@kindex -Bsymbolic-functions
@item -Bsymbolic-functions
When creating a shared library, bind references to global function
-symbols to the definition within the shared library, if any.
+symbols to the definition within the shared library, if any.
This option is only meaningful on ELF platforms which support shared
libraries.
The @option{--reduce-memory-overheads} switch may be also be used to
enable other tradeoffs in future versions of the linker.
+@kindex --build-id
+@kindex --build-id=@var{style}
+@item --build-id
+@itemx --build-id=@var{style}
+Request creation of @code{.note.gnu.build-id} ELF note section.
+The contents of the note are unique bits identifying this linked
+file. @var{style} can be @code{uuid} to use 128 random bits,
+@code{md5} to use a 128-bit @sc{MD5} hash on the normative parts
+of the output contents, or @code{0x@var{hexstring}} to use a
+chosen bit string specified as an even number of hexadecimal
+digits (@code{-} and @code{:} characters between digit pairs are
+ignored). If @var{style} is omitted, @code{md5} is used.
+
+The @code{md5} style produces an identifier that is always the
+same in an identical output file, but will be unique among all
+nonidentical output files. It is not intended to be compared as
+a checksum for the file's contents. A linked file may be
+changed later by other tools, but the build ID bit string
+identifying the original linked file does not change.
+
+Passing @code{none} for @var{style} disables the setting from any
+@code{--build-id} options earlier on the command line.
@end table
@c man end
This message occurs when some (sub)expression accesses an address
ultimately given by the sum of two constants (Win32 import tables only
-allow one). Instances where this may occur include accesses to member
-fields of struct variables imported from a DLL, as well as using a
-constant index into an array variable imported from a DLL. Any
+allow one). Instances where this may occur include accesses to member
+fields of struct variables imported from a DLL, as well as using a
+constant index into an array variable imported from a DLL. Any
multiword variable (arrays, structs, long long, etc) may trigger
this error condition. However, regardless of the exact data type
of the offending exported variable, ld will always detect it, issue
of adjusting references in your client code for runtime environment, so
this method works only when runtime environment supports this feature.
-A second solution is to force one of the 'constants' to be a variable --
-that is, unknown and un-optimizable at compile time. For arrays,
-there are two possibilities: a) make the indexee (the array's address)
+A second solution is to force one of the 'constants' to be a variable --
+that is, unknown and un-optimizable at compile time. For arrays,
+there are two possibilities: a) make the indexee (the array's address)
a variable, or b) make the 'constant' index a variable. Thus:
@example
extern type extern_array[];
-extern_array[1] -->
+extern_array[1] -->
@{ volatile type *t=extern_array; t[1] @}
@end example
@example
extern type extern_array[];
-extern_array[1] -->
+extern_array[1] -->
@{ volatile int t=1; extern_array[t] @}
@end example
-For structs (and most other multiword data types) the only option
+For structs (and most other multiword data types) the only option
is to make the struct itself (or the long long, or the ...) variable:
@example
extern struct s extern_struct;
-extern_struct.field -->
+extern_struct.field -->
@{ volatile struct s *t=&extern_struct; t->field @}
@end example
@end example
A third method of dealing with this difficulty is to abandon
-'auto-import' for the offending symbol and mark it with
+'auto-import' for the offending symbol and mark it with
@code{__declspec(dllimport)}. However, in practise that
requires using compile-time #defines to indicate whether you are
-building a DLL, building client code that will link to the DLL, or
-merely building/linking to a static library. In making the choice
-between the various methods of resolving the 'direct address with
+building a DLL, building client code that will link to the DLL, or
+merely building/linking to a static library. In making the choice
+between the various methods of resolving the 'direct address with
constant offset' problem, you should consider typical real-world usage:
Original:
@}
@end example
-A fourth way to avoid this problem is to re-code your
+A fourth way to avoid this problem is to re-code your
library to use a functional interface rather than a data interface
for the offending variables (e.g. set_foo() and get_foo() accessor
functions).
