diff options
Diffstat (limited to 'ld')
| -rw-r--r-- | ld/ChangeLog | 2 | ||||
| -rw-r--r-- | ld/ld.texinfo | 135 |
2 files changed, 135 insertions, 2 deletions
diff --git a/ld/ChangeLog b/ld/ChangeLog index be8f7d2..827504e 100644 --- a/ld/ChangeLog +++ b/ld/ChangeLog @@ -4,6 +4,8 @@ Tue Oct 1 16:17:33 1996 Joel Sherrill <joel@oarcorp.com> Tue Oct 1 15:50:34 1996 Ian Lance Taylor <ian@cygnus.com> + * ld.texinfo (Options): Give more detail on -l option. + * scripttempl/elfmips.sc: Handle CREATE_SHLIB the same way that elf.sc does, so that glibc works better. diff --git a/ld/ld.texinfo b/ld/ld.texinfo index d279d31..16ebb69 100644 --- a/ld/ld.texinfo +++ b/ld/ld.texinfo @@ -392,6 +392,24 @@ path-list for occurrences of @code{lib@var{archive}.a} for every @var{archive} specified. File extensions other than @code{.a} may be used on certain systems. +The linker will search an archive only once, at the location where it is +specified on the command line. If the archive defines a symbol which +was undefined in some object which appeared before the archive on the +command line, the linker will include the appropriate file(s) from the +archive. However, an undefined symbol in an object appearing later on +the command line will not cause the linker to search the archive again. + +See the @code{-(} option for a way to force the linker to search +archives multiple times. + +You may list the same archive multiple times on the command line. + +@ifset GENERIC +This type of archive searching is standard for Unix linkers. However, +if you are using @code{ld} on AIX, note that it is different from the +behaviour of the AIX linker. +@end ifset + @cindex search directory, from cmd line @kindex -L@var{dir} @kindex --library-path=@var{dir} @@ -1682,6 +1700,14 @@ Return the size in bytes of the output file's headers. You can use this number as the start address of the first section, if you choose, to facilitate paging. +@kindex MAX +@item MAX(@var{exp1}, @var{exp2}) +Returns the maximum of @var{exp1} and @var{exp2}. + +@kindex MIN +@item MIN(@var{exp1}, @var{exp2}) +Returns the minimum of @var{exp1} and @var{exp2}. + @end table @node Semicolons @@ -1822,6 +1848,7 @@ output file will match the order in the first input file. * Section Placement:: Section Placement * Section Data Expressions:: Section Data Expressions * Section Options:: Optional Section Attributes +* Overlays:: Overlays @end menu @node Section Definition @@ -2351,11 +2378,115 @@ of a section definition. @end table +@node Overlays +@subsection Overlays +@kindex OVERLAY +@cindex overlays + +The @code{OVERLAY} command provides an easy way to describe sections +which are to be loaded as part of a single memory image but are to be +run at the same memory address. At run time, some sort of overlay +manager will copy the overlaid sections in and out of the runtime memory +address as required, perhaps by simply manipulating addressing bits. +This approach can be useful, for example, when a certain region of +memory is faster than another. + +The @code{OVERLAY} command is used within a @code{SECTIONS} command. It +appears as follows: +@smallexample +@group + OVERLAY @var{start} : [ NOCROSSREFS ] AT ( @var{ldaddr} ) + @{ + @var{secname1} @{ @var{contents} @} :@var{phdr} =@var{fill} + @var{secname2} @{ @var{contents} @} :@var{phdr} =@var{fill} + @dots{} + @} >@var{region} :@var{phdr} =@var{fill} +@end group +@end smallexample + +Everything is optional except @code{OVERLAY} (a keyword), and each +section must have a name (@var{secname1} and @var{secname2} above). The +section definitions within the @code{OVERLAY} construct are identical to +those within the general @code{SECTIONS} contruct (@pxref{SECTIONS}), +except that no addresses and no memory regions may be defined for +sections within an @code{OVERLAY}. + +The sections are all defined with the same starting address. The load +addresses of the sections are arranged such that they are consecutive in +memory starting at the load address used for the @code{OVERLAY} as a +whole (as with normal section definitions, the load address is optional, +and defaults to the start address; the start address is also optional, +and defaults to @code{.}). + +If the @code{NOCROSSREFS} keyword is used, and there any references +among the sections, the linker will report an error. Since the sections +all run at the same address, it normally does not make sense for one +section to refer directly to another. @xref{Option Commands, +NOCROSSREFS}. + +For each section within the @code{OVERLAY}, the linker automatically +defines two symbols. The symbol @code{__load_start_@var{secname}} is +defined as the starting load address of the section. The symbol +@code{__load_stop_@var{secname}} is defined as the final load address of +the section. Any characters within @var{secname} which are not legal +within C identifiers are removed. C (or assembler) code may use these +symbols to move the overlaid sections around as necessary. + +At the end of the overlay, the value of @code{.} is set to the start +address of the overlay plus the size of the largest section. + +Here is an example. Remember that this would appear inside a +@code{SECTIONS} construct. + +@smallexample +@group + OVERLAY 0x1000 : AT (0x4000) + @{ + .text0 @{ o1/*.o(.text) @} + .text1 @{ o2/*.o(.text) @} + @} +@end group +@end smallexample + +This will define both @code{.text0} and @code{.text1} to start at +address 0x1000. @code{.text0} will be loaded at address 0x4000, and +@code{.text1} will be loaded immediately after @code{.text0}. The +following symbols will be defined: @code{__load_start_text0}, +@code{__load_stop_text0}, @code{__load_start_text1}, +@code{__load_stop_text1}. + +C code to copy overlay @code{.text1} into the overlay area might look +like the following. + +@smallexample +@group + extern char __load_start_text1, __load_stop_text1; + memcpy ((char *) 0x1000, &__load_start_text1, + &__load_stop_text1 - &__load_start_text1); +@end group +@end smallexample + +Note that the @code{OVERLAY} command is just syntactic sugar, since +everything it does can be done using the more basic commands. The above +example could have been written identically as follows. + +@smallexample +@group + .text0 0x1000 : AT (0x4000) @{ o1/*.o(.text) @} + __load_start_text0 = LOADADDR (.text0); + __load_stop_text0 = LOADADDR (.text0) + SIZEOF (.text0); + .text1 0x1000 : AT (0x4000 + SIZEOF (.text0)) @{ o2/*.o(.text) @} + __load_start_text1 = LOADADDR (.text1); + __load_stop_text1 = LOADADDR (.text1) + SIZEOF (.text1); + . = 0x1000 + MAX (SIZEOF (.text0), SIZEOF (.text1)); +@end group +@end smallexample + @node PHDRS @section ELF Program Headers @kindex PHDRS -@kindex program headers -@kindex ELF program headers +@cindex program headers +@cindex ELF program headers The ELF object file format uses @dfn{program headers}, which are read by the system loader and describe how the program should be loaded into |