Commit Graph

599 Commits

Author SHA1 Message Date
Hans Wennborg 36c23cad15 Revert r362743 "Revert "Revert "Reland D61583 [ELF] Error on relocations to STT_SECTION symbols if the sections were discarded"""
(In effect, reverting "[ELF] Error on relocations to STT_SECTION symbols if the sections were discarded".)

It caused debug info problems in LibreOffice [1] and Chromium/V8 [2].
Reverting until those can be fixed.

It also reverts r362497 "STT_SECTION symbol should be defined" on .eh_frame, .debug*, .zdebug* and .gcc_except_table"
which was landed as a follow-up to the above.

> With -r or --emit-relocs, we warn `STT_SECTION symbol should be defined`
> on relocations to discarded section symbol. This was added as an error
> in rLLD319404, but was not so effective before D61583 (it turned the
> error to a warning).
>
> Relocations from .eh_frame .debug* .zdebug* .gcc_except_table to
> discarded .text are very common and somewhat expected. Don't warn/error
> on them. As a reference, ld.bfd has a similar logic in
> _bfd_elf_default_action_discarded() to allow these cases.
>
> Delete invalid-undef-section-symbol.test because what it intended to
> check is now covered by the updated comdat-discarded-reloc.s
>
> Delete relocatable-eh-frame.s because we allow relocations from
> .eh_frame as a special case now.

And finally it reverts r362218 "[ELF] Replace a dead test in getSymVA() with assert()"
as that also depended on the main change reverted here.

> Symbols relative to discarded comdat sections are Undefined instead of
> Defined now (after D59649 and D61583). The `== &InputSection::Discarded`
> test becomes dead. I cannot find a test related to this behavior.

 [1] http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20190603/659848.html
 [2] https://bugs.chromium.org/p/chromium/issues/detail?id=978067

llvm-svn: 364321
2019-06-25 14:58:46 +00:00
Fangrui Song 4ce0a519c1 [ELF][RISCV] Treat R_RISCV_{ADD,SET,SUB}* as link-time constants
R_RISCV_{ADD,SET,SUB}* are used for local label computation.
Add a new RelExpr member R_RISCV_ADD to represent them.

R_RISCV_ADD is treated as a link-time constant because otherwise
R_RISCV_{ADD,SET,SUB}* are not allowed in -pie/-shared mode.
In glibc Scrt1.o, .rela.eh_frame contains such relocations.
Because .eh_frame is not writable, we get this error:

    ld.lld: error: can't create dynamic relocation R_RISCV_ADD32 against symbol: .L0 in readonly segment; recompil object files with -fPIC or pass '-Wl,-z,notext' to allow text relocations in the output
    >>> defined in ..../riscv64-linux-gnu/lib/Scrt1.o

With D63076 and this patch, I can run -pie/-shared programs linked against glibc.

Note llvm-mc cannot currently produce R_RISCV_SET* so they are not tested.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D63183

llvm-svn: 363128
2019-06-12 07:53:06 +00:00
Fangrui Song 11549e5c46 [ELF][PPC64] Don't report "relocation refers to a discarded section" for .toc
Summary:
clang (as of 2019-06-12) / gcc (as of 8.2.1) PPC64 may emit a .rela.toc
which references an embedded switch table in a discarded .rodata/.text
section. The .toc and the .rela.toc are incorrectly not placed in the
comdat.

Technically a relocation from outside the group is not allowed by the ELF spec:

> A symbol table entry with STB_LOCAL binding that is defined relative
> to one of a group's sections, and that is contained in a symbol table
> section that is not part of the group, must be discarded if the group
> members are discarded. References to this symbol table entry from
> outside the group are not allowed.

Don't report errors to work around the bug.

This should fix the ppc64le-lld-multistage-test bot while linking llvm-tblgen:

    ld.lld: error: relocation refers to a discarded section: .rodata._ZNK4llvm3MVT13getSizeInBitsEv
    >>> defined in utils/TableGen/CMakeFiles/llvm-tblgen.dir/CodeGenRegisters.cpp.o
    >>> referenced by CodeGenRegisters.cpp
    >>> utils/TableGen/CMakeFiles/llvm-tblgen.dir/CodeGenRegisters.cpp.o:(.toc+0x0)

Some other PPC specific sections may have similar problems. We can blacklist more
section names when problems occur.

