Commit Graph

69 Commits

Author SHA1 Message Date
Fangrui Song 44361e5b90 [ELF] Add --export-dynamic-symbol-list
This is available in GNU ld 2.35 and can be seen as a shortcut for multiple
--export-dynamic-symbol, or a --dynamic-list variant without the symbolic intention.

In the long term, this option probably should be preferred over --dynamic-list.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D107317
2021-08-03 09:01:03 -07:00
Fangrui Song b06426da76 [ELF] Add -Bsymbolic-non-weak-functions
This option is a subset of -Bsymbolic-functions. It applies to STB_GLOBAL
STT_FUNC definitions.

The address of a vague linkage function (STB_WEAK STT_FUNC, e.g. an inline
function, a template instantiation) seen by a -Bsymbolic-functions linked
shared object may be different from the address seen from outside the shared
object. Such cases are uncommon. (ELF/Mach-O programs may use
`-fvisibility-inlines-hidden` to break such pointer equality.  On Windows,
correct dllexport and dllimport are needed to make pointer equality work.
Windows link.exe enables /OPT:ICF by default so different inline functions may
have the same address.)

```
// a.cc -> a.o -> a.so (-Bsymbolic-functions)
inline void f() {}
void *g() { return (void *)&f; }

// b.cc -> b.o -> exe
// The address is different!
inline void f() {}
```

-Bsymbolic-non-weak-functions is a safer (C++ conforming) subset of
-Bsymbolic-functions, which can make such programs work.

Implementations usually emit a vague linkage definition in a COMDAT group.  We
could detect the group (with more code) but I feel that we should just check
STB_WEAK for simplicity. A weak definition will thus serve as an escape hatch
for rare cases when users want interposition on definitions.

GNU ld feature request: https://sourceware.org/bugzilla/show_bug.cgi?id=27871

Longer write-up: https://maskray.me/blog/2021-05-16-elf-interposition-and-bsymbolic

If Linux distributions migrate to protected non-vague-linkage external linkage
functions by default, the linker option can still be handy because it allows
rapid experiment without recompilation. Protected function addresses currently
have deep issues in GNU ld.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D102570
2021-07-29 14:46:53 -07:00
Fangrui Song 7f0acc4e4f [docs] ld.lld.1: Mention -z nostart-stop-gc 2021-05-21 19:57:51 -07:00
Fangrui Song 4adf7a7604 [ELF] Add -Bno-symbolic
This option will be available in GNU ld 2.27 (https://sourceware.org/bugzilla/show_bug.cgi?id=27834).
This option can cancel previously specified -Bsymbolic and
-Bsymbolic-functions.  This is useful for excluding some links when the
default uses -Bsymbolic-functions.

Reviewed By: jhenderson, peter.smith

Differential Revision: https://reviews.llvm.org/D102383
2021-05-14 09:40:32 -07:00
Ben Dunbobbin 5dd9f44c17 [LLD] Improve --strip-all help text
This is a slight improvement to the help text, as I was slightly
surprised when strip-all did more than remove the symbol table.

Currently, we match gold's help text for strip-all and strip-debug.
I think that the GNU documentation for these options is not particularly
clear. However, I have opted to make only a minor change here and keep
the help text similar to gold's as these are mature options that are
well understood.

ld.bfd (https://sourceware.org/binutils/docs/ld/Options.html) has a
similar implication although it defines strip-debug as a subset of
strip-all. However, felt that noting that strip-all implies strip-debug
is better; because, with the ld.bfd approach you have to read both the
--strip-debug and the --strip-all help text to understand the behaviour
of --strip-all (and the --strip-all help text doesn't indicate that he
--strip-debug help text is related).

Differential Revision: https://reviews.llvm.org/D101890
2021-05-06 12:34:06 +01:00
Fangrui Song 16c30c3c23 [ELF] Change --shuffle-sections=<seed> to --shuffle-sections=<section-glob>=<seed>
`--shuffle-sections=<seed>` applies to all sections.  The new
`--shuffle-sections=<section-glob>=<seed>` makes shuffling selective.  To the
best of my knowledge, the option is only used as debugging, so just drop the
original form.

`--shuffle-sections '.init_array*=-1'` `--shuffle-sections '.fini_array*=-1'`.
reverses static constructors/destructors of the same priority.
Useful to detect some static initialization order fiasco.

`--shuffle-sections '.data*=-1'`
reverses `.data*` sections. Useful to detect unfunded pointer comparison results
of two unrelated objects.

If certain sections have an intrinsic order, the old form cannot be used.

Differential Revision: https://reviews.llvm.org/D98679
2021-03-18 10:18:19 -07:00
Fangrui Song 423cb321df [ELF] Special case --shuffle-sections=-1 to reverse input sections
If the number of sections changes, which is common for re-links after
incremental updates, the section order may change drastically.

