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/*
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Copyright 2013 Google LLC All rights reserved.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at:
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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/*
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american fuzzy lop - wrapper for GNU as
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---------------------------------------
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Written and maintained by Michal Zalewski <lcamtuf@google.com>
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The sole purpose of this wrapper is to preprocess assembly files generated
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by GCC / clang and inject the instrumentation bits included from afl-as.h. It
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is automatically invoked by the toolchain when compiling programs using
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afl-gcc / afl-clang.
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Note that it's an explicit non-goal to instrument hand-written assembly,
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be it in separate .s files or in __asm__ blocks. The only aspiration this
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utility has right now is to be able to skip them gracefully and allow the
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compilation process to continue.
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That said, see experimental/clang_asm_normalize/ for a solution that may
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allow clang users to make things work even with hand-crafted assembly. Just
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note that there is no equivalent for GCC.
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*/
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#define AFL_MAIN
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#include "config.h"
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#include "types.h"
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#include "debug.h"
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#include "alloc-inl.h"
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#include "afl-as.h"
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#include <stdio.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <string.h>
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#include <time.h>
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#include <ctype.h>
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#include <fcntl.h>
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#include <sys/wait.h>
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#include <sys/time.h>
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static u8** as_params; /* Parameters passed to the real 'as' */ //传递给as的参数数组
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static u8* input_file; /* Originally specified input file */
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static u8* modified_file; /* Instrumented file for the real 'as' */ //用于as的插有instrumentation的文件
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static u8 be_quiet, /* Quiet mode (no stderr output) */ //是否开启安静模式（不输出到stderr）
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clang_mode, /* Running in clang mode? */ // 是否在clang模式下运行
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pass_thru, /* Just pass data through? */ //是否只是简单地传递数据
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just_version, /* Just show version? */ //是否只显示版本号
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sanitizer; /* Using ASAN / MSAN */ //是否使用ASAN或MSAN
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static u32 inst_ratio = 100, /* Instrumentation probability (%) */ //Instrumentation概率（%）
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as_par_cnt = 1; /* Number of params to 'as' */ //传递给as的参数数量
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/* If we don't find --32 or --64 in the command line, default to
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instrumentation for whichever mode we were compiled with. This is not
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perfect, but should do the trick for almost all use cases. */
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#ifdef WORD_SIZE_64
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static u8 use_64bit = 1;
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#else
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static u8 use_64bit = 0;
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#ifdef __APPLE__
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# error "Sorry, 32-bit Apple platforms are not supported."
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#endif /* __APPLE__ */
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#endif /* ^WORD_SIZE_64 */
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/* Examine and modify parameters to pass to 'as'. Note that the file name
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is always the last parameter passed by GCC, so we exploit this property
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to keep the code simple. */
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//处理和修改传递给as（GNU assembler）的参数。这个函数会检查命令行参数，并根据这些参数来设置全局变量，如use_64bit和as_params
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static void edit_params(int argc, char** argv) {
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u8 *tmp_dir = getenv("TMPDIR"), *afl_as = getenv("AFL_AS");
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u32 i;
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#ifdef __APPLE__
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u8 use_clang_as = 0;
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/* On MacOS X, the Xcode cctool 'as' driver is a bit stale and does not work
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with the code generated by newer versions of clang that are hand-built
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by the user. See the thread here: http://goo.gl/HBWDtn.
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To work around this, when using clang and running without AFL_AS
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specified, we will actually call 'clang -c' instead of 'as -q' to
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compile the assembly file.