    // A simple program that reproduces the bug.
    // Note .rela.toc (outside the group) references a section symbol (STB_LOCAL) in a group.
    void puts(const char *);
    struct A {
      void foo(int a) {
        switch (a) {
        case 0: puts("0"); break;
        case 1: puts("1"); puts("1"); break;
        case 2: puts("2"); break;
        case 3: puts("3"); puts("4"); break;
        case 4: puts("4"); break;
        case 5: puts("5"); puts("5"); break;
        case 6: puts("6"); break;
        }
      }
      int a;
    };
    void foo(A x) { x.foo(x.a); }

Reviewers: ruiu, sfertile, espindola

Reviewed By: ruiu

Subscribers: emaste, nemanjai, arichardson, kbarton, jsji, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63182

llvm-svn: 363126
2019-06-12 07:35:42 +00:00
Sean Fertile 6a573e3ec3 Revert "Revert "[ELF] Suppress "STT_SECTION symbol should be defined" on .eh_frame, .debug*, .zdebug* and .gcc_except_table""
This reverts commit f49f58527a6d8147524d8d6f2eb1feb70f856292.

llvm-svn: 362744
2019-06-06 20:16:59 +00:00
Sean Fertile 6ba76dd779 Revert "Revert "Reland D61583 [ELF] Error on relocations to STT_SECTION symbols if the sections were discarded""
This reverts commit 729111cf1824159bb4dd331cab8a829eab30313f.

Reverting the previous commit breaks other LLD buildbots.

llvm-svn: 362743
2019-06-06 20:16:53 +00:00
Sean Fertile f1d9b3180e Revert "Reland D61583 [ELF] Error on relocations to STT_SECTION symbols if the sections were discarded"
This reverts commit 5d3b3188f7.

Breaks the PowerPC multi-stage buildbot.

llvm-svn: 362739
2019-06-06 19:34:26 +00:00
Sean Fertile a0a63b2f90 Revert "[ELF] Suppress "STT_SECTION symbol should be defined" on .eh_frame, .debug*, .zdebug* and .gcc_except_table"
This reverts commit dcba4828a9.

This commit builds on  dcba4828a9 which breaks the
multi-staged PowerPC buildbot.

llvm-svn: 362738
2019-06-06 19:34:18 +00:00
Fangrui Song 7ccfdad7ab [PPC32] Support GD/LD/IE/LE TLS models and their relaxations
Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D62940

llvm-svn: 362722
2019-06-06 17:03:10 +00:00
Fangrui Song 82442adfc0 [PPC32] Improve the 32-bit PowerPC port
Many -static/-no-pie/-shared/-pie applications linked against glibc or musl
should work with this patch. This also helps FreeBSD PowerPC64 to migrate
their lib32 (PR40888).

* Fix default image base and max page size.
* Support new-style Secure PLT (see below). Old-style BSS PLT is not
  implemented, so it is not suitable for FreeBSD rtld now because it doesn't
  support Secure PLT yet.
* Support more initial relocation types:
  R_PPC_ADDR32, R_PPC_REL16*, R_PPC_LOCAL24PC, R_PPC_PLTREL24, and R_PPC_GOT16.
  The addend of R_PPC_PLTREL24 is special: it decides the call stub PLT type
  but it should be ignored for the computation of target symbol VA.
* Support GNU ifunc
* Support .glink used for lazy PLT resolution in glibc
* Add a new thunk type: PPC32PltCallStub that is similar to PPC64PltCallStub.
  It is used by R_PPC_REL24 and R_PPC_PLTREL24.

A PLT stub used in -fPIE/-fPIC usually loads an address relative to
.got2+0x8000 (-fpie/-fpic code uses _GLOBAL_OFFSET_TABLE_ relative
addresses).
Two .got2 sections in two object files have different addresses, thus a PLT stub
can't be shared by two object files. To handle this incompatibility,
change the parameters of Thunk::isCompatibleWith to
`const InputSection &, const Relocation &`.

PowerPC psABI specified an old-style .plt (BSS PLT) that is both
writable and executable. Linkers don't make separate RW- and RWE segments,
which causes all initially writable memory (think .data) executable.
This is a big security concern so a new PLT scheme (secure PLT) was developed to
address the security issue.