Special case -1 to reverse input sections. This is a stable transform.
The section order is more resilient to incremental updates.  Usually the
code issue (e.g. Static Initialization Order Fiasco, assuming pointer
comparison result of two unrelated objects) is due to the relative order
between two problematic input files A and B.  Checking the regular order
and the reversed order is sufficient.

Differential Revision: https://reviews.llvm.org/D98445
2021-03-17 09:32:44 -07:00
Fangrui Song 4bbcd63eea [ELF] Add -z start-stop-gc to let __start_/__stop_ not retain C identifier name sections
For one metadata section usage, each text section references a metadata section.
The metadata sections have a C identifier name to allow the runtime to collect them via `__start_/__stop_` symbols.

Since `__start_`/`__stop_` references are always present from live sections, the
C identifier name sections appear like GC roots, which means they cannot be
discarded by `ld --gc-sections`.

To make such sections GCable, either SHF_LINK_ORDER or a section group is needed.

SHF_LINK_ORDER is not suitable for the references can be inlined into other functions
(See D97430:
Function A (in the section .text.A) references its `__sancov_guard` section.
Function B inlines A (so now .text.B references `__sancov_guard` - this is invalid with the semantics of SHF_LINK_ORDER).

In the linking stage,
if `.text.A` gets discarded, and `__sancov_guard` is retained via the reference from `.text.B`,
the output will be invalid because `__sancov_guard` references the discarded `.text.A`.
LLD errors "sh_link points to discarded section".
)

A section group have size overhead, and is cumbersome when there is just one metadata section.

Add `-z start-stop-gc` to drop the "__start_/__stop_ references retain
non-SHF_LINK_ORDER non-SHF_GROUP C identifier name sections" rule.
We reserve the rights to switch the default in the future.

Reviewed By: phosek, jrtc27

Differential Revision: https://reviews.llvm.org/D96914
2021-02-25 15:46:37 -08:00
Fangrui Song eea34aae2e [ELF] Inspect -EL & -EB for OUTPUT_FORMAT(default, big, little)
Choose big if -EB is specified, little if -EL is specified, or default if neither is specified.
The new behavior matches GNU ld.

Fixes: https://github.com/ClangBuiltLinux/linux/issues/1025

Differential Revision: https://reviews.llvm.org/D96214
2021-02-08 10:34:57 -08:00
Fangrui Song d24b94f070 [ELF] --wrap: retain __wrap_foo if foo is defined in an object/bitcode file
If foo is referenced in any object file, bitcode file or shared object,
`__wrap_foo` should be retained as the redirection target of sym
(f96ff3c0f8).

If the object file defining foo has foo references, we cannot easily distinguish
the case from cases where foo is not referenced (we haven't scanned
relocations). Retain `__wrap_foo` because we choose to wrap sym references
regardless of whether sym is defined to keep non-LTO/LTO/relocatable links' behaviors similar
https://sourceware.org/bugzilla/show_bug.cgi?id=26358 .

If foo is defined in a shared object, `__wrap_foo` can still be omitted
(`wrap-dynamic-undef.s`).

Reviewed By: andrewng

Differential Revision: https://reviews.llvm.org/D95152
2021-01-22 09:20:29 -08:00
Sean Fertile 8f91f38148 [LLD] Search archives for symbol defs to override COMMON symbols.
This patch changes the archive handling to enable the semantics needed
for legacy FORTRAN common blocks and block data. When we have a COMMON
definition of a symbol and are including an archive, LLD will now
search the members for global/weak defintions to override the COMMON
symbol. The previous LLD behavior (where a member would only be included
if it satisifed some other needed symbol definition) can be re-enabled with the
option '-no-fortran-common'.

Differential Revision: https://reviews.llvm.org/D86142
2020-12-07 10:09:19 -05:00
serge-sans-paille 1e70ec10eb [lld] Provide a hook to customize undefined symbols error handling
This is a follow up to https://reviews.llvm.org/D87758, implementing the missing
symbol part, as done by binutils.

