\input texinfo
@setfilename ldint.info
-@c Copyright 1992, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2003
-@c Free Software Foundation, Inc.
+@c Copyright (C) 1992-2017 Free Software Foundation, Inc.
-@ifinfo
-@format
-START-INFO-DIR-ENTRY
+@ifnottex
+@dircategory Software development
+@direntry
* Ld-Internals: (ldint). The GNU linker internals.
-END-INFO-DIR-ENTRY
-@end format
-@end ifinfo
+@end direntry
+@end ifnottex
-@ifinfo
+@copying
This file documents the internals of the GNU linker ld.
-Copyright 1992, 1994, 1995, 1996, 1997, 1998, 1999, 2000
-Free Software Foundation, Inc.
+Copyright @copyright{} 1992-2017 Free Software Foundation, Inc.
Contributed by Cygnus Support.
- Permission is granted to copy, distribute and/or modify this document
- under the terms of the GNU Free Documentation License, Version 1.1
- or any later version published by the Free Software Foundation;
- with no Invariant Sections, with no Front-Cover Texts, and with no
- Back-Cover Texts. A copy of the license is included in the
- section entitled "GNU Free Documentation License".
+Permission is granted to copy, distribute and/or modify this document
+under the terms of the GNU Free Documentation License, Version 1.3 or
+any later version published by the Free Software Foundation; with the
+Invariant Sections being ``GNU General Public License'' and ``Funding
+Free Software'', the Front-Cover texts being (a) (see below), and with
+the Back-Cover Texts being (b) (see below). A copy of the license is
+included in the section entitled ``GNU Free Documentation License''.
+
+(a) The FSF's Front-Cover Text is:
-@ignore
-Permission is granted to process this file through Tex and print the
-results, provided the printed document carries copying permission
-notice identical to this one except for the removal of this paragraph
-(this paragraph not being relevant to the printed manual).
+ A GNU Manual
-@end ignore
-@end ifinfo
+(b) The FSF's Back-Cover Text is:
+
+ You have freedom to copy and modify this GNU Manual, like GNU
+ software. Copies published by the Free Software Foundation raise
+ funds for GNU development.
+@end copying
@iftex
@finalout
@end tex
@vskip 0pt plus 1filll
-Copyright @copyright{} 1992, 93, 94, 95, 96, 97, 1998, 2000
-Free Software Foundation, Inc.
+Copyright @copyright{} 1992-2017 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
- under the terms of the GNU Free Documentation License, Version 1.1
+ under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, with no Front-Cover Texts, and with no
Back-Cover Texts. A copy of the license is included in the
Some @file{scripttempl} scripts use this to set the start address of the
@samp{.text} section.
-@item NONPAGED_TEXT_START_ADDR
-If this is defined, the @file{genscripts.sh} script sets
-@code{TEXT_START_ADDR} to its value before running the
-@file{scripttempl} script for the @code{-n} and @code{-N} options
-(@pxref{linker scripts}).
-
@item SEGMENT_SIZE
The @file{genscripts.sh} script uses this to set the default value of
@code{DATA_ALIGNMENT} when running the @file{scripttempl} script.
invoke @file{scripttempl/@var{script}.sc}.
The @file{genscripts.sh} script will invoke the @file{scripttempl}
-script 5 to 8 times. Each time it will set the shell variable
+script 5 to 9 times. Each time it will set the shell variable
@code{LD_FLAG} to a different value. When the linker is run, the
options used will direct it to select a particular script. (Script
selection is controlled by the @code{get_script} emulation entry point;
The @file{emultempl} script must arrange to use this script at the
appropriate time, normally when the linker is invoked with the @code{-shared
-z combreloc} option. The output has an extension of @file{.xsc}.
+@item auto_import
+The @file{scripttempl} script is only invoked with @code{LD_FLAG} set to
+this value if @code{GENERATE_AUTO_IMPORT_SCRIPT} is defined in the
+@file{emulparams} file. The @file{emultempl} script must arrange to
+use this script at the appropriate time, normally when the linker is
+invoked with the @code{--enable-auto-import} option. The output has
+an extension of @file{.xa}.