TLS will be implemented in D62940.

glibc older than ~2012 requires .rela.dyn to include .rela.plt, it can
not handle the DT_RELA+DT_RELASZ == DT_JMPREL case correctly. A hack
(not included in this patch) in LinkerScript.cpp addOrphanSections() to
work around the issue:

    if (Config->EMachine == EM_PPC) {
      // Older glibc assumes .rela.dyn includes .rela.plt
      Add(In.RelaDyn);
      if (In.RelaPlt->isLive() && !In.RelaPlt->Parent)
        In.RelaDyn->getParent()->addSection(In.RelaPlt);
    }

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D62464

llvm-svn: 362721
2019-06-06 17:03:00 +00:00
Fangrui Song dcba4828a9 [ELF] Suppress "STT_SECTION symbol should be defined" on .eh_frame, .debug*, .zdebug* and .gcc_except_table
Summary:
With -r or --emit-relocs, we warn `STT_SECTION symbol should be defined`
on relocations to discarded section symbol. This was added as an error
in rLLD319404, but was not so effective before D61583 (it turned the
error to a warning).

Relocations from .eh_frame .debug* .zdebug* .gcc_except_table to
discarded .text are very common and somewhat expected. Don't warn/error
on them. As a reference, ld.bfd has a similar logic in
_bfd_elf_default_action_discarded() to allow these cases.

Delete invalid-undef-section-symbol.test because what it intended to
check is now covered by the updated comdat-discarded-reloc.s

Delete relocatable-eh-frame.s because we allow relocations from
.eh_frame as a special case now.

Reviewers: grimar, phosek, ruiu, espindola

Reviewed By: ruiu

Subscribers: emaste, arichardson, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62840

llvm-svn: 362497
2019-06-04 13:41:29 +00:00
Fangrui Song 8522d579b8 [ELF][PPC64] Rename some PPC64 ELFv2 specific RelExpr from R_PPC_* to R_PPC64_*
The following abstract relocation types (RelExpr) are PPC64 ELFv2 ABI specific,
not used by PPC32. So rename them to prevent confusion when the PPC32 port is improved.

* R_PPC_CALL R_PPC_CALL_PLT:
  R_PPC_CALL_PLT represents R_PPC64_REL14 and R_PPC64_REL24.
  If the function is not preemptable, R_PPC_CALL_PLT can be optimized to R_PPC_CALL:
  the formula adjusts the symbol VA from the global entry point to the local entry point.
* R_PPC_TOC: represents R_PPC64_TOC.  We don't have a test. Add one to ppc64-relocs.s
  Rename it to R_PPC64_TOCBASE because `@tocbase` is the assembly form.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D62800

llvm-svn: 362359
2019-06-03 06:21:33 +00:00
Fangrui Song 0526c0cd8e [ELF] Implement Local Dynamic style TLSDESC for x86-64
For the Local Dynamic case of TLSDESC, _TLS_MODULE_BASE_ is defined as a
special TLS symbol that makes:

1) Without relaxation: it produces a dynamic TLSDESC relocation that
computes 0. Adding @dtpoff to access a TLS symbol.
2) With LD->LE relaxation: _TLS_MODULE_BASE_@tpoff = 0 (lowest address in
the TLS block). Adding @tpoff to access a TLS symbol.

For 1), this saves dynamic relocations and GOT slots as otherwise
(General Dynamic) we would create an R_X86_64_TLSDESC and reserve two
GOT slots for each symbol.

Add ElfSym::TlsModuleBase and change the signature of getTlsTpOffset()
to special case _TLS_MODULE_BASE_.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D62577

llvm-svn: 362078
2019-05-30 10:00:20 +00:00
Peter Collingbourne ba2816be82 ELF: Add basic partition data structures and behaviours.
This change causes us to read partition specifications from partition
specification sections and split output sections into partitions according
to their reachability from partition entry points.

This is only the first step towards a full implementation of partitions. Later
changes will add additional synthetic sections to each partition so that
they can be loaded independently.

Differential Revision: https://reviews.llvm.org/D60353

llvm-svn: 361925
2019-05-29 03:55:20 +00:00
Fangrui Song 719322411c [ELF] Implement General Dynamic style TLSDESC for x86-64
This handles two initial relocation types R_X86_64_GOTPC32_TLSDESC and
R_X86_64_TLSDESC_CALL, as well as the GD->LE and GD->IE relaxations.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D62513

llvm-svn: 361911
2019-05-29 02:03:56 +00:00
Fangrui Song 5d3b3188f7 Reland D61583 [ELF] Error on relocations to STT_SECTION symbols if the sections were discarded
This is implemented by creating Undefined (instead of Defined) for such
local STT_SECTION symbols. It allows us to catch errors when there are
relocations to such discarded sections (e.g. in PR41693, ld.bfd and gold
error but we don't). Updated comdat-discarded-error.s checks we emit
friendly error message.