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The tools aren't cmdline-compatible, but at least for now, we can
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seemingly get away with this by making only very minor tweaks. Thanks
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to Nico Weber for the idea. */
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if (clang_mode && !afl_as) {
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use_clang_as = 1;
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afl_as = getenv("AFL_CC");
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if (!afl_as) afl_as = getenv("AFL_CXX");
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if (!afl_as) afl_as = "clang";
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}
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#endif /* __APPLE__ */
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/* Although this is not documented, GCC also uses TEMP and TMP when TMPDIR
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is not set. We need to check these non-standard variables to properly
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handle the pass_thru logic later on. */
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//检查TMPDIR、AFL_AS等环境变量，确定临时目录和汇编器路径
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if (!tmp_dir) tmp_dir = getenv("TEMP");
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if (!tmp_dir) tmp_dir = getenv("TMP");
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if (!tmp_dir) tmp_dir = "/tmp";
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as_params = ck_alloc((argc + 32) * sizeof(u8*));
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as_params[0] = afl_as ? afl_as : (u8*)"as";
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as_params[argc] = 0;
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for (i = 1; i < argc - 1; i++) {
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if (!strcmp(argv[i], "--64")) use_64bit = 1;
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else if (!strcmp(argv[i], "--32")) use_64bit = 0;
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#ifdef __APPLE__
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/* The Apple case is a bit different... */
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//这段代码检查命令行参数中是否有 -arch，并检查其后的参数。
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//如果 -arch 后面是 x86_64，则设置 use_64bit 为 1，表示使用 64 位模式。
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//如果 -arch 后面是 i386，则输出错误信息并终止程序，因为 32 位的 Apple 平台不被支持
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if (!strcmp(argv[i], "-arch") && i + 1 < argc) {
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if (!strcmp(argv[i + 1], "x86_64")) use_64bit = 1;
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else if (!strcmp(argv[i + 1], "i386"))
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FATAL("Sorry, 32-bit Apple platforms are not supported.");
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}
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/* Strip options that set the preference for a particular upstream
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assembler in Xcode. */
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//如果当前处于 clang 模式，并且命令行参数中有 -q 或 -Q，则跳过这些参数，不将它们传递给汇编器
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if (clang_mode && (!strcmp(argv[i], "-q") || !strcmp(argv[i], "-Q")))
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continue;
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#endif /* __APPLE__ */
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//将当前处理的命令行参数 argv[i] 添加到 as_params 数组中，as_par_cnt 用于记录已添加的参数数量
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as_params[as_par_cnt++] = argv[i];
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}
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#ifdef __APPLE__
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/* When calling clang as the upstream assembler, append -c -x assembler
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and hope for the best. */
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//如果 use_clang_as 为真（即在 macOS 下使用 clang 作为汇编器）
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//则向 as_params 数组中添加 -c、-x 和 assembler 参数
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//以确保 clang 正确处理汇编文件
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if (use_clang_as) {
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as_params[as_par_cnt++] = "-c";
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as_params[as_par_cnt++] = "-x";
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as_params[as_par_cnt++] = "assembler";
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}
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#endif /* __APPLE__ */
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//如果是 --version，则设置 just_version 为 1，并跳转到 wrap_things_up，直接返回版本信息。
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//如果输入文件以 - 开头但不是 --version，则输出错误信息并终止程序。
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//如果输入文件是单独的 -，则将 input_file 设置为 NULL，表示从标准输入读取
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input_file = argv[argc - 1];
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if (input_file[0] == '-') {
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if (!strcmp(input_file + 1, "-version")) {
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just_version = 1;
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modified_file = input_file;
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goto wrap_things_up;
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}
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if (input_file[1]) FATAL("Incorrect use (not called through afl-gcc?)");
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else input_file = NULL;
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} else {
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/* Check if this looks like a standard invocation as a part of an attempt