@kindex --disable-auto-import
@item --disable-auto-import
-Do not attempt to do sophisticated linking of @code{_symbol} to
+Do not attempt to do sophisticated linking of @code{_symbol} to
@code{__imp__symbol} for DATA imports from DLLs.
[This option is specific to the i386 PE targeted port of the linker]
If your code contains expressions described in --enable-auto-import section,
that is, DATA imports from DLL with non-zero offset, this switch will create
a vector of 'runtime pseudo relocations' which can be used by runtime
-environment to adjust references to such data in your client code.
+environment to adjust references to such data in your client code.
[This option is specific to the i386 PE targeted port of the linker]
@kindex --disable-runtime-pseudo-reloc
@smallexample
@group
extern char start_of_ROM, end_of_ROM, start_of_FLASH;
-
+
memcpy (& start_of_FLASH, & start_of_ROM, & end_of_ROM - & start_of_ROM);
@end group
@end smallexample
It will sort the input sections by alignment first, then by name if 2
sections have the same alignment.
@item
-@code{SORT_BY_NAME} (@code{SORT_BY_NAME} (wildcard section pattern)) is
+@code{SORT_BY_NAME} (@code{SORT_BY_NAME} (wildcard section pattern)) is
treated the same as @code{SORT_BY_NAME} (wildcard section pattern).
@item
@code{SORT_BY_ALIGNMENT} (@code{SORT_BY_ALIGNMENT} (wildcard section pattern))
region, the linker will issue an error message.
It is possible to access the origin and length of a memory in an
-expression via the @code{ORIGIN(@var{memory})} and
+expression via the @code{ORIGIN(@var{memory})} and
@code{LENGTH(@var{memory})} functions:
@smallexample
@group
- _fstack = ORIGIN(ram) + LENGTH(ram) - 4;
+ _fstack = ORIGIN(ram) + LENGTH(ram) - 4;
@end group
@end smallexample
VERS_2.0 @{
bar1; bar2;
- extern "C++" @{
+ extern "C++" @{
ns::*;
"int f(int, double)";
- @}
+ @}
@} VERS_1.2;
@end smallexample
VERSION extern "lang" @{ version-script-commands @}
@end smallexample
-The supported @samp{lang}s are @samp{C}, @samp{C++}, and @samp{Java}.
+The supported @samp{lang}s are @samp{C}, @samp{C++}, and @samp{Java}.
The linker will iterate over the list of symbols at the link time and
demangle them according to @samp{lang} before matching them to the
patterns specified in @samp{version-script-commands}.
top page of memory).
@item bit manipulation instructions
-@command{ld} finds all bit manipulation instructions like @code{band, bclr,
+@command{ld} finds all bit manipulation instructions like @code{band, bclr,
biand, bild, bior, bist, bixor, bld, bnot, bor, bset, bst, btst, bxor}
-which use 32 bit and 16 bit absolute address form, but refer to the top
+which use 32 bit and 16 bit absolute address form, but refer to the top
page of memory, and changes them to use the 8 bit address form.
(That is: the linker turns @samp{bset #xx:3,@code{@@}@var{aa}:32} into
-@samp{bset #xx:3,@code{@@}@var{aa}:8} whenever the address @var{aa} is in
+@samp{bset #xx:3,@code{@@}@var{aa}:8} whenever the address @var{aa} is in
the top page of memory).
@item system control instructions
-@command{ld} finds all @code{ldc.w, stc.w} instructions which use the
-32 bit absolute address form, but refer to the top page of memory, and
+@command{ld} finds all @code{ldc.w, stc.w} instructions which use the
+32 bit absolute address form, but refer to the top page of memory, and
changes them to use 16 bit address form.
(That is: the linker turns @samp{ldc.w @code{@@}@var{aa}:32,ccr} into
-@samp{ldc.w @code{@@}@var{aa}:16,ccr} whenever the address @var{aa} is in
+@samp{ldc.w @code{@@}@var{aa}:16,ccr} whenever the address @var{aa} is in
the top page of memory).