For relocatable-eh-frame.s, ld.lld -r a.o a.o will now error
"STT_SECTION symbol should be defined" because the section .eh_frame
refers to is now an Undefined instead of a Defined.
So I have to change `error()` to `warn()` to retain the output.

rLLD361144 inadvertently enabled the error for --gdb-index
(in LLDDwarfObj<ELFT>::findAux()).

Relocations from .debug_info (not in comdat) to .text.* (in comdat) for
DW_AT_low_pc are common. If an .text.* was discarded, rLLD361144 would error,
which was unexpected. (Note, if we don't error as this patch does,
InputSection::relocateNonAlloc() will resolve such relocations).

llvm-svn: 361830
2019-05-28 14:34:28 +00:00
Haojian Wu 241dcb386e Revert [ELF] Error on relocations to STT_SECTION symbols if the sections were discarded
This reverts r361792 (git commit cfca5095df), the
revision causes link errors internally, will share more details with the
author.

llvm-svn: 361806
2019-05-28 11:21:59 +00:00
Fangrui Song cfca5095df [ELF] Error on relocations to STT_SECTION symbols if the sections were discarded
This is implemented by creating Undefined (instead of Defined) for such
local STT_SECTION symbols. It allows us to catch errors when there are
relocations to such discarded sections (e.g. in PR41693, ld.bfd and gold
error but we don't). Updated comdat-discarded-error.s checks we emit
friendly error message.

For relocatable-eh-frame.s, ld.lld -r a.o a.o will now error
"STT_SECTION symbol should be defined" because the section .eh_frame
refers to is now an Undefined instead of a Defined.
So I have to change `error()` to `warn()` to retain the output.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D61583

llvm-svn: 361792
2019-05-28 06:34:52 +00:00
Fangrui Song 2109572464 [ELF] Fix getRelocTargetVA formulae of R_TLS and R_NEG_TLS
For R_TLS:
1) Delete Sym.isTls() . The assembler ensures the symbol is STT_TLS.
   If not (the input is broken), we would crash (dereferencing null Out::TlsPhdr).
2) Change Sym.isUndefWeak() to Sym.isUndefined(), otherwise with --noinhibit-exec
   we would still evaluate the symbol and crash.
3) Return A if the symbol is undefined. This is PR40570.
   The case is probably unrealistic but returning A matches R_ABS and the
   behavior of several dynamic loaders.

R_NEG_TLS is obsoleted Sun TLS we don't fully support, but
R_RELAX_TLS_GD_TO_LE_NEG is still used by GD->LE relaxation (subl $var@tpoff,%eax).

They should add the addend. Unfortunately I can't test it as compilers don't seem to generate non-zero implicit addends.

Reviewed By: ruiu

Differential Revision: https://reviews.llvm.org/D62098

llvm-svn: 361146
2019-05-20 11:47:31 +00:00
Fangrui Song ed2ad77ccb [ARM][AArch64] Revert Android Bionic PT_TLS overaligning hack
This reverts D53906.

D53906 increased p_align of PT_TLS on ARM/AArch64 to 32/64 to make the
static TLS layout compatible with Android Bionic's ELF TLS. However,
this may cause glibc ARM/AArch64 programs to crash (see PR41527).

The faulty PT_TLS in the executable satisfies p_vaddr%p_align != 0. The
remainder is normally 0 but may be non-zero with the hack in place. The
problem is that we increase PT_TLS's p_align after OutputSections'
addresses are fixed (assignAddress()). It is possible that
p_vaddr%old_p_align = 0 while p_vaddr%new_p_align != 0.

For a thread local variable defined in the executable, lld computed TLS
offset (local exec) is different from glibc computed TLS offset from
another module (initial exec/generic dynamic). Note: PR41527 said the
bug affects initial exec but actually generic dynamic is affected as
well.

(glibc is correct in that it compute offsets that satisfy
`offset%p_align == p_vaddr%p_align`, which is a basic ELF requirement.
This hack appears to work on FreeBSD rtld, musl<=1.1.22, and Bionic, but
that is just because they (and lld) incorrectly compute offsets that
satisfy `offset%p_align = 0` instead.)

Android developers are fine to revert this patch, carry this patch in
their tree before figuring out a long-term solution (e.g. a dummy .tdata
with sh_addralign=64 sh_size={0,1} in crtbegin*.o files. The overhead is
now insignificant after D62059).

