binutils-gdb/ld
Nick Alcock 3d16b64e28 bfd, include, ld, binutils, libctf: CTF should use the dynstr/sym
This is embarrassing.

The whole point of CTF is that it remains intact even after a binary is
stripped, providing a compact mapping from symbols to types for
everything in the externally-visible interface of an ELF object: it has
connections to the symbol table for that purpose, and to the string
table to avoid duplicating symbol names.  So it's a shame that the hooks
I implemented last year served to hook it up to the .symtab and .strtab,
which obviously disappear on strip, leaving any accompanying the CTF
dict containing references to strings (and, soon, symbols) which don't
exist any more because their containing strtab has been vaporized.  The
original Solaris design used .dynsym and .dynstr (well, actually,
.ldynsym, which has more symbols) which do not disappear. So should we.

Thankfully the work we did before serves as guide rails, and adjusting
things to use the .dynstr and .dynsym was fast and easy.  The only
annoyance is that the dynsym is assembled inside elflink.c in a fairly
piecemeal fashion, so that the easiest way to get the symbols out was to
hook in before every call to swap_symbol_out (we also leave in a hook in
front of symbol additions to the .symtab because it seems plausible that
we might want to hook them in future too: for now that hook is unused).
We adjust things so that rather than being offered a whole hash table of
symbols at once, libctf is now given symbols one at a time, with st_name
indexes already resolved and pointing at their final .dynstr offsets:
it's now up to libctf to resolve these to names as needed using the
strtab info we pass it separately.

Some bits might be contentious.  The ctf_new_dynstr callback takes an
elf_internal_sym, and this remains an elf_internal_sym right down
through the generic emulation layers into ldelfgen.  This is no worse
than the elf_sym_strtab we used to pass down, but in the future when we
gain non-ELF CTF symtab support we might want to lower the
elf_internal_sym to some other representation (perhaps a
ctf_link_symbol) in bfd or in ldlang_ctf_new_dynsym.  We rename the
'apply_strsym' hooks to 'acquire_strings' instead, becuse they no longer
have anything to do with symbols.

There are some API changes to pieces of API which are technically public
but actually totally unused by anything and/or unused by anything but ld
so they can change freely: the ctf_link_symbol gains new fields to allow
symbol names to be given as strtab offsets as well as strings, and a
symidx so that the symbol index can be passed in.  ctf_link_shuffle_syms
loses its callback parameter: the idea now is that linkers call the new
ctf_link_add_linker_symbol for every symbol in .dynsym, feed in all the
strtab entries with ctf_link_add_strtab, and then a call to
ctf_link_shuffle_syms will apply both and arrange to use them to reorder
the CTF symtab at CTF serialization time (which is coming in the next
commit).

Inside libctf we have a new preamble flag CTF_F_DYNSTR which is always
set in v3-format CTF dicts from this commit forwards: CTF dicts without
this flag are associated with .strtab like they used to be, so that old
dicts' external strings don't turn to garbage when loaded by new libctf.
Dicts with this flag are associated with .dynstr and .dynsym instead.
(The flag is not the next in sequence because this commit was written
quite late: the missing flags will be filled in by the next commit.)

Tests forthcoming in a later commit in this series.

bfd/ChangeLog
2020-11-20  Nick Alcock  <nick.alcock@oracle.com>

	* elflink.c (elf_finalize_dynstr): Call examine_strtab after
	dynstr finalization.
	(elf_link_swap_symbols_out): Don't call it here.  Call
	ctf_new_symbol before swap_symbol_out.
	(elf_link_output_extsym): Call ctf_new_dynsym before
	swap_symbol_out.
	(bfd_elf_final_link): Likewise.
	* elf.c (swap_out_syms): Pass in bfd_link_info.  Call
	ctf_new_symbol before swap_symbol_out.
	(_bfd_elf_compute_section_file_positions): Adjust.

binutils/ChangeLog
2020-11-20  Nick Alcock  <nick.alcock@oracle.com>

	* readelf.c (dump_section_as_ctf): Use .dynsym and .dynstr, not
	.symtab and .strtab.

