@section Linker Functions
|
@section Linker Functions
|
@cindex Linker
|
@cindex Linker
|
The linker uses three special entry points in the BFD target
|
The linker uses three special entry points in the BFD target
|
vector. It is not necessary to write special routines for
|
vector. It is not necessary to write special routines for
|
these entry points when creating a new BFD back end, since
|
these entry points when creating a new BFD back end, since
|
generic versions are provided. However, writing them can
|
generic versions are provided. However, writing them can
|
speed up linking and make it use significantly less runtime
|
speed up linking and make it use significantly less runtime
|
memory.
|
memory.
|
|
|
The first routine creates a hash table used by the other
|
The first routine creates a hash table used by the other
|
routines. The second routine adds the symbols from an object
|
routines. The second routine adds the symbols from an object
|
file to the hash table. The third routine takes all the
|
file to the hash table. The third routine takes all the
|
object files and links them together to create the output
|
object files and links them together to create the output
|
file. These routines are designed so that the linker proper
|
file. These routines are designed so that the linker proper
|
does not need to know anything about the symbols in the object
|
does not need to know anything about the symbols in the object
|
files that it is linking. The linker merely arranges the
|
files that it is linking. The linker merely arranges the
|
sections as directed by the linker script and lets BFD handle
|
sections as directed by the linker script and lets BFD handle
|
the details of symbols and relocs.
|
the details of symbols and relocs.
|
|
|
The second routine and third routines are passed a pointer to
|
The second routine and third routines are passed a pointer to
|
a @code{struct bfd_link_info} structure (defined in
|
a @code{struct bfd_link_info} structure (defined in
|
@code{bfdlink.h}) which holds information relevant to the link,
|
@code{bfdlink.h}) which holds information relevant to the link,
|
including the linker hash table (which was created by the
|
including the linker hash table (which was created by the
|
first routine) and a set of callback functions to the linker
|
first routine) and a set of callback functions to the linker
|
proper.
|
proper.
|
|
|
The generic linker routines are in @code{linker.c}, and use the
|
The generic linker routines are in @code{linker.c}, and use the
|
header file @code{genlink.h}. As of this writing, the only back
|
header file @code{genlink.h}. As of this writing, the only back
|
ends which have implemented versions of these routines are
|
ends which have implemented versions of these routines are
|
a.out (in @code{aoutx.h}) and ECOFF (in @code{ecoff.c}). The a.out
|
a.out (in @code{aoutx.h}) and ECOFF (in @code{ecoff.c}). The a.out
|
routines are used as examples throughout this section.
|
routines are used as examples throughout this section.
|
|
|
@menu
|
@menu
|
* Creating a Linker Hash Table::
|
* Creating a Linker Hash Table::
|
* Adding Symbols to the Hash Table::
|
* Adding Symbols to the Hash Table::
|
* Performing the Final Link::
|
* Performing the Final Link::
|
@end menu
|
@end menu
|
|
|
@node Creating a Linker Hash Table, Adding Symbols to the Hash Table, Linker Functions, Linker Functions
|
@node Creating a Linker Hash Table, Adding Symbols to the Hash Table, Linker Functions, Linker Functions
|
@subsection Creating a linker hash table
|
@subsection Creating a linker hash table
|
@cindex _bfd_link_hash_table_create in target vector
|
@cindex _bfd_link_hash_table_create in target vector
|
@cindex target vector (_bfd_link_hash_table_create)
|
@cindex target vector (_bfd_link_hash_table_create)
|
The linker routines must create a hash table, which must be
|
The linker routines must create a hash table, which must be
|
derived from @code{struct bfd_link_hash_table} described in
|
derived from @code{struct bfd_link_hash_table} described in
|
@code{bfdlink.c}. @xref{Hash Tables}, for information on how to
|
@code{bfdlink.c}. @xref{Hash Tables}, for information on how to
|
create a derived hash table. This entry point is called using
|
create a derived hash table. This entry point is called using
|
the target vector of the linker output file.
|
the target vector of the linker output file.
|
|
|
The @code{_bfd_link_hash_table_create} entry point must allocate
|
The @code{_bfd_link_hash_table_create} entry point must allocate
|
and initialize an instance of the desired hash table. If the
|
and initialize an instance of the desired hash table. If the
|
back end does not require any additional information to be
|
back end does not require any additional information to be
|
stored with the entries in the hash table, the entry point may
|
stored with the entries in the hash table, the entry point may
|
simply create a @code{struct bfd_link_hash_table}. Most likely,
|
simply create a @code{struct bfd_link_hash_table}. Most likely,
|
however, some additional information will be needed.