Reviewed By: rprichard, srhines

Differential Revision: https://reviews.llvm.org/D62055

llvm-svn: 361090
2019-05-18 03:16:00 +00:00
Fangrui Song 898896836d [ELF][X86] Fix R_RELAX_TLS_GD_TO_LE_NEG and R_NEG_TLS after D62059
After D62059, we don't align p_memsz of PT_TLS to p_align. The
getRelocTargetVA formula should align it instead.

It becomes clear that R_NEG_TLS and R_TLS are opposite from each other.

In i386-tls-le-align.s, I put ret after call ___tls_get_addr@plt as
otherwise ld.bfd would reject the relaxation:
TLS transition from R_386_TLS_GD to R_386_TLS_LE_32 against `a' at 0x3 in section `.text' failed

llvm-svn: 361088
2019-05-18 01:58:40 +00:00
Fangrui Song 348731aeed [ELF] Fix TP offset of TLS Variant I after D62059
As Ryan Prichard pointed out, after D62059, the TP offset is incorrect.

Add x86-64-tls-le-align.s to check this.  Better formulae for both
variants should take p_vaddr%p_align into account (offset%p_align =
p_vaddr%p_align is a basic ELF requirement), but I can't find a way to
test the behavior.

llvm-svn: 361084
2019-05-18 00:43:10 +00:00
Fangrui Song f3a3b93f54 [ELF] -r: fix R_*_NONE to section symbols on Elf*_Rel targets
On Elf*_Rel targets, for a relocation to a section symbol, an R_ABS is
added which will be used by relocateOne() to compute the implicit
addend.

Addends of R_*_NONE should be ignored, so don't emit an R_ABS.

This fixes crashes on X86 and ARM because their relocateOne() do not
handle R_*_NONE.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D62052

llvm-svn: 361036
2019-05-17 14:11:03 +00:00
Bob Haarman 5ff1eb6418 Revert r358069 "Discard debuginfo for object files empty after GC"
The change broke some scenarios where debug information is still
needed, although MarkLive cannot see it, including the
Chromium/Android build. Reverting to unbreak that build.

llvm-svn: 360955
2019-05-16 23:33:06 +00:00
Fangrui Song 912251e82f [PPC64] toc-indirect to toc-relative relaxation
This is based on D54720 by Sean Fertile.

When accessing a global symbol which is not defined in the translation unit,
compilers will generate instructions that load the address from the toc entry.

If the symbol is defined, non-preemptable, and addressable with a 32-bit
signed offset from the toc pointer, the address can be computed
directly. e.g.

    addis 3, 2, .LC0@toc@ha  # R_PPC64_TOC16_HA
    ld    3, .LC0@toc@l(3)   # R_PPC64_TOC16_LO_DS, load the address from a .toc entry
    ld/lwa 3, 0(3)           # load the value from the address

    .section .toc,"aw",@progbits
    .LC0: .tc var[TC],var

can be relaxed to

    addis 3,2,var@toc@ha     # this may be relaxed to a nop,
    addi  3,3,var@toc@l      # then this becomes addi 3,2,var@toc
    ld/lwa 3, 0(3)           # load the value from the address

We can delete the test ppc64-got-indirect.s as its purpose is covered by
newly added ppc64-toc-relax.s and ppc64-toc-relax-constants.s

Reviewed By: ruiu, sfertile

Differential Revision: https://reviews.llvm.org/D60958

llvm-svn: 360112
2019-05-07 04:26:05 +00:00
Fangrui Song 98b70f6705 [ELF] Change std::max<uint64_t> to uint32_t for section alignment
Summary:
We use `uint32_t SectionBase::Alignment` and `uint32_t
PhdrEntry::p_align` despite alignments being 64 bits in ELF64.
Fix the std::max template arguments accordingly.

The currently 160-byte InputSection will become 168 bytes if we make SectionBase::Alignment uint64_t.

Differential Revision: https://reviews.llvm.org/D61171

llvm-svn: 359268
2019-04-26 04:07:58 +00:00
Fangrui Song d986e41fe4 [PPC64] Allow R_PPC64_DTPREL* to preemptable local-dynamic symbols
Similar to D60945.

Differential Revision: https://reviews.llvm.org/D60994

llvm-svn: 358950
2019-04-23 06:31:44 +00:00
George Rimar 3275742898 [LLD][ELF] - Do not forget to use ch_addralign field after decompressing the sections.
LLD did not use ELF::Chdr::ch_addralign for decompressed sections.
This resulted in a broken output.