@end table
@cindex trampoline generation on M68HC12
For 68HC11 and 68HC12, @command{ld} can generate trampoline code to
call a far function using a normal @code{jsr} instruction. The linker
-will also change the relocation to some far function to use the
+will also change the relocation to some far function to use the
trampoline address instead of the function address. This is typically the
case when a pointer to a function is taken. The pointer will in fact
point to the function trampoline.
Defines an information memory section (if applicable). Any code in
this section will be uploaded to the MPU.
-@item @samp{.infomemnobits}
+@item @samp{.infomemnobits}
This is the same as the @samp{.infomem} section except that any code
in this section will not be uploaded to the MPU.
@item @samp{.noinit}
Denotes a portion of RAM located above @samp{.bss} section.
-The last two sections are used by gcc.
+The last two sections are used by gcc.
@end table
@ifclear GENERIC
the address range 0 to 256k. This option may be used to change the
range. Disable the check entirely with @option{--local-store=0:0}.
-@cindex SPU
+@cindex SPU
@kindex --stack-analysis
@item --stack-analysis
SPU local store space is limited. Over-allocation of stack space
is requested, detailed information about each function's stack usage
and calls will be given.
-@cindex SPU
+@cindex SPU
@kindex --emit-stack-syms
@item --emit-stack-syms
This option, if given along with @option{--stack-analysis} will result
functions. @code{<number>} is the section id in hex. The value of
such symbols is the stack requirement for the corresponding function.
The symbol size will be zero, type @code{STT_NOTYPE}, binding
-@code{STB_LOCAL}, and section @code{SHN_ABS}.
+@code{STB_LOCAL}, and section @code{SHN_ABS}.
@end table
@ifclear GENERIC
@node WIN32
@section @command{ld} and WIN32 (cygwin/mingw)
-This section describes some of the win32 specific @command{ld} issues.
+This section describes some of the win32 specific @command{ld} issues.
See @ref{Options,,Command Line Options} for detailed description of the
command line options mentioned here.
@table @emph
-@cindex import libraries
-@item import libraries
+@cindex import libraries
+@item import libraries
The standard Windows linker creates and uses so-called import
libraries, which contains information for linking to dll's. They are
regular static archives and are handled as any other static
support for creating such libraries provided with the
@samp{--out-implib} command line option.
-@item exporting DLL symbols
-@cindex exporting DLL symbols
+@item exporting DLL symbols
+@cindex exporting DLL symbols
The cygwin/mingw @command{ld} has several ways to export symbols for dll's.
@table @emph
@item --exclude-libs
@end itemize
-If, however, @samp{--export-all-symbols} is not given explicitly on the
+If, however, @samp{--export-all-symbols} is not given explicitly on the
command line, then the default auto-export behavior will be @emph{disabled}
if either of the following are true:
@item Any symbol in any object file was marked with the __declspec(dllexport) attribute.
@end itemize
-@item using a DEF file
-@cindex using a DEF file
+@item using a DEF file
+@cindex using a DEF file
Another way of exporting symbols is using a DEF file. A DEF file is
an ASCII file containing definitions of symbols which should be
exported when a dll is created. Usually it is named @samp{<dll
_bar = bar
another_foo = abc.dll.afoo
var1 DATA
-@end example
+@end example
This example defines a DLL with a non-default base address and five
symbols in the export table. The third exported symbol @code{_bar} is an
When the .DEF file is used to build an application, rather than a
library, the @code{NAME <name>} command should be used instead of
@code{LIBRARY}. If @samp{<name>} does not include a suffix, the default
-executable suffix, @samp{.EXE} is appended.
+executable suffix, @samp{.EXE} is appended.
With either @code{LIBRARY <name>} or @code{NAME <name>} the optional
specification @code{BASE = <number>} may be used to specify a
-non-default base address for the image.
+non-default base address for the image.
