Darwin uses two-level-namespace lookup for symbols which means the static
linker records where each symbol must be found at runtime. Thus defining a
symbol in a dylib loaded earlier will not effect where symbols needed by
later dylibs will be found. Instead overriding is done through a section
of type S_INTERPOSING which contains tuples of <interposer, interposee>.
llvm-svn: 221421
The local variable `cfi` became dead in r220730 when it's use was
obviated; it was replaced with a call to read32.
No functionality change intended.
llvm-svn: 221412
All compiler generated mach-o object files are marked with MH_SUBSECTIONS_VIA_SYMBOLS.
But hand written assembly files need to opt-in if they are written correctly.
The flag means the linker can break up a sections at symbol addresses and
dead strip or re-order functions.
This change recognizes object files without the flag and marks its atoms as
not dead strippable and adds a layout-after chain of references so that the
atoms cannot be re-ordered.
llvm-svn: 220348
First, add a comment to support more variation in FDE formats. Second, refactor
fde -> function handling into a separate function living in the ArchHandler.
llvm-svn: 219959
Not all situations are representable in the compressed __unwind_info format,
and when this happens the entry needs to point to the more general __eh_frame
description.
Just x86_64 implementation for now.
rdar://problem/18208653
llvm-svn: 219836
We'll also need references back to the CIE eventually, but for now making sure
we can work out what an FDE is referring to is enough.
The actual kind of reference needs to be different between architectures,
probably because of MachO's chronic shortage of relocation types but I don't
really want to know in case I find out something that distresses me even more.
rdar://problem/18208653
llvm-svn: 219824
Most of the changes are in the new file ArchHandler_arm64.cpp. But a few
things had to be fixed to support 16KB pages (instead of 4KB) which iOS arm64
requires. In addition the StubInfo struct had to be expanded because
arm64 uses two instruction (ADRP/LDR) to load a global which requires two
relocations. The other mach-o arches just needed one relocation.
llvm-svn: 217469
On Darwin at runtime, dyld will prefer to use the export trie of a dylib instead
of the traditional symbol table (which is large and requires a binary search).
This change enables the linker to generate an export trie and to prefer it if
found in a dylib being linked against. This also simples the yaml for dylibs
because the yaml form of the trie can be reduced to just a sequence of names.
llvm-svn: 217066
Mach-O symbols can have an attribute on them means their content should never be
dead code stripped. This translates to deadStrip() == deadStripNever.
llvm-svn: 216234
In general two-level namespace means each program records exactly which dylib
each undefined (imported) symbol comes from. But, sometimes the implementor
wants to hide the implementation dylib. For instance libSytem.dylib is the base
dylib all Darwin programs must link with. A few years ago it was split up
into two dozen dylibs by all are hidden behind libSystem.dylib which re-exports
each sub-dylib. All clients still think libSystem.dylib is the implementor.
To support this, the linker must load "indirect" dylibs and not just the
"direct" dylibs specified on the command line. This is done in the
createImplicitFiles() method after all command line specified files are
loaded. Since an indirect dylib may have already been loaded as a direct dylib
(or indirectly via a previous direct dylib), the MachOLinkingContext keeps
a list of all loaded dylibs.
With this change hello world can now be linked against the real OS or SDK.
llvm-svn: 215605
Sometimes compilers emit data into code sections (e.g. constant pools or
jump tables). These runs of data can throw off disassemblers. The solution
in mach-o is that ranges of data-in-code are encoded into a table pointed to
by the LC_DATA_IN_CODE load command.
The way the data-in-code information is encoded into lld's Atom model is that
that start and end of each data run is marked with a Reference whose offset
is the start/end of the data run. For arm, the switch back to code also marks
whether it is thumb or arm code.
llvm-svn: 213901
This patch just supports marking ranges that are thumb code (vs arm code).
Future patches will mark data and jump table ranges. The ranges are encoded
as References with offsetInAtom being the start of the range and the target
being the same atom.
llvm-svn: 213712
Over time the symbols and relocations have changed for dwarf unwind info
in the __eh_frame section. Add test cases for older and new style.
llvm-svn: 213585
All architecture specific handling is now done in the appropriate
ArchHandler subclass.
The StubsPass and GOTPass have been simplified. All architecture specific
variations in stubs are now encoded in a table which is vended by the
current ArchHandler.
llvm-svn: 213187
This converts the very complicated mach-o arm
relocations into the simple Reference Kinds in lld.
The next patch will use the internal Reference kinds
to fix up arm/thumb code.
llvm-svn: 212306
This is first step in reworking how mach-o relocations are processed.
The existing KindHandler is going to become a delgate/helper object for
processing architecture specific references. The KindHandler knows how
to convert mach-o relocations into References and back, as well, as fixing
up the content the relocation is on.
One of the messy things about mach-o relocations is that they sometime
come in pairs, but the pairs still convert to one lld::Reference. So, the
conversion has to detect pairs (arch specific) and change the stride.
llvm-svn: 211921
The previous function returned true for "s < s", which could completely mess up
the sorting of symbols within a section.
Unfortunately, I don't think there's a robust way to write a test for this.
Anything I come up with will be making assumptions about the particular
implementation of std::sort.
llvm-svn: 211704
When looking through sections with zero-terminated string-literals (__cstring
or __ustring) we were constantly rechecking the first few bytes of the string
for '\0' rather than advancing along. This obviously failed unless all strings
within the section had the same length as that first one.
llvm-svn: 211682
We were trying to examine the first symbol in a section that we wanted to
atomize by symbols, even when there wasn't one. Instead, we should make the
initial anonymous symbol cover the entire section in that situation.
llvm-svn: 211681
In sections that are broken into atoms at symbols, if the first symbol in the
section is not at the start of the section, then make an anonymous atom for
the section content that is before the first symbol.
llvm-svn: 210142
Previously each section kind had its own code to loop over the section and
parse it into atoms. This refactoring has two tables. The first maps sections
to ContentType. The second maps ContentType to information on how to find
the atom boundaries.
A few bugs in test cases were discovered as part of the refactoring.
No change in functionality intended.
llvm-svn: 210138
This is a short-term fix to allow lld Readers to return error messages
with dynamic content.
The long term fix will be to enhance ErrorOr<> to work with errors other
than error_code. Or to change the interface to Readers to pass down a
diagnostics object through which all error messages are written.
llvm-svn: 209681
Nick Kledzik