ptrace.c revision 69f4cd7f5add7a7c7f5915e5292aab7eb2a42e9f 
1/*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#define LOG_TAG "Corkscrew"
18//#define LOG_NDEBUG 0
19
20#include "ptrace-arch.h"
21#include <corkscrew/ptrace.h>
22
23#include <errno.h>
24#include <sys/ptrace.h>
25#include <cutils/log.h>
26
27static const uint32_t ELF_MAGIC = 0x464C457f; // "ELF\0177"
28
29#ifndef PAGE_SIZE
30#define PAGE_SIZE 4096
31#endif
32
33#ifndef PAGE_MASK
34#define PAGE_MASK (~(PAGE_SIZE - 1))
35#endif
36
37bool try_get_word(pid_t tid, uintptr_t ptr, uint32_t* out_value) {
38    if (ptr & 3) {
39        ALOGV("try_get_word: invalid pointer 0x%08x", ptr);
40        *out_value = 0;
41        return false;
42    }
43    if (tid < 0) {
44#if 0 /*unreliable, unclear whether this is safe from a signal handler context*/
45        // Determine whether the pointer is likely to be valid before dereferencing it.
46        unsigned char vec[1];
47        while (mincore((void*)(ptr & PAGE_MASK), sizeof(uint32_t), vec)) {
48            if (errno != EAGAIN && errno != EINTR) {
49                ALOGV("try_get_word: invalid pointer 0x%08x, mincore() errno=%d", ptr, errno);
50                *out_value = 0;
51                return false;
52            }
53        }
54#endif
55        *out_value = *(uint32_t*)ptr;
56        return true;
57    } else {
58        // ptrace() returns -1 and sets errno when the operation fails.
59        // To disambiguate -1 from a valid result, we clear errno beforehand.
60        errno = 0;
61        *out_value = ptrace(PTRACE_PEEKTEXT, tid, (void*)ptr, NULL);
62        if (*out_value == 0xffffffffL && errno) {
63            ALOGV("try_get_word: invalid pointer 0x%08x, ptrace() errno=%d", ptr, errno);
64            *out_value = 0;
65            return false;
66        }
67        return true;
68    }
69}
70
71static void load_ptrace_map_info_data(pid_t pid, map_info_t* mi) {
72    if (mi->is_executable) {
73        uint32_t elf_magic;
74        if (try_get_word(pid, mi->start, &elf_magic) && elf_magic == ELF_MAGIC) {
75            map_info_data_t* data = (map_info_data_t*)calloc(1, sizeof(map_info_data_t));
76            if (data) {
77                mi->data = data;
78                if (mi->name[0]) {
79                    data->symbol_table = load_symbol_table(mi->name);
80                }
81#ifdef CORKSCREW_HAVE_ARCH
82                load_ptrace_map_info_data_arch(pid, mi, data);
83#endif
84            }
85        }
86    }
87}
88
89ptrace_context_t* load_ptrace_context(pid_t pid) {
90    ptrace_context_t* context =
91            (ptrace_context_t*)calloc(1, sizeof(ptrace_context_t));
92    if (context) {
93        context->map_info_list = load_map_info_list(pid);
94        for (map_info_t* mi = context->map_info_list; mi; mi = mi->next) {
95            load_ptrace_map_info_data(pid, mi);
96        }
97    }
98    return context;
99}
100
101static void free_ptrace_map_info_data(map_info_t* mi) {
102    map_info_data_t* data = (map_info_data_t*)mi->data;
103    if (data) {
104        if (data->symbol_table) {
105            free_symbol_table(data->symbol_table);
106        }
107#ifdef CORKSCREW_HAVE_ARCH
108        free_ptrace_map_info_data_arch(mi, data);
109#endif
110        free(data);
111        mi->data = NULL;
112    }
113}
114
115void free_ptrace_context(ptrace_context_t* context) {
116    for (map_info_t* mi = context->map_info_list; mi; mi = mi->next) {
117        free_ptrace_map_info_data(mi);
118    }
119    free_map_info_list(context->map_info_list);
120}
121
122void find_symbol_ptrace(const ptrace_context_t* context,
123        uintptr_t addr, const map_info_t** out_map_info, const symbol_t** out_symbol) {
124    const map_info_t* mi = find_map_info(context->map_info_list, addr);
125    const symbol_t* symbol = NULL;
126    if (mi) {
127        const map_info_data_t* data = (const map_info_data_t*)mi->data;
128        if (data && data->symbol_table) {
129            symbol = find_symbol(data->symbol_table, addr - mi->start);
130        }
131    }
132    *out_map_info = mi;
133    *out_symbol = symbol;
134}
135