This commit adds support for chained fixups, which were introduced in
Apple's late 2020 OS releases. This format replaces the dyld opcodes
used for supplying rebase and binding information, and encodes most of
that data directly in the memory location that will have the fixup
applied.
This reduces binary size and is a requirement for page-in linking, which
will be available starting with macOS 13.
A high-level overview of the format and my implementation can be found
in SyntheticSections.h.
This feature is currently gated behind the `-fixup_chains` flag, and
will be enabled by default for supported targets in a later commit.
Like in ld64, lazy binding is disabled when chained fixups are in use,
and the `-init_offsets` transformation is performed by default.
Differential Revision: https://reviews.llvm.org/D132560
Previously, we would add entries to DataInCodeSection in the order they
appeared in input files. Because of this, entries would not be sorted if
sections were reordered due to e.g. `-order_file` or call graph profile
sorting. ld64 always keeps data-in-code information sorted.
This commit also fixes an incorrect assertion. The original assertion
from D103006 used to check that data-in-code entries are sorted in the
input objects -- likely because we use binary search on that data. In
D115556, the assertion was moved into `collectDataInCodeEntries`, but
the checked variable's name was not changed, so it ended up checking the
final contents of the DataInCodeSection.
We no longer crash when building LLVM with PGO using an asserts build of
LLD as the linker.
Fixes https://bugs.chromium.org/p/chromium/issues/detail?id=1265937
Numbers for linking the Chromium Framework reproducer from #48001, which
has 6829 data-in-code entries:
x before
+ after
N Min Max Median Avg Stddev
x 20 2.1076453 2.3059683 2.1132485 2.1350302 0.049905767
+ 20 2.1069031 2.3915262 2.14465 2.1728429 0.084065898
No difference proven at 95.0% confidence
Differential Revision: https://reviews.llvm.org/D133581
This section stores 32-bit `__TEXT` segment offsets of initializer
functions, and is used instead of `__mod_init_func` when chained fixups
are enabled.
Storing the offsets lets us avoid emitting fixups for the initializers.
Differential Revision: https://reviews.llvm.org/D132947
We now re-use the existing needsBinding() helper to determine if a
branch has to go through a stub. The logic for determining which type of
binding is needed is moved inside StubsSection::addEntry().
This is an NFC refactor that simplifies my diff that adds support for
chained fixups.
Differential Revision: https://reviews.llvm.org/D132476
Apple Clang in Xcode 14 introduced a new feature for reducing the
overhead of objc_msgSend calls by deduplicating the setup calls for each
individual selector. This works by clang adding undefined symbols for
each selector called in a translation unit, such as `_objc_msgSend$foo`
for calling the `foo` method on any `NSObject`. There are 2
different modes for this behavior, the default directly does the setup
for `_objc_msgSend` and calls it, and the smaller option does the
selector setup, and then calls the standard `_objc_msgSend` stub
function.
The general overview of how this works is:
- Undefined symbols with the given prefix are collected
- The suffix of each matching undefined symbol is added as a string to
`__objc_methname`
- A pointer is added for every method name in the `__objc_selrefs`
section
- A `got` entry is emitted for `_objc_msgSend`
- Stubs are emitting pointing to the synthesized locations
Notes:
- Both `__objc_methname` and `__objc_selrefs` can also exist from object
files, so their contents are merged with our synthesized contents
- The compiler emits method names for defined methods, but not for
undefined symbols you call, but stubs are used for both
- This only implements the default "fast" mode currently just to reduce
the diff, I also doubt many folks will care to swap modes
- This only implements this for arm64 and x86_64, we don't need to
implement this for 32 bit iOS archs, but we should implement it for
watchOS archs in a later diff
Differential Revision: https://reviews.llvm.org/D128108
Some header files used
namespace lld {
namespace macho {
// ...
} // namespace macho
std::string toString(const Type &t);
} // namespace lld
In those files, I didn't use a nested namespace since it's not a big win there.
No behavior change.
Differential Revision: https://reviews.llvm.org/D131354
Previously, we treated it as a regular ConcatInputSection. However, ld64
actually parses its contents and uses that to synthesize a single image
info struct, generating one 8-byte section instead of `8 * number of
object files with ObjC code`.
