Referencing one symbol from another in the same section does not
generally require a relocation. However, the MS linker has a feature
called /INCREMENTAL which enables incremental links. It achieves this
by creating thunks to the actual function and redirecting all
relocations to point to the thunk.
This breaks down with the old scheme if you have a function which
references, say, itself. On x86_64, we would use %rip relative
addressing to reference the start of the function from out current
position. This would lead to miscompiles because other references might
reference the thunk instead, breaking function pointer equality.
This fixes PR21520.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221678 91177308-0d34-0410-b5e6-96231b3b80d8
COFF normally doesn't allow us to describe the alignment of COMMON
symbols.
It turns out that most linkers use the symbol size as a hint as to how
aligned the symbol should be.
However the BFD folks have added a .drectve command, which we
now support as of r219229, that allows us to specify the alignment
precisely. With this in mind, stop rounding sizes up.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219281 91177308-0d34-0410-b5e6-96231b3b80d8
The GNU linker supports an -aligncomm directive that allows for power-of-2
alignment of common data. Add support to emit this directive.
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Nico Rieck added support for this 32-bit COFF relocation some time ago
for Win64 stuff. It appears that as an oversight, the assembly output
used "foo"@IMGREL32 instead of "foo"@IMGREL, which is what we can parse.
Sadly, there were actually tests that took in IMGREL and put out
IMGREL32, and we didn't notice the inconsistency. Oh well. Now LLVM can
assemble it's own output with slightly more fidelity.
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link.exe:
Fuzz testing has shown that COMMON symbols with size > 32 will always
have an alignment of at least 32 and all symbols with size < 32 will
have an alignment of at least the largest power of 2 less than the size
of the symbol.
binutils:
The BFD linker essentially work like the link.exe behavior but with
alignment 4 instead of 32. The BFD linker also supports an extension to
COFF which adds an -aligncomm argument to the .drectve section which
permits specifying a precise alignment for a variable but MC currently
doesn't support editing .drectve in this way.
With all of this in mind, we decide to play a little trick: we can
ensure that the alignment will be respected by bumping the size of the
global to it's alignment.
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We had a few bugs:
- We were considering the GVKind instead of just looking at the section
characteristics
- We would never print out 'y' when a section was meant to be unreadable
- We would never print out 's' when a section was meant to be shared
- We translated IMAGE_SCN_MEM_DISCARDABLE to 'n' when it should've meant
IMAGE_SCN_LNK_REMOVE
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A problem with our old behavior becomes observable under x86-64 COFF
when we need a read-only GV which has an initializer which is referenced
using a relocation: we would mark the section as writable. Marking the
section as writable interferes with section merging.
This fixes PR21009.
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This adds support for reading the "bigobj" variant of COFF produced by
cl's /bigobj and mingw's -mbig-obj.
The most significant difference that bigobj brings is more than 2**16
sections to COFF.
bigobj brings a few interesting differences with it:
- It doesn't have a Characteristics field in the file header.
- It doesn't have a SizeOfOptionalHeader field in the file header (it's
only used in executable files).
- Auxiliary symbol records have the same width as a symbol table entry.
Since symbol table entries are bigger, so are auxiliary symbol
records.
Write support will come soon.
Differential Revision: http://reviews.llvm.org/D5259
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Summary:
This fixes a long standing issue where we would emit many little .text
sections and only one .pdata and .xdata section. Now we generate one
.pdata / .xdata pair per .text section and associate them correctly.
Fixes PR19667.
Reviewers: majnemer
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D5181
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MC was aping a binutils bug where aliases would default their linkage to
private instead of internal.
I've sent a patch to the binutils maintainers and they've recently
applied it to the GNU assembler sources.
This fixes PR20152.
Differential Revision: http://reviews.llvm.org/D4395
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Summary: This test ensures that we can correctly specify a full Windows path to the clang ASAN runtime libraries. This is in preparation to fix PR20246.
Reviewers: rafael
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D4427
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COFF sections in MC were represented by a tuple of section-name and
COMDAT-name. This is not sufficient to represent a .text section
associated with another .text section; we need a way to distinguish
between the key section and the one marked associative.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211913 91177308-0d34-0410-b5e6-96231b3b80d8
to match llvm-size and other UNIX systems for their nm(1).
Tweak test cases that used llvm-nm with standard input to add a "-" to
indicate that and add a test case to check the default of a.out for llvm-nm.
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Prevent the early elimination of sections in the object writer. There may be
references to the section itself by other symbols, which may potentially not be
possible to resolve. ML (Visual Studio's Macro Assembler) also seems to retain
empty sections.
The elimination of symbols and sections which are unused should really occur at
the link phase. This will not cause any change in the resulting binary, simply
in the generated object files.
The adjustments to the other unit tests account for the fluctuating section
index caused by the appearance of sections which were previously discarded.
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* Section association cannot use just the section name as many
sections can have the same name. With this patch, the comdat symbol in
an assoc section is interpreted to mean a symbol in the associated
section and the mapping is discovered from it.
* Comdat symbols were not being set correctly. Instead we were getting
whatever was output first for that section.
A consequence is that associative sections now must use .section to
set the association. Using .linkonce would not work since it is not
possible to change a sections comdat symbol (it is used to decide if
we should create a new section or reuse an existing one).
