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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. |
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emulparams | ||
emultempl | ||
po | ||
scripttempl | ||
testsuite | ||
.gitignore | ||
aclocal.m4 | ||
ChangeLog | ||
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 | ||
configure.ac | ||
configure.host | ||
configure.tgt | ||
deffile.h | ||
deffilep.y | ||
dep-in.sed | ||
elf-hints-local.h | ||
fdl.texi | ||
gen-doc.texi | ||
genscrba.sh | ||
genscripts.sh | ||
h8-doc.texi | ||
ld.h | ||
ld.texi | ||
ldbuildid.c | ||
ldbuildid.h | ||
ldcref.c | ||
ldctor.c | ||
ldctor.h | ||
ldelf.c | ||
ldelf.h | ||
ldelfgen.c | ||
ldelfgen.h | ||
ldemul.c | ||
ldemul.h | ||
ldexp.c | ||
ldexp.h | ||
ldfile.c | ||
ldfile.h | ||
ldgram.y | ||
ldint.texi | ||
ldlang.c | ||
ldlang.h | ||
ldlex-wrapper.c | ||
ldlex.h | ||
ldlex.l | ||
ldmain.c | ||
ldmain.h | ||
ldmisc.c | ||
ldmisc.h | ||
ldver.c | ||
ldver.h | ||
ldwrite.c | ||
ldwrite.h | ||
lexsup.c | ||
libdep_plugin.c | ||
MAINTAINERS | ||
Makefile.am | ||
Makefile.in | ||
mri.c | ||
mri.h | ||
NEWS | ||
pe-dll.c | ||
pe-dll.h | ||
pep-dll.c | ||
pep-dll.h | ||
plugin.c | ||
plugin.h | ||
README | ||
stamp-h.in | ||
sysdep.h | ||
testplug2.c | ||
testplug3.c | ||
testplug4.c | ||
testplug.c | ||
TODO |
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
notice and this notice are preserved.