|
however, some additional information will be needed.
|
|
|
For example, with each entry in the hash table the a.out
|
For example, with each entry in the hash table the a.out
|
linker keeps the index the symbol has in the final output file
|
linker keeps the index the symbol has in the final output file
|
(this index number is used so that when doing a relocatable
|
(this index number is used so that when doing a relocatable
|
link the symbol index used in the output file can be quickly
|
link the symbol index used in the output file can be quickly
|
filled in when copying over a reloc). The a.out linker code
|
filled in when copying over a reloc). The a.out linker code
|
defines the required structures and functions for a hash table
|
defines the required structures and functions for a hash table
|
derived from @code{struct bfd_link_hash_table}. The a.out linker
|
derived from @code{struct bfd_link_hash_table}. The a.out linker
|
hash table is created by the function
|
hash table is created by the function
|
@code{NAME(aout,link_hash_table_create)}; it simply allocates
|
@code{NAME(aout,link_hash_table_create)}; it simply allocates
|
space for the hash table, initializes it, and returns a
|
space for the hash table, initializes it, and returns a
|
pointer to it.
|
pointer to it.
|
|
|
When writing the linker routines for a new back end, you will
|
When writing the linker routines for a new back end, you will
|
generally not know exactly which fields will be required until
|
generally not know exactly which fields will be required until
|
you have finished. You should simply create a new hash table
|
you have finished. You should simply create a new hash table
|
which defines no additional fields, and then simply add fields
|
which defines no additional fields, and then simply add fields
|
as they become necessary.
|
as they become necessary.
|
|
|
@node Adding Symbols to the Hash Table, Performing the Final Link, Creating a Linker Hash Table, Linker Functions
|
@node Adding Symbols to the Hash Table, Performing the Final Link, Creating a Linker Hash Table, Linker Functions
|
@subsection Adding symbols to the hash table
|
@subsection Adding symbols to the hash table
|
@cindex _bfd_link_add_symbols in target vector
|
@cindex _bfd_link_add_symbols in target vector
|
@cindex target vector (_bfd_link_add_symbols)
|
@cindex target vector (_bfd_link_add_symbols)
|
The linker proper will call the @code{_bfd_link_add_symbols}
|
The linker proper will call the @code{_bfd_link_add_symbols}
|
entry point for each object file or archive which is to be
|
entry point for each object file or archive which is to be
|
linked (typically these are the files named on the command
|
linked (typically these are the files named on the command
|
line, but some may also come from the linker script). The
|
line, but some may also come from the linker script). The
|
entry point is responsible for examining the file. For an
|
entry point is responsible for examining the file. For an
|
object file, BFD must add any relevant symbol information to
|
object file, BFD must add any relevant symbol information to
|
the hash table. For an archive, BFD must determine which
|
the hash table. For an archive, BFD must determine which
|
elements of the archive should be used and adding them to the
|
elements of the archive should be used and adding them to the
|
link.
|
link.
|
|
|
The a.out version of this entry point is
|
The a.out version of this entry point is
|
@code{NAME(aout,link_add_symbols)}.
|
@code{NAME(aout,link_add_symbols)}.
|
|
|
@menu
|
@menu
|
* Differing file formats::
|
* Differing file formats::
|
* Adding symbols from an object file::
|
* Adding symbols from an object file::
|
* Adding symbols from an archive::
|
* Adding symbols from an archive::
|
@end menu
|
@end menu
|
|
|
@node Differing file formats, Adding symbols from an object file, Adding Symbols to the Hash Table, Adding Symbols to the Hash Table
|
@node Differing file formats, Adding symbols from an object file, Adding Symbols to the Hash Table, Adding Symbols to the Hash Table
|
@subsubsection Differing file formats
|
@subsubsection Differing file formats
|
Normally all the files involved in a link will be of the same
|
Normally all the files involved in a link will be of the same
|
format, but it is also possible to link together different
|
format, but it is also possible to link together different
|
format object files, and the back end must support that. The
|
format object files, and the back end must support that. The
|
@code{_bfd_link_add_symbols} entry point is called via the target
|
@code{_bfd_link_add_symbols} entry point is called via the target
|
vector of the file to be added. This has an important
|
vector of the file to be added. This has an important
|
consequence: the function may not assume that the hash table
|
consequence: the function may not assume that the hash table
|
is the type created by the corresponding
|
is the type created by the corresponding
|
@code{_bfd_link_hash_table_create} vector. All the
|
@code{_bfd_link_hash_table_create} vector. All the
|
@code{_bfd_link_add_symbols} function can assume about the hash
|
@code{_bfd_link_add_symbols} function can assume about the hash
|
table is that it is derived from @code{struct
|
table is that it is derived from @code{struct
|
bfd_link_hash_table}.
