EAX can turn out to be alive here, when shrink wrapping is done
(which is allowed when using dwarf exceptions, contrary to the
normal case with WinCFI).
This fixes PR36487.
Differential Revision: https://reviews.llvm.org/D43968
llvm-svn: 326764
The prologue-end line record must be emitted after the last
instruction that is part of the function frame setup code and before
the instruction that marks the beginning of the function body.
Patch by Carlos Alberto Enciso!
Differential Revision: https://reviews.llvm.org/D41762
llvm-svn: 325143
If we are saving/restoring k-registers, the default behavior of getMinimalRegisterClass will find the VK64 class with a spill size of 64 bits. This will cause the KMOVQ opcode to be used for save/restore. If we don't have have BWI instructions we need to constrain the class returned to give us VK16 with a 16-bit spill size. We can do this by passing the either v16i1 or v64i1 into getMinimalRegisterClass.
Also add asserts to make sure BWI is enabled anytime we use KMOVD/KMOVQ. These are what caught this bug.
Fixes PR36256
Differential Revision: https://reviews.llvm.org/D42989
llvm-svn: 324533
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
(Target)FrameLowering::determineCalleeSaves can be called multiple
times. I don't think it should have side-effects as creating stack
objects and setting global MachineFunctionInfo state as it is doing
today (in other back-ends as well).
This moves the creation of stack objects from determineCalleeSaves to
assignCalleeSavedSpillSlots.
Differential Revision: https://reviews.llvm.org/D41703
llvm-svn: 321987
This makes sure that functions that only clobber xmm registers
(on win64) also get the right cfi directives, if dwarf exceptions
are enabled.
Differential Revision: https://reviews.llvm.org/D40191
llvm-svn: 318591
This reverts r317579, originally committed as r317100.
There is a design issue with marking CFI instructions duplicatable. Not
all targets support the CFIInstrInserter pass, and targets like Darwin
can't cope with duplicated prologue setup CFI instructions. The compact
unwind info emission fails.
When the following code is compiled for arm64 on Mac at -O3, the CFI
instructions end up getting tail duplicated, which causes compact unwind
info emission to fail:
int a, c, d, e, f, g, h, i, j, k, l, m;
void n(int o, int *b) {
if (g)
f = 0;
for (; f < o; f++) {
m = a;
if (l > j * k > i)
j = i = k = d;
h = b[c] - e;
}
}
We get assembly that looks like this:
; BB#1: ; %if.then
Lloh3:
adrp x9, _f@GOTPAGE
Lloh4:
ldr x9, [x9, _f@GOTPAGEOFF]
mov w8, wzr
Lloh5:
str wzr, [x9]
stp x20, x19, [sp, #-16]! ; 8-byte Folded Spill
.cfi_def_cfa_offset 16
.cfi_offset w19, -8
.cfi_offset w20, -16
cmp w8, w0
b.lt LBB0_3
b LBB0_7
LBB0_2: ; %entry.if.end_crit_edge
Lloh6:
adrp x8, _f@GOTPAGE
Lloh7:
ldr x8, [x8, _f@GOTPAGEOFF]
Lloh8:
ldr w8, [x8]
stp x20, x19, [sp, #-16]! ; 8-byte Folded Spill
.cfi_def_cfa_offset 16
.cfi_offset w19, -8
.cfi_offset w20, -16
cmp w8, w0
b.ge LBB0_7
LBB0_3: ; %for.body.lr.ph
Note the multiple .cfi_def* directives. Compact unwind info emission
can't handle that.
llvm-svn: 317726
Reland r317100 with minor fix regarding ComputeCommonTailLength function in
BranchFolding.cpp. Skipping top CFI instructions block needs to executed on
several more return points in ComputeCommonTailLength().
Original r317100 message:
"Correct dwarf unwind information in function epilogue for X86"
This patch aims to provide correct dwarf unwind information in function
epilogue for X86.
It consists of two parts. The first part inserts CFI instructions that set
appropriate cfa offset and cfa register in emitEpilogue() in
X86FrameLowering. This part is X86 specific.
The second part is platform independent and ensures that:
- CFI instructions do not affect code generation
- Unwind information remains correct when a function is modified by
different passes. This is done in a late pass by analyzing information
about cfa offset and cfa register in BBs and inserting additional CFI
directives where necessary.
Changed CFI instructions so that they:
- are duplicable
- are not counted as instructions when tail duplicating or tail merging
- can be compared as equal
Added CFIInstrInserter pass:
- analyzes each basic block to determine cfa offset and register valid at
its entry and exit
- verifies that outgoing cfa offset and register of predecessor blocks match
incoming values of their successors
- inserts additional CFI directives at basic block beginning to correct the
rule for calculating CFA
Having CFI instructions in function epilogue can cause incorrect CFA
calculation rule for some basic blocks. This can happen if, due to basic
block reordering, or the existence of multiple epilogue blocks, some of the
blocks have wrong cfa offset and register values set by the epilogue block
above them.
