The issue with Thumb IT (if/then) instructions is the IT instruction preceeds up to four instructions that are made conditional. If a breakpoint is placed on one of the conditional instructions, the instruction either needs to match the thumb opcode size (2 or 4 bytes) or a BKPT instruction needs to be used as these are always unconditional (even in a IT instruction). If BKPT instructions are used, then we might end up stopping on an instruction that won't get executed. So if we do stop at a BKPT instruction, we need to continue if the condition is not true.
When using the BKPT isntructions are easy in that you don't need to detect the size of the breakpoint that needs to be used when setting a breakpoint even in a thumb IT instruction. The bad part is you will now always stop at the opcode location and let LLDB determine if it should auto-continue. If the BKPT instruction is used, the BKPT that is used for ARM code should be something that also triggers the BKPT instruction in Thumb in case you set a breakpoint in the middle of code and the code is actually Thumb code. A value of 0xE120BE70 will work since the lower 16 bits being 0xBE70 happens to be a Thumb BKPT instruction.
The alternative is to use trap or illegal instructions that the kernel will translate into breakpoint hits. On Mac this was 0xE7FFDEFE for ARM and 0xDEFE for Thumb. The darwin kernel currently doesn't recognize any 32 bit Thumb instruction as a instruction that will get turned into a breakpoint exception (EXC_BREAKPOINT), so we had to use the BKPT instruction on Mac. The linux kernel recognizes a 16 and a 32 bit instruction as valid thumb breakpoint opcodes. The benefit of using 16 or 32 bit instructions is you don't stop on opcodes in a IT block when the condition doesn't match.
To further complicate things, single stepping on ARM is often implemented by modifying the BCR/BVR registers and setting the processor to stop when the PC is not equal to the current value. This means single stepping is another way the ARM target can stop on instructions that won't get executed.
This patch does the following:
1 - Fix the internal debugserver for Apple to use the BKPT instruction for ARM and Thumb
2 - Fix LLDB to catch when we stop in the middle of a Thumb IT instruction and continue if we stop at an instruction that won't execute
3 - Fixes this in a way that will work for any target on any platform as long as it is ARM/Thumb
4 - Adds a patch for ignoring conditions that don't match when in ARM mode (see below)
This patch also provides the code that implements the same thing for ARM instructions, though it is disabled for now. The ARM patch will check the condition of the instruction in ARM mode and continue if the condition isn't true (and therefore the instruction would not be executed). Again, this is not enable, but the code for it has been added.
<rdar://problem/19145455>
llvm-svn: 223851
bool
Address::SetLoadAddress (lldb::addr_t load_addr, Target *target);
Added an == and != operator to RegisterValue.
Modified the ThreadPlanTracer to use RegisterValue objects to store the
register values when single stepping. Also modified the output to be a bit
less wide.
Fixed the ABIMacOSX_arm to not overwrite stuff on the stack. Also made the
trivial function call be able to set the ARM/Thumbness of the target
correctly, and also sets the return value ARM/Thumbness.
Fixed the encoding on the arm s0-s31 and d16 - d31 registers when the default
register set from a standard GDB server register sets.
llvm-svn: 131517
are defined as enumerations. Current bits include:
eEmulateInstructionOptionAutoAdvancePC
eEmulateInstructionOptionIgnoreConditions
Modified the EmulateInstruction class to have a few more pure virtuals that
can help clients understand how many instructions the emulator can handle:
virtual bool
SupportsEmulatingIntructionsOfType (InstructionType inst_type) = 0;
Where instruction types are defined as:
//------------------------------------------------------------------
/// Instruction types
//------------------------------------------------------------------
typedef enum InstructionType
{
eInstructionTypeAny, // Support for any instructions at all (at least one)
eInstructionTypePrologueEpilogue, // All prologue and epilogue instructons that push and pop register values and modify sp/fp
eInstructionTypePCModifying, // Any instruction that modifies the program counter/instruction pointer
eInstructionTypeAll // All instructions of any kind
} InstructionType;
This allows use to tell what an emulator can do and also allows us to request
these abilities when we are finding the plug-in interface.
Added the ability for an EmulateInstruction class to get the register names
for any registers that are part of the emulation. This helps with being able
to dump and log effectively.
The UnwindAssembly class now stores the architecture it was created with in
case it is needed later in the unwinding process.
Added a function that can tell us DWARF register names for ARM that goes
along with the source/Utility/ARM_DWARF_Registers.h file:
source/Utility/ARM_DWARF_Registers.c
Took some of plug-ins out of the lldb_private namespace.
llvm-svn: 130189
Create two helper methods EmulateShiftImm() and EmulateShiftReg() and have ASR, LSL, and LSR
delegate to the helper methods which take an extra ARM_ShifterType parameter.
The opcodes tables have not been updated yet to reflect these new entries.
llvm-svn: 125633
Greg Clayton