binutils-gdb/ld
H.J. Lu 74e315dbfe elf: Set p_align to the minimum page size if possible
Currently, on 32-bit and 64-bit ARM, it seems that ld generates p_align
values of 0x10000 even if no section alignment is greater than 0x1000.
The issue is more general and probably affects other targets with multiple
page sizes.

While file layout absolutely must take 64K page size into account, that
does not have to be reflected in the p_align value.  If running on a 64K
kernel, the file will be loaded at a 64K page boundary by necessity. On
a 4K kernel, 64K alignment is not needed.

The glibc loader has been fixed to honor p_align:

https://sourceware.org/bugzilla/show_bug.cgi?id=28676

similar to kernel:

commit ce81bb256a224259ab686742a6284930cbe4f1fa
Author: Chris Kennelly <ckennelly@google.com>
Date:   Thu Oct 15 20:12:32 2020 -0700

    fs/binfmt_elf: use PT_LOAD p_align values for suitable start address

This means that on 4K kernels, we will start to do extra work for 64K
p_align, but this pointless for pretty much all binaries (whose section
alignment rarely exceeds 16).

The minimum page size is used, instead of the maximum section alignment
due to this glibc bug:

https://sourceware.org/bugzilla/show_bug.cgi?id=28688

It has been fixed in glibc 2.35.  But linker output must work on existing
glibc binaries.

1. Set p_align to the minimum page size while laying out segments aligning
to the maximum page size or section alignment.  The run-time loader can
align segments to the minimum page size or above, depending on system page
size.
2. If -z max-page-size=NNN is used, p_align will be set to the maximum
page size or the largest section alignment.
3. If a section requires alignment higher than the minimum page size,
don't set p_align to the minimum page size.
4. If a section requires alignment higher than the maximum page size,
set p_align to the section alignment.
5. For objcopy, when the minimum page size != the maximum page size,
p_align may be set to the minimum page size while segments are aligned
to the maximum page size.  In this case, the input p_align will be
ignored and the maximum page size will be used to align the ouput
segments.
6. Update linker to disallow the common page size > the maximum page size.
7. Update linker to avoid the common page size > the maximum page size.
8. Adjust pru_irq_map-1.d to expect p_align == sh_addralign:

Section Headers:
  [Nr] Name   Type            Addr     Off    Size   ES Flg Lk Inf Al
  [ 0]        NULL            00000000 000000 000000 00      0   0  0
  [ 1] .text  PROGBITS        20000000 00007c 000004 00  AX  0   0  4
...
Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  LOAD           0x000074 0x00000000 0x00000000 0x00008 0x00008 RW  0x1
  LOAD           0x00007c 0x20000000 0x20000000 0x00004 0x00004 R E 0x4

vs.

Section Headers:
  [Nr] Name   Type            Addr     Off    Size   ES Flg Lk Inf Al
  [ 0]        NULL            00000000 000000 000000 00      0   0  0
  [ 1] .text  PROGBITS        20000000 00007c 000004 00  AX  0   0  4
...
Program Headers:
  Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
  LOAD           0x000074 0x00000000 0x00000000 0x00008 0x00008 RW  0x1
  LOAD           0x00007c 0x20000000 0x20000000 0x00004 0x00004 R E 0x1

To enable this linker optimization, the backend should define ELF_P_ALIGN
to ELF_MINPAGESIZE.

bfd/

	PR ld/28689
	PR ld/28695
	* elf-bfd.h (elf_backend_data): Add p_align.
	* elf.c (assign_file_positions_for_load_sections): Set p_align
	to the default p_align value while laying out segments aligning
	to maximum page size or section alignment.
	(elf_is_p_align_valid): New function.
	(copy_elf_program_header): Call elf_is_p_align_valid to determine
	if p_align is valid.
	* elfxx-target.h (ELF_P_ALIGN): New.  Default to 0.
	(elfNN_bed): Add ELF_P_ALIGN.
	* elfxx-x86.h (ELF_P_ALIGN): New.  Set to ELF_MINPAGESIZE.