I'm not entirely sure what impact this section has on the runtime, so I
just tried to follow ld64's semantics as closely as possible in this
diff. My main motivation though was to reduce binary size.
No significant perf change on chromium_framework on my 16-core Mac Pro:
base diff difference (95% CI)
sys_time 1.764 ± 0.062 1.748 ± 0.032 [ -2.4% .. +0.5%]
user_time 5.112 ± 0.104 5.106 ± 0.046 [ -0.9% .. +0.7%]
wall_time 6.111 ± 0.184 6.085 ± 0.076 [ -1.6% .. +0.8%]
samples 30 32
Reviewed By: #lld-macho, thakis
Differential Revision: https://reviews.llvm.org/D130125
The error used to look like this:
ld64.lld: error: undefined symbol: _foo
>>> referenced by /path/to/bar.o:(symbol _baz+0x4)
If DWARF line information is available, we now show where in the source
the references are coming from:
ld64.lld: error: unreferenced symbol: _foo
>>> referenced by: bar.cpp:42 (/path/to/bar.cpp:42)
>>> /path/to/bar.o:(symbol _baz+0x4)
The reland is identical to the first time this landed. The fix was in D128294.
This reverts commit 0cc7ad4175.
Differential Revision: https://reviews.llvm.org/D128184
The error used to look like this:
ld64.lld: error: undefined symbol: _foo
>>> referenced by /path/to/bar.o:(symbol _baz+0x4)
If DWARF line information is available, we now show where in the source
the references are coming from:
ld64.lld: error: unreferenced symbol: _foo
>>> referenced by: bar.cpp:42 (/path/to/bar.cpp:42)
>>> /path/to/bar.o:(symbol _baz+0x4)
Differential Revision: https://reviews.llvm.org/D128184
Previously, we only allowed this for DylibSymbols. However, in order to
properly support `-flat_namespace` as well as `-interposable`, we need
to allow this for Defined symbols too. Therefore we hoist the
`lazyBindOffset` and the `stubsHelperIndex` into the parent Symbol
class.
The actual change to support interposition under `-flat_namespace` is in
{D119294}; the NFC changes here have been split out for easier review.
Perf regression isn't stat sig on my 3.2 GHz 16-Core Intel Xeon W linking
chromium_framework:
base diff difference (95% CI)
sys_time 1.227 ± 0.021 1.234 ± 0.031 [ -0.3% .. +1.5%]
user_time 3.665 ± 0.036 3.674 ± 0.035 [ -0.2% .. +0.7%]
wall_time 4.596 ± 0.055 4.609 ± 0.064 [ -0.3% .. +0.9%]
samples 34 47
Max RSS regression is barely stat sig:
base diff difference (95% CI)
time 1003664356.324 ± 15404053.912 1010380403.613 ± 10578309.455 [ +0.0% .. +1.3%]
samples 37 31
Reviewed By: modimo
Differential Revision: https://reviews.llvm.org/D121351
Previously, we aligned every cstring to 16 bytes as a temporary hack to
deal with https://github.com/llvm/llvm-project/issues/50135. However, it
was highly wasteful in terms of binary size.
To recap, in contrast to ELF, which puts strings that need different
alignments into different sections, `clang`'s Mach-O backend puts them
all in one section. Strings that need to be aligned have the .p2align
directive emitted before them, which simply translates into zero padding
in the object file. In other words, we have to infer the alignment of
the cstrings from their addresses.
We differ slightly from ld64 in how we've chosen to align these
cstrings. Both LLD and ld64 preserve the number of trailing zeros in
each cstring's address in the input object files. When deduplicating
identical cstrings, both linkers pick the cstring whose address has more
trailing zeros, and preserve the alignment of that address in the final
binary. However, ld64 goes a step further and also preserves the offset
of the cstring from the last section-aligned address. I.e. if a cstring
is at offset 18 in the input, with a section alignment of 16, then both
LLD and ld64 will ensure the final address is 2-byte aligned (since
`18 == 16 + 2`). But ld64 will also ensure that the final address is of
the form 16 * k + 2 for some k (which implies 2-byte alignment).