Differential Revision: https://reviews.llvm.org/D89687
2020-11-09 13:28:48 +01:00
serge-sans-paille cfc32267e2 Provide a hook to customize missing library error handling
Make it possible for lld users to provide a custom script that would help to
find missing libraries. A possible scenario could be:

    % clang /tmp/a.c -fuse-ld=lld -loauth -Wl,--error-handling-script=/tmp/addLibrary.py
    unable to find library -loauth
    looking for relevant packages to provides that library

        liboauth-0.9.7-4.el7.i686
        liboauth-devel-0.9.7-4.el7.i686
        liboauth-0.9.7-4.el7.x86_64
        liboauth-devel-0.9.7-4.el7.x86_64
        pix-1.6.1-3.el7.x86_64

Where addLibrary would be called with the missing library name as first argument
(in that case addLibrary.py oauth)

Differential Revision: https://reviews.llvm.org/D87758
2020-11-03 11:01:29 +01:00
Fangrui Song 4ce56b8122 [ELF] Add -z dead-reloc-in-nonalloc=<section_glob>=<value>
... to customize the tombstone value we use for an absolute relocation
referencing a discarded symbol. This can be used as a workaround when
some debug processing tool has trouble with current -1 tombstone value
(https://bugs.chromium.org/p/chromium/issues/detail?id=1102223#c11 )

For example, to get the current built-in rules (not considering the .debug_line special case for ICF):

```
-z dead-reloc-in-nonalloc='.debug_*=0xffffffffffffffff'
-z dead-reloc-in-nonalloc=.debug_loc=0xfffffffffffffffe
-z dead-reloc-in-nonalloc=.debug_ranges=0xfffffffffffffffe
```

To get GNU ld (as of binutils 2.35)'s behavior:

```
-z dead-reloc-in-nonalloc='*=0'
-z dead-reloc-in-nonalloc=.debug_ranges=1
```

This option has other use cases. For example, if we want to check
whether a non-SHF_ALLOC section has dead relocations.
With this patch, we can run a regular LLD and run another with a special
-z dead-reloc-in-nonalloc=, then compare their output.

Reviewed By: thakis

Differential Revision: https://reviews.llvm.org/D83264
2020-07-08 10:15:16 -07:00
Fangrui Song 09b81a72ac [ELF] Ignore --no-relax for RISC-V
In GNU ld, --no-relax can disable x86-64 GOTPCRELX relaxation.
It is not useful, so we don't implement it.

For RISC-V, --no-relax disables linker relaxations which have larger
impact.
Linux kernel specifies --no-relax when CONFIG_DYNAMIC_FTRACE is specified
(since http://git.kernel.org/linus/a1d2a6b4cee858a2f27eebce731fbf1dfd72cb4e ).
LLD has not implemented the relaxations, so this option is a no-op.

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D81359
2020-07-07 09:48:13 -07:00
Fangrui Song 751f18e7d4 [ELF] Refine --export-dynamic-symbol semantics to be compatible GNU ld 2.35
GNU ld from binutils 2.35 onwards will likely support
--export-dynamic-symbol but with different semantics.
https://sourceware.org/pipermail/binutils/2020-May/111302.html

Differences:

1. -export-dynamic-symbol is not supported
2. --export-dynamic-symbol takes a glob argument
3. --export-dynamic-symbol can suppress binding the references to the definition within the shared object if (-Bsymbolic or -Bsymbolic-functions)
4. --export-dynamic-symbol does not imply -u

I don't think the first three points can affect any user.
For the fourth point, Not implying -u can lead to some archive members unfetched.
Add -u foo to restore the previous behavior.

Exact semantics:

* -no-pie or -pie: matched non-local defined symbols will be added to the dynamic symbol table.
* -shared: matched non-local STV_DEFAULT symbols will not be bound to definitions within the shared object
  even if they would otherwise be due to -Bsymbolic, -Bsymbolic-functions, or --dynamic-list.

Reviewed By: psmith

Differential Revision: https://reviews.llvm.org/D80487
2020-06-01 11:30:03 -07:00
Fangrui Song 881c5eef98 [ELF] Add -z rel and -z rela
LLD supports both REL and RELA for static relocations, but emits either
of REL and RELA for dynamic relocations. The relocation entry format is
specified by each psABI.

musl ld.so supports both REL and RELA. For such ld.so implementations,
REL (.rel.dyn .rel.plt) has size benefits even if the psABI chooses RELA:
sizeof(Elf64_Rel)=16 < sizeof(Elf64_Rela)=24.

* COPY, GLOB_DAT and J[U]MP_SLOT always have 0 addend. A ld.so
  implementation does not need to read the implicit addend.
  REL is strictly better.
* A RELATIVE has a non-zero addend. Such relocations can be packed
  compactly with the RELR relocation entry format, which is out of scope
  of this patch.
* For other dynamic relocation types (e.g. symbolic relocation R_X86_64_64),
  a ld.so implementation needs to read the implicit addend. REL may have
  minor performance impact, because reading implicit addends forces
  random access reads instead of being able to blast out a bunch of
  writes while chasing the relocation array.

This patch adds -z rel and -z rela to change the relocation entry format
for dynamic relocations. I have tested that a -z rel produced x86-64
executable works with musl ld.so

-z rela may be useful for debugging purposes on processors whose psABIs
specify REL as the canonical format: addends can be easily read by a tool.

