Commit Graph

6096 Commits

Author SHA1 Message Date
Fangrui Song 07837b8f49 [ELF] Use namespace qualifiers (lld:: or elf::) instead of `namespace lld { namespace elf {`
Similar to D74882. This reverts much code from commit
bd8cfe65f5 (D68323) and fixes some
problems before D68323.

Sorry for the churn but D68323 was a mistake. Namespace qualifiers avoid
bugs where the definition does not match the declaration from the
header. See
https://llvm.org/docs/CodingStandards.html#use-namespace-qualifiers-to-implement-previously-declared-functions (D74515)

Differential Revision: https://reviews.llvm.org/D79982
2020-05-15 08:49:53 -07:00
Peter Smith 0ae7990b60 [ELF][ARM] Support /DISCARD/ of subset of .ARM.exidx sections
Both the .ARM.exidx and .eh_frame sections have a custom SyntheticSection
that acts as a container for the InputSections. The InputSections are added
to the SyntheticSection prior to /DISCARD/ which limits the affect a
/DISCARD/ can have to the whole SyntheticSection. In the majority of cases
this is sufficient as it is not common to discard subsets of the
InputSections. The Linux kernel has one of these scripts which has something
like:
/DISCARD/ : { *(.ARM.exidx.exit.text) *(.ARM.extab.exit.text) ... }
The .ARM.exidx.exit.text are not discarded because the InputSection has been
transferred to the Synthetic Section. The *(.ARM.extab.exit.text) sections
have not so they are discarded. When we come to write out the .ARM.exidx
sections the dangling references from .ARM.exidx.exit.text to
.ARM.extab.exit.text currently cause relocation out of range errors, but
could as easily cause a fatal error message if we check for dangling
references at relocation time.

This patch attempts to respect the /DISCARD/ command by running it on the
.ARM.exidx InputSections stored in the SyntheticSection.

The .eh_frame is in theory affected by this problem, but I don't think that
there is a dangling reference problem that can happen with these sections.

Fixes remaining part of pr44824

Differential Revision: https://reviews.llvm.org/D79687
2020-05-11 14:27:13 +01:00
Wei Mi 538208f6c0 [lld] Add a new output section ".text.unknown" for funtions with unknown hotness
For sampleFDO, because the optimized build uses profile generated from previous
release, often we couldn't tell a function without profile was truely cold or
just newly created so we had to treat them conservatively and put them in .text
section instead of .text.unlikely. The result was when we persue the best
performance by locking .text.hot and .text in memory, we wasted a lot of memory
to keep cold functions inside. This problem has been largely solved for regular
sampleFDO using profile-symbol-list (https://reviews.llvm.org/D66374), but for
the case when we use partial profile, we still waste a lot of memory because
of it.

In https://reviews.llvm.org/D62540, we propose to save functions with unknown
hotness information in a special section called ".text.unknown", so that
compiler will treat those functions as luck-warm, but runtime can choose not
to mlock the special section in memory or use other strategy to save memory.
That will solve most of the memory problem even if we use a partial profile.

The patch adds the support in lld for the special section.For sampleFDO,
because the optimized build uses profile generated from previous release,
often we couldn't tell a function without profile was truely cold or just
newly created so we had to treat them conservatively and put them in .text
section instead of .text.unlikely. The result was when we persue the best
performance by locking .text.hot and .text in memory, we wasted a lot of
memory to keep cold functions inside. This problem has been largely solved
for regular sampleFDO using profile-symbol-list
(https://reviews.llvm.org/D66374), but for the case when we use partial
profile, we still waste a lot of memory because of it.

In https://reviews.llvm.org/D62540, we propose to save functions with unknown
hotness information in a special section called ".text.unknown", so that
compiler will treat those functions as luck-warm, but runtime can choose not
to mlock the special section in memory or use other strategy to save memory.
That will solve most of the memory problem even if we use a partial profile.

The patch adds the support in lld for the special section.

Differential Revision: https://reviews.llvm.org/D79590
2020-05-08 11:14:48 -07:00
Fangrui Song e20a215992 [ELF] Add convenience TableGen classes to enforce two dashes for options not supported by GNU ld
Announced on https://lists.llvm.org/pipermail/llvm-dev/2020-May/141416.html

For many options, we have to support either one or two dash to be
compatible with GNU ld. For newer and lld specific options, we can enforce strict double dashes.

Affected options:

* --thinlto-*
* --lto-*
* --shuffle-sections=

This patch does not change `-plugin-opt=*` because clang driver passes
`-plugin-opt=*` and I don't intend to cause churn.

