Support Interface Example (Linker and Libraries Guide)

Linker and Libraries Guide

Support Interface Example

The following example creates a support library that prints the section name of any relocatable object file processed as part of a 32–bit link-edit.

$ cat support.c
#include        <link.h>
#include        <stdio.h>
 
static int      indent = 0;
 
void
ld_start(const char *name, const Elf32_Half type,
    const char *caller)
{
        (void) printf("output image: %s\n", name);
}
 
void
ld_file(const char *name, const Elf_Kind kind, int flags,
    Elf *elf)
{
        if (flags & LD_SUP_EXTRACTED)
                indent = 4;
        else
                indent = 2;
 
        (void) printf("%*sfile: %s\n", indent, "", name);
}
 
void
ld_section(const char *name, Elf32_Shdr *shdr, Elf32_Word sndx,
    Elf_Data *data, Elf *elf)
{
        Elf32_Ehdr *ehdr = elf32_getehdr(elf);
 
        if (ehdr->e_type == ET_REL)
                (void) printf("%*s   section [%ld]: %s\n", indent,
                    "", (long)sndx, name);
}

This support library is dependent upon libelf to provide the ELF access function elf32_getehdr(3ELF) that is used to determine the input file type. The support library is built using the following.

$ cc -o support.so.1 -G -K pic support.c -lelf -lc

The following example shows the section diagnostics resulting from the construction of a trivial application from a relocatable object and a local archive library. The invocation of the support library, in addition to default debugging information processing, is brought about by the -S option usage.

$ LD_OPTIONS=-S./support.so.1 cc -o prog main.c -L. -lfoo

output image: prog
  file: /opt/COMPILER/crti.o
     section [1]: .shstrtab
     section [2]: .text
     .......
  file: /opt/COMPILER/crt1.o
     section [1]: .shstrtab
     section [2]: .text
     .......
  file: /opt/COMPILER/values-xt.o
     section [1]: .shstrtab
     section [2]: .text
     .......
  file: main.o
     section [1]: .shstrtab
     section [2]: .text
     .......
  file: ./libfoo.a
    file: ./libfoo.a(foo.o)
       section [1]: .shstrtab
       section [2]: .text
       .......
  file: /lib/libc.so
  file: /opt/COMPILER/crtn.o
     section [1]: .shstrtab
     section [2]: .text
     .......

Note –

The number of sections that are displayed in this example have been reduced to simplify the output. Also, the files included by the compiler driver can vary.