Reviewed By: grimar, mcgrathr

Differential Revision: https://reviews.llvm.org/D80496
2020-05-29 14:22:03 -07:00
Russell Gallop 85bb9b71b7 [ELF] Update release notes and man page for LLD time-trace
Differential Revision: https://reviews.llvm.org/D79780
2020-05-15 08:35:58 +01:00
Fangrui Song b912b887d8 [ELF] Add --print-archive-stats=
gold has an option --print-symbol-counts= which prints:

  // For each archive
  archive $archive $members $fetched_members
  // For each object file
  symbols $object $defined_symbols $used_defined_symbols

In most cases, `$defined_symbols = $used_defined_symbols` unless weak
symbols are present. Strangely `$used_defined_symbols` includes symbols defined relative to --gc-sections discarded sections.
The `symbols` lines do not appear to be useful.

`archive` lines are useful: `$fetched_members=0` lines correspond to
unused archives. The information can be used to trim dependencies.

This patch implements --print-archive-stats= which prints the number of
members and the number of fetched members for each archive.

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D78983
2020-04-29 18:04:37 -07:00
Fangrui Song 232578804a [ELF] Add --warn-backrefs-exclude=<glob>
D77522 changed --warn-backrefs to not warn for linking sandwich
problems (-ldef1 -lref -ldef2). This removed lots of false positives.

However, glibc still has some problems. libc.a defines some symbols
which are normally in libm.a and libpthread.a, e.g. __isnanl/raise.

For a linking order `-lm -lpthread -lc`, I have seen:

```
// different resolutions: GNU ld/gold select libc.a(s_isnan.o) as the definition
backward reference detected: __isnanl in libc.a(printf_fp.o) refers to libm.a(m_isnanl.o)

// different resolutions: GNU ld/gold select libc.a(raise.o) as the definition
backward reference detected: raise in libc.a(abort.o) refers to libpthread.a(pt-raise.o)
```

To facilitate deployment of --warn-backrefs, add --warn-backrefs-exclude= so that
certain known issues (which may be impractical to fix) can be whitelisted.

Deliberate choices:

* Not a comma-separated list (`--warn-backrefs-exclude=liba.a,libb.a`).
  -Wl, splits the argument at commas, so we cannot use commas.
  --export-dynamic-symbol is similar.
* Not in the style of `--warn-backrefs='*' --warn-backrefs=-liba.a`.
  We just need exclusion, not inclusion. For easier build system
  integration, we should avoid order dependency. With the current
  scheme, we enable --warn-backrefs, and indivial libraries can add
  --warn-backrefs-exclude=<glob> to their LDFLAGS.

Reviewed By: psmith

Differential Revision: https://reviews.llvm.org/D77512
2020-04-20 07:52:15 -07:00
Fangrui Song eb4663d8c6 [lld][COFF][ELF][WebAssembly] Replace --[no-]threads /threads[:no] with --threads={1,2,...} /threads:{1,2,...}
--no-threads is a name copied from gold.
gold has --no-thread, --thread-count and several other --thread-count-*.

There are needs to customize the number of threads (running several lld
processes concurrently or customizing the number of LTO threads).
Having a single --threads=N is a straightforward replacement of gold's
--no-threads + --thread-count.

--no-threads is used rarely. So just delete --no-threads instead of
keeping it for compatibility for a while.

If --threads= is specified (ELF,wasm; COFF /threads: is similar),
--thinlto-jobs= defaults to --threads=,
otherwise all available hardware threads are used.

There is currently no way to override a --threads={1,2,...}. It is still
a debate whether we should use --threads=all.

Reviewed By: rnk, aganea

Differential Revision: https://reviews.llvm.org/D76885
2020-03-31 08:46:12 -07:00
David Bozier 6e2804ce6b [LLD] Add support for --unique option
Summary:
Places orphan sections into a unique output section. This prevents the merging of orphan sections of the same name.
Matches behaviour of GNU ld --unique. --unique=pattern is not implemented.

Motivated user case shown in the test has 2 local symbols as they would appear if C++ source has been compiled with -ffunction-sections. The merging of these sections in the case of a partial link (-r) may limit the effectiveness of -gc-sections of a subsequent link.

Reviewers: espindola, jhenderson, bd1976llvm, edd, andrewng, JonChesterfield, MaskRay, grimar, ruiu, psmith

Reviewed By: MaskRay, grimar

Subscribers: emaste, arichardson, MaskRay, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D75536
2020-03-10 12:20:21 +00:00
Rafael Ávila de Espíndola d48d339156 [lld][ELF] Add --shuffle-sections=seed to shuffle input sections
Summary:
This option causes lld to shuffle sections by assigning different
priorities in each run.