In 2000, GNU ld tried something similar with --omagic
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=e4897a3288f37d5f69e8acd256a6e83e607fe8d8

Reviewed By: tejohnson, psmith

Differential Revision: https://reviews.llvm.org/D79371
2020-05-08 07:37:06 -07:00
Reid Kleckner 932f0276ea [Support] Move LLD's parallel algorithm wrappers to support
Essentially takes the lld/Common/Threads.h wrappers and moves them to
the llvm/Support/Paralle.h algorithm header.

The changes are:
- Remove policy parameter, since all clients use `par`.
- Rename the methods to `parallelSort` etc to match LLVM style, since
  they are no longer C++17 pstl compatible.
- Move algorithms from llvm::parallel:: to llvm::, since they have
  "parallel" in the name and are no longer overloads of the regular
  algorithms.
- Add range overloads
- Use the sequential algorithm directly when 1 thread is requested
  (skips task grouping)
- Fix the index type of parallelForEachN to size_t. Nobody in LLVM was
  using any other parameter, and it made overload resolution hard for
  for_each_n(par, 0, foo.size(), ...) because 0 is int, not size_t.

Remove Threads.h and update LLD for that.

This is a prerequisite for parallel public symbol processing in the PDB
library, which is in LLVM.

Reviewed By: MaskRay, aganea

Differential Revision: https://reviews.llvm.org/D79390
2020-05-05 15:21:05 -07:00
Sid Manning 0e6536fd97 [Hexagon] Add R_HEX_GD_PLT_B22/32_PCREL relocations
Extended versions of GD_PLT_B22_PCREL. These surface when -mlong-calls
is used.

Differential Revision: https://reviews.llvm.org/D79191
2020-05-05 11:47:51 -05:00
Peter Smith 48aebfc908 [ELF][ARM] Do not create .ARM.exidx sections for out of range inputs
A linker will create .ARM.exidx sections for InputSections that don't
have them. This can cause a relocation out of range error If the
InputSection happens to be extremely far away from the other sections.
This is often the case for the vector table on older ARM CPUs as the only
two places that the table can be placed is 0 or 0xffff0000. We fix this
by removing InputSections that need a linker generated .ARM.exidx
section if that would cause an error.

Differential Revision: https://reviews.llvm.org/D79289
2020-05-05 09:59:45 +01:00
Zakk Chen ad5fad0ac5 [LTO] Suppress emission of empty combined module by default
Summary:
That unless the user requested an output object (--lto-obj-path), the an
unused empty combined module is not emitted.

This changed is helpful for some target (ex. RISCV-V) which encoded the
ABI info in IR module flags (target-abi). Empty unused module has no ABI
info so the linker would get the linking error during merging
incompatible ABIs.

Reviewers: tejohnson, espindola, MaskRay

Subscribers: emaste, inglorion, arichardson, hiraditya, simoncook, MaskRay, steven_wu, dexonsmith, PkmX, dang, lenary, s.egerton, luismarques, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78988
2020-05-04 18:31:09 -07:00
Fangrui Song c49f83b6e9 [ELF] Don't advance sh_offset for an empty section whose PT_LOAD is removed (due to p_memsz=0)
removeEmptyPTLoad() removes empty (p_memsz=0) PT_LOAD segments.  In
assignFileOffsets(), setFileOffset() unnecessarily advances file offsets
for containing empty sections.

This is exposed by arm Linux kernel's multi_v5_defconfig
(see https://bugs.llvm.org/show_bug.cgi?id=45632)

```
ld.lld (max-page-size=65536):
  [34] .init.data        PROGBITS        c0c24000 c34000 0128ac 00  WA  0   0 4096
  [35] .text_itcm        PROGBITS        fffe0000 c50000 000000 00  WA  0   0  1
  [36] .data_dtcm        PROGBITS        fffe8000 c58000 000000 00  WA  0   0  1
  [37] .data             PROGBITS        c0c38000 c58000 0647a0 00  WA  0   0 32

arm-linux-gnueabi-ld (max-page-size=65536):
  [23] .init.data        PROGBITS        c0c12000 c22000 0128ac 00  WA  0   0 4096
  [24] .text_itcm        PROGBITS        fffe0000 ca2558 000000 00   W  0   0  1
  [25] .data_dtcm        PROGBITS        fffe8000 ca2558 000000 00   W  0   0  1
  [26] .data             PROGBITS        c0c26000 c36000 0647a0 00  WA  0   0 32
```

This patch clears OutputSection::ptLoad if ptLoad is removed by
removeEmptyPTLoad(). Conceptually this removes "dangling" references.

