ulib/inspector/debug-info.cpp

// Copyright 2016 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "inspector/inspector.h"

#include <inttypes.h>
#include <string.h>

#include <lib/backtrace-request/backtrace-request.h>
#include <pretty/hexdump.h>
#include <zircon/assert.h>
#include <zircon/syscalls.h>
#include <zircon/syscalls/exception.h>
#include <zircon/types.h>

#include "utils-impl.h"

namespace inspector {

// If true then s/w breakpoint instructions do not kill the process.
// After the backtrace is printed the thread quietly resumes.
// TODO: The default is on for now for development purposes.
// Ultimately will want to switch this to off.
static bool swbreak_backtrace_enabled = true;

// Return true if the thread is to be resumed "successfully" (meaning the o/s
// won't kill it, and thus the kill process).
static bool is_resumable_swbreak(zx_excp_type_t excp_type) {
    if (excp_type == ZX_EXCP_SW_BREAKPOINT && swbreak_backtrace_enabled)
        return true;
    return false;
}

#if defined(__x86_64__)

static int have_swbreak_magic(const zx_thread_state_general_regs_t* regs) {
    return regs->rax == BACKTRACE_REQUEST_MAGIC;
}

#elif defined(__aarch64__)

static int have_swbreak_magic(const zx_thread_state_general_regs_t* regs) {
    return regs->r[0] == BACKTRACE_REQUEST_MAGIC;
}

#else

static int have_swbreak_magic(const zx_thread_state_general_regs_t* regs) {
    return 0;
}

#endif

static const char* excp_type_to_str(zx_excp_type_t type) {
    switch (type) {
    case ZX_EXCP_GENERAL:
        return "general fault";
    case ZX_EXCP_FATAL_PAGE_FAULT:
        return "fatal page fault";
    case ZX_EXCP_UNDEFINED_INSTRUCTION:
        return "undefined instruction";
    case ZX_EXCP_SW_BREAKPOINT:
        return "sw breakpoint";
    case ZX_EXCP_HW_BREAKPOINT:
        return "hw breakpoint";
    case ZX_EXCP_UNALIGNED_ACCESS:
        return "alignment fault";
    case ZX_EXCP_POLICY_ERROR:
        return "policy error";
    default:
        // Note: To get a compilation failure when a new exception type has
        // been added without having also updated this function, compile with
        // -Wswitch-enum.
        return "unknown fault";
    }
}

// How much memory to dump, in bytes.
// Space for this is allocated on the stack, so this can't be too large.
static constexpr size_t kMemoryDumpSize = 256;

#if defined(__aarch64__)
static bool write_general_regs(zx_handle_t thread, void* buf, size_t buf_size) {
    // The syscall takes a uint32_t.
    auto to_xfer = static_cast<uint32_t>(buf_size);
    auto status = zx_thread_write_state(thread, ZX_THREAD_STATE_GENERAL_REGS, buf, to_xfer);
    if (status != ZX_OK) {
        print_zx_error("unable to access general regs", status);
        return false;
    }
    return true;
}
#endif

static void dump_memory(zx_handle_t proc, uintptr_t start, size_t len) {
    // Make sure we're not allocating an excessive amount of stack.
    ZX_DEBUG_ASSERT(len <= kMemoryDumpSize);

    uint8_t buf[len];
    auto res = zx_process_read_memory(proc, start, buf, len, &len);
    if (res < 0) {
        printf("failed reading %p memory; error : %d\n", (void*)start, res);
    } else if (len != 0) {
        hexdump_ex(buf, len, start);
    }
}

static void resume_thread(zx_handle_t thread, zx_handle_t exception_port, bool handled) {
    uint32_t options = 0;
    if (!handled)
        options |= ZX_RESUME_TRY_NEXT;
    auto status = zx_task_resume_from_exception(thread, exception_port, options);
    if (status != ZX_OK) {
        print_zx_error("unable to \"resume\" thread", status);
        // This shouldn't happen (unless someone killed it already).
        // The task is now effectively hung (until someone kills it).
        // TODO: Try to forcefully kill it ourselves?
    }
}

static void resume_thread_from_exception(zx_handle_t thread, zx_handle_t exception_port,
                                         zx_excp_type_t excp_type,
                                         const zx_thread_state_general_regs_t* gregs) {
    if (is_resumable_swbreak(excp_type) &&
        gregs != nullptr && have_swbreak_magic(gregs)) {
#if defined(__x86_64__)
// On x86, the pc is left at one past the s/w break insn,
// so there's nothing more we need to do.
#elif defined(__aarch64__)
        zx_thread_state_general_regs_t regs = *gregs;
        // Skip past the brk instruction.
        regs.pc += 4;
        if (!write_general_regs(thread, &regs, sizeof(regs)))
            goto Fail;
#else
        goto Fail;
#endif
        resume_thread(thread, exception_port, true);
        return;
    }

    // For now, we turn policy exceptions into non-fatal warnings, by
    // resuming the thread when these exceptions occur.  TODO(ZX-922):
    // Remove this and make these exceptions fatal after the system has
    // received some amount of testing with ZX_POL_BAD_HANDLE enabled as a
    // warning.
    if (excp_type == ZX_EXCP_POLICY_ERROR) {
        resume_thread(thread, exception_port, true);
        return;
    }

