to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
When the floating point constants are whole numbers they have no decimal point so look like integers, but mean something very different in something like an 'and' instruction.
Ideally we would just print a decimal point and a 0, but I couldn't see how to make APFloat::toString do that.
llvm-svn: 345488
Instead of using the MOVGOT64r pseudo, use the existing
MO_PIC_BASE_OFFSET support on symbol operands. Now I don't have to
create a "scratch register operand" for the pseudo to use, and the
register allocator can make better decisions.
Fixes some X86 verifier errors tracked in PR27481.
llvm-svn: 345219
I've included a fix to DAGCombiner::ForwardStoreValueToDirectLoad that I believe will prevent the previous miscompile.
Original commit message:
Theoretically this was done to simplify the amount of isel patterns that were needed. But it also meant a substantial number of our isel patterns have to match an explicit bitcast. By making the vXi32/vXi16/vXi8 types legal for loads, DAG combiner should be able to change the load type to rem
I had to add some additional plain load instruction patterns and a few other special cases, but overall the isel table has reduced in size by ~12000 bytes. So it looks like this promotion was hurting us more than helping.
I still have one crash in vector-trunc.ll that I'm hoping @RKSimon can help with. It seems to relate to using getTargetConstantFromNode on a load that was shrunk due to an extract_subvector combine after the constant pool entry was created. So we end up decoding more mask elements than the lo
I'm hoping this patch will simplify the number of patterns needed to remove the and/or/xor promotion.
Reviewers: RKSimon, spatel
Reviewed By: RKSimon
Subscribers: llvm-commits, RKSimon
Differential Revision: https://reviews.llvm.org/D53306
llvm-svn: 344965
Summary:
Theoretically this was done to simplify the amount of isel patterns that were needed. But it also meant a substantial number of our isel patterns have to match an explicit bitcast. By making the vXi32/vXi16/vXi8 types legal for loads, DAG combiner should be able to change the load type to remove the bitcast.
I had to add some additional plain load instruction patterns and a few other special cases, but overall the isel table has reduced in size by ~12000 bytes. So it looks like this promotion was hurting us more than helping.
I still have one crash in vector-trunc.ll that I'm hoping @RKSimon can help with. It seems to relate to using getTargetConstantFromNode on a load that was shrunk due to an extract_subvector combine after the constant pool entry was created. So we end up decoding more mask elements than the load size.
I'm hoping this patch will simplify the number of patterns needed to remove the and/or/xor promotion.
Reviewers: RKSimon, spatel
Reviewed By: RKSimon
Subscribers: llvm-commits, RKSimon
Differential Revision: https://reviews.llvm.org/D53306
llvm-svn: 344877
D53306 exposes an issue where we sometimes use constant pool data from bigger vectors than the target shuffle mask. This should be safe to do, but we have to be certain that we're using the bottom most part of the vector as the shuffle mask decoders have no way to peek into subvectors with non-zero offsets.
llvm-svn: 344867
Add the .cv_fpo_stackalign directive so that we can define $T0, or the
VFRAME virtual register, with it. This was overlooked in the initial
implementation because unlike MSVC, we push CSRs before allocating stack
space, so this value is only needed to describe local variable
locations. Variables that the compiler now addresses via ESP are instead
described as being stored at offsets from VFRAME, which for us is ESP
after alignment in the prologue.
This adds tests that show that we use the VFRAME register properly in
our S_DEFRANGE records, and that we emit the correct FPO data to define
it.
Fixes PR38857
llvm-svn: 343603
Consistently try to use APFloat::toString for floating point constant comments to get rid of differences between Constant / ConstantDataSequential values - it should help stop some of the linux-windows buildbot failures matching NaN/INF etc. as well.
Differential Revision: https://reviews.llvm.org/D52702
llvm-svn: 343562
These stubs should never be emitted for internal symbols, and
nothing in AsmPrinter ever actually use this value when producing
the stubs for COFF anyway.
llvm-svn: 341177
Variables declared with the dllimport attribute are accessed via a
stub variable named __imp_<var>. In MinGW configurations, variables that
aren't declared with a dllimport attribute might still end up imported
from another DLL with runtime pseudo relocs.