Reviewed By: psmith

Differential Revision: https://reviews.llvm.org/D79254
2020-05-04 08:07:34 -07:00
Peter Smith 3834385f27 [ELF] Move SHF_LINK_ORDER till OutputSection addresses are known
Sections with the SHF_LINK_ORDER flag must be ordered in the same relative
order as the Sections they have a link to. When using a linker script an
arbitrary expression may be used for the virtual address of the
OutputSection. In some cases the virtual address does not monotonically
increase as the OutputSection index increases, so if we base the ordering
of the SHF_LINK_ORDER sections on the index then we can get the order
wrong. We fix this by moving SHF_LINK_ORDER resolution till after we have
created OutputSection virtual addresses.

Differential Revision: https://reviews.llvm.org/D79286
2020-05-04 14:25:25 +01:00
Fangrui Song b257d3c8a8 [ELF][PPC64] Suppress toc-indirect to toc-relative relaxation if R_PPC64_TOC16_LO is seen
The current implementation assumes that R_PPC64_TOC16_HA is always followed
by R_PPC64_TOC16_LO_DS. This can break with R_PPC64_TOC16_LO:

  // Load the address of the TOC entry, instead of the value stored at that address
  addis 3, 2, .LC0@tloc@ha  # R_PPC64_TOC16_HA
  addi  3, 3, .LC0@tloc@l   # R_PPC64_TOC16_LO
  blr

which is used by boringssl's util/fipstools/delocate/delocate.go
https://github.com/google/boringssl/blob/master/crypto/fipsmodule/FIPS.md has some documentation.
In short, this tool converts an assembly file to avoid any potential relocations.
The distance to an input .toc is not a constant after linking, so it cannot use an `addis;ld` pair.
Instead, it jumps to a stub which loads the TOC entry address with `addis;addi`.

This patch checks the presence of R_PPC64_TOC16_LO and suppresses
toc-indirect to toc-relative relaxation if R_PPC64_TOC16_LO is seen.
This approach is conservative and loses some relaxation opportunities but is easy to implement.

  addis 3, 2, .LC0@toc@ha  # no relaxation
  addi  3, 3, .LC0@toc@l   # no relaxation
  li    9, 0
  addis 4, 2, .LC0@toc@ha  # can relax but suppressed
  ld    4, .LC0@toc@l(4)   # can relax but suppressed

Also note that interleaved R_PPC64_TOC16_HA and R_PPC64_TOC16_LO_DS is
possible and this patch accounts for that.

  addis 3, 2, .LC1@toc@ha  # can relax
  addis 4, 2, .LC2@toc@ha  # can relax
  ld    3, .LC1@toc@l(3)   # can relax
  ld    4, .LC2@toc@l(4)   # can relax

Reviewed By: #powerpc, sfertile

Differential Revision: https://reviews.llvm.org/D78431
2020-04-30 09:16:51 -07:00
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 e96d7b5e9e [ELF] Add --rosegment to complement --no-rosegment
This option can cancel --no-rosegment and it just seems right to have
a corresponding positive option for a --no-* negative option.

Anecdotally, gold had --rosegment but did not have --no-rosegment.
I added --no-rosegment (https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=9a6c68caa9543e09b064b7ac7c2b658f277bc19c) for binutils>=2.35
2020-04-29 18:00:00 -07:00
Fangrui Song 1ccde53342 [ELF] --gdb-index: support .debug_loclists
--gdb-index currently crashes when reading a translation unit with
DWARF v5 .debug_loclists . Call stack:

```
SyntheticSections.cpp GdbIndexSection::create
SyntheticSections.cpp readAddressAreas
DWARFUnit.cpp DWARFUnit::tryExtractDIEsIfNeeded
DWARFListTable.cpp DWARFListTableHeader::extract
...
DWARFDataExtractor.cpp DWARFDataExtractor::getRelocatedValue
lld/ELF/DWARF.cpp LLDDwarfObj<ELFT>::find (sec.sec is nullptr)
...

```

This patch adds support for .debug_loclists to make `DWARFUnit::tryExtractDIEsIfNeeded` happy.
Building --gdb-index does not need .debug_loclists

Reviewed By: dblaikie, grimar

Differential Revision: https://reviews.llvm.org/D79061
2020-04-29 15:04:13 -07:00
Sean Fertile f9106e85c4 Revert "[ELF][PPC64] Don't perform toc-indirect to toc-relative relax... "
This reverts commit 03ffe58605.