Note that ld64's heuristic means that a dedup'ed cstring's final address is
dependent on the order of the input object files. E.g. if in addition to the
cstring at offset 18 above, we have a duplicate one in another file with a
`.cstring` section alignment of 2 and an offset of zero, then ld64 will pick
the cstring from the object file earlier on the command line (since both have
the same number of trailing zeros in their address). So the final cstring may
either be at some address `16 * k + 2` or at some address `2 * k`.
I've opted not to follow this behavior primarily for implementation
simplicity, and secondarily to save a few more bytes. It's not clear to me
that preserving the section alignment + offset is ever necessary, and there
are many cases that are clearly redundant. In particular, if an x86_64 object
file contains some strings that are accessed via SIMD instructions, then the
.cstring section in the object file will be 16-byte-aligned (since SIMD
requires its operand addresses to be 16-byte aligned). However, there will
typically also be other cstrings in the same file that aren't used via SIMD
and don't need this alignment. They will be emitted at some arbitrary address
`A`, but ld64 will treat them as being 16-byte aligned with an offset of
`16 % A`.
I have verified that the two repros in https://github.com/llvm/llvm-project/issues/50135
work well with the new alignment behavior.
Fixes https://github.com/llvm/llvm-project/issues/54036.
Reviewed By: #lld-macho, oontvoo
Differential Revision: https://reviews.llvm.org/D121342
Adds `-pagezero_size`. `-pagezero_size` commonly used for kernel development.
`-pagezero_size` changes the `__PAGEZERO` size, removing that segment if it is set to zero.
One of the four flags from {D118570}
Now with error messages and tests.
Differential Revision: https://reviews.llvm.org/D118724
Added some comments (particularly around finalize() and
finalizeContents()) as well as doing some rephrasing / grammar fixes for
existing comments.
Also did some minor style fixups, such as by putting methods together in
a class definition and having fields of similar types next to each
other.
Reviewed By: #lld-macho, oontvoo
Differential Revision: https://reviews.llvm.org/D118714
Otherwise tools like codesign_allocate will choke. We were already
handling this correctly for the other DYLD_INFO sections.
Doing this correctly is a bit subtle: we don't know if export_size will
be zero until we have run `ExportSection::finalizeContents()`. However,
we must still add the ExportSection to the `__LINKEDIT` segment in order
that it gets sorted during `sortSectionsAndSegments()`.
Reviewed By: #lld-macho, oontvoo
Differential Revision: https://reviews.llvm.org/D112589
WordLiteralSection dedupes literals by content.
WordLiteralInputSection::getOffset() used to read a literal at the passed-in
offset and look up this value in the deduping map to find the offset of the
deduped value.
But it's possible that (e.g.) a 16-byte literal's value is accessed 4 bytes in.
To get the offset at that address, we have to get the deduped value at offset 0
and then apply the offset 4 to the result.
(See also WordLiteralSection::finalizeContents() which fills in those maps.)
Only a problem on arm64 because in x86_64 the offset is part of the instruction
instead of a separate ARM64_RELOC_ADDEND relocation. (See bug for more details.)
Fixes PR51999.
Differential Revision: https://reviews.llvm.org/D112584
**Context:**
This is a second attempt at introducing signature regeneration to llvm-objcopy. In this diff: https://reviews.llvm.org/D109840, a script was introduced to test
the validity of a code signature. In this diff: https://reviews.llvm.org/D109803 (now reverted), an effort was made to extract the signature generation behavior out of LLD into a common location for use in llvm-objcopy. In this diff: https://reviews.llvm.org/D109972 it was decided that there was no appropriate common location and that a small amount of duplication to bring signature generation to llvm-objcopy would be better. This diff introduces this duplication.
**Summary**
Prior to this change, if a LC_CODE_SIGNATURE load command
was included in the binary passed to llvm-objcopy, the command and
associated section were simply copied and included verbatim in the
new binary. If rest of the binary was modified at all, this results
in an invalid Mach-O file. This change regenerates the signature
rather than copying it.
The code_signature_lc.test test was modified to include the yaml
representation of a small signed MachO executable in order to
effectively test the signature generation.
Reviewed By: alexander-shaposhnikov, #lld-macho
Differential Revision: https://reviews.llvm.org/D111164
Move the functionality in lld that handles writing of the LC_CODE_SIGNATURE load command and associated data section to a central reusable location.