include/ChangeLog
2020-11-20  Nick Alcock  <nick.alcock@oracle.com>

	* bfdlink.h (struct elf_sym_strtab): Replace with...
	(struct elf_internal_sym): ... this.
	(struct bfd_link_callbacks) <examine_strtab>: Take only a
	symstrtab argument.
	<ctf_new_symbol>: New.
	<ctf_new_dynsym>: Likewise.
	* ctf-api.h (struct ctf_link_sym) <st_symidx>: New.
	<st_nameidx>: Likewise.
	<st_nameidx_set>: Likewise.
	(ctf_link_iter_symbol_f): Removed.
	(ctf_link_shuffle_syms): Remove most parameters, just takes a
	ctf_dict_t now.
	(ctf_link_add_linker_symbol): New, split from
	ctf_link_shuffle_syms.
	* ctf.h (CTF_F_DYNSTR): New.
	(CTF_F_MAX): Adjust.

ld/ChangeLog
2020-11-20  Nick Alcock  <nick.alcock@oracle.com>

	* ldelfgen.c (struct ctf_strsym_iter_cb_arg): Rename to...
	(struct ctf_strtab_iter_cb_arg): ... this, changing fields:
	<syms>: Remove.
	<symcount>: Remove.
	<symstrtab>: Rename to...
	<strtab>: ... this.
	(ldelf_ctf_strtab_iter_cb): Adjust.
	(ldelf_ctf_symbols_iter_cb): Remove.
	(ldelf_new_dynsym_for_ctf): New, tell libctf about a single
	symbol.
	(ldelf_examine_strtab_for_ctf): Rename to...
	(ldelf_acquire_strings_for_ctf): ... this, only doing the strtab
	portion and not symbols.
	* ldelfgen.h: Adjust declarations accordingly.
	* ldemul.c (ldemul_examine_strtab_for_ctf): Rename to...
	(ldemul_acquire_strings_for_ctf): ... this.
	(ldemul_new_dynsym_for_ctf): New.
	* ldemul.h: Adjust declarations accordingly.
	* ldlang.c (ldlang_ctf_apply_strsym): Rename to...
	(ldlang_ctf_acquire_strings): ... this.
	(ldlang_ctf_new_dynsym): New.
	(lang_write_ctf): Call ldemul_new_dynsym_for_ctf with NULL to do
	the actual symbol shuffle.
	* ldlang.h (struct elf_strtab_hash): Adjust accordingly.
	* ldmain.c (bfd_link_callbacks): Wire up new/renamed callbacks.