Full tile of reverted commit is:
[ELF][PPC64] Don't perform toc-indirect to toc-relative relaxation for
R_PPC64_TOC16_HA not followed by R_PPC64_TOC16_LO_DS

Breaks the multistage lld PowerPC buildbot.
2020-04-29 10:30:35 -04:00
Fangrui Song 03ffe58605 [ELF][PPC64] Don't perform toc-indirect to toc-relative relaxation for R_PPC64_TOC16_HA not followed by R_PPC64_TOC16_LO_DS
The current implementation assumes that R_PPC64_TOC16_HA is always followed
by R_PPC64_TOC16_LO_DS. This can break with:

// Load the address of the TOC entry, instead of the value stored at that address
  addis 3, 2, .LC0@tloc@ha  # R_PPC64_TOC16_HA
  addi  3, 3, .LC0@tloc@l   # R_PPC64_TOC16_LO
  blr

which is used by boringssl's util/fipstools/delocate/delocate.go
https://github.com/google/boringssl/blob/master/crypto/fipsmodule/FIPS.md has some documentation.
In short, this tool converts an assembly file to avoid any potential relocations.
The distance to an input .toc is not a constant after linking, so the assembly cannot use an `addis;ld` pair.
Instead, delocate changes the code to jump to a stub (`addis;addi`) which loads the TOC entry address.

Reviewed By: sfertile

Differential Revision: https://reviews.llvm.org/D78431
2020-04-28 12:13:27 -07:00
Fangrui Song d9786b566b [ELF] Clear lazyObjFiles in lld:🧝:link after D46034 2020-04-28 09:54:20 -07:00
Igor Kudrin 9f65f5acca [LLD][ELF] Eliminate symbols of merged .ARM.exidx sections.
GNU tools generate mapping symbols "$d" for .ARM.exidx sections. The
symbols are added to the symbol table much earlier than the merging
takes place, and after that, they become dangling. Before the patch,
LLD output those symbols as SHN_ABS with the value of 0. The patch
removes such symbols from the symbol table.

Differential Revision: https://reviews.llvm.org/D78820
2020-04-28 18:58:40 +07:00
Hongtao Yu 964ef8eecc [lld] Support --lto-emit-asm and --plugin-opt=emit-asm
Summary: The switch --plugin-opt=emit-asm can be used with the gold linker to dump the final assembly code generated by LTO in a user-friendly way. Unfortunately it doesn't work with lld. I'm hooking it up with lld. With that switch, lld emits assembly code into the output file (specified by -o) and if there are multiple input files, each of their assembly code will be emitted into a separate file named by suffixing the output file name with a unique number, respectively. The linking then stops after generating those assembly files.

Reviewers: espindola, wenlei, tejohnson, MaskRay, grimar

Reviewed By: tejohnson, MaskRay, grimar

Subscribers: pcc, emaste, inglorion, arichardson, hiraditya, MaskRay, steven_wu, dexonsmith, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77231
2020-04-27 11:00:46 -07:00
Igor Kudrin 66e4eb9c1b [LLD][ELF] Implement --discard-* for cases when -r or --emit-relocs are used.
When discarding local symbols with --discard-all or --discard-locals,
the ones which are used in relocations should be preserved. LLD used
the simplest approach and just ignored those switches when -r or
--emit-relocs was specified.

The patch implements handling the --discard-* switches for the cases
when relocations are kept by identifying used local symbols and allowing
removing only unused ones. This makes the behavior of LLD compatible
with GNU linkers.

Differential Revision: https://reviews.llvm.org/D77807
2020-04-25 18:59:41 +07:00
Peter Smith 3b1622d63a [LLD][ELF][ARM] recommit Fix ARM Exidx order for non monotonic section order
Fixed error detected by msan. The size field of the .ARM.exidx synthetic
section needs to be initialized to at least estimation level before
calling assignAddresses as that will use the size field.

This was previously reverted in 1ca16fc4f5.

Differential Revision: https://reviews.llvm.org/D78422
2020-04-24 13:47:28 +01:00
Peter Smith 1ca16fc4f5 Revert "[LLD][ELF][ARM] Fix ARM Exidx order for non monotonic section order"
This reverts commit f969c2aa65.

There are some msan buildbot failures sanitzer-x86_64-linux-fast that
I need to investigate.

Differential Revision: https://reviews.llvm.org/D78422
2020-04-23 16:58:50 +01:00
Peter Smith f969c2aa65 [LLD][ELF][ARM] Fix ARM Exidx order for non monotonic section order
The contents of the .ARM.exidx section must be ordered by SHF_LINK_ORDER
rules. We don't need to know the precise address for this order, but we
do need to know the relative order of sections. We have been using the
sectionIndex for this purpose, this works when the OutputSection order
has a monotonically increasing virtual address, but it is possible to
write a linker script with non-monotonically increasing virtual address.
For these cases we need to evaluate the base address of the OutputSection
so that we can order the .ARM.exidx sections properly.

This change moves the finalisation of .ARM.exidx till after the first
call to AssignAddresses. This permits us to sort on virtual address which
is linker script safe. It also permits a fix for part of pr44824 where
we generate .ARM.exidx section for the vector table when that table is so
far away it is out of range of the .ARM.exidx section. This fix will come
in a follow up patch.

