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elf: define reader functions for the ELF header
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Generate functions that correctly read fields of arbitrary ELF headers,
no matter their classes or data encodings.
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@matheusmoreira
matheusmoreira committed Jul 29, 2024
1 parent cb59a33 commit 6ffe270
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Showing 2 changed files with 93 additions and 0 deletions.
16 changes: 16 additions & 0 deletions include/lone/elf.h
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Original file line number Diff line number Diff line change
Expand Up @@ -512,4 +512,20 @@ struct lone_bytes lone_elf_header_read_ident_magic(struct lone_elf_header *heade
│ │
╰────────────────────────────────────────────────────────────────────────╯ */

struct lone_optional_u16 lone_elf_header_read_type(struct lone_elf_header *header);
struct lone_optional_u16 lone_elf_header_read_machine(struct lone_elf_header *header);
struct lone_optional_u32 lone_elf_header_read_version(struct lone_elf_header *header);

struct lone_elf_value lone_elf_header_read_entry_point(struct lone_elf_header *header);
struct lone_elf_value lone_elf_header_read_segments_offset(struct lone_elf_header *header);
struct lone_elf_value lone_elf_header_read_sections_offset(struct lone_elf_header *header);

struct lone_optional_u32 lone_elf_header_read_flags(struct lone_elf_header *header);
struct lone_optional_u16 lone_elf_header_read_header_size(struct lone_elf_header *header);
struct lone_optional_u16 lone_elf_header_read_segment_size(struct lone_elf_header *header);
struct lone_optional_u16 lone_elf_header_read_segment_count(struct lone_elf_header *header);
struct lone_optional_u16 lone_elf_header_read_section_size(struct lone_elf_header *header);
struct lone_optional_u16 lone_elf_header_read_section_count(struct lone_elf_header *header);
struct lone_optional_u16 lone_elf_header_read_section_names_index(struct lone_elf_header *header);

#endif /* LONE_ELF_HEADER */
77 changes: 77 additions & 0 deletions source/lone/elf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -85,3 +85,80 @@ LONE_ELF_MULTIBYTE_MULTICLASS_VALUE_READER(s, 32)
LONE_ELF_MULTIBYTE_MULTICLASS_VALUE_READER(s, 64)

#undef LONE_ELF_MULTIBYTE_MULTICLASS_VALUE_READER

#define LONE_ELF_HEADER_COMMON_READER(field, sign, bits) \
struct lone_optional_##sign##bits \
lone_elf_header_read_##field(struct lone_elf_header *header) \
{ \
return lone_elf_read_##sign##bits(header, &header->field); \
}

#define LONE_ELF_HEADER_CLASSIFIED_READER(field, sign, bits) \
struct lone_optional_##sign##bits \
lone_elf_header_read_##field(struct lone_elf_header *header) \
{ \
return lone_elf_read_classified_##sign##bits(header, \
&header->as.elf32.field, &header->as.elf64.field); \
}

static struct lone_elf_value lone_elf_read_address_or_offset(struct lone_elf_header *header,
void *address32, void *address64)
{
struct lone_optional_u32 u32;
struct lone_optional_u64 u64;
struct lone_elf_value value = {
.class = LONE_ELF_IDENT_CLASS_INVALID,
.as.u64 = 0,
};

if (!header) { return value; }

switch (header->ident[LONE_ELF_IDENT_INDEX_CLASS]) {
case LONE_ELF_IDENT_CLASS_32BIT:
u32 = lone_elf_read_u32(header, address32);
if (u32.present) {
value.class = LONE_ELF_IDENT_CLASS_32BIT;
value.as.u32 = u32.value;
}
break;
case LONE_ELF_IDENT_CLASS_64BIT:
u64 = lone_elf_read_u64(header, address64);
if (u64.present) {
value.class = LONE_ELF_IDENT_CLASS_64BIT;
value.as.u64 = u64.value;
}
break;
default:
break;
}

return value;
}

#define LONE_ELF_HEADER_ADDRESS_OR_OFFSET_READER(field) \
struct lone_elf_value \
lone_elf_header_read_##field(struct lone_elf_header *header) \
{ \
return lone_elf_read_address_or_offset(header, \
&header->as.elf32.field, &header->as.elf64.field); \
}

LONE_ELF_HEADER_COMMON_READER(type, u, 16)
LONE_ELF_HEADER_COMMON_READER(machine, u, 16)
LONE_ELF_HEADER_COMMON_READER(version, u, 32)

LONE_ELF_HEADER_ADDRESS_OR_OFFSET_READER(entry_point)
LONE_ELF_HEADER_ADDRESS_OR_OFFSET_READER(segments_offset)
LONE_ELF_HEADER_ADDRESS_OR_OFFSET_READER(sections_offset)

LONE_ELF_HEADER_CLASSIFIED_READER(flags, u, 32)
LONE_ELF_HEADER_CLASSIFIED_READER(header_size, u, 16)
LONE_ELF_HEADER_CLASSIFIED_READER(segment_size, u, 16)
LONE_ELF_HEADER_CLASSIFIED_READER(segment_count, u, 16)
LONE_ELF_HEADER_CLASSIFIED_READER(section_size, u, 16)
LONE_ELF_HEADER_CLASSIFIED_READER(section_count, u, 16)
LONE_ELF_HEADER_CLASSIFIED_READER(section_names_index, u, 16)

#undef LONE_ELF_HEADER_ADDRESS_OR_OFFSET_READER
#undef LONE_ELF_HEADER_CLASSIFIED_READER
#undef LONE_ELF_HEADER_COMMON_READER

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