The use case for this is to introduce randomization in benchmarks. The
idea is inspired by the paper "Producing Wrong Data Without Doing
Anything Obviously Wrong!"
(https://www.inf.usi.ch/faculty/hauswirth/publications/asplos09.pdf). Unlike
the paper, we shuffle individual sections, not just input files.

Doing this in lld is particularly convenient as the --reproduce option
makes it easy to collect all the necessary bits for relinking the
program being benchmarked. Once that it is done, all that is needed is
to add --shuffle-sections=0 to the response file and relink before each
run of the benchmark.

Differential Revision: https://reviews.llvm.org/D74791
2020-02-19 13:44:12 -08:00
Fangrui Song 7cd429f27d [ELF] Add -z force-ibt and -z shstk for Intel Control-flow Enforcement Technology
This patch is a joint work by Rui Ueyama and me based on D58102 by Xiang Zhang.

It adds Intel CET (Control-flow Enforcement Technology) support to lld.
The implementation follows the draft version of psABI which you can
download from https://github.com/hjl-tools/x86-psABI/wiki/X86-psABI.

CET introduces a new restriction on indirect jump instructions so that
you can limit the places to which you can jump to using indirect jumps.

In order to use the feature, you need to compile source files with
-fcf-protection=full.

* IBT is enabled if all input files are compiled with the flag. To force enabling ibt, pass -z force-ibt.
* SHSTK is enabled if all input files are compiled with the flag, or if -z shstk is specified.

IBT-enabled executables/shared objects have two PLT sections, ".plt" and
".plt.sec".  For the details as to why we have two sections, please read
the comments.

Reviewed By: xiangzhangllvm

Differential Revision: https://reviews.llvm.org/D59780
2020-01-13 23:39:28 -08:00
Nico Weber efabe427b2 fix a few typos to cycle the bots 2020-01-09 23:10:15 -05:00
Rui Ueyama 6faf8bdcc4 Update the man page
Add a description about the compression level of the debug info.

Differential Revision: https://reviews.llvm.org/D71385
2019-12-13 15:15:00 +09:00
Fangrui Song 5a3a9e9927 [ELF][AArch64] Rename --force-bti to -z force-bti and --pac-plt to -z pac-plt
Summary:
The original design used --foo but the upstream complained that ELF only
options should be -z foo. See https://sourceware.org/ml/binutils/2019-04/msg00151.html
https://sourceware.org/git/?p=binutils-gdb.git;a=commitdiff;h=8bf6d176b0a442a8091d338d4af971591d19922c
made the rename.

Our --force-bti and --pac-plt implement the same functionality, so it
seems wise to be consistent with GNU ld.

Reviewed By: peter.smith

Subscribers: emaste, arichardson, kristof.beyls, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71327
2019-12-11 09:26:32 -08:00
Michał Górny 2a0fcae3d4 [lld] [ELF] Add '-z nognustack' opt to suppress emitting PT_GNU_STACK
Add a new '-z nognustack' option that suppresses emitting PT_GNU_STACK
segment.  This segment is not supported at all on NetBSD (stack is
always non-executable), and the option is meant to be used to disable
emitting it.

Differential Revision: https://reviews.llvm.org/D56554
2019-10-29 17:54:23 +01:00
Fangrui Song 0264950697 [ELF] Add -z separate-loadable-segments to complement separate-code and noseparate-code
D64906 allows PT_LOAD to have overlapping p_offset ranges. In the
default R RX RW RW layout + -z noseparate-code case, we do not tail pad
segments when transiting to another segment. This can save at most
3*maxPageSize bytes.

a) Before D64906, we tail pad R, RX and the first RW.
b) With -z separate-code, we tail pad R and RX, but not the first RW (RELRO).

In some cases, b) saves one file page. In some cases, b) wastes one
virtual memory page. The waste is a concern on Fuchsia. Because it uses
compressed binaries, it doesn't benefit from the saved file page.

This patch adds -z separate-loadable-segments to restore the behavior before
D64906. It can affect section addresses and can thus be used as a
debugging mechanism (see PR43214 and ld.so partition bug in
crbug.com/998712).

Reviewed By: jakehehrlich, ruiu

Differential Revision: https://reviews.llvm.org/D67481

llvm-svn: 372807
2019-09-25 03:39:31 +00:00
Ed Maste 5289bbe4d4 ld.lld.1: explain long options may use one or two dashes
Obtained from FreeBSD r329003

llvm-svn: 370800
2019-09-03 17:58:30 +00:00
Ed Maste 174e083345 ld.lld.1: stylistic changes suggested by igor
igor is an automated man page "proofreader" from FreeBSD - see
http://www.wonkity.com/~wblock/igor/igor.pdf

No content change.

llvm-svn: 370799
2019-09-03 17:58:24 +00:00
Peter Smith 7d6aa7eb7f [ELF] Mention contents of reproduce archive and add help description.
Building on D60557 mention the name of the linker generated contents of
the reproduce archive, response.txt and version.txt.