CFIInstrInserter is currently run only on X86, but can be used by any target
that implements support for adding CFI instructions in epilogue.
Patch by Violeta Vukobrat.
llvm-svn: 317579
Summary:
Calls using invoke in funclet based functions are assumed to clobber
all registers, which causes the stack adjustment using pops to consider
all registers not defined by the call to be undefined, which can
unfortunately include the base pointer, if one is needed.
To prevent this (and possibly other hazards), skip reserved registers
when looking for candidate registers.
This fixes issue #45034 in the Rust compiler.
Reviewers: mkuper
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D39636
llvm-svn: 317551
This patch aims to provide correct dwarf unwind information in function
epilogue for X86.
It consists of two parts. The first part inserts CFI instructions that set
appropriate cfa offset and cfa register in emitEpilogue() in
X86FrameLowering. This part is X86 specific.
The second part is platform independent and ensures that:
- CFI instructions do not affect code generation
- Unwind information remains correct when a function is modified by
different passes. This is done in a late pass by analyzing information
about cfa offset and cfa register in BBs and inserting additional CFI
directives where necessary.
Changed CFI instructions so that they:
- are duplicable
- are not counted as instructions when tail duplicating or tail merging
- can be compared as equal
Added CFIInstrInserter pass:
- analyzes each basic block to determine cfa offset and register valid at
its entry and exit
- verifies that outgoing cfa offset and register of predecessor blocks match
incoming values of their successors
- inserts additional CFI directives at basic block beginning to correct the
rule for calculating CFA
Having CFI instructions in function epilogue can cause incorrect CFA
calculation rule for some basic blocks. This can happen if, due to basic
block reordering, or the existence of multiple epilogue blocks, some of the
blocks have wrong cfa offset and register values set by the epilogue block
above them.
CFIInstrInserter is currently run only on X86, but can be used by any target
that implements support for adding CFI instructions in epilogue.
Patch by Violeta Vukobrat.
Differential Revision: https://reviews.llvm.org/D35844
llvm-svn: 317100
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
Sink the insertion of "pop ebp" out of the frame size calculation
branches. They all check for HasFP.
Our handling of CLEANUPRET and CATCHRET was equivalent, both are
funclets and use the same frame size. We can eliminate the CLEANUPRET
case.
Hoist the hasFP(MF) query into a local bool.
Rename TargetMBB to CatchRetTarget to be more descriptive.
Eliminate the Optional<unsigned> RetOpcode local, now that it has one
use.
It's only a net savings of 10 lines, but hopefully it's *slightly* more
readable.
llvm-svn: 315000
The liveness-tracking code assumes that the registers that were saved
in the function's prolog are live outside of the function. Specifically,
that registers that were saved are also live-on-exit from the function.
This isn't always the case as illustrated by the LR register on ARM.
Differential Revision: https://reviews.llvm.org/D36160
llvm-svn: 310619
CFI instructions that set appropriate cfa offset and cfa register are now
inserted in emitEpilogue() in X86FrameLowering.
Majority of the changes in this patch:
1. Ensure that CFI instructions do not affect code generation.
2. Enable maintaining correct information about cfa offset and cfa register
in a function when basic blocks are reordered, merged, split, duplicated.
These changes are target independent and described below.
Changed CFI instructions so that they:
1. are duplicable
2. are not counted as instructions when tail duplicating or tail merging
3. can be compared as equal
Add information to each MachineBasicBlock about cfa offset and cfa register
that are valid at its entry and exit (incoming and outgoing CFI info). Add
support for updating this information when basic blocks are merged, split,
duplicated, created. Add a verification pass (CFIInfoVerifier) that checks
that outgoing cfa offset and register of predecessor blocks match incoming
values of their successors.
Incoming and outgoing CFI information is used by a late pass
(CFIInstrInserter) that corrects CFA calculation rule for a basic block if
needed. That means that additional CFI instructions get inserted at basic
block beginning to correct the rule for calculating CFA. Having CFI
instructions in function epilogue can cause incorrect CFA calculation rule
for some basic blocks. This can happen if, due to basic block reordering,
or the existence of multiple epilogue blocks, some of the blocks have wrong
cfa offset and register values set by the epilogue block above them.
Patch by Violeta Vukobrat.
Differential Revision: https://reviews.llvm.org/D18046
llvm-svn: 306529
Commit r306010 adjusted the condition as follows:
- if (Is64Bit) {
+ if (!STI.isTargetWin32()) {
The intent was to preserve the behavior on all Windows platforms
but extend the behavior on 64-bit Windows platforms to every
other one. (Before r306010, emitStackProbeCall only ever executed
when emitting code for Windows triples.)
