int)sysconf(_SC_PAGESIZE) * 32) - 1000,
-#endif
-    std::numeric_limits<int>::max()
-  };
-
-  size_t const arrSz = cmArraySize(limits);
-  int sz = *std::min_element(limits, limits + arrSz);
-#if defined(_SC_ARG_MAX)
-  // for instance ARG_MAX is 2096152 on Ubuntu or 262144 on Mac
-  int const szArgMax = static_cast<int>(sysconf(_SC_ARG_MAX));
-  // a return value of -1 signifies an unrestricted value
-  if (szArgMax != -1) {
-    sz = std::min(sz, szArgMax - 1000);
-  }
-#endif
-  if (sz == std::numeric_limits<int>::max()) {
-    return 0;
-  }
-
-  return sz - linkRuleLength;
-}
-
 void cmNinjaNormalTargetGenerator::WriteDeviceLinkStatement()
 {
   cmGeneratorTarget& genTarget = *this->GetGeneratorTarget();
@@ -761,8 +725,9 @@ void cmNinjaNormalTargetGenerator::WriteDeviceLinkStatement()
 
   // Device linking currently doesn't support response files so
   // do not check if the user has explicitly forced a response file.
-  int const commandLineLengthLimit = calculateCommandLineLengthLimit(
-    globalGen.GetRuleCmdLength(this->LanguageLinkerDeviceRule()));
+  int const commandLineLengthLimit =
+    static_cast<int>(cmSystemTools::CalculateCommandLineLengthLimit()) -
+    globalGen.GetRuleCmdLength(this->LanguageLinkerDeviceRule());
 
   const std::string rspfile =
     std::string(cmake::GetCMakeFilesDirectoryPostSlash()) +
@@ -1048,8 +1013,9 @@ void cmNinjaNormalTargetGenerator::WriteLinkStatement()
     !(this->TargetLinkLanguage == "RC" || this->TargetLinkLanguage == "CUDA");
   int commandLineLengthLimit = -1;
   if (!lang_supports_response || !this->ForceResponseFile()) {
-    commandLineLengthLimit = calculateCommandLineLengthLimit(
-      globalGen.GetRuleCmdLength(this->LanguageLinkerRule()));
+    commandLineLengthLimit =
+      static_cast<int>(cmSystemTools::CalculateCommandLineLengthLimit()) -
+      globalGen.GetRuleCmdLength(this->LanguageLinkerRule());
   }
 
   const std::string rspfile =

Source/cmSystemTools.cxx

@@ -570,6 +570,46 @@ std::vector<std::string> cmSystemTools::ParseArguments(const char* command)
   return args;
 }
 
+size_t cmSystemTools::CalculateCommandLineLengthLimit()
+{
+  size_t sz =
+#ifdef _WIN32
+    // There's a maximum of 65536 bytes and thus 32768 WCHARs on Windows
+    // However, cmd.exe itself can only handle 8191 WCHARs and Ninja for
+    // example uses it to spawn processes.
+    size_t(8191);
+#elif defined(__linux)
+    // MAX_ARG_STRLEN is the maximum length of a string permissible for
+    // the execve() syscall on Linux. It's defined as (PAGE_SIZE * 32)
+    // in Linux's binfmts.h
+    static_cast<size_t>(sysconf(_SC_PAGESIZE) * 32);
+#else
+    size_t(0);
+#endif
+
+#if defined(_SC_ARG_MAX)
+  // ARG_MAX is the maximum size of the command and environment
+  // that can be passed to the exec functions on UNIX.
+  // The value in limits.h does not need to be present and may
+  // depend upon runtime memory constraints, hence sysconf()
+  // should be used to query it.
+  long szArgMax = sysconf(_SC_ARG_MAX);
+  // A return value of -1 signifies an undetermined limit, but
+  // it does not imply an infinite limit, and thus is ignored.
+  if (szArgMax != -1) {
+    // We estimate the size of the environment block to be 1000.
+    // This isn't accurate at all, but leaves some headroom.
+    szArgMax = szArgMax < 1000 ? 0 : szArgMax - 1000;
+#if defined(_WIN32) || defined(__linux)
+    sz = std::min(sz, static_cast<size_t>(szArgMax));
+#else
+    sz = static_cast<size_t>(szArgMax);
+#endif
+  }
+#endif
+  return sz;
+}
+
 bool cmSystemTools::RunSingleCommand(std::vector<std::string> const& command,
                                      std::string* captureStdOut,
                                      std::string* captureStdErr, int* retVal,

Source/cmSystemTools.h

@@ -253,6 +253,8 @@ public:
   static void ParseUnixCommandLine(const char* command,
                                    std::vector<std::string>& args);
 
+  static size_t CalculateCommandLineLengthLimit();
+
   static void EnableMessages() { s_DisableMessages = false; }
   static void DisableMessages() { s_DisableMessages = true; }
   static void DisableRunCommandOutput() { s_DisableRunCommandOutput = true; }