For x86_64, this avoids the risk that the target is out of range
for a 32 bit PC relative reference, in case the target DLL is loaded
further than 4 GB from the reference. It also avoids having to make the
text section writable at runtime when doing the runtime fixups, which
makes it worthwhile to do for i386 as well.
Add stub variables for all dso local data references where a definition
of the variable isn't visible within the module, since the DLL data
autoimporting might make them imported even though they are marked as
dso local within LLVM.
Don't do this for variables that actually are defined within the same
module, since we then know for sure that it actually is dso local.
Don't do this for references to functions, since there's no need for
runtime pseudo relocations for autoimporting them; if a function from
a different DLL is called without the appropriate dllimport attribute,
the call just gets routed via a thunk instead.
GCC does something similar since 4.9 (when compiling with -mcmodel=medium
or large; from that version, medium is the default code model for x86_64
mingw), but only for x86_64.
Differential Revision: https://reviews.llvm.org/D51288
llvm-svn: 340942
subtarget features for indirect calls and indirect branches.
This is in preparation for enabling *only* the call retpolines when
using speculative load hardening.
I've continued to use subtarget features for now as they continue to
seem the best fit given the lack of other retpoline like constructs so
far.
The LLVM side is pretty simple. I'd like to eventually get rid of the
old feature, but not sure what backwards compatibility issues that will
cause.
This does remove the "implies" from requesting an external thunk. This
always seemed somewhat questionable and is now clearly not desirable --
you specify a thunk the same way no matter which set of things are
getting retpolines.
I really want to keep this nicely isolated from end users and just an
LLVM implementation detail, so I've moved the `-mretpoline` flag in
Clang to no longer rely on a specific subtarget feature by that name and
instead to be directly handled. In some ways this is simpler, but in
order to preserve existing behavior I've had to add some fallback code
so that users who relied on merely passing -mretpoline-external-thunk
continue to get the same behavior. We should eventually remove this
I suspect (we have never tested that it works!) but I've not done that
in this patch.
Differential Revision: https://reviews.llvm.org/D51150
llvm-svn: 340515
At one point in time acquire implied mayLoad and mayStore as did release. Thus we needed separate pseudos that also carried that property. This appears to no longer be the case. I believe it was changed in 2012 with a comment saying that atomic memory accesses are marked volatile which preserves the ordering.
So from what I can tell we shouldn't need additional pseudos since they aren't carry any flags that are different from the normal instructions. The only thing I can think of is that we may consider them for load folding candidates in the peephole pass now where we didn't before. If that's important hopefully there's something in the memory operand we can check to prevent the folding without relying on pseudo instructions.
Differential Revision: https://reviews.llvm.org/D50212
llvm-svn: 338925
Don't try to generate large PIC code for non-ELF targets. Neither COFF
nor MachO have relocations for large position independent code, and
users have been using "large PIC" code models to JIT 64-bit code for a
while now. With this change, if they are generating ELF code, their
JITed code will truly be PIC, but if they target MachO or COFF, it will
contain 64-bit immediates that directly reference external symbols. For
a JIT, that's perfectly fine.
llvm-svn: 337740
It looks like someone ran clang-format over this entire file which reformatted these switches into a multiline form. But I think the single line form is more useful here.
llvm-svn: 336077
Reverting because this is causing failures in the LLDB test suite on
GreenDragon.