Fixes https://bugs.llvm.org/show_bug.cgi?id=40482.

Differential revision: https://reviews.llvm.org/D60959

llvm-svn: 358885
2019-04-22 13:40:42 +00:00
Fangrui Song bc4b159bb1 [ELF][X86] Allow R_386_TLS_LDO_32 and R_X86_64_DTPOFF{32,64} to preemptable local-dynamic symbols
Summary:
Fixes PR35242. A simplified reproduce:

    thread_local int i; int f() { return i; }

% {g++,clang++} -fPIC -shared -ftls-model=local-dynamic -fuse-ld=lld a.cc
ld.lld: error: can't create dynamic relocation R_X86_64_DTPOFF32 against symbol: i in readonly segment; recompile object files with -fPIC or pass '-Wl,-z,notext' to allow text relocations in the output

In isStaticLinkTimeConstant(), Syn.IsPreemptible is true, so it is not
seen as a constant. The error is then issued in processRelocAux().

A symbol of the local-dynamic TLS model cannot be preempted but it can
preempt symbols of the global-dynamic TLS model in other DSOs.
So it makes some sense that the variable is not static.

This patch fixes the linking error by changing getRelExpr() on
R_386_TLS_LDO_32 and R_X86_64_DTPOFF{32,64} from R_ABS to R_DTPREL.
R_PPC64_DTPREL_* and R_MIPS_TLS_DTPREL_* need similar fixes, but they are not handled in this patch.

As a bonus, we use `if (Expr == R_ABS && !Config->Shared)` to find
ld-to-le opportunities. R_ABS is overloaded here for such STT_TLS symbols.
A dedicated R_DTPREL is clearer.

Differential Revision: https://reviews.llvm.org/D60945

llvm-svn: 358870
2019-04-22 03:10:40 +00:00
Fangrui Song e1f3191a0d [ELF][X86] Rename R_RELAX_TLS_GD_TO_IE_END to R_RELAX_TLS_GD_TO_IE_GOTPLT
Summary:
This relocation type is used by R_386_TLS_GD. Its formula is the same as
R_GOTPLT (e.g R_X86_64_GOT{32,64} R_386_TLS_GOTIE). Rename it to be clearer.

Differential Revision: https://reviews.llvm.org/D60941

llvm-svn: 358868
2019-04-22 02:48:37 +00:00
Fangrui Song 2bc3a19a49 [ELF] Use llvm::bsearch. NFC
Differential Revision: https://reviews.llvm.org/D60813

llvm-svn: 358565
2019-04-17 08:00:46 +00:00
Rui Ueyama 3a8bb7cd2c Discard debuginfo for object files empty after GC
Patch by Robert O'Callahan.

Rust projects tend to link in all object files from all dependent
libraries and rely on --gc-sections to strip unused code and data.
Unfortunately --gc-sections doesn't currently strip any debuginfo
associated with GC'ed sections, so lld links in the full debuginfo from
all dependencies even if almost all that code has been discarded. See
https://github.com/rust-lang/rust/issues/56068 for some details.

Properly stripping debuginfo for discarded sections would be difficult,
but a simple approach that helps significantly is to mark debuginfo
sections as live only if their associated object file has at least one
live code/data section. This patch does that. In a (contrived but not
totally artificial) Rust testcase linked above, it reduces the final
binary size from 46MB to 5.1MB.

Differential Revision: https://reviews.llvm.org/D54747

llvm-svn: 358069
2019-04-10 10:37:10 +00:00
Rui Ueyama 68b9f45fee Replace `typedef A B` with `using B = A`. NFC.
I did this using Perl.

Differential Revision: https://reviews.llvm.org/D60003

llvm-svn: 357372
2019-04-01 00:11:24 +00:00
Fangrui Song 210949a221 [ELF] Change GOT*_FROM_END (relative to end(.got)) to GOTPLT* (start(.got.plt))
Summary:
This should address remaining issues discussed in PR36555.