Unfortunately,
if (Is64Bit && STI.isOSWindows())
is not the same as
if (!STI.isTargetWin32())
because of the way isTargetWin32() is defined:
bool isTargetWin32() const {
return !In64BitMode && (isTargetCygMing() ||
isTargetKnownWindowsMSVC());
}
In practice this broke the JIT tests on 32-bit Windows, which did not
satisfy the new condition:
LLVM :: ExecutionEngine/MCJIT/2003-01-15-AlignmentTest.ll
LLVM :: ExecutionEngine/MCJIT/2003-08-15-AllocaAssertion.ll
LLVM :: ExecutionEngine/MCJIT/2003-08-23-RegisterAllocatePhysReg.ll
LLVM :: ExecutionEngine/MCJIT/test-loadstore.ll
LLVM :: ExecutionEngine/OrcMCJIT/2003-01-15-AlignmentTest.ll
LLVM :: ExecutionEngine/OrcMCJIT/2003-08-15-AllocaAssertion.ll
LLVM :: ExecutionEngine/OrcMCJIT/2003-08-23-RegisterAllocatePhysReg.ll
LLVM :: ExecutionEngine/OrcMCJIT/test-loadstore.ll
because %esp was not updated correctly. The failures are only visible
on a MSVC 2017 Debug build, for which we do not have bots.
llvm-svn: 306142
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
The frame pointer (when used as frame pointer) is a reserved register.
We do not track liveness of reserved registers and hence do not need to
add them to the basic block livein lists.
llvm-svn: 304274
1. RegisterClass::getSize() is split into two functions:
- TargetRegisterInfo::getRegSizeInBits(const TargetRegisterClass &RC) const;
- TargetRegisterInfo::getSpillSize(const TargetRegisterClass &RC) const;
2. RegisterClass::getAlignment() is replaced by:
- TargetRegisterInfo::getSpillAlignment(const TargetRegisterClass &RC) const;
This will allow making those values depend on subtarget features in the
future.
Differential Revision: https://reviews.llvm.org/D31783
llvm-svn: 301221
Re-Commit of r300922 and r300923 with less aggressive assert (see
discussion at the end of https://reviews.llvm.org/D32205)
X86RegisterInfo::eliminateFrameIndex() and
X86FrameLowering::getFrameIndexReference() both had logic to compute the
base register. This consolidates the code.
Also use MachineInstr::isReturn instead of manually enumerating tail
call instructions (return instructions were not included in the previous
list because they never reference frame indexes).
Differential Revision: https://reviews.llvm.org/D32206
llvm-svn: 301211
It seems we have on situation in a sanitizer enable bootstrap build
where the return instruction has a frame index operand that does not
point to a fixed object and fails the assert added here.
This reverts commit r300923.
This reverts commit r300922.
llvm-svn: 301024
X86RegisterInfo::eliminateFrameIndex() and
X86FrameLowering::getFrameIndexReference() both had logic to compute the
base register. This consolidates the code.
Also use MachineInstr::isReturn instead of manually enumerating tail
call instructions (return instructions were not included in the previous
list because they never reference frame indexes).
Differential Revision: https://reviews.llvm.org/D32206
llvm-svn: 300923
Debug information is calculated with getFrameIndexReference() which was
missing some logic for the fixed object cases (= parameters on the stack).
rdar://24557797
Differential Revision: https://reviews.llvm.org/D32204
llvm-svn: 300781
Instructions CALLSEQ_START..CALLSEQ_END and their target dependent
counterparts keep data like frame size, stack adjustment etc. These
data are accessed by getOperand using hard coded indices. It is
error prone way. This change implements the access by special methods,
which improve readability and allow changing data representation without
massive changes of index values.
Differential Revision: https://reviews.llvm.org/D31953
llvm-svn: 300196
The x86_64 ABI requires that the stack is 16 byte aligned on function calls. Thus, the 8-byte error code, which is pushed by the CPU for certain exceptions, leads to a misaligned stack. This results in bugs such as Bug 26413, where misaligned movaps instructions are generated.
This commit fixes the misalignment by adjusting the stack pointer in these cases. The adjustment is done at the beginning of the prologue generation by subtracting another 8 bytes from the stack pointer. These additional bytes are popped again in the function epilogue.
Fixes Bug 26413
Patch by Philipp Oppermann.