Differential Revision: https://reviews.llvm.org/D78422
2020-04-23 15:46:44 +01:00
Fangrui Song c384ca3c6a [ELF] For relative paths in INPUT() and GROUP(), search the directory of the current linker script before searching other paths
For a relative path in INPUT() or GROUP(), this patch changes the search order by adding the directory of the current linker script.
The new search order (consistent with GNU ld >= 2.35 regarding the new test `test/ELF/input-relative.s`):

1. the directory of the current linker script (GNU ld from Binutils 2.35 onwards; https://sourceware.org/bugzilla/show_bug.cgi?id=25806)
2. the current working directory
3. library paths (-L)

This behavior makes it convenient to replace a .so or .a with a linker script with additional input. For example, glibc

```
% cat /usr/lib/x86_64-linux-gnu/libm.a
/* GNU ld script
*/
OUTPUT_FORMAT(elf64-x86-64)
GROUP ( /usr/lib/x86_64-linux-gnu/libm-2.29.a /usr/lib/x86_64-linux-gnu/libmvec.a )
```

could be simplified as `GROUP(libm-2.29.a libmvec.a)`.

Another example is to make libc++.a a linker script:
```
INPUT(libc++.a.1 libc++abi.a)
```

Note, -l is not affected.

Reviewed By: psmith

Differential Revision: https://reviews.llvm.org/D77779
2020-04-22 12:34:20 -07:00
Fangrui Song 01d2a01e79 [ELF] Fix a null pointer dereference when relocating a Local-Exec TLS relocation for a lazy symbol
If there is no SHF_TLS section, there will be no PT_TLS and Out::tlsPhdr may be a nullptr.
If the symbol referenced by an R_TLS is lazy, we should treat the symbol as undefined.

Also reorganize tls-in-archive.s and tls-weak-undef.s . They do not test what they intended to test.
2020-04-21 15:39:31 -07:00
Fangrui Song 497c76e96d [ELF] Keep local symbols when both --emit-relocs and --discard-all are specified
This fixes a bug as exposed by D77807.

Add tests for {--emit-relocs,-r} x {--discard-locals,--discard-all}. They add coverage for previously undertested cases:

* STT_SECTION associated to GCed sections (`gc`)
* STT_SECTION associated to retained sections (`text`)
* STT_SECTION associated to non-SHF_ALLOC sections (`.comment`)
* STB_LOCAL in GCed sections (`unused_gc`)

Reviewed By: grimar, ikudrin

Differential Revision: https://reviews.llvm.org/D78389
2020-04-21 08:28:12 -07:00
Fangrui Song 58207d6fe1 [ELF] Fix "TLS attribute mismatch" false positives for STT_NOTYPE undefined symbols
D13550 added the diagnostic to address/work around a crash.
The rule was refined by D19836 (test/ELF/tls-archive.s) to exclude Lazy symbols.

https://bugs.llvm.org/show_bug.cgi?id=45598 reported another case where the current logic has a false positive:

Bitcode does not record undefined module-level inline assembly symbols
(`IRSymtab.cpp:Builder::addSymbol`). Such an undefined symbol does not
have the FB_tls bit and lld will not consider it STT_TLS. When the symbol is
later replaced by a STT_TLS Defined, lld will error "TLS attribute mismatch".

This patch fixes this false positive by allowing a STT_NOTYPE undefined
symbol to be replaced by a STT_TLS.

Considered alternative:

Moving the diagnostics to scanRelocs() can improve the diagnostics (PR36049)
but that requires a fair amount of refactoring. We will need more
RelExpr members. It requires more thoughts whether it is worthwhile.

See `test/ELF/tls-mismatch.s` for behavior differences. We will fail to
diagnose a likely runtime bug (STT_NOTYPE non-TLS relocation referencing
a TLS definition). This is probably acceptable because compiler
generated code sets symbol types properly.

Reviewed By: grimar, psmith

Differential Revision: https://reviews.llvm.org/D78438
2020-04-21 07:56:35 -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
Tobias Hieta 87383e408d [ELF][ARM] Increase default max-page-size from 4096 to 6536
See http://lists.llvm.org/pipermail/llvm-dev/2020-April/140549.html

For the record, GNU ld changed to 64k max page size in 2014
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=7572ca8989ead4c3425a1500bc241eaaeffa2c89
"[RFC] ld/ARM: Increase maximum page size to 64kB"

Android driver forced 4k page size in AArch64 (D55029) and ARM (D77746).

A binary linked with max-page-size=4096 does not run on a system with a
higher page size configured. There are some systems out there that do
this and it leads to the binary getting `Killed!` by the kernel.

In the non-linker-script cases, when linked with -z noseparate-code
(default), the max-page-size increase should not cause any size
difference. There may be some VMA usage differences, though.

