The ARM.exidx section contains a table of 8-byte entries with the first
word of each entry an offset to the function it describes and the second
word instructions for unwinding if an exception is thrown from that
function. The SHF_LINK_ORDER processing will order the table in ascending
order of the functions described by the exception table entries. As the
address range of an exception table entry is terminated by the next table
entry, it is possible to merge consecutive table entries that have
identical unwind instructions.
For this implementation we define a table entry to be identical if:
- Both entries are the special EXIDX_CANTUNWIND.
- Both entries have the same inline unwind instructions.
We do not attempt to establish if table entries that are references to
.ARM.extab sections are identical.
This implementation works at a granularity of a single .ARM.exidx
InputSection. If all entries in the InputSection are identical to the
previous table entry we can remove the InputSection. A more sophisticated
but more complex implementation would rewrite InputSection contents so that
duplicates within a .ARM.exidx InputSection can be merged.
Differential Revision: https://reviews.llvm.org/D40967
llvm-svn: 320803
This patch provides the mechanism to fix instances of the instruction
sequence that may trigger the cortex-a53 843419 erratum. The fix is
provided by an alternative instruction sequence to remove one of the
erratum conditions. To reach this alternative instruction sequence we
replace the original instruction with a branch to the alternative
sequence. The alternative sequence is responsible for branching back to
the original.
As there is only erratum to fix the implementation is specific to
AArch64 and the specific erratum conditions. It should be generalizable
to other targets and erratum if needed.
Differential Revision: https://reviews.llvm.org/D36749
llvm-svn: 320800
It is currently in InputSectionBase. Only InputSections are used in
ICF, so Repl should be move to InputSection to clear the class
hierarchy or, like this patch does, to SectionBase for convenience.
The convenience of having it on the base class is that we can just
access the replacement without having to first check if it is an
InputSection. It is a bit less code and a bit faster as some of this
code is very hot.
I got up to 1.77% improvement in clang-gdb-index and no regressions
according to lnt.
llvm-svn: 320654
By moving this step before thunk creation and other processing that depends
on the size of sections, we permit removal of duplicates in the .ARM.exidx
section.
Differential Revision: https://reviews.llvm.org/D40964
llvm-svn: 320477
This fixes pr35570.
We were creating these symbols after parsing version scripts, so they
could not be versioned.
We cannot move the version script parsing later because we need it for
lto.
One option is to move both addReservedSymbols and
createSyntheticSections earlier. The disadvantage is that some
sections created by createSyntheticSections replace other input
sections. For example, gdb index replaces .debug_gnu_pubnames, so it
wants to run after gc sections so that it can set S->Live to false.
What this patch does instead is to move just the ElfHeader creation
early.
llvm-svn: 320390
Add a new file AArch64ErrataFix.cpp that implements the logic to scan for
the Cortex-A53 Erratum 843419. This involves finding all the executable
code, disassembling the instructions that might trigger the erratum and
reporting a message if the sequence is detected.
At this stage we do not attempt to fix the erratum, this functionality
will be added in a later patch. See D36749 for proposal.
Differential Revision: https://reviews.llvm.org/D36742
llvm-svn: 319780
When a linker script is used with a pattern like { *(.bss .bss.*) } the
InX::BssRelRo section will match against .bss.*. By matching on the name
only, in the same way that .data.rel.ro works we prevent this
from happening, but permit scripts that want to explicitly provide
a .bss.rel.ro OutputSection.
Differential Revision: https://reviews.llvm.org/D40735
llvm-svn: 319755
PR35478 https://bugs.llvm.org/show_bug.cgi?id=35478 points out a flaw
in the implementation of r318924 from D40364. The implementation
depends on the Size field being set or the SyntheticSection::empty()
being accurate. These functions are not reliable as some linker script
commands that have yet to be processed may affect the results, causing
some non-zero size sections to be reported as zero size.
I think the first step is to revert r318924 and come up with a better
solution for the underlying problem rather than trying to layer more
heuristics onto the zero sized output section.
Chances are I'll be out of office by the time anyone sees this so feel
free to commit the revert if you agree with me.
Fixes PR35478
Current thoughts on the underlying problem:
Revisiting the motivation for adding the zero size check in the first
place; it was to prevent 0 sized SyntheticSections that a user does
not have full control over from needlessly breaking the PT_GNU_RELRO,
rather than trying to accommodate arbitrarily complex linker
scripts. Looking at the code, it looks like
removeUnusedSyntheticSections() should remove zero sized synthetic
sections. It does, but it doesn't set the Parent to nullptr, this has
the side effect that Sec == InX::BssRelRo->getParent() will make the
parent OutputSection of InX::BssRelRo RelRo even if there is no
InX::BssRelRo.
