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The next change will move these methods from the base class.
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The object file format specific derived classes are used in context
where the type is statically known. We don't use isa/dyn_cast and we
want to eliminate MCSymbol::Kind in the base class.
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The object file format specific derived classes are used in context
where the type is statically known. We don't use isa/dyn_cast and we
want to eliminate MCSymbol::Kind in the base class.
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The fixed-size content of the MCFragment object will be stored as
trailing data (#150846). Any post-assembler-layout adjustments must
target the variable-size tail.
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The object file format specific derived classes are used in context like
MCStreamer and MCObjectTargetWriter where the type is statically known.
We don't use isa/dyn_cast and we want to eliminate
MCSection::SectionVariant in the base class.
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Make the fixed-size part of MCFragment append-only to support allocating
content as trailing data. The `doneAppending` API is reserved by
MCStreamer API before finish and should not be used by the addrsig and
call-graph-profile features.
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The term BSS (Block Started by Symbol) is a standard, widely recognized
term, available in the a.out object file format and adopted by formats
like COFF, XCOFF, Mach-O (called S_ZEROFILL while `__bss` is also used),
and ELF. To avoid introducing unfamiliar terms, we should use
isBSSSection instead of isVirtualSection.
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Refactor the fragment representation of `push rax; jmp foo; nop; jmp foo`,
previously encoded as
`MCDataFragment(nop); MCRelaxableFragment(jmp foo); MCDataFragment(nop); MCRelaxableFragment(jmp foo)`,
to
```
MCFragment(fixed: push rax, variable: jmp foo)
MCFragment(fixed: nop, variable: jmp foo)
```
Changes:
* Eliminate MCEncodedFragment, moving content and fixup storage to MCFragment.
* The new MCFragment contains a fixed-size content (similar to previous
MCDataFragment) and an optional variable-size tail.
* The variable-size tail supports FT_Relaxable, FT_LEB, FT_Dwarf, and
FT_DwarfFrame, with plans to extend to other fragment types.
dyn_cast/isa should be avoided for the converted fragment subclasses.
* In `setVarFixups`, source fixup offsets are relative to the variable part's start.
Stored fixup (in `FixupStorage`) offsets are relative to the fixed part's start.
A lot of code does `getFragmentOffset(Frag) + Fixup.getOffset()`,
expecting the fixup offset to be relative to the fixed part's start.
* HexagonAsmBackend::fixupNeedsRelaxationAdvanced needs to know the
associated instruction for a fixup. We have to add a `const MCFragment &` parameter.
* In MCObjectStreamer, extend `absoluteSymbolDiff` to apply to
FT_Relaxable as otherwise there would be many more FT_DwarfFrame
fragments in -g compilations.
https://llvm-compile-time-tracker.com/compare.php?from=28e1473e8e523150914e8c7ea50b44fb0d2a8d65&to=778d68ad1d48e7f111ea853dd249912c601bee89&stat=instructions:u
```
stage2-O0-g instructins:u geomeon (-0.07%)
stage1-ReleaseLTO-g (link only) max-rss geomean (-0.39%)
```
```
% /t/clang-old -g -c sqlite3.i -w -mllvm -debug-only=mc-dump &| awk '/^[0-9]+/{s[$2]++;tot++} END{print "Total",tot; n=asorti(s, si); for(i=1;i<=n;i++) print si[i],s[si[i]]}'
Total 59675
Align 2215
Data 29700
Dwarf 12044
DwarfCallFrame 4216
Fill 92
LEB 12
Relaxable 11396
% /t/clang-new -g -c sqlite3.i -w -mllvm -debug-only=mc-dump &| awk '/^[0-9]+/{s[$2]++;tot++} END{print "Total",tot; n=asorti(s, si); for(i=1;i<=n;i++) print si[i],s[si[i]]}'
Total 32287
Align 2215
Data 2312
Dwarf 12044
DwarfCallFrame 4216
Fill 92
LEB 12
Relaxable 11396
```
Pull Request: https://github.com/llvm/llvm-project/pull/148544
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The file used to define `MCFixupKindInfo`, a simple structure,
which is now in MCAsmBackend.h.
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Moved `Contents` and `Fixups` SmallVector storage to MCSection, enabling
trivial destructors for most fragment subclasses and eliminating the need
for MCFragment::destroy in ~MCSection.
For appending content to the current section, use
getContentsForAppending. During assembler relaxation, prefer
setContents/setFixups, which may involve copying and reduce the benefits
of https://reviews.llvm.org/D145791.
Moving only Contents out-of-line caused a slight performance regression
(Alexis Engelke's 2024 prototype). By also moving Fragments out-of-line,
fragment destructors become trivial, resulting in
neglgible instructions:u increase for "stage2-O0-g" and [large max-rss decrease](https://llvm-compile-time-tracker.com/compare.php?from=84e82746c3ff63ec23a8b85e9efd4f7fccf92590&to=555a28c0b2f8250a9cf86fd267a04b0460283e15&stat=max-rss&linkStats=on)
for the "stage1-ReleaseLTO-g (link only)" benchmark.