Reviewed By: psmith, MaskRay

Differential Revision: https://reviews.llvm.org/D77330
2020-04-18 08:19:45 -07:00
LemonBoy aff950e95d [ELF] Support a few more SPARCv9 relocations
Implemented a bunch of relocations found in binaries with medium/large code model and the Local-Exec TLS model. The binaries link and run fine in Qemu.
In addition, the emulation `elf64_sparc` is now recognized.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D77672
2020-04-17 08:12:15 -07:00
Fangrui Song cd5d5ce235 [ELF] Refactor the way we handle -plugin-opt= (GCC collect2 or clang LTO related options)
GCC collect2 passes several options to the linker even if LTO is not used
(note, lld does not support GCC LTO). The lto-wrapper may be a relative
path (especially during development, when gcc is in a build directory), e.g.

  -plugin-opt=relative/path/to/lto-wrapper

We need to ignore such options, which are currently interpreted by
cl::ParseCommandLineOptions() and will fail with `error: --plugin-opt: ld.lld: Unknown command line argument 'relative/path/to/lto-wrapper'`
because the path is apparently not an option registered by an `llvm:🆑:opt`.

See lto-plugin-ignore.s for how we interpret various -plugin-opt= options now.

Reviewed By: grimar, tejohnson

Differential Revision: https://reviews.llvm.org/D78158
2020-04-15 08:00:50 -07:00
Brian Cain f3da6b7ab5 Add duplex to R_HEX_GOT_16_X
Building 'espresso' from llvm-test-suite revealed missing support
for duplex instructions with R_HEX_GOT_16_X.
2020-04-13 19:32:44 -05:00
Fangrui Song a27a7b98cd [ELF] --warn-backrefs: don't warn if -u/--export-dynamic-symbol
Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D77630
2020-04-08 09:33:22 -07:00
Peter Smith 28b172e341 [LLD][ELF][ARM] Implement ARM pc-relative relocations for ADR and LDR
The R_ARM_ALU_PC_G0 and R_ARM_LDR_PC_G0 relocations are used by the
ADR and LDR pseudo instructions, and are the basis of the group
relocations that can load an arbitrary constant via a series of add, sub
and ldr instructions.

The relocations need to be obtained via the .reloc directive.

R_ARM_ALU_PC_G0 is much more complicated as the add/sub instruction uses
a modified immediate encoding of an 8-bit immediate rotated right by an
even 4-bit field. This means that the range of representable immediates
is sparse. We extract the encoding and decoding functions for the modified
immediate from llvm/lib/Target/ARM/MCTargetDesc/ARMAddressingModes.h as
this header file is not accessible from LLD. Duplication of code isn't
ideal, but as these are well-defined mathematical functions they are
unlikely to change.

Differential Revision: https://reviews.llvm.org/D75349
2020-04-08 12:43:44 +01:00
Fangrui Song 03c825c224 [ELF] --warn-backrefs: don't warn for linking sandwich problems
This is an alternative design to D77512.

D45195 added --warn-backrefs to detect

* A. certain input orders which GNU ld either errors ("undefined reference")
  or has different resolution semantics
* B. (byproduct) some latent multiple definition problems (-ldef1 -lref -ldef2) which I
  call "linking sandwich problems". def2 may or may not be the same as def1.

When an archive appears more than once (-ldef -lref -ldef), lld and GNU
ld may have the same resolution but --warn-backrefs may warn. This is
not uncommon. For example, currently lld itself has such a problem:

```
liblldCommon.a liblldCOFF.a ... liblldCommon.a
  _ZN3lld10DWARFCache13getDILineInfoEmm in liblldCOFF.a refers to liblldCommon.a(DWARF.cpp.o)
libLLVMSupport.a also appears twice and has a similar warning
```

glibc has such problems. It is somewhat destined because of its separate
libc/libpthread/... and arbitrary grouping. The situation is getting
improved over time but I have seen:
```
-lc __isnanl references -lm
-lc _IO_funlockfile references -lpthread
```

There are also various issues in interaction with other runtime
libraries such as libgcc_eh and libunwind:
```
-lc __gcc_personality_v0 references -lgcc_eh
-lpthread __gcc_personality_v0 references -lgcc_eh
-lpthread _Unwind_GetCFA references -lunwind
```

These problems are actually benign. We want --warn-backrefs to focus on
its main task A and defer task B (which is also useful) to a more
specific future feature (see gold --detect-odr-violations and
https://bugs.llvm.org/show_bug.cgi?id=43110).

Instead of warning immediately, we store the message and only report it
if no subsequent lazy definition exists.

