| // Copyright 2019 The Pigweed Authors |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); you may not |
| // use this file except in compliance with the License. You may obtain a copy of |
| // the License at |
| // |
| // https://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, WITHOUT |
| // WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the |
| // License for the specific language governing permissions and limitations under |
| // the License. |
| |
| #include "pw_cpu_exception/entry.h" |
| |
| #include <cstdint> |
| #include <cstring> |
| |
| #include "pw_cpu_exception/handler.h" |
| #include "pw_cpu_exception_cortex_m/cpu_state.h" |
| #include "pw_cpu_exception_cortex_m_private/cortex_m_constants.h" |
| #include "pw_preprocessor/compiler.h" |
| |
| // TODO(pwbug/311): Deprecated naming. |
| PW_EXTERN_C PW_NO_PROLOGUE __attribute__((alias("pw_cpu_exception_Entry"))) void |
| pw_CpuExceptionEntry(void); |
| |
| namespace pw::cpu_exception { |
| namespace { |
| |
| // If the CPU fails to capture some registers, the captured struct members will |
| // be populated with this value. The only registers that this value should be |
| // loaded into are pc, lr, and psr when the CPU fails to push an exception |
| // context frame. |
| // |
| // 0xFFFFFFFF is an illegal lr value, which is why it was selected for this |
| // purpose. pc and psr values of 0xFFFFFFFF are dubious too, so this constant |
| // is clear enough at expressing that the registers weren't properly captured. |
| constexpr uint32_t kInvalidRegisterValue = 0xFFFFFFFF; |
| |
| // Checks exc_return in the captured CPU state to determine which stack pointer |
| // was in use prior to entering the exception handler. |
| bool PspWasActive(const pw_cpu_exception_State& cpu_state) { |
| return cpu_state.extended.exc_return & kExcReturnStackMask; |
| } |
| |
| // Checks exc_return to determine if FPU state was pushed to the stack in |
| // addition to the base CPU context frame. |
| bool FpuStateWasPushed(const pw_cpu_exception_State& cpu_state) { |
| return !(cpu_state.extended.exc_return & kExcReturnBasicFrameMask); |
| } |
| |
| // If the CPU successfully pushed context on exception, copy it into cpu_state. |
| // |
| // For more information see (See ARMv7-M Section B1.5.11, derived exceptions |
| // on exception entry). |
| void CloneBaseRegistersFromPsp(pw_cpu_exception_State* cpu_state) { |
| // If CPU succeeded in pushing context to PSP, copy it to the MSP. |
| if (!(cpu_state->extended.cfsr & kCfsrStkerrMask) && |
| !(cpu_state->extended.cfsr & kCfsrMstkerrMask)) { |
| // TODO(amontanez): {r0-r3,r12} are captured in pw_cpu_exception_Entry(), |
| // so this only really needs to copy pc, lr, and psr. Could |
| // (possibly) improve speed, but would add marginally more |
| // complexity. |
| std::memcpy(&cpu_state->base, |
| reinterpret_cast<void*>(cpu_state->extended.psp), |
| sizeof(CortexMExceptionRegisters)); |
| } else { |
| // If CPU context wasn't pushed to stack on exception entry, we can't |
| // recover psr, lr, and pc from exception-time. Make these values clearly |
| // invalid. |
| cpu_state->base.lr = kInvalidRegisterValue; |
| cpu_state->base.pc = kInvalidRegisterValue; |
| cpu_state->base.psr = kInvalidRegisterValue; |
| } |
| } |
| |
| // If the CPU successfully pushed context on exception, restore it from |
| // cpu_state. Otherwise, don't attempt to restore state. |
| // |
| // For more information see (See ARMv7-M Section B1.5.11, derived exceptions |
| // on exception entry). |
| void RestoreBaseRegistersToPsp(pw_cpu_exception_State* cpu_state) { |
| // If CPU succeeded in pushing context to PSP on exception entry, restore the |
| // contents of cpu_state to the CPU-pushed register frame so the CPU can |
| // continue. Otherwise, don't attempt as we'll likely end up in an escalated |