LLVM ERROR: unsupported relocation with subtraction expression, symbol
'__GLOBAL_OFFSET_TABLE_' can not be undefined in a subtraction
expression
llvm-svn: 335894
The large code model allows code and data segments to exceed 2GB, which
means that some symbol references may require a displacement that cannot
be encoded as a displacement from RIP. The large PIC model even relaxes
the assumption that the GOT itself is within 2GB of all code. Therefore,
we need a special code sequence to materialize it:
.LtmpN:
leaq .LtmpN(%rip), %rbx
movabsq $_GLOBAL_OFFSET_TABLE_-.LtmpN, %rax # Scratch
addq %rax, %rbx # GOT base reg
From that, non-local references go through the GOT base register instead
of being PC-relative loads. Local references typically use GOTOFF
symbols, like this:
movq extern_gv@GOT(%rbx), %rax
movq local_gv@GOTOFF(%rbx), %rax
All calls end up being indirect:
movabsq $local_fn@GOTOFF, %rax
addq %rbx, %rax
callq *%rax
The medium code model retains the assumption that the code segment is
less than 2GB, so calls are once again direct, and the RIP-relative
loads can be used to access the GOT. Materializing the GOT is easy:
leaq _GLOBAL_OFFSET_TABLE_(%rip), %rbx # GOT base reg
DSO local data accesses will use it:
movq local_gv@GOTOFF(%rbx), %rax
Non-local data accesses will use RIP-relative addressing, which means we
may not always need to materialize the GOT base:
movq extern_gv@GOTPCREL(%rip), %rax
Direct calls are basically the same as they are in the small code model:
They use direct, PC-relative addressing, and the PLT is used for calls
to non-local functions.
This patch adds reasonably comprehensive testing of LEA, but there are
lots of interesting folding opportunities that are unimplemented.
I restricted the MCJIT/eh-lg-pic.ll test to Linux, since the large PIC
code model is not implemented for MachO yet.
Differential Revision: https://reviews.llvm.org/D47211
llvm-svn: 335508
Summary:
The large code model allows code and data segments to exceed 2GB, which
means that some symbol references may require a displacement that cannot
be encoded as a displacement from RIP. The large PIC model even relaxes
the assumption that the GOT itself is within 2GB of all code. Therefore,
we need a special code sequence to materialize it:
.LtmpN:
leaq .LtmpN(%rip), %rbx
movabsq $_GLOBAL_OFFSET_TABLE_-.LtmpN, %rax # Scratch
addq %rax, %rbx # GOT base reg
From that, non-local references go through the GOT base register instead
of being PC-relative loads. Local references typically use GOTOFF
symbols, like this:
movq extern_gv@GOT(%rbx), %rax
movq local_gv@GOTOFF(%rbx), %rax
All calls end up being indirect:
movabsq $local_fn@GOTOFF, %rax
addq %rbx, %rax
callq *%rax
The medium code model retains the assumption that the code segment is
less than 2GB, so calls are once again direct, and the RIP-relative
loads can be used to access the GOT. Materializing the GOT is easy:
leaq _GLOBAL_OFFSET_TABLE_(%rip), %rbx # GOT base reg
DSO local data accesses will use it:
movq local_gv@GOTOFF(%rbx), %rax
Non-local data accesses will use RIP-relative addressing, which means we
may not always need to materialize the GOT base:
movq extern_gv@GOTPCREL(%rip), %rax
Direct calls are basically the same as they are in the small code model:
They use direct, PC-relative addressing, and the PLT is used for calls
to non-local functions.
This patch adds reasonably comprehensive testing of LEA, but there are
lots of interesting folding opportunities that are unimplemented.
Reviewers: chandlerc, echristo
Subscribers: hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D47211
llvm-svn: 335297
We've been running doxygen with the autobrief option for a couple of
years now. This makes the \brief markers into our comments
redundant. Since they are a visual distraction and we don't want to
encourage more \brief markers in new code either, this patch removes
them all.
Patch produced by
for i in $(git grep -l '\\brief'); do perl -pi -e 's/\\brief //g' $i & done
Differential Revision: https://reviews.llvm.org/D46290
llvm-svn: 331272
Summary:
Add an LLVM intrinsic for type discriminated event logging with XRay.
Similar to the existing intrinsic for custom events, but also accepts
a type tag argument to allow plugins to be aware of different types
and semantically interpret logged events they know about without
choking on those they don't.
Relies on a symbol defined in compiler-rt patch D43668. I may wait
to submit before I can see demo everything working together including
a still to come clang patch.
