* ld.texinfo (Options): Give more detail on -l option.
PR 10418.
This commit is contained in:
Ian Lance Taylor
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b61364cc71
@ -4,6 +4,8 @@ Tue Oct 1 16:17:33 1996 Joel Sherrill <joel@oarcorp.com>
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Tue Oct 1 15:50:34 1996 Ian Lance Taylor <ian@cygnus.com>
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* ld.texinfo (Options): Give more detail on -l option.
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* scripttempl/elfmips.sc: Handle CREATE_SHLIB the same way that
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elf.sc does, so that glibc works better.
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135
ld/ld.texinfo
135
ld/ld.texinfo
@ -392,6 +392,24 @@ path-list for occurrences of @code{lib@var{archive}.a} for every
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@var{archive} specified. File extensions other than @code{.a} may be
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used on certain systems.
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The linker will search an archive only once, at the location where it is
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specified on the command line. If the archive defines a symbol which
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was undefined in some object which appeared before the archive on the
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command line, the linker will include the appropriate file(s) from the
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archive. However, an undefined symbol in an object appearing later on
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the command line will not cause the linker to search the archive again.
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See the @code{-(} option for a way to force the linker to search
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archives multiple times.
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You may list the same archive multiple times on the command line.
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@ifset GENERIC
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This type of archive searching is standard for Unix linkers. However,
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if you are using @code{ld} on AIX, note that it is different from the
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behaviour of the AIX linker.
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@end ifset
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@cindex search directory, from cmd line
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@kindex -L@var{dir}
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@kindex --library-path=@var{dir}
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@ -1682,6 +1700,14 @@ Return the size in bytes of the output file's headers. You can use this number
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as the start address of the first section, if you choose, to facilitate
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paging.
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@kindex MAX
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@item MAX(@var{exp1}, @var{exp2})
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Returns the maximum of @var{exp1} and @var{exp2}.
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@kindex MIN
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@item MIN(@var{exp1}, @var{exp2})
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Returns the minimum of @var{exp1} and @var{exp2}.
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@end table
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@node Semicolons
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@ -1822,6 +1848,7 @@ output file will match the order in the first input file.
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* Section Placement:: Section Placement
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* Section Data Expressions:: Section Data Expressions
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* Section Options:: Optional Section Attributes
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* Overlays:: Overlays
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@end menu
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@node Section Definition
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@ -2351,11 +2378,115 @@ of a section definition.
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@end table
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@node Overlays
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@subsection Overlays
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@kindex OVERLAY
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@cindex overlays
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The @code{OVERLAY} command provides an easy way to describe sections
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which are to be loaded as part of a single memory image but are to be
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run at the same memory address. At run time, some sort of overlay
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manager will copy the overlaid sections in and out of the runtime memory
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address as required, perhaps by simply manipulating addressing bits.
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This approach can be useful, for example, when a certain region of
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memory is faster than another.
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The @code{OVERLAY} command is used within a @code{SECTIONS} command. It
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appears as follows:
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@smallexample
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@group
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OVERLAY @var{start} : [ NOCROSSREFS ] AT ( @var{ldaddr} )
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@{
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@var{secname1} @{ @var{contents} @} :@var{phdr} =@var{fill}
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@var{secname2} @{ @var{contents} @} :@var{phdr} =@var{fill}
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@dots{}
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@} >@var{region} :@var{phdr} =@var{fill}
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@end group
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@end smallexample
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Everything is optional except @code{OVERLAY} (a keyword), and each
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section must have a name (@var{secname1} and @var{secname2} above). The
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section definitions within the @code{OVERLAY} construct are identical to
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those within the general @code{SECTIONS} contruct (@pxref{SECTIONS}),
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except that no addresses and no memory regions may be defined for
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sections within an @code{OVERLAY}.
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The sections are all defined with the same starting address. The load
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addresses of the sections are arranged such that they are consecutive in
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memory starting at the load address used for the @code{OVERLAY} as a
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whole (as with normal section definitions, the load address is optional,
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and defaults to the start address; the start address is also optional,
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and defaults to @code{.}).
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If the @code{NOCROSSREFS} keyword is used, and there any references
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among the sections, the linker will report an error. Since the sections
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all run at the same address, it normally does not make sense for one
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section to refer directly to another. @xref{Option Commands,
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NOCROSSREFS}.
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For each section within the @code{OVERLAY}, the linker automatically
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defines two symbols. The symbol @code{__load_start_@var{secname}} is
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defined as the starting load address of the section. The symbol
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@code{__load_stop_@var{secname}} is defined as the final load address of
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the section. Any characters within @var{secname} which are not legal
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within C identifiers are removed. C (or assembler) code may use these
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symbols to move the overlaid sections around as necessary.
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At the end of the overlay, the value of @code{.} is set to the start
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address of the overlay plus the size of the largest section.
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Here is an example. Remember that this would appear inside a
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@code{SECTIONS} construct.
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@smallexample
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@group
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OVERLAY 0x1000 : AT (0x4000)
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@{
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.text0 @{ o1/*.o(.text) @}
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.text1 @{ o2/*.o(.text) @}
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@}
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@end group
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@end smallexample
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This will define both @code{.text0} and @code{.text1} to start at
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address 0x1000. @code{.text0} will be loaded at address 0x4000, and
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@code{.text1} will be loaded immediately after @code{.text0}. The
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following symbols will be defined: @code{__load_start_text0},
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@code{__load_stop_text0}, @code{__load_start_text1},
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@code{__load_stop_text1}.
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C code to copy overlay @code{.text1} into the overlay area might look
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like the following.
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@smallexample
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@group
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extern char __load_start_text1, __load_stop_text1;
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memcpy ((char *) 0x1000, &__load_start_text1,
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&__load_stop_text1 - &__load_start_text1);
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@end group
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@end smallexample
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Note that the @code{OVERLAY} command is just syntactic sugar, since
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everything it does can be done using the more basic commands. The above
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example could have been written identically as follows.
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@smallexample
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@group
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.text0 0x1000 : AT (0x4000) @{ o1/*.o(.text) @}
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__load_start_text0 = LOADADDR (.text0);
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__load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0);
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.text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) @{ o2/*.o(.text) @}
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__load_start_text1 = LOADADDR (.text1);
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__load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1);
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. = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1));
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@end group
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@end smallexample
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@node PHDRS
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@section ELF Program Headers
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@kindex PHDRS
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@kindex program headers
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@kindex ELF program headers
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@cindex program headers
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@cindex ELF program headers
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The ELF object file format uses @dfn{program headers}, which are read by
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the system loader and describe how the program should be loaded into
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