The use of the static variable `backrefDiags` is similar to `undefs` in
Relocations.cpp

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D77522
2020-04-07 10:25:23 -07:00
Fangrui Song 4e907e93fb [ELF] -M/-Map: fix VMA/LMA/Size columns of symbol assignments when address/size>=2**32
SymbolAssignment::addr stores the location counter. The type should be
uint64_t instead of unsigned. The upper half of the address space is
commonly used by operating system kernels.

Similarly, SymbolAssignment::size should be an uint64_t. A kernel linker
script can move the location counter from 0 to the upper half of the
address space.

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D77445
2020-04-07 10:15:15 -07:00
Sriraman Tallam 94317878d8 LLD Support for Basic Block Sections
This is part of the Propeller framework to do post link code layout
optimizations. Please see the RFC here:
https://groups.google.com/forum/#!msg/llvm-dev/ef3mKzAdJ7U/1shV64BYBAAJ and the
detailed RFC doc here:
https://github.com/google/llvm-propeller/blob/plo-dev/Propeller_RFC.pdf

This patch adds lld support for basic block sections and performs relaxations
after the basic blocks have been reordered.

After the linker has reordered the basic block sections according to the
desired sequence, it runs a relaxation pass to optimize jump instructions.
Currently, the compiler emits the long form of all jump instructions. AMD64 ISA
supports variants of jump instructions with one byte offset or a four byte
offset. The compiler generates jump instructions with R_X86_64 32-bit PC
relative relocations. We would like to use a new relocation type for these jump
instructions as it makes it easy and accurate while relaxing these instructions.

The relaxation pass does two things:

First, it deletes all explicit fall-through direct jump instructions between
adjacent basic blocks. This is done by discarding the tail of the basic block
section.

Second, If there are consecutive jump instructions, it checks if the first
conditional jump can be inverted to convert the second into a fall through and
delete the second.

The jump instructions are relaxed by using jump instruction mods, something
like relocations. These are used to modify the opcode of the jump instruction.
Jump instruction mods contain three values, instruction offset, jump type and
size. While writing this jump instruction out to the final binary, the linker
uses the jump instruction mod to determine the opcode and the size of the
modified jump instruction. These mods are required because the input object
files are memory-mapped without write permissions and directly modifying the
object files requires copying these sections. Copying a large number of basic
block sections significantly bloats memory.

Differential Revision: https://reviews.llvm.org/D68065
2020-04-07 06:55:57 -07:00
Fangrui Song c1c679e2d2 [ELF] Make --version-script/--dynamic-list work for lazy symbols fetched by LTO libcalls
Fixes https://bugs.llvm.org/show_bug.cgi?id=45391

The LTO code generator happens after version script scanning and may
create references which will fetch some lazy symbols.

Currently a version script does not assign VER_NDX_LOCAL to lazy symbols
and such symbols will be made global after they are fetched.

Change findByVersion and findAllByVersion to work on lazy symbols.
For unfetched lazy symbols, we should keep them non-local (D35263).
Check isDefined() in computeBinding() as a compensation.

This patch fixes a companion bug that --dynamic-list does not export
libcall fetched symbols.

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D77280
2020-04-06 09:47:06 -07:00
Fangrui Song 9195b01911 [ELF][PPC64] Enable R_PPC64_REL14 trunks
The thunk implementation is available but an assertion disallows it.
Linux kernel has such a use case: in arch/powerpc/kernel/exceptions-64s.S:handle_page_fault,
beq+ ret_from_except_lite may get out of range.

Link: https://github.com/ClangBuiltLinux/linux/issues/951

Differential Revision: https://reviews.llvm.org/D76904
2020-04-04 10:59:17 -07:00
Fangrui Song 56decd982d [ELF] Allow invalid sh_size%sh_entsize!=0 for non-SHF_MERGE sections
Fixes https://bugs.llvm.org/show_bug.cgi?id=45370
Fixes https://github.com/Clozure/ccl/issues/273

.stab holds a table of 12-byte entries. GNU as before 2.35 incorrectly
sets sh_entsize(.stab) to 20 on 64-bit architectures:
https://sourceware.org/bugzilla/show_bug.cgi?id=25768

We should not emit the confusing error:
"SHF_MERGE section size (...) must be a multiple of sh_entsize (20)

Reviewed By: grimar, psmith

Differential Revision: https://reviews.llvm.org/D77368
2020-04-03 08:48:30 -07:00
Sid Manning c484b3e334 [Hexagon] Fix issue with non-preemptible STT_TLS symbols
A PC-relative relocation referencing a non-preemptible absolute symbol
(due to STT_TLS) is not representable in -pie/-shared mode.