Also write a shorter description in the ld.lld --help that is closer to
the documentation.

Differential Revision: https://reviews.llvm.org/D66641

llvm-svn: 369762
2019-08-23 14:41:25 +00:00
Rui Ueyama 72d1089a3a Explain --reproduce option
I think --reproduce is no longer a debug-only option but a useful
option that a common user may want to use. So, this patch updates
the description of the option in the manual page.

Differential Revision: https://reviews.llvm.org/D60557

llvm-svn: 369740
2019-08-23 08:52:55 +00:00
Rui Ueyama 6ef01c3e2b Add a description about multiple linker scripts
Differential Revision: https://reviews.llvm.org/D66630

llvm-svn: 369737
2019-08-23 07:50:09 +00:00
Rui Ueyama 43f4b037d5 Add --undefined-glob which is an --undefined with wildcard pattern match
This patch adds new command line option `--undefined-glob` to lld.
That option is a variant of `--undefined` but accepts wildcard
patterns so that all symbols that match with a given pattern are
handled as if they were given by `-u`.

`-u foo` is to force resolve symbol foo if foo is not a defined symbol
and there's a static archive that contains a definition of symbol foo.

Now, you can specify a wildcard pattern as an argument for `--undefined-glob`.
So, if you want to include all JNI symbols (which start with "Java_"), you
can do that by passing `--undefined-glob "Java_*"` to the linker, for example.

In this patch, I use the same glob pattern matcher as the version script
processor is using, so it does not only support `*` but also `?` and `[...]`.

Differential Revision: https://reviews.llvm.org/D63244

llvm-svn: 363396
2019-06-14 14:00:59 +00:00
Peter Smith e208208a31 [ELF][AArch64] Support for BTI and PAC
Branch Target Identification (BTI) and Pointer Authentication (PAC) are
architecture features introduced in v8.5a and 8.3a respectively. The new
instructions have been added in the hint space so that binaries take
advantage of support where it exists yet still run on older hardware. The
impact of each feature is:

BTI: For executable pages that have been guarded, all indirect branches
must have a destination that is a BTI instruction of the appropriate type.
For the static linker, this means that PLT entries must have a "BTI c" as
the first instruction in the sequence. BTI is an all or nothing
property for a link unit, any indirect branch not landing on a valid
destination will cause a Branch Target Exception.

PAC: The dynamic loader encodes with PACIA the address of the destination
that the PLT entry will load from the .plt.got, placing the result in a
subset of the top-bits that are not valid virtual addresses. The PLT entry
may authenticate these top-bits using the AUTIA instruction before
branching to the destination. Use of PAC in PLT sequences is a contract
between the dynamic loader and the static linker, it is independent of
whether the relocatable objects use PAC.

BTI and PAC are independent features that can be combined. So we can have
several combinations of PLT:
- Standard with no BTI or PAC
- BTI PLT with "BTI c" as first instruction.
- PAC PLT with "AUTIA1716" before the indirect branch to X17.
- BTIPAC PLT with "BTI c" as first instruction and "AUTIA1716" before the
  first indirect branch to X17.
    
The use of BTI and PAC in relocatable object files are encoded by feature
bits in the .note.gnu.property section in a similar way to Intel CET. There
is one AArch64 specific program property GNU_PROPERTY_AARCH64_FEATURE_1_AND
and two target feature bits defined:
- GNU_PROPERTY_AARCH64_FEATURE_1_BTI
-- All executable sections are compatible with BTI.
- GNU_PROPERTY_AARCH64_FEATURE_1_PAC
-- All executable sections have return address signing enabled.

Due to the properties of FEATURE_1_AND the static linker can tell when all
input relocatable objects have the BTI and PAC feature bits set. The static
linker uses this to enable the appropriate PLT sequence.
Neither -> standard PLT
GNU_PROPERTY_AARCH64_FEATURE_1_BTI -> BTI PLT
GNU_PROPERTY_AARCH64_FEATURE_1_PAC -> PAC PLT
Both properties -> BTIPAC PLT

In addition to the .note.gnu.properties there are two new command line
options:
--force-bti : Act as if all relocatable inputs had
GNU_PROPERTY_AARCH64_FEATURE_1_BTI and warn for every relocatable object
that does not.
--pac-plt : Act as if all relocatable inputs had
GNU_PROPERTY_AARCH64_FEATURE_1_PAC. As PAC is a contract between the loader
and static linker no warning is given if it is not present in an input.

