app links libgcov.a: close is renamed to myst_gcov_close with objcopy tool CRT: ../gcov/gcovclient.c: int myst_gcov_close(int fd) { long params[6] = {(long)fd}; return (int)myst_gcov(__FUNCTION__, params); } ../crt/enter.c: long myst_gcov(const char* func, long gcov_params[6]) { long params[6] = {(long)func, (long)gcov_params}; return myst_syscall(SYS_myst_gcov, params); } Kernel: ../kernel/syscall.c: case SYS_myst_gcov: { const char* func = (const char*)x1; long* gcov_params = (long*)x2; _strace(n, "func=%s gcov_params=%p", func, gcov_params); long ret = myst_gcov(func, gcov_params); BREAK(_return(n, ret)); } long myst_gcov(const char* func, long gcov_params[6]) { long params[6] = {(long)func, (long)gcov_params}; return myst_tcall(MYST_TCALL_GCOV, params); } Target (enclave): ../target/sgx/enclave/tcall.c case MYST_TCALL_GCOV: { extern long myst_gcov(const char* func, long gcov_params[6]); const char* func = (const char*)x1; long* gcov_params = (long*)x2; return myst_gcov(func, gcov_params); } ../tools/myst/enc/gcov.c: long myst_gcov(const char* func, long params[6]) { if (strcmp(func, "myst_gcov_close") == 0) { int fd = (int)params[0]; int r; if ((r = _close(fd)) < 0) { errno = -r; return -1; } return 0; } else if (...) { } } static int _close(int fd) { long params[6] = {(long)fd}; return (int)myst_handle_tcall(SYS_close, params); } ../tools/myst/enc/syscall.c: long myst_handle_tcall(long n, long params[6]) { /* calls _close() */ } static long _close(int fd) { long ret; RETURN(myst_close_ocall(&ret, fd)); } Target (host): long myst_close_ocall(int fd) { return close(fd); }