ARM ELF

Note A DT_SONAME entry is mandatory only for shared objects, not for dynamically linked executables.

Following the dynamic array, the dynamic segment includes:

A hash table section (see 4.7.4, The hash table section).

A symbol table section (called .dynsym in the section view—see 3.5, Symbol Table).

A string table section (see 3.4, String Table).

Relocation sections (see 3.6, Relocation).

The order of these sections is unimportant. The offset of each in the dynamic segment is given by the corresponding entry in the dynamic array.

4.7.4 The hash table section

The hash table section is described by the following pseudo-C structure:

struct Elf32_HashTable { Elf32_Word nBuckets; Elf32_Word nChains; Elf32_Word bucket[nBuckets]; Elf32_Word chain[nChains];

};

Both bucket and chain hold symbol table indexes. Indexes start at 0. Bucket can have any convenient size. There is one chain entry for each symbol in the symbol table (nChains = number of symbols).

Bucket and chain implement a chained overflow hash table access structure for the symbol table. If h is the result of applying the ELF hash function (see Figure 4-19, The ELF hash function) to a symbol’s name, the start of the chain of symbols that hash to this bucket is given by:

bucket[h % nBuckets]

For each symbol index s, chain[s] gives the index of the next symbol that hashes to the same bucket. Zero indexes the dummy symbol and is used as the end of chain pointer.

Figure 4-19, The ELF hash function

unsigned long elf_hash(const unsigned char *name)

{

unsigned long h, g;

for (h = 0; *name != 0; ++name)

{

h = (h << 4) + *name; g = h & 0xf0000000;

if (g != 0) h ^= g >> 24; h &= ~g;

}

return h;

}