ARM ELF

4.3.3 Link and info fields

Figure 4-6, Interpretation of sh_link and sh_info

4.4 Symbols

4.4.1 Symbol value

See also section 3.5.1, Symbol Values.

In a re-locatable file:

For a COMMON symbol defined in the SHN_COMMON section, st_value gives its alignment constraint (the allocated address of the symbol must be zero modulo st_value).

For a symbol definition, st_value gives its offset within the section identified by st_shndx.

In executable and shared object files:

For symbols defined in sections included in executable program segments, st_value is a target-system virtual address assigned when the ELF file is statically linked.

Otherwise, st_value is a virtual address in an address space specific to the operating environment (for example, symbols defined in debugging tables).

4.4.2 Symbol size

For a symbol definition of type STT_FUNC, st_size gives the length of the function in bytes, or 0 if this is unknown.

For a symbol definition of type STT_OBJECT, st_size gives the length in bytes of the associated data object or 0 if this is unknown.

4.4.3 Weak symbols

No library is searched to satisfy an undefined weak symbol (st_shndx = SHN_UNDEF, ELF32_ST_BIND = STB_WEAK), or weak reference. It is not an error for a weak reference to remain unsatisfied.

The value of an undefined weak symbol is:

P + 4 if location P is subject to branch relocation (R_ARM_PC24, .R_ARM_THM_PC22, R_ARM_XPC25,

R_ARM_THM_XPC22).

P if location P is subject to a PC-relative or SB-relative relocation.

Otherwise, 0.

You can think of these values as branch offset 0 (branch to the next instruction), offset 0, and absolute 0, respectively. That is, the value of an undefined weak symbol is always the sort of 0 appropriate to the relocation directive referring to it.

A weak symbol definition may coexist with a non-weak definition, but all references to the symbol resolve to the non-weak definition.