Two processor specific dynamic tags are used to communicate that a non
standard PLT sequence is being used.
DTI_AARCH64_BTI_PLT and DTI_AARCH64_BTI_PAC.

Differential Revision: https://reviews.llvm.org/D62609

llvm-svn: 362793
2019-06-07 13:00:17 +00:00
Rui Ueyama 471f11805f Add --sort-common to the man page.
Differential Revision: https://reviews.llvm.org/D62799

llvm-svn: 362354
2019-06-03 05:11:44 +00:00
Fangrui Song b372259ace [docs] Fix troff macro (.F1 -> .Fl) in ld.lld.1
llvm-svn: 361345
2019-05-22 02:15:25 +00:00
Fangrui Song e041d15f5e [LLD][ELF] Add the -z ifunc-noplt option
Patch by Mark Johnston!

Summary:
When the option is configured, ifunc calls do not go through the PLT;
rather, they appear as regular function calls with relocations
referencing the ifunc symbol, and the resolver is invoked when
applying the relocation.  This is intended for use in freestanding
environments where text relocations are permissible and is incompatible
with the -z text option.  The option is motivated by ifunc usage in the
FreeBSD kernel, where ifuncs are used to elide CPU feature flag bit
checks in hot paths.  Instead of replacing the cost of a branch with that
of an indirect function call, the -z ifunc-noplt option is used to ensure
that ifunc calls carry no hidden overhead relative to normal function
calls.

Test Plan:
I added a couple of regression tests and tested the FreeBSD kernel
build using the latest lld sources.

To demonstrate the effects of the change, I used a micro-benchmark
which results in frequent invocations of a FreeBSD kernel ifunc.  The
benchmark was run with and without IBRS enabled, and with and without
-zifunc-noplt configured.  The observed speedup is small and consistent,
and is significantly larger with IBRS enabled:

https://people.freebsd.org/~markj/ifunc-noplt/noibrs.txt
https://people.freebsd.org/~markj/ifunc-noplt/ibrs.txt

Reviewed By: ruiu, MaskRay

Differential Revision: https://reviews.llvm.org/D61613

llvm-svn: 360685
2019-05-14 15:25:21 +00:00
Peter Smith 4e21c770ec [ELF] Full support for -n (--nmagic) and -N (--omagic) via common page
The -n (--nmagic) disables page alignment, and acts as a -Bstatic
The -N (--omagic) does what -n does but also marks the executable segment as
writeable. As page alignment is disabled headers are not allocated unless
explicit in the linker script.

To disable page alignment in LLD we choose to set the page sizes to 1 so
that any alignment based on the page size does nothing. To set the
Target->PageSize to 1 we implement -z common-page-size, which has the side
effect of allowing the user to set the value as well.

Setting the page alignments to 1 does mean that any use of
CONSTANT(MAXPAGESIZE) or CONSTANT(COMMONPAGESIZE) in a linker script will
return 1, unlike in ld.bfd. However given that -n and -N disable paging
these probably shouldn't be used in a linker script where -n or -N is in
use.

Differential Revision: https://reviews.llvm.org/D61688

llvm-svn: 360593
2019-05-13 16:01:26 +00:00
Francis Visoiu Mistrih dd42236c6c Reland "[Remarks] Add -foptimization-record-passes to filter remark emission"
Currently we have -Rpass for filtering the remarks that are displayed as
diagnostics, but when using -fsave-optimization-record, there is no way
to filter the remarks while generating them.

This adds support for filtering remarks by passes using a regex.
Ex: `clang -fsave-optimization-record -foptimization-record-passes=inline`

will only emit the remarks coming from the pass `inline`.

This adds:

* `-fsave-optimization-record` to the driver
* `-opt-record-passes` to cc1
* `-lto-pass-remarks-filter` to the LTOCodeGenerator
* `--opt-remarks-passes` to lld
* `-pass-remarks-filter` to llc, opt, llvm-lto, llvm-lto2
* `-opt-remarks-passes` to gold-plugin

Differential Revision: https://reviews.llvm.org/D59268

Original llvm-svn: 355964

llvm-svn: 355984
2019-03-12 21:22:27 +00:00
Francis Visoiu Mistrih 1d6c47ad2b Revert "[Remarks] Add -foptimization-record-passes to filter remark emission"
This reverts commit 20fff32b7d.

llvm-svn: 355976
2019-03-12 20:54:18 +00:00
Francis Visoiu Mistrih 20fff32b7d [Remarks] Add -foptimization-record-passes to filter remark emission
Currently we have -Rpass for filtering the remarks that are displayed as
diagnostics, but when using -fsave-optimization-record, there is no way
to filter the remarks while generating them.