Currently R_GOT*_FROM_END are exclusively used by x86 and x86_64 to
express relocations types relative to the GOT base. We have
_GLOBAL_OFFSET_TABLE_ (GOT base) = start(.got.plt) but end(.got) !=
start(.got.plt)

This can have problems when _GLOBAL_OFFSET_TABLE_ is used as a symbol, e.g.
glibc dl_machine_dynamic assumes _GLOBAL_OFFSET_TABLE_ is start(.got.plt),
which is not true.

  extern const ElfW(Addr) _GLOBAL_OFFSET_TABLE_[] attribute_hidden;
  return _GLOBAL_OFFSET_TABLE_[0]; // R_X86_64_GOTPC32

In this patch, we

* Change all GOT*_FROM_END to GOTPLT* to fix the problem.
* Add HasGotPltOffRel to denote whether .got.plt should be kept even if
  the section is empty.
* Simplify GotSection::empty and GotPltSection::empty by setting
  HasGotOffRel and HasGotPltOffRel according to GlobalOffsetTable early.

The change of R_386_GOTPC makes X86::writePltHeader simpler as we don't
have to compute the offset start(.got.plt) - Ebx (it is constant 0).

We still diverge from ld.bfd (at least in most cases) and gold in that
.got.plt and .got are not adjacent, but the advantage doing that is
unclear.

Reviewers: ruiu, sivachandra, espindola

Subscribers: emaste, mehdi_amini, arichardson, dexonsmith, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59594

llvm-svn: 356968
2019-03-25 23:46:19 +00:00
Peter Collingbourne e2b8c40a77 ELF: Use bump pointer allocator for uncompressed section buffers. NFCI.
This shaves another word off SectionBase and makes it possible to clone a
section using the implicit copy constructor.

This basically reverts r311056, which removed the mutex in order to
make the code easier to understand. On balance I think it's probably more
straightforward to have a mutex here than to have an unusual copy constructor
in SectionBase.

Differential Revision: https://reviews.llvm.org/D59269

llvm-svn: 355966
2019-03-12 20:32:30 +00:00
George Rimar cc19dc75fb [LLD][ELF] - Improve "sh_addralign is not a power of 2" diagnostics.
This patch removes the precompiled binary from inputs,
replacing it with a YAML. And teaches LLD to report a
section name in case of such error.

Differential revision: https://reviews.llvm.org/D58670

llvm-svn: 354959
2019-02-27 10:28:23 +00:00
Rui Ueyama 980fb790c1 Remove a comparator from header and instead use lambdas for simplicity. NFC.
llvm-svn: 354052
2019-02-14 19:21:10 +00:00
Rui Ueyama b8b81e9b43 Improve error message for unknown relocations.
Previously, we showed the following message for an unknown relocation:

  foo.o: unrecognized reloc 256

This patch improves it so that the error message includes a symbol name:

  foo.o: unknown relocation (256) against symbol bar

llvm-svn: 354040
2019-02-14 18:02:20 +00:00
Peter Collingbourne 8331f61a51 ELF: Allow GOT relocs pointing to non-preemptable ifunc to resolve to an IRELATIVE where possible.
Non-GOT non-PLT relocations to non-preemptible ifuncs result in the
creation of a canonical PLT, which now takes the identity of the IFUNC
in the symbol table. This (a) ensures address consistency inside and
outside the module, and (b) fixes a bug where some of these relocations
end up pointing to the resolver.

Fixes (at least) PR40474 and PR40501.

Differential Revision: https://reviews.llvm.org/D57371

llvm-svn: 353981
2019-02-13 21:49:55 +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
Sean Fertile 3ca494b2ee Modify InputSectionBase::getLocation to add section and offset to every loc.
The section and offset can be very helpful in diagnosing certian errors.
For example on a relocation overflow or misalignment diagnostic:

test.c:(function  foo): relocation R_PPC64_ADDR16_DS out of range: ...

The function foo can have many R_PPC64_ADDR16_DS relocations. Adding the offset
and section will identify exactly which relocation is causing the failure.

Differential Revision: https://reviews.llvm.org/D56453

llvm-svn: 350828
2019-01-10 15:08:06 +00:00
Ryan Prichard d7d2369c09 [ARM][AArch64] Increase TLS alignment to reserve space for Android's TCB
ARM and AArch64 use TLS variant 1, where the first two words after the
thread pointer are reserved for the TCB, followed by the executable's TLS
segment. Both the thread pointer and the TLS segment are aligned to at
least the TLS segment's alignment.

Android/Bionic historically has not supported ELF TLS, and it has
allocated memory after the thread pointer for several Bionic TLS slots
(currently 9 but soon only 8). At least one of these allocations
(TLS_SLOT_STACK_GUARD == 5) is widespread throughout Android/AArch64
binaries and can't be changed.