include/

	PR ld/28689
	PR ld/28695
	* bfdlink.h (bfd_link_info): Add maxpagesize_is_set.

ld/

	PR ld/28689
	PR ld/28695
	* emultempl/elf.em (gld${EMULATION_NAME}_handle_option): Set
	link_info.maxpagesize_is_set for -z max-page-size=NNN.
	* ldelf.c (ldelf_after_parse): Disallow link_info.commonpagesize
	> link_info.maxpagesize.
	* testsuite/ld-elf/elf.exp: Pass -z max-page-size=0x4000 to
	linker to build mbind2a and mbind2b.
	* testsuite/ld-elf/header.d: Add -z common-page-size=0x100.
	* testsuite/ld-elf/linux-x86.exp: Add PR ld/28689 tests.
	* testsuite/ld-elf/p_align-1.c: New file.
	* testsuite/ld-elf/page-size-1.d: New test.
	* testsuite/ld-elf/pr26936.d: Add -z common-page-size=0x1000.
	* testsuite/ld-elf/seg.d: Likewise.
	* testsuite/ld-scripts/rgn-at5.d: Likewise.
	* testsuite/ld-pru/pru_irq_map-1.d: Append 1 to name.  Adjust
	expected PT_LOAD segment alignment.
	* testsuite/ld-pru/pru_irq_map-2.d: Append 2 to name.
	* testsuite/ld-scripts/pr23571.d: Add -z max-page-size=0x1000.
2022-01-05 05:06:18 -08:00
..
emulparams Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
emultempl elf: Set p_align to the minimum page size if possible 2022-01-05 05:06:18 -08:00
po Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
scripttempl Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
testsuite elf: Set p_align to the minimum page size if possible 2022-01-05 05:06:18 -08:00
.gitignore
aclocal.m4 unify 64-bit bfd checks 2022-01-01 12:49:07 -05:00
ChangeLog Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ChangeLog-0001
ChangeLog-0203
ChangeLog-2004
ChangeLog-2005
ChangeLog-2006
ChangeLog-2007
ChangeLog-2008
ChangeLog-2009
ChangeLog-2010
ChangeLog-2011
ChangeLog-2012
ChangeLog-2013
ChangeLog-2014
ChangeLog-2015
ChangeLog-2016
ChangeLog-2017
ChangeLog-2018
ChangeLog-2019
ChangeLog-2020
ChangeLog-9197
ChangeLog-9899
config.in
configure unify 64-bit bfd checks 2022-01-01 12:49:07 -05:00
configure.ac Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
configure.host Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
configure.tgt Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
deffile.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
deffilep.y Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
dep-in.sed
elf-hints-local.h
fdl.texi
gen-doc.texi Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
genscrba.sh
genscripts.sh Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
h8-doc.texi Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ld.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ld.texi Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldbuildid.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldbuildid.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldcref.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldctor.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldctor.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldelf.c elf: Set p_align to the minimum page size if possible 2022-01-05 05:06:18 -08:00
ldelf.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldelfgen.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldelfgen.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldemul.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldemul.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldexp.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldexp.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldfile.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldfile.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldgram.y Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldint.texi Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldlang.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldlang.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldlex-wrapper.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldlex.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldlex.l Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldmain.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldmain.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldmisc.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldmisc.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldver.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldver.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldwrite.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
ldwrite.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
lexsup.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
libdep_plugin.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
MAINTAINERS Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
Makefile.am Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
Makefile.in Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
mri.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
mri.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
NEWS Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
pe-dll.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
pe-dll.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
pep-dll.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
pep-dll.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
plugin.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
plugin.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
README Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
stamp-h.in
sysdep.h Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
testplug2.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
testplug3.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
testplug4.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
testplug.c Update year range in copyright notice of binutils files 2022-01-02 12:04:28 +10:30
TODO

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		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.

Copyright (C) 2012-2022 Free Software Foundation, Inc.

Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
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