If neither @code{LIBRARY <name>} nor @code{NAME <name>} is specified,
or they specify an empty string, the internal name is the same as the
( ( ( <name1> [ = <name2> ] )
| ( <name1> = <module-name> . <external-name>))
[ @@ <integer> ] [NONAME] [DATA] [CONSTANT] [PRIVATE] ) *
-@end example
+@end example
Declares @samp{<name1>} as an exported symbol from the DLL, or declares
@samp{<name1>} as an exported alias for @samp{<name2>}; or declares
symbol can still be imported using the @code{LoadLibrary/GetProcAddress}
API at runtime or by by using the GNU ld extension of linking directly to
the DLL without an import library.
-
+
See ld/deffilep.y in the binutils sources for the full specification of
other DEF file statements
the @samp{--export-all-symbols} option is also used.
Note that object files that wish to access these symbols must @emph{not}
-decorate them with dllexport. Instead, they should use dllimport,
+decorate them with dllexport. Instead, they should use dllimport,
instead:
@example
__declspec(dllimport) void a_function(int with_args)
@end example
-This complicates the structure of library header files, because
-when included by the library itself the header must declare the
+This complicates the structure of library header files, because
+when included by the library itself the header must declare the
variables and functions as dllexport, but when included by client
code the header must declare them as dllimport. There are a number
-of idioms that are typically used to do this; often client code can
+of idioms that are typically used to do this; often client code can
omit the __declspec() declaration completely. See
@samp{--enable-auto-import} and @samp{automatic data imports} for more
information.
-@end table
+@end table
@cindex automatic data imports
@item automatic data imports
The standard Windows dll format supports data imports from dlls only
by adding special decorations (dllimport/dllexport), which let the
compiler produce specific assembler instructions to deal with this
-issue. This increases the effort necessary to port existing Un*x
+issue. This increases the effort necessary to port existing Un*x
code to these platforms, especially for large
c++ libraries and applications. The auto-import feature, which was
-initially provided by Paul Sokolovsky, allows one to omit the
+initially provided by Paul Sokolovsky, allows one to omit the
decorations to achieve a behavior that conforms to that on POSIX/Un*x
-platforms. This feature is enabled with the @samp{--enable-auto-import}
+platforms. This feature is enabled with the @samp{--enable-auto-import}
command-line option, although it is enabled by default on cygwin/mingw.
The @samp{--enable-auto-import} option itself now serves mainly to
suppress any warnings that are ordinarily emitted when linked objects
trigger the feature's use.
-auto-import of variables does not always work flawlessly without
+auto-import of variables does not always work flawlessly without
additional assistance. Sometimes, you will see this message
-"variable '<var>' can't be auto-imported. Please read the
+"variable '<var>' can't be auto-imported. Please read the
documentation for ld's @code{--enable-auto-import} for details."
-The @samp{--enable-auto-import} documentation explains why this error
-occurs, and several methods that can be used to overcome this difficulty.
-One of these methods is the @emph{runtime pseudo-relocs} feature, described
+The @samp{--enable-auto-import} documentation explains why this error
+occurs, and several methods that can be used to overcome this difficulty.
+One of these methods is the @emph{runtime pseudo-relocs} feature, described
below.
@cindex runtime pseudo-relocation
-For complex variables imported from DLLs (such as structs or classes),
-object files typically contain a base address for the variable and an
-offset (@emph{addend}) within the variable--to specify a particular
-field or public member, for instance. Unfortunately, the runtime loader used
-in win32 environments is incapable of fixing these references at runtime
+For complex variables imported from DLLs (such as structs or classes),
+object files typically contain a base address for the variable and an
+offset (@emph{addend}) within the variable--to specify a particular
+field or public member, for instance. Unfortunately, the runtime loader used
+in win32 environments is incapable of fixing these references at runtime
without the additional information supplied by dllimport/dllexport decorations.
-The standard auto-import feature described above is unable to resolve these
+The standard auto-import feature described above is unable to resolve these
references.
