Introduce WITH_/WITHOUT_LLVM_COV to match GCC's WITH_/WITHOUT_GCOV.
It is intended to provide a superset of the interface and functionality
of gcov.
It is enabled by default when building Clang, similarly to gcov and GCC.
This change moves one file in libllvm to be compiled unconditionally.
Previously it was included only when WITH_CLANG_EXTRAS was set, but the
complexity of a new special case for (CLANG_EXTRAS | LLVM_COV) is not
worth avoiding a tiny increase in build time.
Reviewed by: dim, imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D142645
-Wno-error=tautological-constant-compare again (this flag is now out of
-Wextra after upstream https://reviews.llvm.org/rL322901). Otherwise
the MK_SYSTEM_COMPILER logic will not build a cross-tools compiler.
Reported by: jpaetzel, tuexen, Stefan Hagen
6.0.0 (branches/release_60 r324090).
This introduces retpoline support, with the -mretpoline flag. The
upstream initial commit message (r323155 by Chandler Carruth) contains
quite a bit of explanation. Quoting:
Introduce the "retpoline" x86 mitigation technique for variant #2 of
the speculative execution vulnerabilities disclosed today,
specifically identified by CVE-2017-5715, "Branch Target Injection",
and is one of the two halves to Spectre.
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 typic al 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
MFC after: 3 months
X-MFC-With: r327952
PR: 224669
Allow usage of X86-prefixes as separate instrs.
Differential Revision: https://reviews.llvm.org/D42102
This should fix parse errors when x86 prefixes (such as 'lock' and
'rep') are followed by various non-mnemonic tokens, e.g. comments, .byte
directives and labels.
PR: 224669,225054
This allows the _SKIP_DEPEND optimization to work, avoiding reading
the files when not needed. It also fixes META_MODE incorrectly
reading these files when not needed.
Sponsored by: Dell EMC Isilon
The Makefile.inc1 TARGET_TRIPLE is for specifying which -target is used
during the build of world.
MFC after: 2 weeks
Reviewed by: dim, imp
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D12792
Make armv7 as a new MACHINE_ARCH.
Copy all the places we do armv6 and add armv7 as basically an
alias. clang appears to generate code for armv7 by default. armv7 hard
float isn't supported by the the in-tree gcc, so it hasn't been
updated to have a new default.
Support armv7 as a new valid MACHINE_ARCH (and by extension
TARGET_ARCH).
Add armv7 to the universe build.
Differential Revision: https://reviews.freebsd.org/D12010
the upstream release_50 branch. This corresponds to 5.0.0 rc4.
As of this version, the cad/stepcode port should now compile in a more
reasonable time on i386 (see bug 221836 for more information).
PR: 221836
MFC after: 2 months
X-MFC-with: r321369
the upstream release_50 branch.
As of this version, lib/msun's trig test should also work correctly
again (see bug 220989 for more information).
PR: 220989
MFC after: 2 months
X-MFC-with: r321369
- Include debug symbols in static libraries. This permits binaries
to include debug symbols for functions obtained from static libraries.
- Permit the C/C++ compiler flags added for MK_DEBUG_FILES to be
overridden by setting DEBUG_FILES_CFLAGS. Use this to limit the debug
information for llvm libraries and binaries.
Reviewed by: emaste
Sponsored by: DARPA / AFRL
Differential Revision: https://reviews.freebsd.org/D12025
The files are only ever generated to .OBJDIR, not to WORLDTMP (as a
sysroot) and are only ever included from a compilation. So using
a beforebuild target here removes the file before the compilation
tries to include it.
MFC after: 2 months
X-MFC-With: r321369
linking the lldb executable in some cases. In particular, when the
-ffunction-sections -fdata-sections options are turned off, or
ineffective.
Reported by: Shawn Webb, Mark Millard
MFC after: 2 months
X-MFC-With: r308421