|
bfd_link_hash_table}.
|
|
|
Sometimes the @code{_bfd_link_add_symbols} function must store
|
Sometimes the @code{_bfd_link_add_symbols} function must store
|
some information in the hash table entry to be used by the
|
some information in the hash table entry to be used by the
|
@code{_bfd_final_link} function. In such a case the output bfd
|
@code{_bfd_final_link} function. In such a case the output bfd
|
xvec must be checked to make sure that the hash table was
|
xvec must be checked to make sure that the hash table was
|
created by an object file of the same format.
|
created by an object file of the same format.
|
|
|
The @code{_bfd_final_link} routine must be prepared to handle a
|
The @code{_bfd_final_link} routine must be prepared to handle a
|
hash entry without any extra information added by the
|
hash entry without any extra information added by the
|
@code{_bfd_link_add_symbols} function. A hash entry without
|
@code{_bfd_link_add_symbols} function. A hash entry without
|
extra information will also occur when the linker script
|
extra information will also occur when the linker script
|
directs the linker to create a symbol. Note that, regardless
|
directs the linker to create a symbol. Note that, regardless
|
of how a hash table entry is added, all the fields will be
|
of how a hash table entry is added, all the fields will be
|
initialized to some sort of null value by the hash table entry
|
initialized to some sort of null value by the hash table entry
|
initialization function.
|
initialization function.
|
|
|
See @code{ecoff_link_add_externals} for an example of how to
|
See @code{ecoff_link_add_externals} for an example of how to
|
check the output bfd before saving information (in this
|
check the output bfd before saving information (in this
|
case, the ECOFF external symbol debugging information) in a
|
case, the ECOFF external symbol debugging information) in a
|
hash table entry.
|
hash table entry.
|
|
|
@node Adding symbols from an object file, Adding symbols from an archive, Differing file formats, Adding Symbols to the Hash Table
|
@node Adding symbols from an object file, Adding symbols from an archive, Differing file formats, Adding Symbols to the Hash Table
|
@subsubsection Adding symbols from an object file
|
@subsubsection Adding symbols from an object file
|
When the @code{_bfd_link_add_symbols} routine is passed an object
|
When the @code{_bfd_link_add_symbols} routine is passed an object
|
file, it must add all externally visible symbols in that
|
file, it must add all externally visible symbols in that
|
object file to the hash table. The actual work of adding the
|
object file to the hash table. The actual work of adding the
|
symbol to the hash table is normally handled by the function
|
symbol to the hash table is normally handled by the function
|
@code{_bfd_generic_link_add_one_symbol}. The
|
@code{_bfd_generic_link_add_one_symbol}. The
|
@code{_bfd_link_add_symbols} routine is responsible for reading
|
@code{_bfd_link_add_symbols} routine is responsible for reading
|
all the symbols from the object file and passing the correct
|
all the symbols from the object file and passing the correct
|
information to @code{_bfd_generic_link_add_one_symbol}.
|
information to @code{_bfd_generic_link_add_one_symbol}.
|
|
|
The @code{_bfd_link_add_symbols} routine should not use
|
The @code{_bfd_link_add_symbols} routine should not use
|
@code{bfd_canonicalize_symtab} to read the symbols. The point of
|
@code{bfd_canonicalize_symtab} to read the symbols. The point of
|
providing this routine is to avoid the overhead of converting
|
providing this routine is to avoid the overhead of converting
|
the symbols into generic @code{asymbol} structures.
|
the symbols into generic @code{asymbol} structures.
|
|
|
@findex _bfd_generic_link_add_one_symbol
|
@findex _bfd_generic_link_add_one_symbol
|
@code{_bfd_generic_link_add_one_symbol} handles the details of
|
@code{_bfd_generic_link_add_one_symbol} handles the details of
|
combining common symbols, warning about multiple definitions,
|
combining common symbols, warning about multiple definitions,
|
and so forth. It takes arguments which describe the symbol to
|
and so forth. It takes arguments which describe the symbol to
|
add, notably symbol flags, a section, and an offset. The
|
add, notably symbol flags, a section, and an offset. The
|
symbol flags include such things as @code{BSF_WEAK} or
|
symbol flags include such things as @code{BSF_WEAK} or
|
@code{BSF_INDIRECT}. The section is a section in the object
|
@code{BSF_INDIRECT}. The section is a section in the object
|
file, or something like @code{bfd_und_section_ptr} for an undefined
|
file, or something like @code{bfd_und_section_ptr} for an undefined
|
symbol or @code{bfd_com_section_ptr} for a common symbol.
