Consolidate the knowledge of what arm cores are always executing

in thumb mode into one method in ArchSpec, replace checks for
specific cores in the disassembler with calls to this.  Also call
this from the arm instruction emulation code.

The determination of whether a given ArchSpec is thumb-only is still
a bit of a hack, but at least the hack is consolidated into a single
place.  In my original version of this patch http://reviews.llvm.org/D13578
I was calling into llvm's feature arm feature tables to make this
determination, like

#include "llvm/Support/TargetRegistry.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/../../lib/Target/ARM/ARMGenRegisterInfo.inc"
#include "llvm/../../lib/Target/ARM/ARMFeatures.h"

[...]

        std::string triple (GetTriple().getTriple());
        const char *cpu = "";
        const char *features_str = "";
        const llvm::Target *curr_target = llvm::TargetRegistry::lookupTarget(triple.c_str(), Error);
        std::unique_ptr<llvm::MCSubtargetInfo> subtarget_info_up (curr_target->createMCSubtargetInfo(triple.c_str(), cpu, features_str));
        if (subtarget_info_up->getFeatureBits()[llvm::ARM::FeatureNoARM])
        {
            return true;
        }

but those tables are post-llvm-build generated and linking against them
for all of our different build system methods was a big hiccup that I
haven't had time to revisit convincingly.

I'll keep that reviews.llvm.org patch around to remind myself that I
need to take another run at linking against the necessary tables 
again in llvm.

<rdar://problem/23022803> 

llvm-svn: 265377

5 files changed, 65 insertions, 26 deletions

diff --git a/lldb/include/lldb/Core/ArchSpec.h b/lldb/include/lldb/Core/ArchSpec.h
index 70ac9548a7f..0b2ee900915 100644
--- a/lldb/include/lldb/Core/ArchSpec.h
+++ b/lldb/include/lldb/Core/ArchSpec.h
@@ -622,6 +622,22 @@ public:
                             bool &os_version_different,
                             bool &env_different);
     
+    //------------------------------------------------------------------
+    /// Detect whether this architecture uses thumb code exclusively
+    ///
+    /// Some embedded ARM chips (e.g. the ARM Cortex M0-7 line) can
+    /// only execute the Thumb instructions, never Arm.  We should normally
+    /// pick up arm/thumbness from their the processor status bits (cpsr/xpsr)
+    /// or hints on each function - but when doing bare-boards low level
+    /// debugging (especially common with these embedded processors), we may
+    /// not have those things easily accessible.
+    ///
+    /// @return true if this is an arm ArchSpec which can only execute Thumb
+    ///         instructions
+    //------------------------------------------------------------------
+    bool
+    IsAlwaysThumbInstructions () const;
+
     uint32_t
     GetFlags () const
     {
diff --git a/lldb/source/Core/ArchSpec.cpp b/lldb/source/Core/ArchSpec.cpp
index 0852a49c3d3..ecbd884ec52 100644
--- a/lldb/source/Core/ArchSpec.cpp
+++ b/lldb/source/Core/ArchSpec.cpp
@@ -898,6 +898,17 @@ ArchSpec::MergeFrom(const ArchSpec &other)
         if (other.TripleVendorWasSpecified())
             GetTriple().setEnvironment(other.GetTriple().getEnvironment());
     }
+    // If this and other are both arm ArchSpecs and this ArchSpec is a generic "some kind of arm"
+    // spec but the other ArchSpec is a specific arm core, adopt the specific arm core.
+    if (GetTriple().getArch() == llvm::Triple::arm
+        && other.GetTriple().getArch() == llvm::Triple::arm
+        && IsCompatibleMatch (other)
+        && GetCore() == ArchSpec::eCore_arm_generic
+        && other.GetCore() != ArchSpec::eCore_arm_generic)
+    {
+        m_core = other.GetCore();
+        CoreUpdated (true);
+    }
 }
 
 bool
@@ -1522,6 +1533,31 @@ ArchSpec::PiecewiseTripleCompare (const ArchSpec &other,
     env_different = (me.getEnvironment() != them.getEnvironment());
 }
 
+bool
+ArchSpec::IsAlwaysThumbInstructions () const
+{
+    std::string Error;
+    if (GetTriple().getArch() == llvm::Triple::arm || GetTriple().getArch() == llvm::Triple::thumb)
+    {
+        // v. https://en.wikipedia.org/wiki/ARM_Cortex-M
+        //
+        // Cortex-M0 through Cortex-M7 are ARM processor cores which can only
+        // execute thumb instructions.  We map the cores to arch names like this:
+        //
+        // Cortex-M0, Cortex-M0+, Cortex-M1:  armv6m
+        // Cortex-M3: armv7m
+        // Cortex-M4, Cortex-M7: armv7em
+
+        if (GetCore() == ArchSpec::Core::eCore_arm_armv7m
+            || GetCore() == ArchSpec::Core::eCore_arm_armv7em
+            || GetCore() == ArchSpec::Core::eCore_arm_armv6m)
+        {
+            return true;
+        }
+    }
+    return false;
+}
+
 void
 ArchSpec::DumpTriple(Stream &s) const
 {
diff --git a/lldb/source/Core/Disassembler.cpp b/lldb/source/Core/Disassembler.cpp
index 39843a0f028..9ef716d3f3f 100644
--- a/lldb/source/Core/Disassembler.cpp
+++ b/lldb/source/Core/Disassembler.cpp
@@ -1236,10 +1236,7 @@ Disassembler::Disassembler(const ArchSpec& arch, const char *flavor) :
     // If this is an arm variant that can only include thumb (T16, T32)
     // instructions, force the arch triple to be "thumbv.." instead of
     // "armv..."
-    if ((arch.GetTriple().getArch() == llvm::Triple::arm || arch.GetTriple().getArch() == llvm::Triple::thumb)
-        && (arch.GetCore() == ArchSpec::Core::eCore_arm_armv7m
-            || arch.GetCore() == ArchSpec::Core::eCore_arm_armv7em
-            || arch.GetCore() == ArchSpec::Core::eCore_arm_armv6m))
+    if (arch.IsAlwaysThumbInstructions())
     {
         std::string thumb_arch_name (arch.GetTriple().getArchName().str());
         // Replace "arm" with "thumb" so we get all thumb variants correct
diff --git a/lldb/source/Plugins/Disassembler/llvm/DisassemblerLLVMC.cpp b/lldb/source/Plugins/Disassembler/llvm/DisassemblerLLVMC.cpp
index 5bc782c19db..ed858c1675b 100644
--- a/lldb/source/Plugins/Disassembler/llvm/DisassemblerLLVMC.cpp
+++ b/lldb/source/Plugins/Disassembler/llvm/DisassemblerLLVMC.cpp
@@ -647,18 +647,8 @@ DisassemblerLLVMC::DisassemblerLLVMC (const ArchSpec &arch, const char *flavor_s
 
