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Benedek László 2024-04-12 14:50:11 +02:00
commit 807527310d
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196
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#include "classfile.h"
#include <memory.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#define SWAP_ENDIANNESS
void read_u2(void *ptr, size_t n, FILE *file) {
u2 buffer[n];
fread(&buffer, sizeof(u2), n, file);
#ifdef SWAP_ENDIANNESS
for (size_t i = 0; i < n; i++) {
buffer[i] = (buffer[i] >> 8) | (buffer[i] << 8);
}
#endif
memcpy(ptr, &buffer, n*sizeof(u2));
}
void read_u4(void *ptr, size_t n, FILE *file) {
u4 buffer[n];
fread(&buffer, sizeof(u2), n, file);
#ifdef SWAP_ENDIANNESS
for (size_t i = 0; i < n; i++) {
buffer[i] = ((buffer[i] >> 24) & 0xff) | // move byte 3 to byte 0
((buffer[i] << 8) & 0xff0000) | // move byte 1 to byte 2
((buffer[i] >> 8) & 0xff00) | // move byte 2 to byte 1
((buffer[i] << 24) & 0xff000000);
}
#endif
memcpy(ptr, &buffer, n*sizeof(u4));
}
ClassFile *ClassFile_load(const char *path) {
FILE *file = fopen(path, "rb");
if (file == NULL)
return NULL;
ClassFile *cf = (ClassFile *)malloc(sizeof(ClassFile));
// magic 4bytes, minor_version 2bytes, major_version 2bytes,
// constant_pool_count 2bytes
fread(&(cf->magic), 4 + 2 + 2 + 2, 1, file);
// constant_pool
cf->constant_pool =
(cp_info *)malloc(sizeof(cp_info) * (cf->constant_pool_count - 1));
for (u2 i = 0; i < (cf->constant_pool_count - 1); i++) {
// cp_info.tag 2bytes
fread(&(cf->constant_pool[i].tag), 2, 1, file);
size_t size;
switch (cf->constant_pool[i].tag) {
case CONSTANT_Class:
size = sizeof(CONSTANT_Class_info);
break;
case CONSTANT_Fieldref:
size = sizeof(CONSTANT_Fieldref_info);
break;
case CONSTANT_Methodref:
size = sizeof(CONSTANT_Methodref_info);
break;
case CONSTANT_InterfaceMethodref:
size = sizeof(CONSTANT_InterfaceMethodref_info);
break;
case CONSTANT_String:
size = sizeof(CONSTANT_String_info);
break;
case CONSTANT_Integer:
size = sizeof(CONSTANT_Integer_info);
break;
case CONSTANT_Float:
size = sizeof(CONSTANT_Float_info);
break;
case CONSTANT_Long:
size = sizeof(CONSTANT_Long_info);
break;
case CONSTANT_Double:
size = sizeof(CONSTANT_Double_info);
break;
case CONSTANT_NameAndType:
size = sizeof(CONSTANT_NameAndType_info);
break;
case CONSTANT_Utf8:
size = sizeof(CONSTANT_Utf8_info);
break;
case CONSTANT_MethodHandle:
size = sizeof(CONSTANT_MethodHandle_info);
break;
case CONSTANT_MethodType:
size = sizeof(CONSTANT_MethodType_info);
break;
case CONSTANT_Dynamic:
size = sizeof(CONSTANT_Dynamic_info);
break;
case CONSTANT_InvokeDynamic:
size = sizeof(CONSTANT_InvokeDynamic_info);
break;
case CONSTANT_Module:
size = sizeof(CONSTANT_Module_info);
break;
case CONSTANT_Package:
size = sizeof(CONSTANT_Package_info);
break;
}
cf->constant_pool[i].info = (void *)malloc(size);
fread(cf->constant_pool[i].info, size, 1, file);
}
// access_flags 2bytes, this_class 2bytes, super_class 2bytes, interface_count
// 2bytes
fread(&(cf->access_flags), 2 + 2 + 2 + 2, 1, file);
// interfaces
cf->interfaces = (u2 *)malloc(2 * cf->interfaces_count);