This change is in preparation for another change that modifies llvm-objcopy to reproduce the LC_CODE_SIGNATURE load command and corresponding
data section to maintain the validity of signed macho object files passed through llvm-objcopy.
Reviewed By: #lld-macho, int3, oontvoo
Differential Revision: https://reviews.llvm.org/D109803
ICF previously operated only within a given OutputSection. We would
merge all CFStrings first, then merge all regular code sections in a
second phase. This worked fine since CFStrings would never reference
regular `__text` sections. However, I would like to expand ICF to merge
functions that reference unwind info. Unwind info references the LSDA
section, which can in turn reference the `__text` section, so we cannot
perform ICF in phases.
In order to have ICF operate on InputSections spanning multiple
OutputSections, we need a way to distinguish InputSections that are
destined for different OutputSections, so that we don't fold across
section boundaries. We achieve this by creating OutputSections early,
and setting `InputSection::parent` to point to them. This is what
LLD-ELF does. (This change should also make it easier to implement the
`section$start$` symbols.)
This diff also folds InputSections w/o checking their flags, which I
think is the right behavior -- if they are destined for the same
OutputSection, they will have the same flags in the output (even if
their input flags differ). I.e. the `parent` pointer check subsumes the
`flags` check. In practice this has nearly no effect (ICF did not become
any more effective on chromium_framework).
I've also updated ICF.cpp's block comment to better reflect its current
status.
Reviewed By: #lld-macho, smeenai
Differential Revision: https://reviews.llvm.org/D105641
Size-wise, BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM is the most
expensive opcode, since it comes with an associated symbol string. We
were previously emitting it once per binding, instead of once per
symbol. This diff groups all bindings for a given symbol together and
ensures we only emit one such opcode per symbol. This matches ld64's
behavior.
While this is a relatively small win on chromium_framework (-72KiB), for
programs that have more dynamic bindings, the difference can be quite
large.
This change is perf-neutral when linking chromium_framework.
Reviewed By: #lld-macho, thakis
Differential Revision: https://reviews.llvm.org/D105075
This is a pretty big refactoring diff, so here are the motivations:
Previously, ICF ran after scanRelocations(), where we emitting
bind/rebase opcodes etc. So we had a bunch of redundant leftovers after
ICF. Having ICF run before Writer seems like a better design, and is
what LLD-ELF does, so this diff refactors it accordingly.
However, ICF had two dependencies on things occurring in Writer: 1) it
needs literals to be deduplicated beforehand and 2) it needs to know
which functions have unwind info, which was being handled by
`UnwindInfoSection::prepareRelocations()`.
In order to do literal deduplication earlier, we need to add literal
input sections to their corresponding output sections. So instead of
putting all input sections into the big `inputSections` vector, and then
filtering them by type later on, I've changed things so that literal
sections get added directly to their output sections during the 'gather'
phase. Likewise for compact unwind sections -- they get added directly
to the UnwindInfoSection now. This latter change is not strictly
necessary, but makes it easier for ICF to determine which functions have
unwind info.
Adding literal sections directly to their output sections means that we
can no longer determine `inputOrder` from iterating over
`inputSections`. Instead, we store that order explicitly on
InputSection. Bloating the size of InputSection for this purpose would
be unfortunate -- but LLD-ELF has already solved this problem: it reuses
`outSecOff` to store this order value.
One downside of this refactor is that we now make an additional pass
over the unwind info relocations to figure out which functions have
unwind info, since want to know that before `processRelocations()`. I've
made sure to run that extra loop only if ICF is enabled, so there should
be no overhead in non-optimizing runs of the linker.
The upside of all this is that the `inputSections` vector now contains
only ConcatInputSections that are destined for ConcatOutputSections, so
we can clean up a bunch of code that just existed to filter out other
elements from that vector.
I will test for the lack of redundant binds/rebases in the upcoming
cfstring deduplication diff. While binds/rebases can also happen in the
regular `.text` section, they're more common in `.data` sections, so it
seems more natural to test it that way.
This change is perf-neutral when linking chromium_framework.