Differential Revision: https://reviews.llvm.org/D30049
llvm-svn: 299383
Summary:
Use this code pattern when RAX is live, instead of emitting up to 2
billion adjustments:
pushq %rax
movabsq +-$Offset+-8, %rax
addq %rsp, %rax
xchg %rax, (%rsp)
movq (%rsp), %rsp
Try to clean this code up a bit while I'm here. In particular, hoist the
logic that handles the entire adjustment with `movabsq $imm, %rax` out
of the loop.
This negates the offset in the prologue and uses ADD because X86 only
has a two operand subtract which always subtracts from the destination
register, which can no longer be RSP.
Fixes PR31962
Reviewers: majnemer, sdardis
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D30052
llvm-svn: 298116
Summary:
In mergeSPUpdates, debug values need to be ignored when getting the
previous element, otherwise debug data could have an impact on codegen.
In eliminateCallFramePseudoInstr, debug values after the erased element
could have an impact on codegen and should be skipped.
Closes PR31319 (https://llvm.org/bugs/show_bug.cgi?id=31319)
Reviewers: aprantl, MatzeB, mkuper
Subscribers: gbedwell, llvm-commits
Differential Revision: https://reviews.llvm.org/D27688
llvm-svn: 290955
Summary:
In mergeSPUpdates, debug values need to be ignored when getting the
previous element, otherwise debug data could have an impact on codegen.
In eliminateCallFramePseudoInstr, debug values after the erased element
could have an impact on codegen and should be skipped.
Closes PR31319 (https://llvm.org/bugs/show_bug.cgi?id=31319)
Reviewers: mkuper, MatzeB, aprantl
Subscribers: gbedwell, llvm-commits
Differential Revision: https://reviews.llvm.org/D27688
llvm-svn: 290423
Summary: This patch makes sure FirstCSPop and MBBI never point to DBG_VALUE instructions, which affected the code generated.
Reviewers: mkuper, aprantl, MatzeB
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D27343
llvm-svn: 288794
Recommitting r288293 with some extra fixes for GlobalISel code.
Most of the exception handling members in MachineModuleInfo is actually
per function data (talks about the "current function") so it is better
to keep it at the function instead of the module.
This is a necessary step to have machine module passes work properly.
Also:
- Rename TidyLandingPads() to tidyLandingPads()
- Use doxygen member groups instead of "//===- EH ---"... so it is clear
where a group ends.
- I had to add an ugly const_cast at two places in the AsmPrinter
because the available MachineFunction pointers are const, but the code
wants to call tidyLandingPads() in between
(markFunctionEnd()/endFunction()).
Differential Revision: https://reviews.llvm.org/D27227
llvm-svn: 288405
Most of the exception handling members in MachineModuleInfo is actually
per function data (talks about the "current function") so it is better
to keep it at the function instead of the module.
This is a necessary step to have machine module passes work properly.
Also:
- Rename TidyLandingPads() to tidyLandingPads()
- Use doxygen member groups instead of "//===- EH ---"... so it is clear
where a group ends.
- I had to add an ugly const_cast at two places in the AsmPrinter
because the available MachineFunction pointers are const, but the code
wants to call tidyLandingPads() in between
(markFunctionEnd()/endFunction()).
Differential Revision: https://reviews.llvm.org/D27227
llvm-svn: 288293
This is per function data so it is better kept at the function instead
of the module.
This is a necessary step to have machine module passes work properly.
Differential Revision: https://reviews.llvm.org/D27185
llvm-svn: 288291
We don't need to return a MachineInstr* from these stack probe insertion
calls anyway. If we ever need to add it back, we can return an iterator
instead.
Based on a patch by David Kreitzer
This bug is a consequence of
r279314 | dexonsmith | 2016-08-19 13:40:12 -0700 (Fri, 19 Aug 2016) | 110 lines
We hit the "Assertion `!NodePtr->isKnownSentinel()' failed" assertion,
but only when inserting a stack probe call at the end of an MBB, which
isn't necessarily a common situation.
Differential Revision: https://reviews.llvm.org/D25566
llvm-svn: 284130
According to MSDN (see the PR), functions which don't touch any callee-saved
registers (including %rsp) don't need any unwind info.
This patch makes LLVM not emit unwind info for such functions, to save
binary size.
Differential Revision: https://reviews.llvm.org/D24748
llvm-svn: 282185
The x64 ABI has two major function types:
- frame functions
- leaf functions
A frame function is one which requires a stack frame. A leaf function
is one which does not. A frame function may or may not have a frame
pointer.
A leaf function does not require a stack frame and may never modify SP
except via a return (RET, tail call via JMP).
A frame function which has a frame pointer is permitted to use the LEA
instruction in the epilogue, a frame function without which doesn't
establish a frame pointer must use ADD to adjust the stack pointer epilogue.
Fun fact: Leaf functions don't require a function table entry
(associated PDATA/XDATA).
llvm-svn: 281006
Martin Storsjo