[x86/retpoline] Split the LLVM concept of retpolines into separate

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

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@340515 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/clang/Driver/Options.td b/include/clang/Driver/Options.td
index 5d27a9a7dc90972bf53f4efe6a84f50d9f5a86f3..bbdbe7cfbb6a8766aa1c7c5a5332ca92201a3ab9 100644 (file)
--- a/include/clang/Driver/Options.td
+++ b/include/clang/Driver/Options.td
@@ -1999,6 +1999,9 @@ def mno_rtd: Flag<["-"], "mno-rtd">, Group<m_Group>;
 def mno_soft_float : Flag<["-"], "mno-soft-float">, Group<m_Group>;
 def mno_stackrealign : Flag<["-"], "mno-stackrealign">, Group<m_Group>;
 
+def mretpoline : Flag<["-"], "mretpoline">, Group<m_Group>, Flags<[CoreOption,DriverOption]>;
+def mno_retpoline : Flag<["-"], "mno-retpoline">, Group<m_Group>, Flags<[CoreOption,DriverOption]>;
+
 def mrelax : Flag<["-"], "mrelax">, Group<m_riscv_Features_Group>,
   HelpText<"Enable linker relaxation">;
 def mno_relax : Flag<["-"], "mno-relax">, Group<m_riscv_Features_Group>,
@@ -2824,8 +2827,6 @@ def mxsaves : Flag<["-"], "mxsaves">, Group<m_x86_Features_Group>;
 def mno_xsaves : Flag<["-"], "mno-xsaves">, Group<m_x86_Features_Group>;
 def mshstk : Flag<["-"], "mshstk">, Group<m_x86_Features_Group>;
 def mno_shstk : Flag<["-"], "mno-shstk">, Group<m_x86_Features_Group>;
-def mretpoline : Flag<["-"], "mretpoline">, Group<m_x86_Features_Group>;
-def mno_retpoline : Flag<["-"], "mno-retpoline">, Group<m_x86_Features_Group>;
 def mretpoline_external_thunk : Flag<["-"], "mretpoline-external-thunk">, Group<m_x86_Features_Group>;
 def mno_retpoline_external_thunk : Flag<["-"], "mno-retpoline-external-thunk">, Group<m_x86_Features_Group>;
 

diff --git a/lib/Basic/Targets/X86.cpp b/lib/Basic/Targets/X86.cpp
index e295cff9d5d2c62be957ab66cbd212354626c81d..eaca1811c0fe04f865d7cb7a64c4b35c3a4468b0 100644 (file)
--- a/lib/Basic/Targets/X86.cpp
+++ b/lib/Basic/Targets/X86.cpp
@@ -796,8 +796,6 @@ bool X86TargetInfo::handleTargetFeatures(std::vector<std::string> &Features,
       HasCLDEMOTE = true;
     } else if (Feature == "+rdpid") {
       HasRDPID = true;
-    } else if (Feature == "+retpoline") {
-      HasRetpoline = true;
     } else if (Feature == "+retpoline-external-thunk") {
       HasRetpolineExternalThunk = true;
     } else if (Feature == "+sahf") {
@@ -1397,7 +1395,6 @@ bool X86TargetInfo::hasFeature(StringRef Feature) const {
       .Case("rdpid", HasRDPID)
       .Case("rdrnd", HasRDRND)
       .Case("rdseed", HasRDSEED)
-      .Case("retpoline", HasRetpoline)
       .Case("retpoline-external-thunk", HasRetpolineExternalThunk)
       .Case("rtm", HasRTM)
       .Case("sahf", HasLAHFSAHF)

