Software Capability Address Space Restriction Processing

64–bit objects that are identified with the SF1_SUNW_ADDR32 software capabilities flag can contain optimized code that requires a 32–bit address space. 64–bit objects that are identified in this manner can interoperate with any other 64–bit objects whether they are identified with the SF1_SUNW_ADDR32 flag or not. An occurrence of the SF1_SUNW_ADDR32 flag within a 64–bit input relocatable object is propagated to the CA_SUNW_SF_1 value that is created for the output file being created by the link-editor.

The existence of the SF1_SUNW_ADDR32 flag within a 64–bit executable ensures that the associated process is restricted to the lower 32–bit address space. This restricted address space includes the process stack and all process dependencies. Within such a process, all objects, whether they are identified with the SF1_SUNW_ADDR32 flag or not, are loaded within the restricted 32–bit address space.

64–bit shared objects can contain the SF1_SUNW_ADDR32 flag. However, the restricted address space requirement can only be established by a 64–bit executable containing the SF1_SUNW_ADDR32 flag. Therefore, a 64–bit SF1_SUNW_ADDR32 shared object must be a dependency of a 64–bit SF1_SUNW_ADDR32 executable.

A 64–bit SF1_SUNW_ADDR32 shared object that is encountered by the link-editor when building an unrestricted 64–bit executable results in a warning.

$ cc -m64 -o main main.c -lfoo
ld: warning: file libfoo.so: section .SUNW_cap: software capability ADDR32: \
    requires executable be built with ADDR32 capability

A 64–bit SF1_SUNW_ADDR32 shared object that is encountered at runtime by a process that is created from an unrestricted 64–bit executable, results in a fatal error.

$ ldd main
        libfoo.so =>     ./libfoo.so  - software capability unsupported: \ 
                         0x4  [ ADDR32 ]
        ....
$ main
ld.so.1: main: fatal: ./libfoo.so: software capability unsupported: 0x4  [ ADDR32 ]

An executable can be seeded with the SF1_SUNW_ADDR32 using a mapfile.

$ cat mapfile
$mapfile_version 2
CAPABILITY {
        SF += ADDR32;
};
$ cc -m64 -o main main.c -Mmapfile -lfoo
$ elfdump -H main

Capabilities Section:  .SUNW_cap

 Object Capabilities:
     index  tag               value
       [0]  CA_SUNW_SF_1     0x4  [ SF1_SUNW_ADDR32 ]