Files
binutils-gdb/ld
Michael Matz 670c91c0c5 Fix PR30358, performance with --sort-section
since af31506c we only use the binary tree when section sorting is
required.  While its unbalanced and hence can degrade to a linear list
it should otherwise have been equivalent to the old code relying on
insertion sort.  Unfortunately it was not.  The old code directly used
lang_add_section to populate the sorted list, the new code first
populates the tree and only then does lang_add_section on the sorted
result.

In the testcase we have very many linkonce section groups, and hence
lang_add_section won't actually insert anything for most of them.  That
limited the to-be-sorted list length previously.  The tree-sorting code
OTOH first created a tree of all candidates sections, including those
that wouldn't be inserted by lang_add_section, hence increasing the size
of the sorting problem.  In the testcase the chain length went from
about 1500 to 106000, and in the degenerated case (as in the testcase)
that goes in quadratically.

This splits out most of the early-out code from lang_add_section to its
own function and uses the latter to avoid inserting into the tree.  This
refactoring slightly changes the order of early-out tests (the ones
based on section flags is now done last, and only in lang_add_section).
The new function is not a pure predicate: it can give warnings and it
might change output_section, like the old early-out code did.  I have
also added a skip-warning case in the first discard case, whose
non-existence seemed to have been an oversight.

	PR 30358
	* ldlang.c (wont_add_section_p): Split out from ...
	(lang_add_section): ... here.
	(output_section_callback_sort): Use wont_add_section_p to not
	always add sections to the sort tree.
2023-04-27 16:15:26 +02:00
..
2023-03-19 22:19:19 +10:30
2023-03-17 21:10:05 +10:30
2023-04-21 07:54:19 +02:00
2023-04-20 09:03:53 +09:30
2023-03-10 21:22:16 +10:30

		README for LD

This is the GNU linker.  It is distributed with other "binary
utilities" which should be in ../binutils.  See ../binutils/README for
more general notes, including where to send bug reports.

There are many features of the linker:

* The linker uses a Binary File Descriptor library (../bfd)
  that it uses to read and write object files.  This helps
  insulate the linker itself from the format of object files.

* The linker supports a number of different object file
  formats.  It can even handle multiple formats at once:
  Read two input formats and write a third.

* The linker can be configured for cross-linking.

* The linker supports a control language.

* There is a user manual (ld.texi), as well as the
  beginnings of an internals manual (ldint.texi).

Installation
============

See ../binutils/README.

If you want to make a cross-linker, you may want to specify
a different search path of -lfoo libraries than the default.
You can do this by setting the LIB_PATH variable in ./Makefile
or using the --with-lib-path configure switch.

To build just the linker, make the target all-ld from the top level
directory (one directory above this one).

Porting to a new target
=======================

See the ldint.texi manual.

Reporting bugs etc
===========================

See ../binutils/README.

Known problems
==============

The Solaris linker normally exports all dynamic symbols from an
executable.  The GNU linker does not do this by default.  This is
because the GNU linker tries to present the same interface for all
similar targets (in this case, all native ELF targets).  This does not
matter for normal programs, but it can make a difference for programs
which try to dlopen an executable, such as PERL or Tcl.  You can make
the GNU linker export all dynamic symbols with the -E or
--export-dynamic command line option.

HP/UX 9.01 has a shell bug that causes the linker scripts to be
generated incorrectly.  The symptom of this appears to be "fatal error
- scanner input buffer overflow" error messages.  There are various
workarounds to this:
  * Build and install bash, and build with "make SHELL=bash".
  * Update to a version of HP/UX with a working shell (e.g., 9.05).
  * Replace "(. ${srcdir}/scripttempl/${SCRIPT_NAME}.sc)" in
    genscripts.sh with "sh ${srcdir}..." (no parens) and make sure the
    emulparams script used exports any shell variables it sets.

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