(
An older version using fewer inline functions: https://llvm-compile-time-tracker.com/compare.php?from=bb982e733cfcda7e4cfb0583544f68af65211ed1&to=f12d55f97c47717d438951ecddecf8ebd28c296b&linkStats=on
)
Now using plain SmallVector in MCSection for storage, with potential for
future allocator optimizations, such as allocating `Contents` as the
trailing object of MCDataFragment. (GNU Assembler uses gnulib's obstack
for fragment management.)
Co-authored-by: Alexis Engelke <engelke@in.tum.de>
Pull Request: https://github.com/llvm/llvm-project/pull/146307
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... due to their close relationship. MCSection's inline functions (e.g.
iterator) access MCFragment, and we want MCFragment's inline functions
to access MCSection similarly (#146307).
Pull Request: https://github.com/llvm/llvm-project/pull/146315
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Similar to b65760bc7fcdee8179bf1e57fce3786737528dd8 for ELF.
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* Remove the MCAssembler * argument. Change subclasses to use MCAssembler *MCObjectWriter::Asm.
* Remove pure specifier and add an empty implementation
* Change MCFragment * to MCFragment &
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We will increase the use of raw relocation types and eliminate fixup
kinds that correspond to relocation types. The getFixupKindInfo
functions will return an rvalue instead. Let's update the return type
from a const reference to a value type.
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Mach-O's ARM and X86 writers use MCExpr's `SectionAddrMap *Addrs`
argument to compute label differences, which was a bit of a hack. The
AArch64MachObjectWriter does this better by using `getSymbolAddress` in
its `recordRelocation` function.
This commit:
1. Moves the `SectionAddrMap` logic into the Mach-O code, removing the
workaround.
2. Fixes a bug in `MachObjectWriter::getSymbolAddress` where it failed
to subtract the `SymB` value. This bug has been present since commit
b200f93125eb019d69c220fa447faea4f5d4eb8a (2011).
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We will replace the MCSymbolRefExpr member in MCValue with MCSymbol.
This change reduces dependence on MCSymbolRefExpr.
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We will replace the MCSymbolRefExpr member in MCValue with MCSymbol.
This change reduces dependence on MCSymbolRefExpr.
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MCValue::SymB is a MCSymbolRefExpr *, which might become MCSymbol * in
the future. Simplify some code that uses MCValue::SymB.
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Follow-up to d6fbffa23c84e622735b3e880fd800985c1c0072 . This commit
updates all call sites and removes the argument from the function.
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Identified with misc-include-cleaner.
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In a mach_header, the cpusubtype is a 32-bit field, but it's split in 2
subfields:
- the low 24 bits containing the cpu subtype proper, (e.g.,
CPU_SUBTYPE_ARM64E 2)
- the high 8 bits containing a capability field used for additional
feature flags.
Notably, it's only the subtype subfield that participates in fat file
slice discrimination: the caps are ignored.
arm64e uses the caps subfield to encode a ptrauth ABI version:
- 0x80 (CPU_SUBTYPE_PTRAUTH_ABI) denotes a versioned binary
- 0x40 denotes a kernel-ABI binary
- 0x00-0x0F holds the ptrauth ABI version
This teaches the basic obj tools to decode that (or ignore it when
unneeded).
It also teaches the MachO writer to default to emitting versioned
binaries, but with a version of 0 (and without the kernel ABI flag).
Modern arm64e requires versioned binaries: a binary with 0x00 caps in
cpusubtype is now rejected by the linker and everything after. We can
live without the sophistication of specifying the version and kernel ABI
for now.
Co-authored-by: Francis Visoiu Mistrih <francisvm@apple.com>
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We could do the same to COFF once WinCOFFObjectWriter is cleaned up
(#100303).
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The section offset field is only 32 bits; if the computed section offset
is larger, make sure we don't emit a corrupt object file.
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size()
The pointers cannot be mutated even if the dereferenced MCSection can.
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and make some cleanup.
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This variable is similar to `Ordinal` but only used for Mach-O to place
zerofill sections ("virtual sections" in MC term) after non-zerofill ones.
Follow-up to 7840c0066837797cdeb62aab63044b964aa7f372.
Pull Request: https://github.com/llvm/llvm-project/pull/97474
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MCAssembler
Continue the MCAsmLayout removal work started by 67957a45ee1ec42ae1671cdbfa0d73127346cc95.
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Otherwise llvm/test/MC/MachO/empty-twice.ll might fail.
Fixes: 7840c0066837797cdeb62aab63044b964aa7f372 ("[MC] Move MCAsmLayout::SectionOrder to MachObjectWriter::SectionOrder")
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Follow-up to 2c1fb411ce3aed148a278660d215e0f88ff9b9be.
SectionOrder is Mach-O specific to place zerofill sections after
non-zerofill sections in the object writer.
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The MCAsmLayout::* forwarders added by
67957a45ee1ec42ae1671cdbfa0d73127346cc95 have all been removed.
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MCObjectWriter::executePostLayoutBinding
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MCObjectWriter::{writeObject,writeSectionData}
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