// Copyright 2017 The Abseil 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. // // Produce stack trace. I'm guessing (hoping!) the code is much like // for x86. For apple machines, at least, it seems to be; see // https://developer.apple.com/documentation/mac/runtimehtml/RTArch-59.html // https://www.linux-foundation.org/spec/ELF/ppc64/PPC-elf64abi-1.9.html#STACK // Linux has similar code: http://patchwork.ozlabs.org/linuxppc/patch?id=8882 #ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_POWERPC_INL_H_ #define ABSL_DEBUGGING_INTERNAL_STACKTRACE_POWERPC_INL_H_ #if defined(__linux__) #include <asm/ptrace.h> // for PT_NIP. #include <ucontext.h> // for ucontext_t #endif #include <unistd.h> #include <cassert> #include <cstdint> #include <cstdio> #include "absl/base/attributes.h" #include "absl/base/optimization.h" #include "absl/base/port.h" #include "absl/debugging/stacktrace.h" #include "absl/debugging/internal/address_is_readable.h" #include "absl/debugging/internal/vdso_support.h" // a no-op on non-elf or non-glibc systems // Given a stack pointer, return the saved link register value. // Note that this is the link register for a callee. static inline void *StacktracePowerPCGetLR(void **sp) { // PowerPC has 3 main ABIs, which say where in the stack the // Link Register is. For DARWIN and AIX (used by apple and // linux ppc64), it's in sp[2]. For SYSV (used by linux ppc), // it's in sp[1]. #if defined(_CALL_AIX) || defined(_CALL_DARWIN) return *(sp+2); #elif defined(_CALL_SYSV) return *(sp+1); #elif defined(__APPLE__) || defined(__FreeBSD__) || \ (defined(__linux__) && defined(__PPC64__)) // This check is in case the compiler doesn't define _CALL_AIX/etc. return *(sp+2); #elif defined(__linux) // This check is in case the compiler doesn't define _CALL_SYSV. return *(sp+1); #else #error Need to specify the PPC ABI for your archiecture. #endif } // Given a pointer to a stack frame, locate and return the calling // stackframe, or return null if no stackframe can be found. Perform sanity // checks (the strictness of which is controlled by the boolean parameter // "STRICT_UNWINDING") to reduce the chance that a bad pointer is returned. template<bool STRICT_UNWINDING, bool IS_WITH_CONTEXT> ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS // May read random elements from stack. ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY // May read random elements from stack. static void **NextStackFrame(void **old_sp, const void *uc) { void **new_sp = (void **) *old_sp; enum { kStackAlignment = 16 }; // Check that the transition from frame pointer old_sp to frame // pointer new_sp isn't clearly bogus if (STRICT_UNWINDING) { // With the stack growing downwards, older stack frame must be // at a greater address that the current one. if (new_sp <= old_sp) return nullptr; // Assume stack frames larger than 100,000 bytes are bogus. if ((uintptr_t)new_sp - (uintptr_t)old_sp > 100000) return nullptr; } else { // In the non-strict mode, allow discontiguous stack frames. // (alternate-signal-stacks for example). if (new_sp == old_sp) return nullptr; // And allow frames upto about 1MB. if ((new_sp > old_sp) && ((uintptr_t)new_sp - (uintptr_t)old_sp > 1000000)) return nullptr; } if ((uintptr_t)new_sp % kStackAlignment != 0) return nullptr; #if defined(__linux__) enum StackTraceKernelSymbolStatus { kNotInitialized = 0, kAddressValid, kAddressInvalid }; if (IS_WITH_CONTEXT && uc != nullptr) { static StackTraceKernelSymbolStatus kernel_symbol_status = kNotInitialized; // Sentinel: not computed yet. // Initialize with sentinel value: __kernel_rt_sigtramp_rt64 can not // possibly be there. static const unsigned char *kernel_sigtramp_rt64_address = nullptr; if (kernel_symbol_status == kNotInitialized) { absl::debugging_internal::VDSOSupport vdso; if (vdso.IsPresent()) { absl::debugging_internal::VDSOSupport::SymbolInfo sigtramp_rt64_symbol_info; if (!vdso.LookupSymbol( "__kernel_sigtramp_rt64", "LINUX_2.6.15", absl::debugging_internal::VDSOSupport::kVDSOSymbolType, &sigtramp_rt64_symbol_info) || sigtramp_rt64_symbol_info.address == nullptr) { // Unexpected: VDSO is present, yet the expected symbol is missing // or null. assert(false && "VDSO is present, but doesn't have expected symbol"); kernel_symbol_status = kAddressInvalid; } else { kernel_sigtramp_rt64_address = reinterpret_cast<const unsigned char *>( sigtramp_rt64_symbol_info.address); kernel_symbol_status = kAddressValid; } } else { kernel_symbol_status = kAddressInvalid; } } if (new_sp != nullptr && kernel_symbol_status == kAddressValid && StacktracePowerPCGetLR(new_sp) == kernel_sigtramp_rt64_address) { const ucontext_t* signal_context = reinterpret_cast<const ucontext_t*>(uc); void **const sp_before_signal = #if defined(__PPC64__) reinterpret_cast<void **>(signal_context->uc_mcontext.gp_regs[PT_R1]); #else reinterpret_cast<void **>( signal_context->uc_mcontext.uc_regs->gregs[PT_R1]); #endif // Check that alleged sp before signal is nonnull and is reasonably // aligned. if (sp_before_signal != nullptr && ((uintptr_t)sp_before_signal % kStackAlignment) == 0) { // Check that alleged stack pointer is actually readable. This is to // prevent a "double fault" in case we hit the first fault due to e.g. // a stack corruption. if (absl::debugging_internal::AddressIsReadable(sp_before_signal)) { // Alleged stack pointer is readable, use it for further unwinding. new_sp = sp_before_signal; } } } } #endif return new_sp; } // This ensures that absl::GetStackTrace sets up the Link Register properly. ABSL_ATTRIBUTE_NOINLINE static void AbslStacktracePowerPCDummyFunction() { ABSL_BLOCK_TAIL_CALL_OPTIMIZATION(); } template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT> ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS // May read random elements from stack. ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY // May read random elements from stack. static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count, const void *ucp, int *min_dropped_frames) { void **sp; // Apple macOS uses an old version of gnu as -- both Darwin 7.9.0 (Panther) // and Darwin 8.8.1 (Tiger) use as 1.38. This means we have to use a // different asm syntax. I don't know quite the best way to discriminate // systems using the old as from the new one; I've gone with __APPLE__. #ifdef __APPLE__ __asm__ volatile ("mr %0,r1" : "=r" (sp)); #else __asm__ volatile ("mr %0,1" : "=r" (sp)); #endif // On PowerPC, the "Link Register" or "Link Record" (LR), is a stack // entry that holds the return address of the subroutine call (what // instruction we run after our function finishes). This is the // same as the stack-pointer of our parent routine, which is what we // want here. While the compiler will always(?) set up LR for // subroutine calls, it may not for leaf functions (such as this one). // This routine forces the compiler (at least gcc) to push it anyway. AbslStacktracePowerPCDummyFunction(); // The LR save area is used by the callee, so the top entry is bogus. skip_count++; int n = 0; // Unlike ABIs of X86 and ARM, PowerPC ABIs say that return address (in // the link register) of a function call is stored in the caller's stack // frame instead of the callee's. When we look for the return address // associated with a stack frame, we need to make sure that there is a // caller frame before it. So we call NextStackFrame before entering the // loop below and check next_sp instead of sp for loop termination. // The outermost frame is set up by runtimes and it does not have a // caller frame, so it is skipped. // The absl::GetStackFrames routine is called when we are in some // informational context (the failure signal handler for example). // Use the non-strict unwinding rules to produce a stack trace // that is as complete as possible (even if it contains a few // bogus entries in some rare cases). void **next_sp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(sp, ucp); while (next_sp && n < max_depth) { if (skip_count > 0) { skip_count--; } else { result[n] = StacktracePowerPCGetLR(sp); if (IS_STACK_FRAMES) { if (next_sp > sp) { sizes[n] = (uintptr_t)next_sp - (uintptr_t)sp; } else { // A frame-size of 0 is used to indicate unknown frame size. sizes[n] = 0; } } n++; } sp = next_sp; next_sp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(sp, ucp); } if (min_dropped_frames != nullptr) { // Implementation detail: we clamp the max of frames we are willing to // count, so as not to spend too much time in the loop below. const int kMaxUnwind = 1000; int j = 0; for (; next_sp != nullptr && j < kMaxUnwind; j++) { next_sp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(next_sp, ucp); } *min_dropped_frames = j; } return n; } namespace absl { ABSL_NAMESPACE_BEGIN namespace debugging_internal { bool StackTraceWorksForTest() { return true; } } // namespace debugging_internal ABSL_NAMESPACE_END } // namespace absl #endif // ABSL_DEBUGGING_INTERNAL_STACKTRACE_POWERPC_INL_H_