WASI Build Guard Sites Documentation

This document lists all locations in OCCT source code that require #ifdef __wasi__ guards for WASI compatibility.

Current Status

Required CMake Flags

Add to CMake configuration for WASI builds:

-DCMAKE_C_FLAGS="${CMAKE_C_FLAGS} -D_WASI_EMULATED_PROCESS_CLOCKS -D_WASI_EMULATED_GETPID"
-DCMAKE_CXX_FLAGS="${CMAKE_CXX_FLAGS} -D_WASI_EMULATED_PROCESS_CLOCKS -D_WASI_EMULATED_GETPID"
-DCMAKE_EXE_LINKER_FLAGS="${CMAKE_EXE_LINKER_FLAGS} -lwasi-emulated-process-clocks -lwasi-emulated-getpid"

Guard Sites Detail

1. OSD_Chronometer.cxx - GetProcessCPU()

Lines ~53-70 (original source)

void OSD_Chronometer::GetProcessCPU(double& theUserSeconds, double& theSystemSeconds)
{
#if defined(__linux__) || defined(__FreeBSD__) || defined(__ANDROID__) || defined(__QNX__) \
    || defined(__EMSCRIPTEN__)
  static const long aCLK_TCK = sysconf(_SC_CLK_TCK);
#else
  static const long aCLK_TCK = CLK_TCK;
#endif

#ifdef __wasi__
  theUserSeconds = theSystemSeconds = 0.0;
#else
  tms aCurrentTMS{};
  times(&aCurrentTMS);
  theUserSeconds   = (double)aCurrentTMS.tms_utime / aCLK_TCK;
  theSystemSeconds = (double)aCurrentTMS.tms_stime / aCLK_TCK;
#endif
}

Also needs: times() stub at top of file (after CLK_TCK define)

#ifdef __wasi__
// WASI doesn't have times() or struct tms
static clock_t times(struct tms *buf) {
  return 0;
}
#endif

2. OSD_Directory.cxx - Build()

Lines ~107-110 (original source)

myPath.SystemName(aBuffer);
#ifdef __wasi__
  // WASI doesn't have umask
#else
  umask(0);
#endif
int aStatus = mkdir(aBuffer.ToCString(), anInternalProt);

3. OSD_Directory.cxx - BuildTemporary()

Lines ~155-165 (original source)

#ifdef __wasi__
  // WASI doesn't have mkdtemp, use a simple random name
  static int counter = 0;
  char aTmpName[64];
  snprintf(aTmpName, sizeof(aTmpName), "/tmp/occt_%d_%d", getpid(), counter++);
  if (mkdir(aTmpName, 0700) != 0)
#else
  char aTmpName[] = "/tmp/CSFXXXXXX";
  if (nullptr == mkdtemp(aTmpName))
#endif
  {
    return OSD_Directory(); // can't create a directory
  }

4. OSD_Environment.cxx - Global mutex usage

Lines ~137-138 (original source)

static std::mutex           aMutex;
std::lock_guard<std::mutex> aLock(aMutex);

Guard needed: Wrap mutex usage or use WASI-compatible synchronization.

5. OSD_File.cxx - Multiple locations

• Line ~767: mkstemp(aTmpName) - temporary file creation
• Lines ~1394-1404: F_WRLCK, F_RDLCK, F_SETLKW, F_UNLCK, F_SETLK - file locking
• Line ~1509-1510: F_UNLCK, F_SETLK - file unlocking

All need __wasi__ guards with alternative implementations or stubs.

Patch Files

Current patches in Scripts/patches-wasi/:

• wasi-osd-chronometer.patch - Guards for OSD_Chronometer
• wasi-osd-directory.patch - Guards for OSD_Directory

Next Steps

1. Create patches for OSD_Environment.cxx (mutex)
2. Create patches for OSD_File.cxx (mkstemp, fcntl locking)
3. Add emulation flags to build script CMake configuration
4. Test full build to identify any remaining guard sites

Build Command

./Scripts/build-occt-wasm.sh

Output artifacts:

• Libraries/libOCCT-wasm.a - Combined static library
• Libraries/occt-headers-wasm/ - Headers for SwiftPM linking