Global _drsys_arg_t::value: For 32-bit applications, some platforms (namely MacOS) support 64-bit arguments. For such cases, this field will hold only the bottom 32 bits of the value. Use the value64 field to retrieve the whole value. For cross-platform code, we recommend using value64 rather than this field.
Global drsys_pre_syscall_arg (void *drcontext, uint argnum, DR_PARAM_OUT ptr_uint_t *value): For 32-bit applications, some platforms (namely MacOS) support 64-bit arguments. For such cases, the value returned here will hold only the bottom 32 bits of the value. We recommend using drsys_pre_syscall_arg64() instead for cross-platform code.