|
symbol or @code{bfd_com_section_ptr} for a common symbol.
|
|
|
If the @code{_bfd_final_link} routine is also going to need to
|
If the @code{_bfd_final_link} routine is also going to need to
|
read the symbol information, the @code{_bfd_link_add_symbols}
|
read the symbol information, the @code{_bfd_link_add_symbols}
|
routine should save it somewhere attached to the object file
|
routine should save it somewhere attached to the object file
|
BFD. However, the information should only be saved if the
|
BFD. However, the information should only be saved if the
|
@code{keep_memory} field of the @code{info} argument is TRUE, so
|
@code{keep_memory} field of the @code{info} argument is TRUE, so
|
that the @code{-no-keep-memory} linker switch is effective.
|
that the @code{-no-keep-memory} linker switch is effective.
|
|
|
The a.out function which adds symbols from an object file is
|
The a.out function which adds symbols from an object file is
|
@code{aout_link_add_object_symbols}, and most of the interesting
|
@code{aout_link_add_object_symbols}, and most of the interesting
|
work is in @code{aout_link_add_symbols}. The latter saves
|
work is in @code{aout_link_add_symbols}. The latter saves
|
pointers to the hash tables entries created by
|
pointers to the hash tables entries created by
|
@code{_bfd_generic_link_add_one_symbol} indexed by symbol number,
|
@code{_bfd_generic_link_add_one_symbol} indexed by symbol number,
|
so that the @code{_bfd_final_link} routine does not have to call
|
so that the @code{_bfd_final_link} routine does not have to call
|
the hash table lookup routine to locate the entry.
|
the hash table lookup routine to locate the entry.
|
|
|
@node Adding symbols from an archive, , Adding symbols from an object file, Adding Symbols to the Hash Table
|
@node Adding symbols from an archive, , Adding symbols from an object file, Adding Symbols to the Hash Table
|
@subsubsection Adding symbols from an archive
|
@subsubsection Adding symbols from an archive
|
When the @code{_bfd_link_add_symbols} routine is passed an
|
When the @code{_bfd_link_add_symbols} routine is passed an
|
archive, it must look through the symbols defined by the
|
archive, it must look through the symbols defined by the
|
archive and decide which elements of the archive should be
|
archive and decide which elements of the archive should be
|
included in the link. For each such element it must call the
|
included in the link. For each such element it must call the
|
@code{add_archive_element} linker callback, and it must add the
|
@code{add_archive_element} linker callback, and it must add the
|
symbols from the object file to the linker hash table.
|
symbols from the object file to the linker hash table.
|
|
|
@findex _bfd_generic_link_add_archive_symbols
|
@findex _bfd_generic_link_add_archive_symbols
|
In most cases the work of looking through the symbols in the
|
In most cases the work of looking through the symbols in the
|
archive should be done by the
|
archive should be done by the
|
@code{_bfd_generic_link_add_archive_symbols} function. This
|
@code{_bfd_generic_link_add_archive_symbols} function. This
|
function builds a hash table from the archive symbol table and
|
function builds a hash table from the archive symbol table and
|
looks through the list of undefined symbols to see which
|
looks through the list of undefined symbols to see which
|
elements should be included.
|
elements should be included.
|
@code{_bfd_generic_link_add_archive_symbols} is passed a function
|
@code{_bfd_generic_link_add_archive_symbols} is passed a function
|
to call to make the final decision about adding an archive
|
to call to make the final decision about adding an archive
|
element to the link and to do the actual work of adding the
|
element to the link and to do the actual work of adding the
|
symbols to the linker hash table.
|
symbols to the linker hash table.
|
|
|
The function passed to
|
The function passed to
|
@code{_bfd_generic_link_add_archive_symbols} must read the
|
@code{_bfd_generic_link_add_archive_symbols} must read the
|
symbols of the archive element and decide whether the archive
|
symbols of the archive element and decide whether the archive
|
element should be included in the link. If the element is to
|
element should be included in the link. If the element is to
|
be included, the @code{add_archive_element} linker callback
|
be included, the @code{add_archive_element} linker callback
|
routine must be called with the element as an argument, and
|
routine must be called with the element as an argument, and
|
the elements symbols must be added to the linker hash table
|
the elements symbols must be added to the linker hash table
|
just as though the element had itself been passed to the
|
just as though the element had itself been passed to the
|
@code{_bfd_link_add_symbols} function.
|
@code{_bfd_link_add_symbols} function.