libctf/ChangeLog
2020-11-20  Nick Alcock  <nick.alcock@oracle.com>

	* ctf-link.c (ctf_link_shuffle_syms): Adjust.
	(ctf_link_add_linker_symbol): New, unimplemented stub.
	* libctf.ver: Add it.
	* ctf-create.c (ctf_serialize): Set CTF_F_DYNSTR on newly-serialized
	dicts.
	* ctf-open-bfd.c (ctf_bfdopen_ctfsect): Check for the flag: open the
	symtab/strtab if not present, dynsym/dynstr otherwise.
	* ctf-archive.c (ctf_arc_bufpreamble): New, get the preamble from
	some arbitrary member of a CTF archive.
	* ctf-impl.h (ctf_arc_bufpreamble): Declare it.
2020-11-20 13:34:07 +00:00
..
emulparams Fix compile time warning 2020-11-03 08:56:27 +00:00
emultempl bfd, include, ld, binutils, libctf: CTF should use the dynstr/sym 2020-11-20 13:34:07 +00:00
po Update the Spanish translation for the ld/ subdirectory. 2020-11-16 12:32:06 +00:00
scripttempl MSP430: Fix alignment of __*_array_start symbols in default linker script 2020-08-28 14:01:10 +01:00
testsuite Fix SHF_GNU_RETAIN testsuite fallout 2020-11-20 10:33:28 +00:00
.gitignore
aclocal.m4 binutils, ld: work with --disable-libctf 2020-06-26 15:56:39 +01:00
ChangeLog bfd, include, ld, binutils, libctf: CTF should use the dynstr/sym 2020-11-20 13:34:07 +00:00
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config.in Add a new option to the linker: --error-handling-script=<NAME>. Run the script <NAME> if an undefined symbol or unfound library error is encountered. 2020-10-16 11:37:26 +01:00
configure Add a new option to the linker: --error-handling-script=<NAME>. Run the script <NAME> if an undefined symbol or unfound library error is encountered. 2020-10-16 11:37:26 +01:00
configure.ac Add a new option to the linker: --error-handling-script=<NAME>. Run the script <NAME> if an undefined symbol or unfound library error is encountered. 2020-10-16 11:37:26 +01:00
configure.host
configure.tgt PR26667, Add powerpc64le-*-freebsd* support 2020-10-06 17:09:27 +10:30
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: new options --ctf-variables and --ctf-share-types 2020-07-22 18:03:57 +01:00
ld.texi Support SHF_GNU_RETAIN ELF section flag 2020-11-18 11:51:13 +00:00
ldbuildid.c
ldbuildid.h
ldcref.c
ldctor.c
ldctor.h
ldelf.c elf: Set rel_from_abs to 1 for __ehdr_start 2020-11-13 15:44:47 -08:00
ldelf.h
ldelfgen.c bfd, include, ld, binutils, libctf: CTF should use the dynstr/sym 2020-11-20 13:34:07 +00:00
ldelfgen.h bfd, include, ld, binutils, libctf: CTF should use the dynstr/sym 2020-11-20 13:34:07 +00:00
ldemul.c bfd, include, ld, binutils, libctf: CTF should use the dynstr/sym 2020-11-20 13:34:07 +00:00
ldemul.h bfd, include, ld, binutils, libctf: CTF should use the dynstr/sym 2020-11-20 13:34:07 +00:00
ldexp.c ld: Set non_ir_ref_regular on source for assignment 2020-06-24 03:56:16 -07:00
ldexp.h
ldfile.c Add a new option to the linker: --error-handling-script=<NAME>. Run the script <NAME> if an undefined symbol or unfound library error is encountered. 2020-10-16 11:37:26 +01:00
ldfile.h
ldgram.y
ldint.texi
ldlang.c bfd, include, ld, binutils, libctf: CTF should use the dynstr/sym 2020-11-20 13:34:07 +00:00
ldlang.h bfd, include, ld, binutils, libctf: CTF should use the dynstr/sym 2020-11-20 13:34:07 +00:00
ldlex-wrapper.c
ldlex.h Add a new option to the linker: --error-handling-script=<NAME>. Run the script <NAME> if an undefined symbol or unfound library error is encountered. 2020-10-16 11:37:26 +01:00
ldlex.l Use xmalloc rather than malloc 2020-08-03 10:59:38 +09:30
ldmain.c bfd, include, ld, binutils, libctf: CTF should use the dynstr/sym 2020-11-20 13:34:07 +00:00
ldmain.h Add a new option to the linker: --error-handling-script=<NAME>. Run the script <NAME> if an undefined symbol or unfound library error is encountered. 2020-10-16 11:37:26 +01:00
ldmisc.c LD: Add new %pU vfinfo format for printing linker script name 2020-08-28 14:00:54 +01:00
ldmisc.h
ldver.c
ldver.h
ldwrite.c
ldwrite.h
lexsup.c Extend ld's -Map=<dir> functionality by allowing '%' to be replaced with the output file path. 2020-11-06 14:36:45 +00:00
MAINTAINERS
Makefile.am Fix regexp for development.exp 2020-11-09 12:05:39 +01:00
Makefile.in Fix regexp for development.exp 2020-11-09 12:05:39 +01:00
mri.c
mri.h
NEWS Support SHF_GNU_RETAIN ELF section flag 2020-11-18 11:51:13 +00:00
pe-dll.c Change the default characteristics of DLLs built by the linker to more secure settings. 2020-08-27 12:58:27 +01:00
pe-dll.h
pep-dll.c
pep-dll.h
plugin.c ld: Override the IR definition for non-ELF targets 2020-09-30 05:23:35 -07:00
plugin.h
README
stamp-h.in
sysdep.h
testplug2.c Do without ld ENABLE_PLUGINS 2020-06-21 22:16:10 +09:30
testplug3.c Do without ld ENABLE_PLUGINS 2020-06-21 22:16:10 +09:30
testplug4.c Do without ld ENABLE_PLUGINS 2020-06-21 22:16:10 +09:30
testplug.c Do without ld ENABLE_PLUGINS 2020-06-21 22:16:10 +09:30
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.

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