@end table
Besides the shell variables set by the @file{emulparams} script, and the
@chapter Some Architecture Specific Notes
This is the place for notes on the behavior of @code{ld} on
-specific platforms. Currently, only Intel x86 is documented (and
+specific platforms. Currently, only Intel x86 is documented (and
of that, only the auto-import behavior for DLLs).
@menu
@table @emph
@code{ld} can create DLLs that operate with various runtimes available
-on a common x86 operating system. These runtimes include native (using
+on a common x86 operating system. These runtimes include native (using
the mingw "platform"), cygwin, and pw.
-@item auto-import from DLLs
+@item auto-import from DLLs
@enumerate
@item
-With this feature on, DLL clients can import variables from DLL
+With this feature on, DLL clients can import variables from DLL
without any concern from their side (for example, without any source
-code modifications). Auto-import can be enabled using the
-@code{--enable-auto-import} flag, or disabled via the
+code modifications). Auto-import can be enabled using the
+@code{--enable-auto-import} flag, or disabled via the
@code{--disable-auto-import} flag. Auto-import is disabled by default.
@item
This is done completely in bounds of the PE specification (to be fair,
-there's a minor violation of the spec at one point, but in practice
+there's a minor violation of the spec at one point, but in practice
auto-import works on all known variants of that common x86 operating
-system) So, the resulting DLL can be used with any other PE
+system) So, the resulting DLL can be used with any other PE
compiler/linker.
@item
@item
Overhead (space): 8 bytes per imported symbol, plus 20 for each
-reference to it; Overhead (load time): negligible; Overhead
-(virtual/physical memory): should be less than effect of DLL
+reference to it; Overhead (load time): negligible; Overhead
+(virtual/physical memory): should be less than effect of DLL
relocation.
@end enumerate
Motivation
-The obvious and only way to get rid of dllimport insanity is
-to make client access variable directly in the DLL, bypassing
+The obvious and only way to get rid of dllimport insanity is
+to make client access variable directly in the DLL, bypassing
the extra dereference imposed by ordinary DLL runtime linking.
I.e., whenever client contains something like
@code{mov dll_var,%eax,}
-address of dll_var in the command should be relocated to point
-into loaded DLL. The aim is to make OS loader do so, and than
-make ld help with that. Import section of PE made following
-way: there's a vector of structures each describing imports
-from particular DLL. Each such structure points to two other
-parallel vectors: one holding imported names, and one which
-will hold address of corresponding imported name. So, the
-solution is de-vectorize these structures, making import
+address of dll_var in the command should be relocated to point
+into loaded DLL. The aim is to make OS loader do so, and than
+make ld help with that. Import section of PE made following
+way: there's a vector of structures each describing imports
+from particular DLL. Each such structure points to two other
+parallel vectors: one holding imported names, and one which
+will hold address of corresponding imported name. So, the
+solution is de-vectorize these structures, making import
locations be sparse and pointing directly into code.
Implementation
-For each reference of data symbol to be imported from DLL (to
-set of which belong symbols with name <sym>, if __imp_<sym> is
-found in implib), the import fixup entry is generated. That
-entry is of type IMAGE_IMPORT_DESCRIPTOR and stored in .idata$3
-subsection. Each fixup entry contains pointer to symbol's address
-within .text section (marked with __fuN_<sym> symbol, where N is
-integer), pointer to DLL name (so, DLL name is referenced by
-multiple entries), and pointer to symbol name thunk. Symbol name
-thunk is singleton vector (__nm_th_<symbol>) pointing to
-IMAGE_IMPORT_BY_NAME structure (__nm_<symbol>) directly containing
-imported name. Here comes that "om the edge" problem mentioned above:
-PE specification rambles that name vector (OriginalFirstThunk) should
-run in parallel with addresses vector (FirstThunk), i.e. that they
+For each reference of data symbol to be imported from DLL (to
+set of which belong symbols with name <sym>, if __imp_<sym> is
+found in implib), the import fixup entry is generated. That
+entry is of type IMAGE_IMPORT_DESCRIPTOR and stored in .idata$3
+subsection. Each fixup entry contains pointer to symbol's address
+within .text section (marked with __fuN_<sym> symbol, where N is
+integer), pointer to DLL name (so, DLL name is referenced by
+multiple entries), and pointer to symbol name thunk. Symbol name
+thunk is singleton vector (__nm_th_<symbol>) pointing to
+IMAGE_IMPORT_BY_NAME structure (__nm_<symbol>) directly containing
+imported name. Here comes that "om the edge" problem mentioned above:
+PE specification rambles that name vector (OriginalFirstThunk) should
+run in parallel with addresses vector (FirstThunk), i.e. that they
should have same number of elements and terminated with zero. We violate
-this, since FirstThunk points directly into machine code. But in
-practice, OS loader implemented the sane way: it goes thru
-OriginalFirstThunk and puts addresses to FirstThunk, not something
-else. It once again should be noted that dll and symbol name
-structures are reused across fixup entries and should be there
-anyway to support standard import stuff, so sustained overhead is
-20 bytes per reference. Other question is whether having several
-IMAGE_IMPORT_DESCRIPTORS for the same DLL is possible. Answer is yes,
-it is done even by native compiler/linker (libth32's functions are in
-fact resident in windows9x kernel32.dll, so if you use it, you have
-two IMAGE_IMPORT_DESCRIPTORS for kernel32.dll). Yet other question is
-whether referencing the same PE structures several times is valid.