|
|
|
When the a.out @code{_bfd_link_add_symbols} function receives an
|
When the a.out @code{_bfd_link_add_symbols} function receives an
|
archive, it calls @code{_bfd_generic_link_add_archive_symbols}
|
archive, it calls @code{_bfd_generic_link_add_archive_symbols}
|
passing @code{aout_link_check_archive_element} as the function
|
passing @code{aout_link_check_archive_element} as the function
|
argument. @code{aout_link_check_archive_element} calls
|
argument. @code{aout_link_check_archive_element} calls
|
@code{aout_link_check_ar_symbols}. If the latter decides to add
|
@code{aout_link_check_ar_symbols}. If the latter decides to add
|
the element (an element is only added if it provides a real,
|
the element (an element is only added if it provides a real,
|
non-common, definition for a previously undefined or common
|
non-common, definition for a previously undefined or common
|
symbol) it calls the @code{add_archive_element} callback and then
|
symbol) it calls the @code{add_archive_element} callback and then
|
@code{aout_link_check_archive_element} calls
|
@code{aout_link_check_archive_element} calls
|
@code{aout_link_add_symbols} to actually add the symbols to the
|
@code{aout_link_add_symbols} to actually add the symbols to the
|
linker hash table.
|
linker hash table.
|
|
|
The ECOFF back end is unusual in that it does not normally
|
The ECOFF back end is unusual in that it does not normally
|
call @code{_bfd_generic_link_add_archive_symbols}, because ECOFF
|
call @code{_bfd_generic_link_add_archive_symbols}, because ECOFF
|
archives already contain a hash table of symbols. The ECOFF
|
archives already contain a hash table of symbols. The ECOFF
|
back end searches the archive itself to avoid the overhead of
|
back end searches the archive itself to avoid the overhead of
|
creating a new hash table.
|
creating a new hash table.
|
|
|
@node Performing the Final Link, , Adding Symbols to the Hash Table, Linker Functions
|
@node Performing the Final Link, , Adding Symbols to the Hash Table, Linker Functions
|
@subsection Performing the final link
|
@subsection Performing the final link
|
@cindex _bfd_link_final_link in target vector
|
@cindex _bfd_link_final_link in target vector
|
@cindex target vector (_bfd_final_link)
|
@cindex target vector (_bfd_final_link)
|
When all the input files have been processed, the linker calls
|
When all the input files have been processed, the linker calls
|
the @code{_bfd_final_link} entry point of the output BFD. This
|
the @code{_bfd_final_link} entry point of the output BFD. This
|
routine is responsible for producing the final output file,
|
routine is responsible for producing the final output file,
|
which has several aspects. It must relocate the contents of
|
which has several aspects. It must relocate the contents of
|
the input sections and copy the data into the output sections.
|
the input sections and copy the data into the output sections.
|
It must build an output symbol table including any local
|
It must build an output symbol table including any local
|
symbols from the input files and the global symbols from the
|
symbols from the input files and the global symbols from the
|
hash table. When producing relocatable output, it must
|
hash table. When producing relocatable output, it must
|
modify the input relocs and write them into the output file.
|
modify the input relocs and write them into the output file.
|
There may also be object format dependent work to be done.
|
There may also be object format dependent work to be done.
|
|
|
The linker will also call the @code{write_object_contents} entry
|
The linker will also call the @code{write_object_contents} entry
|
point when the BFD is closed. The two entry points must work
|
point when the BFD is closed. The two entry points must work
|
together in order to produce the correct output file.
|
together in order to produce the correct output file.
|
|
|
The details of how this works are inevitably dependent upon
|
The details of how this works are inevitably dependent upon
|
the specific object file format. The a.out
|
the specific object file format. The a.out
|
@code{_bfd_final_link} routine is @code{NAME(aout,final_link)}.
|
@code{_bfd_final_link} routine is @code{NAME(aout,final_link)}.
|
|
|
@menu
|
@menu
|
* Information provided by the linker::
|
* Information provided by the linker::
|
* Relocating the section contents::
|
* Relocating the section contents::
|
* Writing the symbol table::
|
* Writing the symbol table::
|
@end menu
|
@end menu
|
|
|
@node Information provided by the linker, Relocating the section contents, Performing the Final Link, Performing the Final Link
|
@node Information provided by the linker, Relocating the section contents, Performing the Final Link, Performing the Final Link
|
@subsubsection Information provided by the linker
|
@subsubsection Information provided by the linker
|
Before the linker calls the @code{_bfd_final_link} entry point,
|
Before the linker calls the @code{_bfd_final_link} entry point,
|
it sets up some data structures for the function to use.
