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- // 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 architecture.
- #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 num_dropped_frames = 0;
- for (int j = 0; next_sp != nullptr && j < kMaxUnwind; j++) {
- if (skip_count > 0) {
- skip_count--;
- } else {
- num_dropped_frames++;
- }
- next_sp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(next_sp, ucp);
- }
- *min_dropped_frames = num_dropped_frames;
- }
- 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_
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