I tried a quick experiment with setting the Parent to nullptr and this
flushed out a few interesting test failures, it feels like playing
Jenga with every change:
In the isRelroSection() we have to consider the case where there
is no .plt and .plt.got but there is a ifunc plt with accompanying
(ifunc .got or .plt.got)
The PPC64 has PltHeaderSize == 0. Unfortunately HeaderSize == 0 is
used to choose between the ifunc plt or normal plt. We seem to get
away with this at the moment, but tests start to fail when Parent
is set to nullptr for the .got.plt.
The InX::BssRelRo and InX::Bss never get their sizes set and they
are always removed by removeUnusedSyntheticSections(), their
purpose seems to be as some kind of proxy for add .bss or
.bss.relro InputSections into their parent OutputSections, they
therefore don't behave like other SyntheticSections anyway.
My thinking is that some work is needed to make sure that the Sec ==
SyntheticSection->getParent() does a bit more checking before
returning true, particularly for InX::BssRelRo as that has special
behaviour. I'll hope to post something for review as soon as possible.
Patch by Peter Smith!
llvm-svn: 319563
This is for "Bug 35474 - --emit-relocs produces wrongly-named reloc sections".
LLD currently for scripts like:
.text.boot : { *(.text.boot) }
emits relocation section with name .rela.text because does not take
redefined name of output section into account and builds section name
using rules for non-scripted case. Patch fixes this oddness.
Differential revision: https://reviews.llvm.org/D40652
llvm-svn: 319526
This includes a fix to mark copy reloc aliases as used.
Original message:
[ELF] Do not keep symbols if they referenced only from discarded sections.
This patch also ensures that in case of "--as-needed" is used,
DT_NEEDED entries are not created if they are required only by
these eliminated symbols.
llvm-svn: 319215
This patch also ensures that in case of "--as-needed" is used,
DT_NEEDED entries are not created if they are required only by
these eliminated symbols.
Differential Revision: https://reviews.llvm.org/D38790
llvm-svn: 319008
LLD uses .bss.rel.ro for read-only copy relocations whereas the ld.bfd and
gold linkers use .data.rel.ro. In some linker scripts including ld.bfd's
internal linker script, the relro sections are placed sequentially assuming
.data.rel.ro is used. LLD's use of .bss.rel.ro means that the copy
relocations get matched into the .bss section causing the relro sections to
be non-contiguous.
This change checks for a .data.rel.ro OutputSection when a linker script
with the SECTIONS command is used. The section will match in the
.data.rel.ro output section and will maintain contiguous relro.
Differential Revision: https://reviews.llvm.org/D40365
Fixes PR35265
llvm-svn: 318940
When checking for contiguous relro sections we can skip over empty sections.
If there is an empty non-relro section in the middle of a contiguous block
of relro sections then it cannot be written to so it is safe to include in
PT_GNU_RELRO header. If there is a contiguous block of empty relro sections
then no PT_GNU_RELRO header is required for them.
Differential Revision: https://reviews.llvm.org/D40364
llvm-svn: 318924
If a linker script is used that names linker generated synthetic sections
it is possible that the OutputSections for which isRelroSection() is true
are not contiguous. When the relro sections are not contiguous we cannot
describe them with a single PT_GNU_RELRO PHDR. Unfortunately at least one
contemporary dynamic loader only supports one PT_GNU_RELRO PHDR so we
cannot output more than one of these PHDRs. As not including relro
sections in the PHDR will lead to security sensitive sections being
writeable we choose to give an error message instead.
Differential Revision: https://reviews.llvm.org/D40359
[ELF] Skip over empty sections when checking for contiguous relro
llvm-svn: 318920
This fixes PR35223.
Here I enabled SHF_MERGE section content merging for -r like
we do for regular linking.
Differential revision: https://reviews.llvm.org/D40026
llvm-svn: 318516
Previously our relocations we rewrote were broken for that case.
We emited incorrect addend and broken relocation info field
because did not produce section symbol for mergeable synthetic sections.
Differential revision: https://reviews.llvm.org/D40070
llvm-svn: 318394
It is really hard to cover restarts in a debugger, SIGKILL or power
failures. I will try to handle them in a followup patch, but it will
not support all the systems lld has to run on.
RemoveFileOnSignal takes care of crashes.
So what is left is making sure all regular exits delete the file. This
patch does that by moving the buffer to error handling. That is a bit
of a hack, but seemed better than to generalize it to take a callback on
construction.