|
it sets up some data structures for the function to use.
|
|
|
The @code{input_bfds} field of the @code{bfd_link_info} structure
|
The @code{input_bfds} field of the @code{bfd_link_info} structure
|
will point to a list of all the input files included in the
|
will point to a list of all the input files included in the
|
link. These files are linked through the @code{link_next} field
|
link. These files are linked through the @code{link_next} field
|
of the @code{bfd} structure.
|
of the @code{bfd} structure.
|
|
|
Each section in the output file will have a list of
|
Each section in the output file will have a list of
|
@code{link_order} structures attached to the @code{map_head.link_order}
|
@code{link_order} structures attached to the @code{map_head.link_order}
|
field (the @code{link_order} structure is defined in
|
field (the @code{link_order} structure is defined in
|
@code{bfdlink.h}). These structures describe how to create the
|
@code{bfdlink.h}). These structures describe how to create the
|
contents of the output section in terms of the contents of
|
contents of the output section in terms of the contents of
|
various input sections, fill constants, and, eventually, other
|
various input sections, fill constants, and, eventually, other
|
types of information. They also describe relocs that must be
|
types of information. They also describe relocs that must be
|
created by the BFD backend, but do not correspond to any input
|
created by the BFD backend, but do not correspond to any input
|
file; this is used to support -Ur, which builds constructors
|
file; this is used to support -Ur, which builds constructors
|
while generating a relocatable object file.
|
while generating a relocatable object file.
|
|
|
@node Relocating the section contents, Writing the symbol table, Information provided by the linker, Performing the Final Link
|
@node Relocating the section contents, Writing the symbol table, Information provided by the linker, Performing the Final Link
|
@subsubsection Relocating the section contents
|
@subsubsection Relocating the section contents
|
The @code{_bfd_final_link} function should look through the
|
The @code{_bfd_final_link} function should look through the
|
@code{link_order} structures attached to each section of the
|
@code{link_order} structures attached to each section of the
|
output file. Each @code{link_order} structure should either be
|
output file. Each @code{link_order} structure should either be
|
handled specially, or it should be passed to the function
|
handled specially, or it should be passed to the function
|
@code{_bfd_default_link_order} which will do the right thing
|
@code{_bfd_default_link_order} which will do the right thing
|
(@code{_bfd_default_link_order} is defined in @code{linker.c}).
|
(@code{_bfd_default_link_order} is defined in @code{linker.c}).
|
|
|
For efficiency, a @code{link_order} of type
|
For efficiency, a @code{link_order} of type
|
@code{bfd_indirect_link_order} whose associated section belongs
|
@code{bfd_indirect_link_order} whose associated section belongs
|
to a BFD of the same format as the output BFD must be handled
|
to a BFD of the same format as the output BFD must be handled
|
specially. This type of @code{link_order} describes part of an
|
specially. This type of @code{link_order} describes part of an
|
output section in terms of a section belonging to one of the
|
output section in terms of a section belonging to one of the
|
input files. The @code{_bfd_final_link} function should read the
|
input files. The @code{_bfd_final_link} function should read the
|
contents of the section and any associated relocs, apply the
|
contents of the section and any associated relocs, apply the
|
relocs to the section contents, and write out the modified
|
relocs to the section contents, and write out the modified
|
section contents. If performing a relocatable link, the
|
section contents. If performing a relocatable link, the
|
relocs themselves must also be modified and written out.
|
relocs themselves must also be modified and written out.
|
|
|
@findex _bfd_relocate_contents
|
@findex _bfd_relocate_contents
|
@findex _bfd_final_link_relocate
|
@findex _bfd_final_link_relocate
|
The functions @code{_bfd_relocate_contents} and
|
The functions @code{_bfd_relocate_contents} and
|
@code{_bfd_final_link_relocate} provide some general support for
|
@code{_bfd_final_link_relocate} provide some general support for
|
performing the actual relocations, notably overflow checking.
|
performing the actual relocations, notably overflow checking.
|
Their arguments include information about the symbol the
|
Their arguments include information about the symbol the
|
relocation is against and a @code{reloc_howto_type} argument
|
relocation is against and a @code{reloc_howto_type} argument
|
which describes the relocation to perform. These functions
|
which describes the relocation to perform. These functions
|
are defined in @code{reloc.c}.
|
are defined in @code{reloc.c}.
|
|
|
The a.out function which handles reading, relocating, and
|
The a.out function which handles reading, relocating, and
|
writing section contents is @code{aout_link_input_section}. The
|
writing section contents is @code{aout_link_input_section}. The
|
actual relocation is done in @code{aout_link_input_section_std}
|
actual relocation is done in @code{aout_link_input_section_std}
|
and @code{aout_link_input_section_ext}.