Reviewers: dberris, pelikan, eizan, rSerge, timshen
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D45633
llvm-svn: 330219
X86InstComments.h is used by tools that only have the MC layer. We shouldn't be importing a file from CodeGen into this.
X86InstrInfo.h isn't a great place, but I couldn't find a better one.
llvm-svn: 327202
64-bit MMX constant generation usually ends up lowering into SSE instructions before being spilled/reloaded as a MMX type.
This patch bitcasts the constant to a double value to allow correct loading directly to the MMX register.
I've added MMX constant asm comment support to improve testing, it's better to always print the double values as hex constants as MMX is mainly an integer unit (and even with 3DNow! its just floats).
Differential Revision: https://reviews.llvm.org/D43616
llvm-svn: 326497
Summary:
First, we need to explain the core of the vulnerability. Note that this
is a very incomplete description, please see the Project Zero blog post
for details:
https://googleprojectzero.blogspot.com/2018/01/reading-privileged-memory-with-side.html
The basis for branch target injection is to direct speculative execution
of the processor to some "gadget" of executable code by poisoning the
prediction of indirect branches with the address of that gadget. The
gadget in turn contains an operation that provides a side channel for
reading data. Most commonly, this will look like a load of secret data
followed by a branch on the loaded value and then a load of some
predictable cache line. The attacker then uses timing of the processors
cache to determine which direction the branch took *in the speculative
execution*, and in turn what one bit of the loaded value was. Due to the
nature of these timing side channels and the branch predictor on Intel
processors, this allows an attacker to leak data only accessible to
a privileged domain (like the kernel) back into an unprivileged domain.
The goal is simple: avoid generating code which contains an indirect
branch that could have its prediction poisoned by an attacker. In many
cases, the compiler can simply use directed conditional branches and
a small search tree. LLVM already has support for lowering switches in
this way and the first step of this patch is to disable jump-table
lowering of switches and introduce a pass to rewrite explicit indirectbr
sequences into a switch over integers.
However, there is no fully general alternative to indirect calls. We
introduce a new construct we call a "retpoline" to implement indirect
calls in a non-speculatable way. It can be thought of loosely as
a trampoline for indirect calls which uses the RET instruction on x86.
Further, we arrange for a specific call->ret sequence which ensures the
processor predicts the return to go to a controlled, known location. The
retpoline then "smashes" the return address pushed onto the stack by the
call with the desired target of the original indirect call. The result
is a predicted return to the next instruction after a call (which can be
used to trap speculative execution within an infinite loop) and an
actual indirect branch to an arbitrary address.
On 64-bit x86 ABIs, this is especially easily done in the compiler by
using a guaranteed scratch register to pass the target into this device.
For 32-bit ABIs there isn't a guaranteed scratch register and so several
different retpoline variants are introduced to use a scratch register if
one is available in the calling convention and to otherwise use direct
stack push/pop sequences to pass the target address.
This "retpoline" mitigation is fully described in the following blog
post: https://support.google.com/faqs/answer/7625886
We also support a target feature that disables emission of the retpoline
thunk by the compiler to allow for custom thunks if users want them.
These are particularly useful in environments like kernels that
routinely do hot-patching on boot and want to hot-patch their thunk to
different code sequences. They can write this custom thunk and use
`-mretpoline-external-thunk` *in addition* to `-mretpoline`. In this
case, on x86-64 thu thunk names must be:
```
__llvm_external_retpoline_r11
```
or on 32-bit:
```
__llvm_external_retpoline_eax
__llvm_external_retpoline_ecx
__llvm_external_retpoline_edx
__llvm_external_retpoline_push
```
And the target of the retpoline is passed in the named register, or in
the case of the `push` suffix on the top of the stack via a `pushl`
instruction.
There is one other important source of indirect branches in x86 ELF
binaries: the PLT. These patches also include support for LLD to
generate PLT entries that perform a retpoline-style indirection.
The only other indirect branches remaining that we are aware of are from
precompiled runtimes (such as crt0.o and similar). The ones we have
found are not really attackable, and so we have not focused on them
here, but eventually these runtimes should also be replicated for
retpoline-ed configurations for completeness.