Reviewed By: oontvoo
Differential Revision: https://reviews.llvm.org/D105044
Previously, we only applied the renames to
ConcatOutputSections.
Reviewed By: #lld-macho, thakis
Differential Revision: https://reviews.llvm.org/D105079
Fixes PR50637.
Downstream bug: https://crbug.com/1218958
Currently, we split __cstring along symbol boundaries with .subsections_via_symbols
when not deduplicating, and along null bytes when deduplicating. This change splits
along null bytes unconditionally, and preserves original alignment in the non-
deduplicated case.
Removing subsections-section-relocs.s because with this change, __cstring
is never reordered based on the order file.
Differential Revision: https://reviews.llvm.org/D104919
Literal sections can be deduplicated before running ICF. That makes it
easy to compare them during ICF: we can tell if two literals are
constant-equal by comparing their offsets in their OutputSection.
LLD-ELF takes a similar approach.
Reviewed By: #lld-macho, gkm
Differential Revision: https://reviews.llvm.org/D104671
...instead of S_NON_LAZY_SYMBOL_POINTERS. This matches ld64.
Part of PR50769.
While here, also remove an old TODO that was done in D87178.
Differential Revision: https://reviews.llvm.org/D104594
I wanted to see if we would get any perf wins out of this, but
it doesn't seem to be the case. But it still seems worth committing.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D104200
We don't need to define any special behavior for this section,
so creating a subclass for it is redundant.
Reviewed By: #lld-macho, thakis
Differential Revision: https://reviews.llvm.org/D104199
Sort the addresses stored in FunctionStarts section.
Previously we were encoding potentially large numbers (due to unsigned overflow).
Test plan: make check-all
Differential revision: https://reviews.llvm.org/D103662
Conceptually, the implementation is pretty straightforward: we put each
literal value into a hashtable, and then write out the keys of that
hashtable at the end.
In contrast with ELF, the Mach-O format does not support variable-length
literals that aren't strings. Its literals are either 4, 8, or 16 bytes
in length. LLD-ELF dedups its literals via sorting + uniq'ing, but since
we don't need to worry about overly-long values, we should be able to do
a faster job by just hashing.
That said, the implementation right now is far from optimal, because we
add to those hashtables serially. To parallelize this, we'll need a
basic concurrent hashtable (only needs to support concurrent writes w/o
interleave reads), which shouldn't be to hard to implement, but I'd like
to punt on it for now.
Numbers for linking chromium_framework on my 3.2 GHz 16-Core Intel Xeon W:
N Min Max Median Avg Stddev
x 20 4.27 4.39 4.315 4.3225 0.033225703
+ 20 4.36 4.82 4.44 4.4845 0.13152846
Difference at 95.0% confidence
0.162 +/- 0.0613971
3.74783% +/- 1.42041%
(Student's t, pooled s = 0.0959262)
This corresponds to binary size savings of 2MB out of 335MB, or 0.6%.
It's not a great tradeoff as-is, but as mentioned our implementation can
be signficantly optimized, and literal dedup will unlock more
opportunities for ICF to identify identical structures that reference
the same literals.
Reviewed By: #lld-macho, gkm
Differential Revision: https://reviews.llvm.org/D103113
Our implementation draws heavily from LLD-ELF's, which in turn delegates
its string deduplication to llvm-mc's StringTableBuilder. The messiness of
this diff is largely due to the fact that we've previously assumed that
all InputSections get concatenated together to form the output. This is
no longer true with CStringInputSections, which split their contents into
StringPieces. StringPieces are much more lightweight than InputSections,
which is important as we create a lot of them. They may also overlap in
the output, which makes it possible for strings to be tail-merged. In
fact, the initial version of this diff implemented tail merging, but
I've dropped it for reasons I'll explain later.
**Alignment Issues**
Mergeable cstring literals are found under the `__TEXT,__cstring`
section. In contrast to ELF, which puts strings that need different
alignments into different sections, clang's Mach-O backend puts them all
in one section. Strings that need to be aligned have the `.p2align`
directive emitted before them, which simply translates into zero padding
in the object file.