|
and @code{aout_link_input_section_ext}.
|
|
|
@node Writing the symbol table, , Relocating the section contents, Performing the Final Link
|
@node Writing the symbol table, , Relocating the section contents, Performing the Final Link
|
@subsubsection Writing the symbol table
|
@subsubsection Writing the symbol table
|
The @code{_bfd_final_link} function must gather all the symbols
|
The @code{_bfd_final_link} function must gather all the symbols
|
in the input files and write them out. It must also write out
|
in the input files and write them out. It must also write out
|
all the symbols in the global hash table. This must be
|
all the symbols in the global hash table. This must be
|
controlled by the @code{strip} and @code{discard} fields of the
|
controlled by the @code{strip} and @code{discard} fields of the
|
@code{bfd_link_info} structure.
|
@code{bfd_link_info} structure.
|
|
|
The local symbols of the input files will not have been
|
The local symbols of the input files will not have been
|
entered into the linker hash table. The @code{_bfd_final_link}
|
entered into the linker hash table. The @code{_bfd_final_link}
|
routine must consider each input file and include the symbols
|
routine must consider each input file and include the symbols
|
in the output file. It may be convenient to do this when
|
in the output file. It may be convenient to do this when
|
looking through the @code{link_order} structures, or it may be
|
looking through the @code{link_order} structures, or it may be
|
done by stepping through the @code{input_bfds} list.
|
done by stepping through the @code{input_bfds} list.
|
|
|
The @code{_bfd_final_link} routine must also traverse the global
|
The @code{_bfd_final_link} routine must also traverse the global
|
hash table to gather all the externally visible symbols. It
|
hash table to gather all the externally visible symbols. It
|
is possible that most of the externally visible symbols may be
|
is possible that most of the externally visible symbols may be
|
written out when considering the symbols of each input file,
|
written out when considering the symbols of each input file,
|
but it is still necessary to traverse the hash table since the
|
but it is still necessary to traverse the hash table since the
|
linker script may have defined some symbols that are not in
|
linker script may have defined some symbols that are not in
|
any of the input files.
|
any of the input files.
|
|
|
The @code{strip} field of the @code{bfd_link_info} structure
|
The @code{strip} field of the @code{bfd_link_info} structure
|
controls which symbols are written out. The possible values
|
controls which symbols are written out. The possible values
|
are listed in @code{bfdlink.h}. If the value is @code{strip_some},
|
are listed in @code{bfdlink.h}. If the value is @code{strip_some},
|
then the @code{keep_hash} field of the @code{bfd_link_info}
|
then the @code{keep_hash} field of the @code{bfd_link_info}
|
structure is a hash table of symbols to keep; each symbol
|
structure is a hash table of symbols to keep; each symbol
|
should be looked up in this hash table, and only symbols which
|
should be looked up in this hash table, and only symbols which
|
are present should be included in the output file.
|
are present should be included in the output file.
|
|
|
If the @code{strip} field of the @code{bfd_link_info} structure
|
If the @code{strip} field of the @code{bfd_link_info} structure
|
permits local symbols to be written out, the @code{discard} field
|
permits local symbols to be written out, the @code{discard} field
|
is used to further controls which local symbols are included
|
is used to further controls which local symbols are included
|
in the output file. If the value is @code{discard_l}, then all
|
in the output file. If the value is @code{discard_l}, then all
|
local symbols which begin with a certain prefix are discarded;
|
local symbols which begin with a certain prefix are discarded;
|
this is controlled by the @code{bfd_is_local_label_name} entry point.
|
this is controlled by the @code{bfd_is_local_label_name} entry point.
|
|
|
The a.out backend handles symbols by calling
|
The a.out backend handles symbols by calling
|
@code{aout_link_write_symbols} on each input BFD and then
|
@code{aout_link_write_symbols} on each input BFD and then
|
traversing the global hash table with the function
|
traversing the global hash table with the function
|
@code{aout_link_write_other_symbol}. It builds a string table
|
@code{aout_link_write_other_symbol}. It builds a string table
|
while writing out the symbols, which is written to the output
|
while writing out the symbols, which is written to the output
|
file at the end of @code{NAME(aout,final_link)}.
|
file at the end of @code{NAME(aout,final_link)}.