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to compile a program, rather than using gcc on an ad-hoc .s file in
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a format we may not understand. This works around an issue compiling
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NSS. */
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//检查输入文件是否位于临时目录（如 /tmp 或 /var/tmp）。
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//如果输入文件不在临时目录中，则设置 pass_thru 为 1，表示直接传递文件内容而不进行插桩
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if (strncmp(input_file, tmp_dir, strlen(tmp_dir)) &&
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strncmp(input_file, "/var/tmp/", 9) &&
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strncmp(input_file, "/tmp/", 5)) pass_thru = 1;
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}
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//生成一个临时文件名，用于存储插桩后的汇编文件。文件名格式为 tmp_dir/.afl-PID-TIMESTAMP.s
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modified_file = alloc_printf("%s/.afl-%u-%u.s", tmp_dir, getpid(),
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(u32)time(NULL));
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//将生成的临时文件名添加到 as_params 数组中，作为汇编器的输入文件，并将数组末尾设置为 NULL，表示参数列表结束
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wrap_things_up:
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as_params[as_par_cnt++] = modified_file;
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as_params[as_par_cnt] = NULL;
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}
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/* Process input file, generate modified_file. Insert instrumentation in all
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the appropriate places. */
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//处理输入文件，并生成一个修改过的文件modified_file，在其中插入 instrumentation（仪器化代码）。这个函数会读取原始的汇编文件，根据配置插入instrumentation代码，并将结果写入新的文件
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static void add_instrumentation(void) {
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//line[MAX_LINE]：用于存储从输入文件中读取的每一行。
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//inf 和 outf：分别表示输入文件和输出文件的指针。
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//outfd：输出文件的文件描述符。
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//ins_lines：记录插桩的行数。
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其他布尔变量用于控制插桩的逻辑（如是否跳过某些部分）
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static u8 line[MAX_LINE];
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FILE* inf;
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FILE* outf;
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s32 outfd;
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u32 ins_lines = 0;
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u8 instr_ok = 0, skip_csect = 0, skip_next_label = 0,
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skip_intel = 0, skip_app = 0, instrument_next = 0;
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#ifdef __APPLE__
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u8* colon_pos;
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#endif /* __APPLE__ */
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//打开输入文件以供读取。
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//如果 input_file 不为空，则打开该文件；否则从标准输入读取
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if (input_file) {
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inf = fopen(input_file, "r");
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if (!inf) PFATAL("Unable to read '%s'", input_file);
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} else inf = stdin;
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//创建并打开输出文件以供写入。
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//使用 open 创建文件，并使用 fdopen 将其转换为 FILE* 类型
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outfd = open(modified_file, O_WRONLY | O_EXCL | O_CREAT, 0600);
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if (outfd < 0) PFATAL("Unable to write to '%s'", modified_file);
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outf = fdopen(outfd, "w");
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if (!outf) PFATAL("fdopen() failed");
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//
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while (fgets(line, MAX_LINE, inf)) {
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/* In some cases, we want to defer writing the instrumentation trampoline
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until after all the labels, macros, comments, etc. If we're in this
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mode, and if the line starts with a tab followed by a character, dump
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the trampoline now. */
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//在适当的位置插入插桩代码。
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//如果满足条件（如不在跳过模式、处于 .text 段、需要插桩等），则插入插桩代码，并增加插桩行数
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if (!pass_thru && !skip_intel && !skip_app && !skip_csect && instr_ok &&
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instrument_next && line[0] == '\t' && isalpha(line[1])) {
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fprintf(outf, use_64bit ? trampoline_fmt_64 : trampoline_fmt_32,
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R(MAP_SIZE));
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instrument_next = 0;
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ins_lines++;
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}
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/* Output the actual line, call it a day in pass-thru mode. */
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//将当前行写入输出文件。
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fputs(line, outf);
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//如果处于 pass_thru 模式，则跳过后续处理
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if (pass_thru) continue;