| // hard fault. |
| if (!(cpu_state->extended.cfsr & kCfsrStkerrMask) && |
| !(cpu_state->extended.cfsr & kCfsrMstkerrMask)) { |
| std::memcpy(reinterpret_cast<void*>(cpu_state->extended.psp), |
| &cpu_state->base, |
| sizeof(CortexMExceptionRegisters)); |
| } |
| } |
| |
| // Determines the size of the CPU-pushed context frame. |
| uint32_t CpuContextSize(const pw_cpu_exception_State& cpu_state) { |
| uint32_t cpu_context_size = sizeof(CortexMExceptionRegisters); |
| if (FpuStateWasPushed(cpu_state)) { |
| cpu_context_size += sizeof(CortexMExceptionRegistersFpu); |
| } |
| if (cpu_state.base.psr & kPsrExtraStackAlignBit) { |
| // Account for the extra 4-bytes the processor |
| // added to keep the stack pointer 8-byte aligned |
| cpu_context_size += 4; |
| } |
| |
| return cpu_context_size; |
| } |
| |
| // On exception entry, the Program Stack Pointer is patched to reflect the state |
| // at exception-time. On exception return, it is restored to the appropriate |
| // location. This calculates the delta that is used for these patch operations. |
| uint32_t CalculatePspDelta(const pw_cpu_exception_State& cpu_state) { |
| // If CPU context was not pushed to program stack (because program stack |
| // wasn't in use, or an error occurred when pushing context), the PSP doesn't |
| // need to be shifted. |
| if (!PspWasActive(cpu_state) || (cpu_state.extended.cfsr & kCfsrStkerrMask) || |
| (cpu_state.extended.cfsr & kCfsrMstkerrMask)) { |
| return 0; |
| } |
| |
| return CpuContextSize(cpu_state); |
| } |
| |
| // On exception entry, the Main Stack Pointer is patched to reflect the state |
| // at exception-time. On exception return, it is restored to the appropriate |
| // location. This calculates the delta that is used for these patch operations. |
| uint32_t CalculateMspDelta(const pw_cpu_exception_State& cpu_state) { |
| if (PspWasActive(cpu_state)) { |
| // TODO(amontanez): Since FPU state isn't captured at this time, we ignore |
| // it when patching MSP. To add FPU capture support, |
| // delete this if block as CpuContextSize() will include |
| // FPU context size in the calculation. |
| return sizeof(CortexMExceptionRegisters) + sizeof(CortexMExtraRegisters); |
| } |
| |
| return CpuContextSize(cpu_state) + sizeof(CortexMExtraRegisters); |
| } |
| |
| } // namespace |
| |
| extern "C" { |
| |
| // Collect remaining CPU state (memory mapped registers), populate memory mapped |
| // registers, and call application exception handler. |
| PW_USED void pw_PackageAndHandleCpuException( |
| pw_cpu_exception_State* cpu_state) { |
| // Capture memory mapped registers. |
| cpu_state->extended.cfsr = cortex_m_cfsr; |
| cpu_state->extended.mmfar = cortex_m_mmfar; |
| cpu_state->extended.bfar = cortex_m_bfar; |
| cpu_state->extended.icsr = cortex_m_icsr; |
| cpu_state->extended.hfsr = cortex_m_hfsr; |
| cpu_state->extended.shcsr = cortex_m_shcsr; |
| |
| // CPU may have automatically pushed state to the program stack. If it did, |
| // the values can be copied into in the pw_cpu_exception_State struct that is |
| // passed to HandleCpuException(). The cpu_state passed to the handler is |
| // ALWAYS stored on the main stack (MSP). |
| if (PspWasActive(*cpu_state)) { |
| CloneBaseRegistersFromPsp(cpu_state); |
| // If PSP wasn't active, this delta is 0. |
| cpu_state->extended.psp += CalculatePspDelta(*cpu_state); |
| } |
| |
| // Patch captured stack pointers so they reflect the state at exception time. |
| cpu_state->extended.msp += CalculateMspDelta(*cpu_state); |
| |
| // Call application-level exception handler. |
| pw_cpu_exception_HandleException(cpu_state); |
| |
| // Restore program stack pointer so exception return can restore state if |
| // needed. |
| // Note: The default behavior of NOT subtracting a delta from MSP is |
| // intentional. This simplifies the assembly to pop the exception state |