-The @samp{--enable-runtime-pseudo-relocs} switch allows these references to
-be resolved without error, while leaving the task of adjusting the references
-themselves (with their non-zero addends) to specialized code provided by the
-runtime environment. Recent versions of the cygwin and mingw environments and
-compilers provide this runtime support; older versions do not. However, the
-support is only necessary on the developer's platform; the compiled result will
+The @samp{--enable-runtime-pseudo-relocs} switch allows these references to
+be resolved without error, while leaving the task of adjusting the references
+themselves (with their non-zero addends) to specialized code provided by the
+runtime environment. Recent versions of the cygwin and mingw environments and
+compilers provide this runtime support; older versions do not. However, the
+support is only necessary on the developer's platform; the compiled result will
run without error on an older system.
-@samp{--enable-runtime-pseudo-relocs} is not the default; it must be explicitly
-enabled as needed.
+@samp{--enable-runtime-pseudo-relocs} is not the default; it must be explicitly
+enabled as needed.
@cindex direct linking to a dll
@item direct linking to a dll
including data symbols, to a dll without the usage of any import
libraries. This is much faster and uses much less memory than does the
traditional import library method, especially when linking large
-libraries or applications. When @command{ld} creates an import lib, each
-function or variable exported from the dll is stored in its own bfd, even
-though a single bfd could contain many exports. The overhead involved in
+libraries or applications. When @command{ld} creates an import lib, each
+function or variable exported from the dll is stored in its own bfd, even
+though a single bfd could contain many exports. The overhead involved in
storing, loading, and processing so many bfd's is quite large, and explains the
-tremendous time, memory, and storage needed to link against particularly
+tremendous time, memory, and storage needed to link against particularly
large or complex libraries when using import libs.
-Linking directly to a dll uses no extra command-line switches other than
+Linking directly to a dll uses no extra command-line switches other than
@samp{-L} and @samp{-l}, because @command{ld} already searches for a number
-of names to match each library. All that is needed from the developer's
+of names to match each library. All that is needed from the developer's
perspective is an understanding of this search, in order to force ld to
select the dll instead of an import library.
before moving on to the next directory in the search path.
-(*) Actually, this is not @samp{cygxxx.dll} but in fact is @samp{<prefix>xxx.dll},
-where @samp{<prefix>} is set by the @command{ld} option
-@samp{--dll-search-prefix=<prefix>}. In the case of cygwin, the standard gcc spec
-file includes @samp{--dll-search-prefix=cyg}, so in effect we actually search for
+(*) Actually, this is not @samp{cygxxx.dll} but in fact is @samp{<prefix>xxx.dll},
+where @samp{<prefix>} is set by the @command{ld} option
+@samp{--dll-search-prefix=<prefix>}. In the case of cygwin, the standard gcc spec
+file includes @samp{--dll-search-prefix=cyg}, so in effect we actually search for
@samp{cygxxx.dll}.
-Other win32-based unix environments, such as mingw or pw32, may use other
-@samp{<prefix>}es, although at present only cygwin makes use of this feature. It
+Other win32-based unix environments, such as mingw or pw32, may use other
+@samp{<prefix>}es, although at present only cygwin makes use of this feature. It
was originally intended to help avoid name conflicts among dll's built for the
various win32/un*x environments, so that (for example) two versions of a zlib dll
could coexist on the same machine.
cygxxx.dll
lib/
libxxx.dll.a (in case of dll's)
- libxxx.a (in case of static archive)
+ libxxx.a (in case of static archive)
@end example
-Linking directly to a dll without using the import library can be
-done two ways:
+Linking directly to a dll without using the import library can be
+done two ways:
1. Use the dll directly by adding the @samp{bin} path to the link line
@example
gcc -Wl,-verbose -o a.exe -L../bin/ -lxxx
-@end example
+@end example
However, as the dll's often have version numbers appended to their names
(@samp{cygncurses-5.dll}) this will often fail, unless one specifies
@example
ln -s bin/cygxxx.dll lib/[cyg|lib|]xxx.dll[.a]
-@end example
+@end example
Then you can link without any make environment changes.