fread(cf->interfaces, 2 * cf->interfaces_count, 1, file);
// fields_count 2bytes
fread(&(cf->fields_count), 2, 1, file);
// fields
cf->fields = (field_info *)malloc(sizeof(field_info) * cf->fields_count);
for (u2 i = 0; i < cf->fields_count; i++) {
// access_flags 2bytes, name_index 2bytes, descriptor_index 2bytes,
// attributes_count 2bytes
fread(&(cf->fields[i].access_flags), 2 + 2 + 2 + 2, 1, file);
cf->fields[i].attributes = (attribute_info *)malloc(
sizeof(attribute_info) * cf->fields[i].attributes_count);
for (u2 j = 0; j < cf->fields[i].attributes_count; j++) {
// attribute_name_index 2bytes, attribute_length 4bytes
fread(&(cf->fields[i].attributes[j].attribute_name_index), 2 + 4, 1,
file);
cf->fields[i].attributes[j].info =
(u1 *)malloc(cf->fields[i].attributes[j].attribute_length);
fread(cf->fields[i].attributes[j].info,
cf->fields[i].attributes[j].attribute_length, 1, file);
}
}
// methods_count 2bytes
fread(&(cf->methods_count), 2, 1, file);
// methods
cf->methods = (method_info *)malloc(sizeof(method_info) * cf->methods_count);
for (u2 i = 0; i < cf->methods_count; i++) {
// access_flags 2bytes, name_index 2bytes, descriptor_index 2bytes,
// attributes_count 2bytes
fread(&(cf->methods[i].access_flags), 2 + 2 + 2 + 2, 1, file);
cf->methods[i].attributes = (attribute_info *)malloc(
sizeof(attribute_info) * cf->methods[i].attributes_count);
for (u2 j = 0; j < cf->methods[i].attributes_count; j++) {
// attribute_name_index 2bytes, attribute_length 4bytes
fread(&(cf->methods[i].attributes[j].attribute_name_index), 2 + 4, 1,
file);
cf->methods[i].attributes[j].info =
(u1 *)malloc(cf->methods[i].attributes[j].attribute_length);
fread(cf->methods[i].attributes[j].info,
cf->methods[i].attributes[j].attribute_length, 1, file);
}
}
// attributes_count 2bytes
fread(&(cf->attributes_count), 2, 1, file);
// attributes
cf->attributes =
(attribute_info *)malloc(sizeof(attribute_info) * cf->attributes_count);
for (u2 i = 0; i < cf->attributes_count; i++) {
// attribute_name_index 2bytes, attribute_length 4bytes
fread(&(cf->attributes[i].attribute_name_index), 2 + 4, 1, file);
cf->attributes[i].info = (u1 *)malloc(cf->attributes[i].attribute_length);
fread(cf->attributes[i].info, cf->attributes[i].attribute_length, 1, file);
}
fclose(file);
return cf;
}
void ClassFile_info(const ClassFile *cf) {
printf("magic=%X\n"
"minor_version=%hu\n"
"major_version=%hu\n"
"constant_pool_count=%hu\n"
"access_flags=%hu\n"
"this_class=%hu\n"
"super_class=%hu\n"
"interfaces_count=%hu\n"
"fields_count=%hu\n"
"methods_count=%hu\n"
"attributes_count=%hu\n",
cf->magic, cf->minor_version, cf->major_version,
cf->constant_pool_count, cf->access_flags, cf->this_class,
cf->super_class, cf->interfaces_count, cf->fields_count,
cf->methods_count, cf->attributes_count);
}

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// types for Java's Classfile structure
// https://docs.oracle.com/javase/specs/jvms/se22/html/jvms-4.html
#include <stdint.h>
#pragma pack(1)
typedef uint8_t u1;
typedef uint16_t u2;
typedef uint32_t u4;
typedef enum {
ACC_PUBLIC = 0x0001,