For kernels or other freestanding or fully static executables, the
compiler switch `-mretpoline` is sufficient to fully mitigate this
particular attack. For dynamic executables, you must compile *all*
libraries with `-mretpoline` and additionally link the dynamic
executable and all shared libraries with LLD and pass `-z retpolineplt`
(or use similar functionality from some other linker). We strongly
recommend also using `-z now` as non-lazy binding allows the
retpoline-mitigated PLT to be substantially smaller.
When manually apply similar transformations to `-mretpoline` to the
Linux kernel we observed very small performance hits to applications
running typical workloads, and relatively minor hits (approximately 2%)
even for extremely syscall-heavy applications. This is largely due to
the small number of indirect branches that occur in performance
sensitive paths of the kernel.
When using these patches on statically linked applications, especially
C++ applications, you should expect to see a much more dramatic
performance hit. For microbenchmarks that are switch, indirect-, or
virtual-call heavy we have seen overheads ranging from 10% to 50%.
However, real-world workloads exhibit substantially lower performance
impact. Notably, techniques such as PGO and ThinLTO dramatically reduce
the impact of hot indirect calls (by speculatively promoting them to
direct calls) and allow optimized search trees to be used to lower
switches. If you need to deploy these techniques in C++ applications, we
*strongly* recommend that you ensure all hot call targets are statically
linked (avoiding PLT indirection) and use both PGO and ThinLTO. Well
tuned servers using all of these techniques saw 5% - 10% overhead from
the use of retpoline.
We will add detailed documentation covering these components in
subsequent patches, but wanted to make the core functionality available
as soon as possible. Happy for more code review, but we'd really like to
get these patches landed and backported ASAP for obvious reasons. We're
planning to backport this to both 6.0 and 5.0 release streams and get
a 5.0 release with just this cherry picked ASAP for distros and vendors.
This patch is the work of a number of people over the past month: Eric, Reid,
Rui, and myself. I'm mailing it out as a single commit due to the time
sensitive nature of landing this and the need to backport it. Huge thanks to
everyone who helped out here, and everyone at Intel who helped out in
discussions about how to craft this. Also, credit goes to Paul Turner (at
Google, but not an LLVM contributor) for much of the underlying retpoline
design.
Reviewers: echristo, rnk, ruiu, craig.topper, DavidKreitzer
Subscribers: sanjoy, emaste, mcrosier, mgorny, mehdi_amini, hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D41723
llvm-svn: 323155
As part of the unification of the debug format and the MIR format,
always print registers as lowercase.
* Only debug printing is affected. It now follows MIR.
Differential Revision: https://reviews.llvm.org/D40417
llvm-svn: 319187
All these headers already depend on CodeGen headers so moving them into
CodeGen fixes the layering (since CodeGen depends on Target, not the
other way around).
llvm-svn: 318490
Summary:
This adds a set of new directives that describe 32-bit x86 prologues.
The directives are limited and do not expose the full complexity of
codeview FPO data. They are merely a convenience for the compiler to
generate more readable assembly so we don't need to generate tons of
labels in CodeGen. If our prologue emission changes in the future, we
can change the set of available directives to suit our needs. These are
modelled after the .seh_ directives, which use a different format that
interacts with exception handling.
The directives are:
.cv_fpo_proc _foo
.cv_fpo_pushreg ebp/ebx/etc
.cv_fpo_setframe ebp/esi/etc
.cv_fpo_stackalloc 200
.cv_fpo_endprologue
.cv_fpo_endproc
.cv_fpo_data _foo
I tried to follow the implementation of ARM EHABI CFI directives by
sinking most directives out of MCStreamer and into X86TargetStreamer.
This helps avoid polluting non-X86 code with WinCOFF specific logic.
I used cdb to confirm that this can show locals in parent CSRs in a few
cases, most importantly the one where we use ESI as a frame pointer,
i.e. the one in http://crbug.com/756153#c28
Once we have cdb integration in debuginfo-tests, we can add integration
tests there.