I *think* ld64 extracts the desired per-string alignment from this data
by preserving each string's offset from the last section-aligned
address. I'm not entirely certain since it doesn't seem consistent about
doing this; but perhaps this can be chalked up to cases where ld64 has
to deduplicate strings with different offset/alignment combos -- it
seems to pick one of their alignments to preserve. This doesn't seem
correct in general; we can in fact can induce ld64 to produce a crashing
binary just by linking in an additional object file that only contains
cstrings and no code. See PR50563 for details.
Moreover, this scheme seems rather inefficient: since unaligned and
aligned strings are all put in the same section, which has a single
alignment value, it doesn't seem possible to tell whether a given string
doesn't have any alignment requirements. Preserving offset+alignments
for strings that don't need it is wasteful.
In practice, the crashes seen so far seem to stem from x86_64 SIMD
operations on cstrings. X86_64 requires SIMD accesses to be
16-byte-aligned. So for now, I'm thinking of just aligning all strings
to 16 bytes on x86_64. This is indeed wasteful, but implementation-wise
it's simpler than preserving per-string alignment+offsets. It also
avoids the aforementioned crash after deduplication of
differently-aligned strings. Finally, the overhead is not huge: using
16-byte alignment (vs no alignment) is only a 0.5% size overhead when
linking chromium_framework.
With these alignment requirements, it doesn't make sense to attempt tail
merging -- most strings will not be eligible since their overlaps aren't
likely to start at a 16-byte boundary. Tail-merging (with alignment) for
chromium_framework only improves size by 0.3%.
It's worth noting that LLD-ELF only does tail merging at `-O2`. By
default (at `-O1`), it just deduplicates w/o tail merging. @thakis has
also mentioned that they saw it regress compressed size in some cases
and therefore turned it off. `ld64` does not seem to do tail merging at
all.
**Performance Numbers**
CString deduplication reduces chromium_framework from 250MB to 242MB, or
about a 3.2% reduction.
Numbers for linking chromium_framework on my 3.2 GHz 16-Core Intel Xeon W:
N Min Max Median Avg Stddev
x 20 3.91 4.03 3.935 3.95 0.034641016
+ 20 3.99 4.14 4.015 4.0365 0.0492336
Difference at 95.0% confidence
0.0865 +/- 0.027245
2.18987% +/- 0.689746%
(Student's t, pooled s = 0.0425673)
As expected, cstring merging incurs some non-trivial overhead.
When passing `--no-literal-merge`, it seems that performance is the
same, i.e. the refactoring in this diff didn't cost us.
N Min Max Median Avg Stddev
x 20 3.91 4.03 3.935 3.95 0.034641016
+ 20 3.89 4.02 3.935 3.9435 0.043197831
No difference proven at 95.0% confidence
Reviewed By: #lld-macho, gkm
Differential Revision: https://reviews.llvm.org/D102964
Also adds support for live_support sections, no_dead_strip sections,
.no_dead_strip symbols.
Chromium Framework 345MB unstripped -> 250MB stripped
(vs 290MB unstripped -> 236M stripped with ld64).
Doing dead stripping is a bit faster than not, because so much less
data needs to be processed:
% ministat lld_*
x lld_nostrip.txt
+ lld_strip.txt
N Min Max Median Avg Stddev
x 10 3.929414 4.07692 4.0269079 4.0089678 0.044214794
+ 10 3.8129408 3.9025559 3.8670411 3.8642573 0.024779651
Difference at 95.0% confidence
-0.144711 +/- 0.0336749
-3.60967% +/- 0.839989%
(Student's t, pooled s = 0.0358398)
This interacts with many parts of the linker. I tried to add test coverage
for all added `isLive()` checks, so that some test will fail if any of them
is removed. I checked that the test expectations for the most part match
ld64's behavior (except for live-support-iterations.s, see the comment
in the test). Interacts with:
- debug info
- export tries
- import opcodes
- flags like -exported_symbol(s_list)
- -U / dynamic_lookup
- mod_init_funcs, mod_term_funcs
- weak symbol handling
- unwind info
- stubs
- map files
- -sectcreate
- undefined, dylib, common, defined (both absolute and normal) symbols
It's possible it interacts with more features I didn't think of,
of course.