ACC_PRIVATE = 0x0002,
ACC_PROTECTED = 0x0004,
ACC_STATIC = 0x0008,
ACC_FINAL = 0x0010,
ACC_SUPER = 0x0020,
ACC_SYNCHRONIZED = 0x0020,
ACC_VOLATLE = 0x0040,
ACC_BRIDGE = 0x0040,
ACC_TRANSIENT = 0x0080,
ACC_VARARGS = 0x0080,
ACC_NATIVE = 0x0100,
ACC_INTERFACE = 0x0200,
ACC_ABSTRACT = 0x0400,
ACC_STRICT = 0x0800,
ACC_SYNTHETIC = 0x1000,
ACC_ANNOTATION = 0x2000,
ACC_ENUM = 0x4000,
ACC_MODULE = 0x8000,
} ACCESS_FLAGS;
typedef enum {
CONSTANT_Class = 7,
CONSTANT_Fieldref = 9,
CONSTANT_Methodref = 10,
CONSTANT_InterfaceMethodref = 11,
CONSTANT_String = 8,
CONSTANT_Integer = 3,
CONSTANT_Float = 4,
CONSTANT_Long = 5,
CONSTANT_Double = 6,
CONSTANT_NameAndType = 12,
CONSTANT_Utf8 = 1,
CONSTANT_MethodHandle = 15,
CONSTANT_MethodType = 16,
CONSTANT_Dynamic = 17,
CONSTANT_InvokeDynamic = 18,
CONSTANT_Module = 19,
CONSTANT_Package = 20,
} CONSTANT_TAGS;
typedef struct {
u1 tag;
void *info;
} cp_info;
typedef struct {
u1 tag;
u2 name_index;
} CONSTANT_Class_info;
typedef struct {
u1 tag;
u2 class_index;
u2 name_and_type_index;
} CONSTANT_Fieldref_info;
typedef CONSTANT_Fieldref_info CONSTANT_Methodref_info;
typedef CONSTANT_Fieldref_info CONSTANT_InterfaceMethodref_info;
typedef struct {
u1 tag;
u2 string_index;
} CONSTANT_String_info;
typedef struct {
u1 tag;
u4 bytes;
} CONSTANT_Integer_info;
typedef CONSTANT_Integer_info CONSTANT_Float_info;
typedef struct {
u1 tag;
u4 high_bytes;
u4 low_bytes;
} CONSTANT_Long_info;
typedef CONSTANT_Long_info CONSTANT_Double_info;
typedef struct {
u1 tag;
u2 name_index;
u2 descriptor_index;
} CONSTANT_NameAndType_info;
typedef struct {
u1 tag;
u2 length;
u1 *bytes;
} CONSTANT_Utf8_info;
typedef struct {
u1 tag;
u1 reference_kind;
u2 reference_index;
} CONSTANT_MethodHandle_info;
typedef struct {
u1 tag;
u2 descriptor_index;
} CONSTANT_MethodType_info;
typedef struct {
u1 tag;
u2 bootstrap_method_attr_index;
u2 name_and_type_index;
} CONSTANT_Dynamic_info;
typedef CONSTANT_Dynamic_info CONSTANT_InvokeDynamic_info;
typedef struct {
u1 tag;
u2 name_index;
} CONSTANT_Module_info;
typedef struct {
u1 tag;
u2 name_index;
} CONSTANT_Package_info;
typedef struct {
u2 attribute_name_index;
u4 attribute_length;
u1 *info;
} attribute_info;
typedef struct {
u2 access_flags;
u2 name_index;
u2 descriptor_index;
u2 attributes_count;
attribute_info *attributes;
} field_info;
typedef struct {
u2 access_flags;
u2 name_index;
u2 descriptor_index;
u2 attributes_count;
attribute_info *attributes;
} method_info;
typedef struct {
u4 magic;
u2 minor_version;
u2 major_version;
u2 constant_pool_count;
cp_info *constant_pool;
u2 access_flags;
u2 this_class;
u2 super_class;
u2 interfaces_count;
u2 *interfaces;
u2 fields_count;
field_info *fields;
u2 methods_count;
method_info *methods;
u2 attributes_count;
attribute_info *attributes;
} ClassFile;
ClassFile *ClassFile_load(const char *path);
void ClassFile_info(const ClassFile *cf);
#pragma pack()

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#include "classfile.h"
int main(int argc, char **argv) {
ClassFile *cf = ClassFile_load("test/Main.class");
ClassFile_info(cf);
}