This adds support for filtering remarks by passes using a regex.
Ex: `clang -fsave-optimization-record -foptimization-record-passes=inline`

will only emit the remarks coming from the pass `inline`.

This adds:

* `-fsave-optimization-record` to the driver
* `-opt-record-passes` to cc1
* `-lto-pass-remarks-filter` to the LTOCodeGenerator
* `--opt-remarks-passes` to lld
* `-pass-remarks-filter` to llc, opt, llvm-lto, llvm-lto2
* `-opt-remarks-passes` to gold-plugin

Differential Revision: https://reviews.llvm.org/D59268

llvm-svn: 355964
2019-03-12 20:28:50 +00:00
Fangrui Song 7507208a9a [ELF] Explain some options in ld.lld.1
Reviewers: ruiu, grimar

Reviewed By: ruiu

Subscribers: srhines, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58669

llvm-svn: 355173
2019-03-01 04:49:42 +00:00
Fangrui Song ae0294375f [ELF] Default to --no-allow-shlib-undefined for executables
Summary:
This follows the ld.bfd/gold behavior.

The error check is useful as it captures a common type of ld.so undefined symbol errors as link-time errors:

    // a.cc => a.so (not linked with -z defs)
    void f(); // f is undefined
    void g() { f(); }

    // b.cc => executable with a DT_NEEDED entry on a.so
    void g();
    int main() { g(); }

    // ld.so errors when g() is executed (lazy binding) or when the program is started (-z now)
    // symbol lookup error: ... undefined symbol: f

Reviewers: ruiu, grimar, pcc, espindola

Reviewed By: ruiu

Subscribers: llvm-commits, emaste, arichardson

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D57569

llvm-svn: 352943
2019-02-02 00:34:28 +00:00
Chandler Carruth 2946cd7010 Update the file headers across all of the LLVM projects in the monorepo
to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

llvm-svn: 351636
2019-01-19 08:50:56 +00:00
Peter Smith 13d134684f [ELF] Implement option to force PIC compatible Thunks
By default LLD will generate position independent Thunks when the --pie or
--shared option is used. Reference to absolute addresses is permitted in
other cases. For some embedded systems position independent thunks are
needed for code that executes before the MMU has been set up. The option
--pic-veneer is used by ld.bfd to force position independent thunks.
    
The patch adds --pic-veneer as the option is needed for the Linux kernel
on Arm.
    
fixes pr39886
    
Differential Revision: https://reviews.llvm.org/D55505

llvm-svn: 351326
2019-01-16 12:09:13 +00:00
George Rimar a1b3ddbfec [ELF] - Implement -z nodefaultlib
This is https://bugs.llvm.org//show_bug.cgi?id=38978

Spec says that:
"Objects may be built with the -z nodefaultlib option to
suppress any search of the default locations at runtime.
Use of this option implies that all the dependencies of an
object can be located using its runpaths.
Without this option, which is the most common case, no
matter how you augment the runtime linker's library
search path, its last element is always /usr/lib for 32-bit
objects and /usr/lib/64 for 64-bit objects."

The patch implements this option.

Differential revision: https://reviews.llvm.org/D54577

llvm-svn: 347647
2018-11-27 09:48:17 +00:00
George Rimar 5f8fc76b4e [LLD][ELF] - Fix mistype. NFC.
llvm-svn: 347485
2018-11-23 07:59:28 +00:00
Ali Tamur 63830b2794 Introduce a flag to warn when ifunc symbols are used with text relocations.
Summary:
This patch adds a new flag, --warn-ifunc-textrel, to work around a glibc bug. When a code with ifunc symbols is used to produce an object file with text relocations, lld always succeeds. However, if that object file is linked using an old version of glibc, the resultant binary just crashes with segmentation fault when it is run (The bug is going to be corrected as of glibc 2.19).

Since there is no way to tell beforehand what library the object file will be linked against in the future, there does not seem to be a fool-proof way for lld to give an error only in cases where the binary will crash. So, with this change (dated 2018-09-25), lld starts to give a warning, contingent on a new command line flag that does not have a gnu counter part. The default value for --warn-ifunc-textrel is false, so lld behaviour will not change unless the user explicitly asks lld to give a warning. Users that link with a glibc library with version 2.19 or newer, or does not use ifunc symbols, or does not generate object files with text relocations do not need to take any action. Other users may consider to start passing warn-ifunc-textrel to lld to get early warnings.

Reviewers: ruiu, espindola

Reviewed By: ruiu

Subscribers: grimar, MaskRay, markj, emaste, arichardson, llvm-commits

Differential Revision: https://reviews.llvm.org/D52430

llvm-svn: 343628
2018-10-02 20:30:22 +00:00