To reconcile this disagreement about TLS memory layout, set the minimum
alignment for executable TLS segments to 8 words on ARM/AArch64, which
reserves at least 8 words of memory after the TP (2 for the ABI-specified
TCB and 6 for alignment padding). For simplicity, and because lld doesn't
know when it's targeting Android, increase the alignment regardless of
operating system.

Differential Revision: https://reviews.llvm.org/D53906

llvm-svn: 350681
2019-01-09 00:09:59 +00:00
Peter Smith fe3015d164 [ELF][AArch64] Fix adrp to undefined weak reference.
In the ABI for the 64-bit Arm architecture the section on weak references
states:
During linking, the symbol value of an undefined weak reference is:
- Zero if the relocation type is absolute
- The address of the place if the relocation type is pc-relative.

The relocations associated with an ADRP are relative so we should resolve
the undefined weak reference to the place instead of 0. This matches GNU
ld.bfd behaviour.

fixes pr34928

Differential Revision: https://reviews.llvm.org/D55599

llvm-svn: 349024
2018-12-13 11:13:01 +00:00
Rui Ueyama c9c34bdc1a Do not use a hash table to uniquify mergeable strings.
Previously, we have a hash table containing strings and their offsets
to manage mergeable strings. Technically we can live without that, because
we can do binary search on a vector of mergeable strings to find a mergeable
strings.

We did have both the hash table and the binary search because we thought
that that is faster.

We recently observed that lld tend to consume more memory than gold when
building an output with debug info. A few percent of memory is consumed by
the hash table. So, we needed to reevaluate whether or not having the extra
hash table is a good CPU/memory tradeoff. I run a few benchmarks with and
without the hash table.

I got a mixed result for the benchmark. We observed a regression for some
programs by removing the hash table (that's what we expected), but we also
observed that performance imrpovements for some programs. This is perhaps
due to reduced memory usage.

Differential Revision: https://reviews.llvm.org/D55234

llvm-svn: 348401
2018-12-05 19:13:31 +00:00
Fangrui Song 01fbb06b12 [ELF] Simplify getSectionPiece
Reviewers: ruiu, espindola

Reviewed By: ruiu

Subscribers: grimar, emaste, arichardson, llvm-commits

Differential Revision: https://reviews.llvm.org/D55248

llvm-svn: 348311
2018-12-04 22:25:05 +00:00
Rui Ueyama aea706083f Inline a function template that is used only once. NFC.
llvm-svn: 348013
2018-11-30 18:19:15 +00:00
George Rimar d2f8db827d [ELF] - Fix R_AARCH64_ADR_GOT_PAGE, R_AARCH64_LD64_GOT_LO12 handling against IFUNC symbols.
This is https://bugs.llvm.org/show_bug.cgi?id=38074.

The issue is that when calling a function, LLD generates a
.got entry that points to the IFUNC resolver function when
instead, it should use the PLT entries properly for
handling the IFUNC.

So we should create a got entry that points to PLT entry,
which itself loads the value from 
.got.plt, relocated with R_*_IRELATIVE to make things work.
Patch do that.

Differential revision: https://reviews.llvm.org/D54314

llvm-svn: 347650
2018-11-27 10:30:46 +00:00
George Rimar 0fc5dcd1c8 [LLD][ELF] - Simplify. NFCI.
This makes getRISCVPCRelHi20 to be static local helper,
and rotates the 'if' condition.

llvm-svn: 347497
2018-11-23 15:13:26 +00:00
George Rimar 8329028b49 [ELF] - Renamed few more AArch64 specific relocation expressions. NFC.
They are AArch64 only, so have to have AARCH64_* prefix.

llvm-svn: 346963
2018-11-15 15:35:44 +00:00
Peter Smith ad51cee866 [AArch64] Fix resolution of R_PLT_PAGE RelExpr
The R_AARCH64_ADR_PREL_PG_HI21 relocation type is given the R_PAGE_PC
RelExpr. This can be transformed to R_PLT_PAGE_PC via toPlt().
Unfortunately the resolution is identical to R_PAGE_PC so instead of
getting the address of the PLT entry we get the address of the symbol
which may not be correct in the case of static ifuncs. The fix is to
handle the cases separately and use getPltVA() + A with R_PLT_PAGE_PC.

Differential Revision: https://reviews.llvm.org/D54474

llvm-svn: 346863
2018-11-14 13:53:47 +00:00
George Rimar 8ef9babb67 [ELF] - Renamed AArch64 specific relocations expressions. NFC.
They did not have AArch64 prefix. Now they do.

llvm-svn: 346749
2018-11-13 10:16:36 +00:00