@example
gcc -Wl,-verbose -o a.exe -L../lib/ -lxxx
-@end example
+@end example
This technique also avoids the version number problems, because the following is
perfectly legal
bin/
cygxxx-5.dll
lib/
- libxxx.dll.a -> ../bin/cygxxx-5.dll
+ libxxx.dll.a -> ../bin/cygxxx-5.dll
@end example
Linking directly to a dll without using an import lib will work
stdcall-decorated assembly names.
So, import libs are not going away. But the ability to replace
-true import libs with a simple symbolic link to (or a copy of)
-a dll, in many cases, is a useful addition to the suite of tools
-binutils makes available to the win32 developer. Given the
+true import libs with a simple symbolic link to (or a copy of)
+a dll, in many cases, is a useful addition to the suite of tools
+binutils makes available to the win32 developer. Given the
massive improvements in memory requirements during linking, storage
requirements, and linking speed, we expect that many developers
will soon begin to use this feature whenever possible.
-@item symbol aliasing
+@item symbol aliasing
@table @emph
-@item adding additional names
-Sometimes, it is useful to export symbols with additional names.
+@item adding additional names
+Sometimes, it is useful to export symbols with additional names.
A symbol @samp{foo} will be exported as @samp{foo}, but it can also be
exported as @samp{_foo} by using special directives in the DEF file
when creating the dll. This will affect also the optional created
-import library. Consider the following DEF file:
+import library. Consider the following DEF file:
-@example
+@example
LIBRARY "xyz.dll" BASE=0x61000000
EXPORTS
-foo
+foo
_foo = foo
-@end example
+@end example
The line @samp{_foo = foo} maps the symbol @samp{foo} to @samp{_foo}.
Another method for creating a symbol alias is to create it in the
source code using the "weak" attribute:
-@example
-void foo () @{ /* Do something. */; @}
+@example
+void foo () @{ /* Do something. */; @}
void _foo () __attribute__ ((weak, alias ("foo")));
-@end example
+@end example
See the gcc manual for more information about attributes and weak
symbols.
@item renaming symbols
Sometimes it is useful to rename exports. For instance, the cygwin
-kernel does this regularly. A symbol @samp{_foo} can be exported as
+kernel does this regularly. A symbol @samp{_foo} can be exported as
@samp{foo} but not as @samp{_foo} by using special directives in the
DEF file. (This will also affect the import library, if it is
-created). In the following example:
+created). In the following example:
-@example
+@example
LIBRARY "xyz.dll" BASE=0x61000000
EXPORTS
_foo = foo
-@end example
+@end example
The line @samp{_foo = foo} maps the exported symbol @samp{foo} to
@samp{_foo}.
-@end table
+@end table
Note: using a DEF file disables the default auto-export behavior,
-unless the @samp{--export-all-symbols} command line option is used.
+unless the @samp{--export-all-symbols} command line option is used.
If, however, you are trying to rename symbols, then you should list
-@emph{all} desired exports in the DEF file, including the symbols
-that are not being renamed, and do @emph{not} use the
-@samp{--export-all-symbols} option. If you list only the
-renamed symbols in the DEF file, and use @samp{--export-all-symbols}
-to handle the other symbols, then the both the new names @emph{and}
-the original names for the renamed symbols will be exported.
-In effect, you'd be aliasing those symbols, not renaming them,
+@emph{all} desired exports in the DEF file, including the symbols
+that are not being renamed, and do @emph{not} use the
+@samp{--export-all-symbols} option. If you list only the
+renamed symbols in the DEF file, and use @samp{--export-all-symbols}
+to handle the other symbols, then the both the new names @emph{and}
+the original names for the renamed symbols will be exported.
+In effect, you'd be aliasing those symbols, not renaming them,
which is probably not what you wanted.
@cindex weak externals
were different, the contents of that location would fool the linker
into doing the right thing despite the bug. Play it safe and give a
specific, complete example. That is the easiest thing for you to do,
-and the most helpful.
+and the most helpful.
Keep in mind that the purpose of a bug report is to enable us to fix
the bug if it is new to us. Therefore, always write your bug reports
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