#if !defined(__x86_64__)
Fail:
#endif
    // Tell the o/s to "resume" the thread by killing the process, the
    // exception has not been handled.
    resume_thread(thread, exception_port, false);
}

static zx_koid_t get_koid(zx_handle_t handle) {
    zx_info_handle_basic_t info;
    zx_status_t status = zx_object_get_info(handle, ZX_INFO_HANDLE_BASIC, &info, sizeof(info), NULL, NULL);
    if (status != ZX_OK) {
        printf("failed to get koid\n");
        return ZX_HANDLE_INVALID;
    }
    return info.koid;
}

static void print_debug_info(zx_handle_t process, zx_handle_t thread, zx_excp_type_t* type, zx_thread_state_general_regs_t* regs) {
    zx_koid_t pid = get_koid(process);
    zx_koid_t tid = get_koid(thread);

    zx_exception_report_t report;
    zx_status_t status = zx_object_get_info(thread, ZX_INFO_THREAD_EXCEPTION_REPORT,
                                            &report, sizeof(report), NULL, NULL);
    if (status != ZX_OK) {
        printf("failed to get exception report for [%" PRIu64 ".%" PRIu64 "] : error %d\n", pid, tid, status);
        return;
    }

    *type = report.header.type;

    if (!ZX_EXCP_IS_ARCH(*type) && *type != ZX_EXCP_POLICY_ERROR) {
        return;
    }

    auto context = report.context;

    zx_vaddr_t pc = 0, sp = 0, fp = 0;
    const char* arch = "unknown";
    const char* fatal = "fatal ";

    if (inspector_read_general_regs(thread, regs) != ZX_OK) {
        return;
    }

#if defined(__x86_64__)
    arch = "x86_64";
    pc = regs->rip;
    sp = regs->rsp;
    fp = regs->rbp;
#elif defined(__aarch64__)
    arch = "aarch64";
    pc = regs->pc;
    sp = regs->sp;
    fp = regs->r[29];
#else
#error unsupported architecture
#endif

    // This won't print "fatal" in the case where this is a s/w bkpt but
    // ZX_CRASHLOGGER_REQUEST_SELF_BT_MAGIC isn't set. Big deal.
    if (is_resumable_swbreak(*type))
        fatal = "";
    // TODO(MA-922): Remove this and make policy exceptions fatal.
    if (*type == ZX_EXCP_POLICY_ERROR)
        fatal = "";

    char process_name[ZX_MAX_NAME_LEN];
    status = zx_object_get_property(process, ZX_PROP_NAME, process_name, sizeof(process_name));
    if (status != ZX_OK) {
        strlcpy(process_name, "unknown", sizeof(process_name));
    }

    char thread_name[ZX_MAX_NAME_LEN];
    status = zx_object_get_property(thread, ZX_PROP_NAME, thread_name, sizeof(thread_name));
    if (status != ZX_OK) {
        strlcpy(thread_name, "unknown", sizeof(thread_name));
    }

    printf("<== %sexception: process %s[%" PRIu64 "] thread %s[%" PRIu64 "]\n", fatal,
           process_name, pid, thread_name, tid);
    printf("<== %s, PC at 0x%" PRIxPTR "\n", excp_type_to_str(report.header.type), pc);

#if defined(__x86_64__)
    inspector_print_general_regs(stdout, regs, &context.arch.u.x86_64);
#elif defined(__aarch64__)
    inspector_print_general_regs(stdout, regs, &context.arch.u.arm_64);

    // Only output the Fault address register and ESR if there's a data fault.
    if (ZX_EXCP_FATAL_PAGE_FAULT == report.header.type) {
        printf(" far %#18" PRIx64 " esr %#18x\n",
               context.arch.u.arm_64.far, context.arch.u.arm_64.esr);
    }
#else
#error unsupported architecture
#endif

    printf("bottom of user stack:\n");
    dump_memory(process, sp, kMemoryDumpSize);

    printf("arch: %s\n", arch);

    {
        // Whether to use libunwind or not.
        // If not then we use a simple algorithm that assumes ABI-specific
        // frame pointers are present.
        const bool use_libunwind = true;

        // TODO (jakehehrlich): Remove old dso format.
        inspector_dsoinfo_t* dso_list = inspector_dso_fetch_list(process);
        inspector_dso_print_list(stdout, dso_list);
        inspector_print_markup_context(stdout, process);
        // TODO (jakehehrlich): Remove the old backtrace format.
        inspector_print_backtrace(stdout, process, thread, dso_list,
                                  pc, sp, fp, use_libunwind);
        inspector_print_backtrace_markup(stdout, process, thread, dso_list,
                                         pc, sp, fp, use_libunwind);
    }

    // TODO(ZX-588): Print a backtrace of all other threads in the process.

    if (verbosity_level >= 1)
        printf("Done handling thread %" PRIu64 ".%" PRIu64 ".\n", pid, tid);
}

} // namespace inspector

void inspector_print_debug_info(zx_handle_t process, zx_handle_t thread) {
    zx_excp_type_t type = 0;
    zx_thread_state_general_regs_t regs;
    inspector::print_debug_info(process, thread, &type, &regs);
}

void inspector_print_debug_info_and_resume_thread(zx_handle_t process, zx_handle_t thread, zx_handle_t exception_port) {
    zx_excp_type_t type = 0;
    zx_thread_state_general_regs_t regs;
    inspector::print_debug_info(process, thread, &type, &regs);

    // allow the thread (and then process) to die, unless the exception is
    // to just trigger a backtrace (if enabled).
    inspector::resume_thread_from_exception(thread, exception_port, type, &regs);
}