     const char *triple_str = triple.getTriple().c_str();
 
-    // v. https://en.wikipedia.org/wiki/ARM_Cortex-M#Silicon_customization
-    // 
-    // Cortex-M3 devices (e.g. armv7m) can only execute thumb (T2) instructions,
-    // so hardcode the primary disassembler to thumb mode.  Same for Cortex-M4 (armv7em).
-    //
-    // Handle the Cortex-M0 (armv6m) the same; the ISA is a subset of the T and T32
-    // instructions defined in ARMv7-A.
-
-    if ((triple.getArch() == llvm::Triple::arm || triple.getArch() == llvm::Triple::thumb)
-        && (arch.GetCore() == ArchSpec::Core::eCore_arm_armv7m
-            || arch.GetCore() == ArchSpec::Core::eCore_arm_armv7em
-            || arch.GetCore() == ArchSpec::Core::eCore_arm_armv6m))
+    // ARM Cortex M0-M7 devices only execute thumb instructions
+    if (arch.IsAlwaysThumbInstructions ())
     {
         triple_str = thumb_arch.GetTriple().getTriple().c_str();
     }
diff --git a/lldb/source/Plugins/Instruction/ARM/EmulateInstructionARM.cpp b/lldb/source/Plugins/Instruction/ARM/EmulateInstructionARM.cpp
index c9e942e6ba6..8b0863e2913 100644
--- a/lldb/source/Plugins/Instruction/ARM/EmulateInstructionARM.cpp
+++ b/lldb/source/Plugins/Instruction/ARM/EmulateInstructionARM.cpp
@@ -13004,7 +13004,7 @@ EmulateInstructionARM::SetInstruction (const Opcode &insn_opcode, const Address
 {
     if (EmulateInstruction::SetInstruction (insn_opcode, inst_addr, target))
     {
-        if (m_arch.GetTriple().getArch() == llvm::Triple::thumb)
+        if (m_arch.GetTriple().getArch() == llvm::Triple::thumb || m_arch.IsAlwaysThumbInstructions ())
             m_opcode_mode = eModeThumb;
         else
         {
@@ -13017,7 +13017,7 @@ EmulateInstructionARM::SetInstruction (const Opcode &insn_opcode, const Address
             else
                 return false;
         }
-        if (m_opcode_mode == eModeThumb)
+        if (m_opcode_mode == eModeThumb || m_arch.IsAlwaysThumbInstructions ())
             m_opcode_cpsr = CPSR_MODE_USR | MASK_CPSR_T;
         else
             m_opcode_cpsr = CPSR_MODE_USR;
@@ -13040,7 +13040,7 @@ EmulateInstructionARM::ReadInstruction ()
             read_inst_context.type = eContextReadOpcode;
             read_inst_context.SetNoArgs ();
                   
-            if (m_opcode_cpsr & MASK_CPSR_T)
+            if ((m_opcode_cpsr & MASK_CPSR_T) || m_arch.IsAlwaysThumbInstructions ())
             {
                 m_opcode_mode = eModeThumb;
                 uint32_t thumb_opcode = MemARead(read_inst_context, pc, 2, 0, &success);
@@ -13678,19 +13678,19 @@ EmulateInstructionARM::TestEmulation (Stream *out_stream, ArchSpec &arch, Option
     }
     test_opcode = value_sp->GetUInt64Value ();
 
-    if (arch.GetTriple().getArch() == llvm::Triple::arm)
-    {
-        m_opcode_mode = eModeARM;
-        m_opcode.SetOpcode32 (test_opcode, GetByteOrder());
-    }
-    else if (arch.GetTriple().getArch() == llvm::Triple::thumb)
+
+    if (arch.GetTriple().getArch() == llvm::Triple::thumb || arch.IsAlwaysThumbInstructions ())
     {
         m_opcode_mode = eModeThumb;
         if (test_opcode < 0x10000)
             m_opcode.SetOpcode16 (test_opcode, GetByteOrder());
         else
             m_opcode.SetOpcode32 (test_opcode, GetByteOrder());
-
+    }
+    else if (arch.GetTriple().getArch() == llvm::Triple::arm)
+    {
+        m_opcode_mode = eModeARM;
+        m_opcode.SetOpcode32 (test_opcode, GetByteOrder());
     }
     else
     {