| // off the main stack on exception return (since MSP currently reflects |
| // exception-time state). |
| cpu_state->extended.psp -= CalculatePspDelta(*cpu_state); |
| |
| // If PSP was active and the CPU pushed a context frame, we must copy the |
| // potentially modified state from cpu_state back to the PSP so the CPU can |
| // resume execution with the modified values. |
| if (PspWasActive(*cpu_state)) { |
| // In this case, there's no need to touch the MSP as it's at the location |
| // before we entering the exception (effectively popping the state initially |
| // pushed to the main stack). |
| RestoreBaseRegistersToPsp(cpu_state); |
| } else { |
| // Since we're restoring context from MSP, we DO need to adjust MSP to point |
| // to CPU-pushed context frame so it can be properly restored. |
| // No need to adjust PSP since nothing was pushed to program stack. |
| cpu_state->extended.msp -= CpuContextSize(*cpu_state); |
| } |
| } |
| |
| // Captures faulting CPU state on the main stack (MSP), then calls the exception |
| // handlers. |
| // This function should be called immediately after an exception. |
| void pw_cpu_exception_Entry(void) { |
| asm volatile( |
| // clang-format off |
| // If PSP was in use at the time of exception, it's possible the CPU |
| // wasn't able to push CPU state. To be safe, this first captures scratch |
| // registers before moving forward. |
| // |
| // Stack flag is bit index 2 (0x4) of exc_return value stored in lr. When |
| // this bit is set, the Process Stack Pointer (PSP) was in use. Otherwise, |
| // the Main Stack Pointer (MSP) was in use. (See ARMv7-M Section B1.5.8 |
| // for more details) |
| // The following block of assembly is equivalent to: |
| // if (lr & (1 << 2)) { |
| // msp -= sizeof(CortexMExceptionRegisters); |
| // CortexMExceptionRegisters* state = |
| // (CortexMExceptionRegisters*) msp; |
| // state->r0 = r0; |
| // state->r1 = r1; |
| // state->r2 = r2; |
| // state->r3 = r3; |
| // state->r12 = r12; |
| // } |
| // |
| " tst lr, #(1 << 2) \n" |
| " itt ne \n" |
| " subne sp, sp, %[base_state_size] \n" |
| " stmne sp, {r0-r3, r12} \n" |
| |
| // Reserve stack space for additional registers. Since we're in exception |
| // handler mode, the main stack pointer is currently in use. |
| // r0 will temporarily store the end of captured_cpu_state to simplify |
| // assembly for copying additional registers. |
| " mrs r0, msp \n" |
| " sub sp, sp, %[extra_state_size] \n" |
| |
| // Store GPRs to stack. |
| " stmdb r0!, {r4-r11} \n" |
| |
| // Load special registers. |
| " mov r1, lr \n" |
| " mrs r2, msp \n" |
| " mrs r3, psp \n" |
| " mrs r4, control \n" |
| |
| // Store special registers to stack. |
| " stmdb r0!, {r1-r4} \n" |
| |
| // Store a pointer to the beginning of special registers in r4 so they can |
| // be restored later. |
| " mov r4, r0 \n" |
| |
| // Restore captured_cpu_state pointer to r0. This makes adding more |
| // memory mapped registers easier in the future since they're skipped in |
| // this assembly. |
| " mrs r0, msp \n" |
| |
| // Call intermediate handler that packages data. |
| " ldr r3, =pw_PackageAndHandleCpuException \n" |
| " blx r3 \n" |
| |
| // Restore state and exit exception handler. |
| // Pointer to saved CPU state was stored in r4. |
| " mov r0, r4 \n" |
| |
| // Restore special registers. |
| " ldm r0!, {r1-r4} \n" |
| " mov lr, r1 \n" |
| " msr control, r4 \n" |
| |
| // Restore GPRs. |
| " ldm r0, {r4-r11} \n" |
| |
| // Restore stack pointers. |
| " msr msp, r2 \n" |
| " msr psp, r3 \n" |
| |
| // Exit exception. |
| " bx lr \n" |
| : /*output=*/ |
| : /*input=*/[base_state_size]"i"(sizeof(CortexMExceptionRegisters)), |
| [extra_state_size]"i"(sizeof(CortexMExtraRegisters)) |
| // clang-format on |
| ); |
| } |
| |
| } // extern "C" |
| } // namespace pw::cpu_exception |