This includes r210298, which was reverted because it was asserting
on an associated section having the same comdat as the associated
section.
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We extended the .section syntax to allow multiple sections with the
same name but different comdats, but currently we don't make sure that
the output section has that comdat symbol.
That happens to work with the code llc produces currently because it looks like
.section secName, "dr", one_only, "COMDATSym"
.globl COMDATSym
COMDATSym:
....
but that is not very friendly to anyone coding in assembly or even to
llc once we get comdat support in the IR.
This patch changes the coff object writer to make sure the comdat symbol is
output just after the section symbol, as required by the coff spec.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210298 91177308-0d34-0410-b5e6-96231b3b80d8
We would previously assert here when trying to figure out the section
for the global.
This makes us handle the situation more gracefully since the IR isn't
malformed.
Differential Revision: http://reviews.llvm.org/D4022
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Rafael correctly pointed out that the restriction is unnecessary. Although the
tests are intended to ensure that we dont abort due to an assertion, running the
tests in all modes is better since it also ensures that we dont crash without
assertions. Always run these tests to ensure that we can handle invalid input
correctly.
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Now that clang can be used as an assembler via the IAS, invalid assembler inputs
would cause the assertions to trigger. Although we cannot recover from the
errors here, nor provide caret diagnostics, attempt to handle them slightly more
gracefully by reporting a fatal error.
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The .drectve section should be marked as IMAGE_SCN_LNK_REMOVE. This matches what
the MSVC toolchain does and accurately reflects that this section should not be
emitted into the final binary. This section is merely information for the
linker, comprising of additional linker directives.
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This allows us to put dynamic initializers for weak data into the same
comdat group as the data being initialized. This is necessary for MSVC
ABI compatibility. Once we have comdats for guard variables, we can use
the combination to help GlobalOpt fire more often for weak data with
guarded initialization on other platforms.
Reviewers: nlewycky
Differential Revision: http://reviews.llvm.org/D3499
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.file records are supposed to have a section identifier of 65534
(IMAGE_SCN_DEBUG) rather than 0. This is spelt out clearly within the PE/COFF
specification. Fix this minor oversight with the implementation for support for
.file records.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207851 91177308-0d34-0410-b5e6-96231b3b80d8
This matches gas' behaviour on COFF.
I think that this yak is now sufficiently shaved for aliases with offset
to work.
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This fixes pr19147.
There are a few more related issues to fix, but the testcase in the bug now
passes.
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This makes the coff writer compute the correct symbol value for the test in
pr19147. The section is still incorrect, that will be fixed in a followup patch.
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Introduce support for WoA PE/COFF object file emission from LLVM. Add the new
target specific PE/COFF Streamer (ARMWinCOFFStreamer) that handles the ARM
specific behaviour of PE/COFF object emission. ARM exception information is not
yet emitted and is a TODO item.
The ARM specific object writer (ARMWinCOFFObjectWriter) handles the ARM specific
relocation handling in conjunction with the WinCOFFObjectWriter in the MC layer.
The MC layer needs to be updated to deal with the relocation adjustments.
Branch relocations are adjusted by 4 bytes (unlikely their ELF counterparts).
Minor tweaks to switch multiple conditional checks into equivalent switch
statements. The ObjectFileInfo is updated to relax the object file setup for
Windows COFF. Move the architecture checks into an assertion. Windows COFF is
currently only supported on x86, x86_64, and ARM (thumb). Rather than
defaulting to ELF, we will refuse to generate an object file. This is better
though as you do not get an (arbitrary) object file which is different from the
request.
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This is dependent on changes that are not fully ready to be merged yet (WoA
object file emission). The test can be re-enabled for that target later.
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Emit the flag to indicate to the assembler that a section contains data if there
is pre-populated data present.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207028 91177308-0d34-0410-b5e6-96231b3b80d8
Adjust the tests to validate the number of auxiliary entries used to store the
filename.
Thanks to majnemer's sharp eye for catching the missing - 1 in the round up
calculation.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206359 91177308-0d34-0410-b5e6-96231b3b80d8
Add support for emitting .file records. This is mostly a quality of
implementation change (more complete support for COFF file emission) that was
noticed while working on COFF file emission for Windows on ARM.
A .file record is emitted as a symbol with storage class FILE (103) and the name
".file". A series of auxiliary format 4 records follow which contain the file
name. The filename is stored as an ANSI string and is padded with NULL if the
length is not a multiple of COFF::SymbolSize (18).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206355 91177308-0d34-0410-b5e6-96231b3b80d8
Summary:
Local common symbols were properly inserted into the .bss section.
However, putting external common symbols in the .bss section would give
them a strong definition.
Instead, encode them as undefined, external symbols who's symbol value
is equivalent to their size.
Reviewers: Bigcheese, rafael, rnk
CC: llvm-commits
Differential Revision: http://reviews.llvm.org/D3324
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Microsoft PE/COFF Spec clearly states that the field is of signed interger
type. However, in reality, it's unsigned. If cl.exe needs to create a large
number of sections for COMDAT sections, it will just create more than 32768
sections. Handling large section number as negative number is not correct.
I think this is a spec bug.
Differential Revision: http://llvm-reviews.chandlerc.com/D3088
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Offsets past the range of single-slash encoding are encoded as base64,
padded to 6 characters, and prefixed with two slashes. This encoding is
undocumented but used by MSVC.
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