I used a C library in my Java code using JNA. I have these C structures of whose members I need to print in Java. Because of the memory alignment and padding the size was differing from what I was actually expecting. Therefore I used pragma pack and this is how the structures look like now.
#define PACK( __Declaration__ ) __pragma( pack(push, 1) ) __Declaration__ __pragma( pack(pop) )
PACK(
typedef struct
{
size_t size;
uint8_t bytes[48];
} ipj_tid_t);
PACK(
typedef struct
{
bool has_epc; //1
ipj_epc_t epc; //64+8
bool has_tid; //1
ipj_tid_t tid; //48+8
bool has_pc; //1
uint32_t pc; //4
bool has_xpc; //1
uint32_t xpc; //4
bool has_crc; //1
uint32_t crc; //4
bool has_timestamp; //1
uint64_t timestamp; //8
bool has_rssi; //1
int32_t rssi; //4
bool has_phase; //1
int32_t phase; //4
bool has_channel; //1
uint32_t channel; //4
bool has_antenna; //1
uint32_t antenna; //4
} ipj_tag); //total size= 174
PACK(
typedef struct
{
bool has_error;
ipj_error error;
bool has_test_id;
uint32_t test_id;
bool has_result_1;
uint32_t result_1;
bool has_result_2;
uint32_t result_2;
bool has_result_3;
uint32_t result_3;
size_t data_count;
uint32_t data[16];
bool has_timestamp;
uint64_t timestamp;
size_t lt_buffer_count;
uint32_t lt_buffer[21];
} ipj_test_report);
PACK(
typedef struct
{
size_t size;
uint8_t bytes[64];
} ipj_tag_operation_data_t);
PACK(
typedef struct
{
bool has_error; //1
ipj_error error; //4
bool has_tag; //1
ipj_tag tag; //174
bool has_tag_operation_type; //1
ipj_tag_operation_type tag_operation_type; //4
bool has_tag_operation_data; //1
ipj_tag_operation_data_t tag_operation_data; //72
bool has_retries; //1
uint32_t retries; //4
bool has_diagnostic; //1
uint32_t diagnostic; //4
bool has_timestamp; //1
uint64_t timestamp; //8
size_t lt_buffer_count; //8
uint32_t lt_buffer[30]; //120
} ipj_tag_operation_report); //405
When I run the code from Visual Studio, I am not getting any errors, exceptions or crashes from it. But when I call this from Java, the jvm is crashing. Why is this happening? There are other structures in the C code too which are not packed. Could it be a reason? Please advice.
The structures I have shown above are used in C. What is returned from the C code is this structure after all the processing.
#define RX_MAX_SIZE 405
#pragma pack(push, 1)
typedef struct _report
{
ipj_report_id report_id;
uint32_t data_size;
uint32_t data[RX_MAX_SIZE];
} report;
#pragma pack(pop)
The equivalent JNA structure that has been used is as follows.
public class _report extends Structure {
public static class ByValue extends _report implements Structure.ByValue {
}
public _report() {
super();
setAlignType(ALIGN_NONE);
}
public _ipj_report_id reportid;
public int data_size;
public int[] data = new int[405];
@Override
protected List getFieldOrder() {
return Arrays.asList("reportid", "data_size", "data");
}
}
public class _ipj_report_id extends Structure {
public int ipj_report_id;
public _ipj_report_id() {
super();
setAlignType(ALIGN_NONE);
}
@Override
protected List getFieldOrder() {
return Arrays.asList("ipj_report_id");
}
}
Below is the structure I get when debugging the JNA code.
_report$ByValue(auto-allocated@0x18918cc0 (1628 bytes)) {
_ipj_report_id reportid@0=_ipj_report_id(allocated@0x18918cc0 (4 bytes) (shared from auto-allocated@0x18918cc0 (1628 bytes))) {
int ipj_report_id@0=0
}
int data_size@4=195
int data[405]@8=[I@78bb0ecb
}
Below is how I call this method in JNA.
rfidlib rlib = (rfidlib) Native.loadLibrary("rfidlib", rfidlib.class);
_report.ByValue report = new _report.ByValue();
report = rlib.get_next_reports();