Differential Revision: https://reviews.llvm.org/D77021
2020-04-03 08:55:23 -05:00
Fangrui Song 42bb5cc502 [ELF] Change some "Alias for " help messages to use double dashed options
The aliased options in the --help output use double dashes. It is
inconsistent to have single-dashed messages. Additionally, -l and -t are
common short options and single-dashed forms prefixed with them can
cause confusion.
2020-04-02 09:27:56 -07:00
Igor Kudrin b0b1f451ae [LLD][ELF] Follow the common pattern in a message about an undefined vtable symbol.
In most cases, LLD prints its multiline diagnostic messages starting
additional lines with ">>> ". That greatly helps external tools to parse
the output, simplifying combining several lines of the log back into one
message. The patch fixes the only message I found that does not follow
the common pattern.

Differential Revision: https://reviews.llvm.org/D77132
2020-04-02 11:39:03 +07:00
Kazuaki Ishizaki 7c5fcb3591 [lld] NFC: fix trivial typos in comments
Differential Revision: https://reviews.llvm.org/D72339
2020-04-02 01:21:36 +09:00
Fangrui Song bb4a36ea28 [ELF] Propagate LMA offset to sections with neither AT() nor AT>
Fixes https://bugs.llvm.org/show_bug.cgi?id=45313
Also fixes linkerscript/{at4.s,overlay.test} LMA address issues exposed by
011b785505.
Related: D74297

This patch improves emulation of GNU ld's heuristics on the difference
between the LMA and the VMA:
https://sourceware.org/binutils/docs/ld/Output-Section-LMA.html#Output-Section-LMA

New test linkerscript/lma-offset.s (based on at4.s) demonstrates some behaviors.

Reviewed By: psmith

Differential Revision: https://reviews.llvm.org/D76995
2020-04-01 08:19:06 -07:00
Fangrui Song f2036a15d3 [ELF] Print symbols with non-default versions for better "undefined symbol" diagnostics
When reporting an "undefined symbol" diagnostic:

* We don't print @ for the reference.
* We don't print @ or @@ for the definition. https://bugs.llvm.org/show_bug.cgi?id=45318

This can lead to confusing diagnostics:

```
// foo may be foo@v2
ld.lld: error: undefined symbol: foo
>>> referenced by t1.o:(.text+0x1)
// foo may be foo@v1 or foo@@v1
>>> did you mean: foo
>>> defined in: t.so
```

There are 2 ways a symbol in symtab may get truncated:

* A @@ definition may be truncated *early* by SymbolTable::insert().
  The name ends with a '\0'.
* A @ definition/reference may be truncated *later* by Symbol::parseSymbolVersion().
  The name ends with a '@'.

This patch detects the second case and improves the diagnostics. The first case is
not improved but the second case is sufficient to make diagnostics not confusing.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D76999
2020-04-01 08:04:36 -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
Peter Smith 2539b4ae47 [LLD][ELF] Allow empty (.init|.preinit|.fini)_array to be RELRO
The default GNU linker script uses the following idiom for the array
sections. I'll use .init_array here, but this also applies to
.preinit_array and .fini_array sections.

  .init_array    :
  {
    PROVIDE_HIDDEN (__init_array_start = .);
    KEEP (*(.init_array))
    PROVIDE_HIDDEN (__init_array_end = .);
  }

The C-library will take references to the _start and _end symbols to
process the array. This will make LLD keep the OutputSection even if there
are no .init_array sections. As the current check for RELRO uses the
section type for .init_array the above example with no .init_array
InputSections fails the checks as there are no .init_array sections to give
the OutputSection a type of SHT_INIT_ARRAY. This often leads to a
non-contiguous RELRO error message.

The simple fix is to a textual section match as well as a section type
match.

Differential Revision: https://reviews.llvm.org/D76915
2020-03-31 12:53:12 +01:00
Kai Wang 581ba35291 [RISCV] ELF attribute section for RISC-V.
Leverage ARM ELF build attribute section to create ELF attribute section
for RISC-V. Extract the common part of parsing logic for this section
into ELFAttributeParser.[cpp|h] and ELFAttributes.[cpp|h].

Differential Revision: https://reviews.llvm.org/D74023
2020-03-31 16:16:19 +08:00
Nico Weber 20eb719f99 lld: Reduce number of references to undefined printed from 10 to 3.
As of a while ago, lld groups all undefined references to a single
symbol in a single diagnostic. Back then, I made it so that we
print up to 10 references to each undefined symbol.

Having used this for a while, I never wished there were more
references, but I sometimes found that this can print a lot of
output. lld prints up to 10 diagnostics by default, and if
each has 10 references (which I've seen in practice), and each
undefined symbol produces 2 (possibly very long) lines of output,
that's over 200 lines of error output.

Let's try it with just 3 references for a while and see how
that feels in practice.

Differential Revision: https://reviews.llvm.org/D77017
2020-03-30 14:31:32 -04:00