|
|
|
@findex bfd_link_split_section
|
@findex bfd_link_split_section
|
@subsubsection @code{bfd_link_split_section}
|
@subsubsection @code{bfd_link_split_section}
|
@strong{Synopsis}
|
@strong{Synopsis}
|
@example
|
@example
|
bfd_boolean bfd_link_split_section (bfd *abfd, asection *sec);
|
bfd_boolean bfd_link_split_section (bfd *abfd, asection *sec);
|
@end example
|
@end example
|
@strong{Description}@*
|
@strong{Description}@*
|
Return nonzero if @var{sec} should be split during a
|
Return nonzero if @var{sec} should be split during a
|
reloceatable or final link.
|
reloceatable or final link.
|
@example
|
@example
|
#define bfd_link_split_section(abfd, sec) \
|
#define bfd_link_split_section(abfd, sec) \
|
BFD_SEND (abfd, _bfd_link_split_section, (abfd, sec))
|
BFD_SEND (abfd, _bfd_link_split_section, (abfd, sec))
|
|
|
@end example
|
@end example
|
|
|
@findex bfd_section_already_linked
|
@findex bfd_section_already_linked
|
@subsubsection @code{bfd_section_already_linked}
|
@subsubsection @code{bfd_section_already_linked}
|
@strong{Synopsis}
|
@strong{Synopsis}
|
@example
|
@example
|
void bfd_section_already_linked (bfd *abfd, asection *sec,
|
void bfd_section_already_linked (bfd *abfd, asection *sec,
|
struct bfd_link_info *info);
|
struct bfd_link_info *info);
|
@end example
|
@end example
|
@strong{Description}@*
|
@strong{Description}@*
|
Check if @var{sec} has been already linked during a reloceatable
|
Check if @var{sec} has been already linked during a reloceatable
|
or final link.
|
or final link.
|
@example
|
@example
|
#define bfd_section_already_linked(abfd, sec, info) \
|
#define bfd_section_already_linked(abfd, sec, info) \
|
BFD_SEND (abfd, _section_already_linked, (abfd, sec, info))
|
BFD_SEND (abfd, _section_already_linked, (abfd, sec, info))
|
|
|
@end example
|
@end example
|
|
|
@findex bfd_generic_define_common_symbol
|
@findex bfd_generic_define_common_symbol
|
@subsubsection @code{bfd_generic_define_common_symbol}
|
@subsubsection @code{bfd_generic_define_common_symbol}
|
@strong{Synopsis}
|
@strong{Synopsis}
|
@example
|
@example
|
bfd_boolean bfd_generic_define_common_symbol
|
bfd_boolean bfd_generic_define_common_symbol
|
(bfd *output_bfd, struct bfd_link_info *info,
|
(bfd *output_bfd, struct bfd_link_info *info,
|
struct bfd_link_hash_entry *h);
|
struct bfd_link_hash_entry *h);
|
@end example
|
@end example
|
@strong{Description}@*
|
@strong{Description}@*
|
Convert common symbol @var{h} into a defined symbol.
|
Convert common symbol @var{h} into a defined symbol.
|
Return TRUE on success and FALSE on failure.
|
Return TRUE on success and FALSE on failure.
|
@example
|
@example
|
#define bfd_define_common_symbol(output_bfd, info, h) \
|
#define bfd_define_common_symbol(output_bfd, info, h) \
|
BFD_SEND (output_bfd, _bfd_define_common_symbol, (output_bfd, info, h))
|
BFD_SEND (output_bfd, _bfd_define_common_symbol, (output_bfd, info, h))
|
|
|
@end example
|
@end example
|
|
|
@findex bfd_find_version_for_sym
|
@findex bfd_find_version_for_sym
|
@subsubsection @code{bfd_find_version_for_sym }
|
@subsubsection @code{bfd_find_version_for_sym }
|
@strong{Synopsis}
|
@strong{Synopsis}
|
@example
|
@example
|
struct bfd_elf_version_tree * bfd_find_version_for_sym
|
struct bfd_elf_version_tree * bfd_find_version_for_sym
|
(struct bfd_elf_version_tree *verdefs,
|
(struct bfd_elf_version_tree *verdefs,
|
const char *sym_name, bfd_boolean *hide);
|
const char *sym_name, bfd_boolean *hide);
|
@end example
|
@end example
|
@strong{Description}@*
|
@strong{Description}@*
|
Search an elf version script tree for symbol versioning
|
Search an elf version script tree for symbol versioning
|
info and export / don't-export status for a given symbol.
|
info and export / don't-export status for a given symbol.
|
Return non-NULL on success and NULL on failure; also sets
|
Return non-NULL on success and NULL on failure; also sets
|
the output @samp{hide} boolean parameter.
|
the output @samp{hide} boolean parameter.
|
|
|
|
|
