8.5.7.5 Checking the Consistency of Allocators

The linker checks the consistency of load and run allocations specified for unions, groups, and sections. The following rules are used:

• Run allocations are only allowed for top-level sections, groups, or unions (sections, groups, or unions that are not nested under any other groups or unions). The linker uses the run address of the top-level structure to compute the run addresses of the components within groups and unions.
• The linker does not accept a load allocation for UNIONs.
• The linker does not accept a load allocation for uninitialized sections.
• In most cases, you must provide a load allocation for an initialized section. However, the linker does not accept a load allocation for an initialized section that is located within a group that already defines a load allocator.
• As a shortcut, you can specify a load allocation for an entire group, to determine the load allocations for every initialized section or subgroup nested within the group. However, a load allocation is accepted for an entire group only if all of the following conditions are true:
  • The group is initialized (that is, it has at least one initialized member).
  • The group is not nested inside another group that has a load allocator.
  • The group does not contain a union containing initialized sections.
• If the group contains a union with initialized sections, it is necessary to specify the load allocation for each initialized section nested within the group. Consider the following example:
SECTIONS { GROUP: load = SLOW_MEM, run = SLOW_MEM { .text1: UNION: { .text2: .text3: } } }

The load allocator given for the group does not uniquely specify the load allocation for the elements within the union: .text2 and .text3. In this case, the linker issues a diagnostic message to request that these load allocations be specified explicitly.