-The answer is why not, prohibiting that (detecting violation) would
+this, since FirstThunk points directly into machine code. But in
+practice, OS loader implemented the sane way: it goes thru
+OriginalFirstThunk and puts addresses to FirstThunk, not something
+else. It once again should be noted that dll and symbol name
+structures are reused across fixup entries and should be there
+anyway to support standard import stuff, so sustained overhead is
+20 bytes per reference. Other question is whether having several
+IMAGE_IMPORT_DESCRIPTORS for the same DLL is possible. Answer is yes,
+it is done even by native compiler/linker (libth32's functions are in
+fact resident in windows9x kernel32.dll, so if you use it, you have
+two IMAGE_IMPORT_DESCRIPTORS for kernel32.dll). Yet other question is
+whether referencing the same PE structures several times is valid.
+The answer is why not, prohibiting that (detecting violation) would
require more work on behalf of loader than not doing it.
@end table
@node GNU Free Documentation License
@chapter GNU Free Documentation License
- GNU Free Documentation License
-
- Version 1.1, March 2000
-
- Copyright (C) 2000 Free Software Foundation, Inc.
- 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
-
- Everyone is permitted to copy and distribute verbatim copies
- of this license document, but changing it is not allowed.
-
-
-0. PREAMBLE
-
-The purpose of this License is to make a manual, textbook, or other
-written document "free" in the sense of freedom: to assure everyone
-the effective freedom to copy and redistribute it, with or without
-modifying it, either commercially or noncommercially. Secondarily,
-this License preserves for the author and publisher a way to get
-credit for their work, while not being considered responsible for
-modifications made by others.
-
-This License is a kind of "copyleft", which means that derivative
-works of the document must themselves be free in the same sense. It
-complements the GNU General Public License, which is a copyleft
-license designed for free software.
-
-We have designed this License in order to use it for manuals for free
-software, because free software needs free documentation: a free
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-software does. But this License is not limited to software manuals;
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-
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-1. APPLICABILITY AND DEFINITIONS
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-entitled "Endorsements."
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-6. COLLECTIONS OF DOCUMENTS
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-7. AGGREGATION WITH INDEPENDENT WORKS
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-and independent documents or works, in or on a volume of a storage or
-distribution medium, does not as a whole count as a Modified Version
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-10. FUTURE REVISIONS OF THIS LICENSE
-
-The Free Software Foundation may publish new, revised versions
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-ADDENDUM: How to use this License for your documents
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-@smallexample
- Copyright (c) YEAR YOUR NAME.
- Permission is granted to copy, distribute and/or modify this document
- under the terms of the GNU Free Documentation License, Version 1.1
- or any later version published by the Free Software Foundation;
- with the Invariant Sections being LIST THEIR TITLES, with the
- Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
- A copy of the license is included in the section entitled "GNU
- Free Documentation License".
-@end smallexample
-
-If you have no Invariant Sections, write "with no Invariant Sections"
-instead of saying which ones are invariant. If you have no
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+@include fdl.texi
@contents
@bye