Base Platform linking model
Enables you to create dynamically linkable images that do not have the memory map enforced by the Base Platform Application Binary Interface (BPABI) linking model.
Note
This topic includes descriptions of [BETA] features.The Base Platform linking model enables you to:
- Create images with a memory map described in a scatter file.
- Have dynamic relocations so the images can be dynamically linked. The dynamic relocations can also target within the same image.
Note
Base Platform is not supported for AArch64 state.Note
The BPABI specification places constraints on the memory model that can be violated using scatter-loading. However, because Base Platform is a superset of BPABI, it is possible to create a BPABI conformant image with Base Platform.To link with the Base Platform model, use the --base_platform
command-line
option.
If you specify this option, the linker acts as if you specified --bpabi
,
with the following exceptions:
Scatter-loading is available with
--scatter
, in addition to the following options:--dll
.--force_so_throw
,--no_force_so_throw
.--pltgot=
is restricted to typestype
none
ordirect
.--ro_base=
.address
--rosplit
.--rw_base=
.address
- [BETA]
--rwpi
.
The default value of the
--pltgot
option is different to that for--bpabi
:- For
--base_platform
, the default is--pltgot=none
. - For
--bpabi
the default is--pltgot=direct
.
- For
If you do not use a scatter file, the linker can ensure that the Procedure Linkage Table (PLT) section is placed correctly, and contains entries for calls only to imported symbols. If you specify a scatter file, the linker might not be able to find a suitable location to place the PLT.
Each load region containing code might require a PLT section to indirect calls from the load region to functions where the address is not known at static link time. The PLT section for a load region
LR
must be placed inLR
and be accessible at all times to code withinLR
.To ensure calls between relocated load regions use a PLT entry:
- Use the
--pltgot=direct
option to turn on PLT generation. - Use the
--pltgot_opts=crosslr
option to add entries in the PLT for calls betweenRELOC
load regions. The linker generates a PLT for each load region so that calls do not have to be extended to reach a distant PLT.
- Use the
Be aware of the following:
- The model by default assumes that shared objects
cannot throw a C++ exception (
--no_force_so_throw
). - You must use symbol versioning to ensure that all the required symbols are available at load time.
- There are restrictions on the type of scatter files you can use.