diff --git a/lib/Basic/Targets/X86.h b/lib/Basic/Targets/X86.h
index 019bc8d51a634cab6c45440bc476626ebddca98e..077b590943418047729401636dc309ec7c78d56e 100644 (file)
--- a/lib/Basic/Targets/X86.h
+++ b/lib/Basic/Targets/X86.h
@@ -98,7 +98,6 @@ class LLVM_LIBRARY_VISIBILITY X86TargetInfo : public TargetInfo {
   bool HasMOVBE = false;
   bool HasPREFETCHWT1 = false;
   bool HasRDPID = false;
-  bool HasRetpoline = false;
   bool HasRetpolineExternalThunk = false;
   bool HasLAHFSAHF = false;
   bool HasWBNOINVD = false;

diff --git a/lib/Driver/ToolChains/Arch/X86.cpp b/lib/Driver/ToolChains/Arch/X86.cpp
index 7a4f836d2e1ae16a12ba515af79103050012e1b2..ff2023c2cbe424f212abcfbceb798285c3776bfa 100644 (file)
--- a/lib/Driver/ToolChains/Arch/X86.cpp
+++ b/lib/Driver/ToolChains/Arch/X86.cpp
@@ -144,6 +144,26 @@ void x86::getX86TargetFeatures(const Driver &D, const llvm::Triple &Triple,
       Features.push_back("+ssse3");
   }
 
+  // Translate the high level `-mretpoline` flag to the specific target feature
+  // flags. We also detect if the user asked for retpoline external thunks but
+  // failed to ask for retpolines themselves. This is a bit hacky but keeps
+  // existing usages working. We should consider deprecated this and instead
+  // warning if the user requests external retpoline thunks and *doesn't*
+  // request some form of retpolines.
+  if (Args.hasArgNoClaim(options::OPT_mretpoline, options::OPT_mno_retpoline)) {
+    if (Args.hasFlag(options::OPT_mretpoline, options::OPT_mno_retpoline,
+                     false)) {
+      Features.push_back("+retpoline-indirect-calls");
+      Features.push_back("+retpoline-indirect-branches");
+    }
+  } else if (Args.hasFlag(options::OPT_mretpoline_external_thunk,
+                          options::OPT_mno_retpoline_external_thunk, false)) {
+    // FIXME: Add a warning about failing to specify `-mretpoline` and
+    // eventually switch to an error here.
+    Features.push_back("+retpoline-indirect-calls");
+    Features.push_back("+retpoline-indirect-branches");
+  }
+
   // Now add any that the user explicitly requested on the command line,
   // which may override the defaults.
   handleTargetFeaturesGroup(Args, Features, options::OPT_m_x86_Features_Group);

diff --git a/test/Driver/x86-target-features.c b/test/Driver/x86-target-features.c
index 515ca425c2b52488239e246e5f80aef936ec7edb..527a9a2cfff8db64ad9e19d850a83e7dd8a228ec 100644 (file)
--- a/test/Driver/x86-target-features.c
+++ b/test/Driver/x86-target-features.c
@@ -132,8 +132,8 @@
 
 // RUN: %clang -target i386-linux-gnu -mretpoline %s -### -o %t.o 2>&1 | FileCheck -check-prefix=RETPOLINE %s
 // RUN: %clang -target i386-linux-gnu -mno-retpoline %s -### -o %t.o 2>&1 | FileCheck -check-prefix=NO-RETPOLINE %s
-// RETPOLINE: "-target-feature" "+retpoline"
-// NO-RETPOLINE: "-target-feature" "-retpoline"
+// RETPOLINE: "-target-feature" "+retpoline-indirect-calls" "-target-feature" "+retpoline-indirect-branches"
+// NO-RETPOLINE-NOT: retpoline
 
 // RUN: %clang -target i386-linux-gnu -mretpoline -mretpoline-external-thunk %s -### -o %t.o 2>&1 | FileCheck -check-prefix=RETPOLINE-EXTERNAL-THUNK %s
 // RUN: %clang -target i386-linux-gnu -mretpoline -mno-retpoline-external-thunk %s -### -o %t.o 2>&1 | FileCheck -check-prefix=NO-RETPOLINE-EXTERNAL-THUNK %s