I will implement this on COFF on the next patch.
llvm-svn: 318060
Now that DefinedRegular is the only remaining derived class of
Defined, we can merge the two classes.
Differential Revision: https://reviews.llvm.org/D39667
llvm-svn: 317448
That class is used only by LinkerScript.cpp, so we should move it to
that file. Also, it no longer has to be a "factory" class. It can just
be a non-member function.
llvm-svn: 317427
Now that we have only SymbolBody as the symbol class. So, "SymbolBody"
is a bit strange name now. This is a mechanical change generated by
perl -i -pe s/SymbolBody/Symbol/g $(git grep -l SymbolBody lld/ELF lld/COFF)
nd clang-format-diff.
Differential Revision: https://reviews.llvm.org/D39459
llvm-svn: 317370
StringTableSection does not implement postThunkContents, so calling it on these
sections is pointless (it calls an empty virtual function), and we can remove it.
Reviewers: ruiu
Differential Revision: https://reviews.llvm.org/D39460
llvm-svn: 317014
SymbolBody and Symbol were separated classes due to a historical reason.
Symbol used to be a pointer to a SymbolBody, and the relationship
between Symbol and SymbolBody was n:1.
r2681780 changed that. Since that patch, SymbolBody and Symbol are
allocated next to each other to improve memory locality, and they have
1:1 relationship now. So, the separation of Symbol and SymbolBody no
longer makes sense.
This patch merges them into one class. In order to avoid updating too
many places, I chose SymbolBody as a unified name. I'll rename it Symbol
in a follow-up patch.
Differential Revision: https://reviews.llvm.org/D39406
llvm-svn: 317006
When there is no SECTION commands given, all sections are
technically orphans, but now we handle script orphans sections
and regular "orphans" sections for non-scripted case differently,
though we can handle them at one place.
Patch do that change.
Differential revision: https://reviews.llvm.org/D39045
llvm-svn: 316984
It does not seem that createSections() is a good place for
applying sorting. Patch changes code to do that inside
sortSections(), which looks more appropriate place.
Differential revision: https://reviews.llvm.org/D39371
llvm-svn: 316893
edata needs to be set to the end of the last mapped initialized
section. We were previously mishandling the case where there were no
non-mapped sections by setting it to the end of the last section in
the output file.
Differential Revision: https://reviews.llvm.org/D39399
llvm-svn: 316877
DSO is short for dynamic shared object, so the function name was a
little confusing because it sounded like it didn't work when we were
a creating statically-linked executable or something.
What we mean by "DSO" here is the current output file that we are
creating. Thus the new name. Alternatively, we could call it the current
ELF module, but "module" is a overloaded word, so I avoided that.
llvm-svn: 316809
The Android relocation packing format is a more compact
format for dynamic relocations in executables and DSOs
that is based on delta encoding and SLEBs. An overview
of the format can be found in the Android source code:
https://android.googlesource.com/platform/bionic/+/refs/heads/master/tools/relocation_packer/src/delta_encoder.h
This patch implements relocation packing using that format.
This implementation uses a more intelligent algorithm for compressing
relative relocations than Android's own relocation packer. As a
result it can generally create smaller relocation sections than
that packer. If I link Chromium for Android targeting ARM32 I get a
.rel.dyn of size 174693 bytes, as compared to 371832 bytes with gold
and the Android packer.
Differential Revision: https://reviews.llvm.org/D39152
llvm-svn: 316775
It was reported (https://reviews.llvm.org/D38724#902841) that when we use
-ffunction-sections --emit-relocs build, REL[A] output section receives the name of first
input section, like .rela.text.first_function_in_text rather than .rela.text.
It is probably not really an issue as sh_info still points to correct target section, but
it does not look clean in output and allows internal section name to leak there,
what at least looks confusing and is not consistent with ld.bfd.
Patch changes this behavior so that target output section name is used as a base.
Differential revision: https://reviews.llvm.org/D39242
llvm-svn: 316760
This moves reporting of garbage collected sections right after
we do GC. That simplifies things.
Differential revision: https://reviews.llvm.org/D39058
llvm-svn: 316759
This change allows Thunks to be added on multiple passes. To do this we must
merge only the thunks added in each pass, and deal with thunks that have
drifted out of range of their callers.
A thunk may end out of range of its caller if enough thunks are added in
between the caller and the thunk. To handle this we create another thunk.
Differential Revision: https://reviews.llvm.org/D34692
llvm-svn: 316754
Igor Kudrin