I also did some manual testing:
- check-llvm check-clang check-lld work with lld with this patch
as host linker and -dead_strip enabled
- Chromium still starts
- Chromium's base_unittests still pass, including unwind tests
Implemenation-wise, this is InputSection-based, so it'll work for
object files with .subsections_via_symbols (which includes all
object files generated by clang). I first based this on the COFF
implementation, but later realized that things are more similar to ELF.
I think it'd be good to refactor MarkLive.cpp to look more like the ELF
part at some point, but I'd like to get a working state checked in first.
Mechanical parts:
- Rename canOmitFromOutput to wasCoalesced (no behavior change)
since it really is for weak coalesced symbols
- Add noDeadStrip to Defined, corresponding to N_NO_DEAD_STRIP
(`.no_dead_strip` in asm)
Fixes PR49276.
Differential Revision: https://reviews.llvm.org/D103324
The ELF format has the concept of merge sections (marked by SHF_MERGE),
which contain data that can be safely deduplicated. The Mach-O
equivalents are called literal sections (marked by S_CSTRING_LITERALS or
S_{4,8,16}BYTE_LITERALS). While the Mach-O format doesn't use the word
'merge', to avoid confusion, I've renamed our MergedOutputSection to
ConcatOutputSection. I believe it's a more descriptive name too.
This renaming sets the stage for {D102964}.
Reviewed By: #lld-macho, alexshap
Differential Revision: https://reviews.llvm.org/D102971
* Move `static_asserts` into cpp instead of header file. I noticed they
had been separated from the main class definition in the header, so I
set about to clean that up, then figured it made more sense as part of
the cpp file so as not to incur unnecessary compile-time overhead.
* Remove unnecessary `virtual`s
* Remove unnecessary comment / reword another comment
Extend the range of calls beyond an architecture's limited branch range by first calling a thunk, which loads the far address into a scratch register (x16 on ARM64) and branches through it.
Other ports (COFF, ELF) use multiple passes with successively-refined guesses regarding the expansion of text-space imposed by thunk-space overhead. This MachO algorithm places thunks during MergedOutputSection::finalize() in a single pass using exact thunk-space overheads. Thunks are kept in a separate vector to avoid the overhead of inserting into the `inputs` vector of `MergedOutputSection`.
FIXME:
* arm64-stubs.s test is broken
* add thunk tests
* Handle thunks to DylibSymbol in MergedOutputSection::finalize()
Differential Revision: https://reviews.llvm.org/D100818
@thakis pointed out that `mach_header` and `mach_header_64`
actually have the same set of (used) fields, with the 64-bit version
having extra padding. So we can access the fields we need using the
single `mach_header` type instead of using templates to switch between
the two.
I also spotted a potential issue where hasObjCSection tries to parse a
file w/o checking if it does indeed match the target arch... As such,
I've added a quick magic number check to ensure we don't access invalid
memory during `findCommand()`.
Addresses PR50180.
Reviewed By: #lld-macho, thakis
Differential Revision: https://reviews.llvm.org/D101724
This diff creates an empty XAR file and copies it into
`__LLVM,__bundle`. Follow-up work will actually populate the contents of
that XAR.
Reviewed By: #lld-macho, gkm
Differential Revision: https://reviews.llvm.org/D100650
This could probably have been part of D99633, but I split it up to make
things a bit more reviewable. I also fixed some bugs in the implementation that
were masked through integer underflows when operating in 64-bit mode.
Reviewed By: #lld-macho, gkm
Differential Revision: https://reviews.llvm.org/D99823
This could probably have been part of D99633, but I split it up to make
things a bit more reviewable. I also fixed some bugs in the implementation that
were masked through integer underflows when operating in 64-bit mode.
Reviewed By: #lld-macho, gkm
Differential Revision: https://reviews.llvm.org/D99823
Benchmarking chromium_framework on a 3.2 GHz 16-Core Intel Xeon W Mac Pro:
N Min Max Median Avg Stddev
x 20 4.33 4.42 4.37 4.37 0.021026299
+ 20 4.12 4.23 4.18 4.175 0.035318103
Difference at 95.0% confidence
-0.195 +/- 0.0186025
-4.46224% +/- 0.425686%
(Student's t, pooled s = 0.0290644)
Reviewed By: #lld-macho, gkm
Differential Revision: https://reviews.llvm.org/D99998
Fangrui Song