Reviewers: majnemer, hans
Subscribers: aemerson, mgorny, kristof.beyls, llvm-commits, hiraditya
Differential Revision: https://reviews.llvm.org/D38776
llvm-svn: 315513
Summary:
This is a re-roll of D36615 which uses PLT relocations in the back-end
to the call to __xray_CustomEvent() when building in -fPIC and
-fxray-instrument mode.
Reviewers: pcc, djasper, bkramer
Subscribers: sdardis, javed.absar, llvm-commits
Differential Revision: https://reviews.llvm.org/D37373
llvm-svn: 312466
Summary:
This change achieves two things:
- Redefine the Custom Event handling instrumentation points emitted by
the compiler to not require dynamic relocation of references to the
__xray_CustomEvent trampoline.
- Remove the synthetic reference we emit at the end of a function that
we used to keep auxiliary sections alive in favour of SHF_LINK_ORDER
associated with the section where the function is defined.
To achieve the custom event handling change, we've had to introduce the
concept of sled versioning -- this will need to be supported by the
runtime to allow us to understand how to turn on/off the new version of
the custom event handling sleds. That change has to land first before we
change the way we write the sleds.
To remove the synthetic reference, we rely on a relatively new linker
feature that preserves the sections that are associated with each other.
This allows us to limit the effects on the .text section of ELF
binaries.
Because we're still using absolute references that are resolved at
runtime for the instrumentation map (and function index) maps, we mark
these sections write-able. In the future we can re-define the entries in
the map to use relative relocations instead that can be statically
determined by the linker. That change will be a bit more invasive so we
defer this for later.
Depends on D36816.
Reviewers: dblaikie, echristo, pcc
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D36615
llvm-svn: 311525
Summary:
When broadcasting from the constant pool its useful to print out the final vector similar to what we do for normal moves from the constant pool.
I changed only a couple tests that were broadcast focused. One of them had been previously hand tweaked after running the script so that it could check the constant pool declaration. But I think this patch makes that unnecessary now since we can check the comment instead.
Reviewers: spatel, RKSimon, zvi
Reviewed By: spatel
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D34923
llvm-svn: 307062
This creates a new library called BinaryFormat that has all of
the headers from llvm/Support containing structure and layout
definitions for various types of binary formats like dwarf, coff,
elf, etc as well as the code for identifying a file from its
magic.
Differential Revision: https://reviews.llvm.org/D33843
llvm-svn: 304864
I did this a long time ago with a janky python script, but now
clang-format has built-in support for this. I fed clang-format every
line with a #include and let it re-sort things according to the precise
LLVM rules for include ordering baked into clang-format these days.
I've reverted a number of files where the results of sorting includes
isn't healthy. Either places where we have legacy code relying on
particular include ordering (where possible, I'll fix these separately)
or where we have particular formatting around #include lines that
I didn't want to disturb in this patch.
This patch is *entirely* mechanical. If you get merge conflicts or
anything, just ignore the changes in this patch and run clang-format
over your #include lines in the files.
Sorry for any noise here, but it is important to keep these things
stable. I was seeing an increasing number of patches with irrelevant
re-ordering of #include lines because clang-format was used. This patch
at least isolates that churn, makes it easy to skip when resolving
conflicts, and gets us to a clean baseline (again).
llvm-svn: 304787
This patch introduces an LLVM intrinsic and a target opcode for custom event
logging in XRay. Initially, its use case will be to allow users of XRay to log
some type of string ("poor man's printf"). The target opcode compiles to a noop
sled large enough to enable calling through to a runtime-determined relative
function call. At runtime, when X-Ray is enabled, the sled is replaced by
compiler-rt with a trampoline to the logic for creating the custom log entries.
Future patches will implement the compiler-rt parts and clang-side support for
emitting the IR corresponding to this intrinsic.
Reviewers: timshen, dberris
Subscribers: igorb, pelikan, rSerge, timshen, echristo, dberris, llvm-commits
Differential Revision: https://reviews.llvm.org/D27503
llvm-svn: 302405
Chandler Carruth