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/* All right, this is where the actual fun begins. For one, we only want to
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instrument the .text section. So, let's keep track of that in processed
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files - and let's set instr_ok accordingly. */
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//检测并处理 .text 段。
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//如果当前行表示 .text 段，则设置 instr_ok 为 1，表示可以插桩。
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//如果当前行表示其他段（如 .bss 或 .data），则设置 instr_ok 为 0，表示跳过插桩
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if (line[0] == '\t' && line[1] == '.') {
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/* OpenBSD puts jump tables directly inline with the code, which is
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a bit annoying. They use a specific format of p2align directives
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around them, so we use that as a signal. */
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if (!clang_mode && instr_ok && !strncmp(line + 2, "p2align ", 8) &&
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isdigit(line[10]) && line[11] == '\n') skip_next_label = 1;
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if (!strncmp(line + 2, "text\n", 5) ||
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!strncmp(line + 2, "section\t.text", 13) ||
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!strncmp(line + 2, "section\t__TEXT,__text", 21) ||
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!strncmp(line + 2, "section __TEXT,__text", 21)) {
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instr_ok = 1;
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continue;
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}
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if (!strncmp(line + 2, "section\t", 8) ||
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!strncmp(line + 2, "section ", 8) ||
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!strncmp(line + 2, "bss\n", 4) ||
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!strncmp(line + 2, "data\n", 5)) {
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instr_ok = 0;
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continue;
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}
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}
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/* Detect off-flavor assembly (rare, happens in gdb). When this is
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encountered, we set skip_csect until the opposite directive is
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seen, and we do not instrument. */
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//处理 .code 指令。
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//如果检测到 .code32 或 .code64，则根据当前模式设置 skip_csect，跳过插桩
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if (strstr(line, ".code")) {
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if (strstr(line, ".code32")) skip_csect = use_64bit;
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if (strstr(line, ".code64")) skip_csect = !use_64bit;
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}
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/* Detect syntax changes, as could happen with hand-written assembly.
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Skip Intel blocks, resume instrumentation when back to AT&T. */
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//处理汇编语法变化。
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//如果检测到 .intel_syntax，则跳过插桩；如果检测到 .att_syntax，则恢复插桩
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if (strstr(line, ".intel_syntax")) skip_intel = 1;
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if (strstr(line, ".att_syntax")) skip_intel = 0;
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/* Detect and skip ad-hoc __asm__ blocks, likewise skipping them. */
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//处理 #APP 和 #NO_APP 块。
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//如果检测到 #APP，则跳过插桩；如果检测到 #NO_APP，则恢复插桩
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if (line[0] == '#' || line[1] == '#') {
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if (strstr(line, "#APP")) skip_app = 1;
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if (strstr(line, "#NO_APP")) skip_app = 0;
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}
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/* If we're in the right mood for instrumenting, check for function
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names or conditional labels. This is a bit messy, but in essence,
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we want to catch:
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^main: - function entry point (always instrumented)
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^.L0: - GCC branch label
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^.LBB0_0: - clang branch label (but only in clang mode)
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^\tjnz foo - conditional branches
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...but not:
|
|
|
|
|
|
^# BB#0: - clang comments
|
|
|
^ # BB#0: - ditto
|
|
|
^.Ltmp0: - clang non-branch labels
|
|
|
^.LC0 - GCC non-branch labels
|
|
|
^.LBB0_0: - ditto (when in GCC mode)
|
|
|
^\tjmp foo - non-conditional jumps
|
|
|
|
|
|
Additionally, clang and GCC on MacOS X follow a different convention
|
|
|
with no leading dots on labels, hence the weird maze of #ifdefs
|
|
|
later on.
|
|
|
|
|
|
*/
|
|
|
//处理函数标签和条件分支。
|
|
|
//如果当前行是条件分支指令（如 jnz），则插入插桩代码
|
|
|
if (skip_intel || skip_app || skip_csect || !instr_ok ||
|
|
|
line[0] == '#' || line[0] == ' ') continue;
|
|
|
|
|
|
/* Conditional branch instruction (jnz, etc). We append the instrumentation
|
|
|
right after the branch (to instrument the not-taken path) and at the
|
|
|
branch destination label (handled later on). */
|
|
|
|
|
|
if (line[0] == '\t') {
|
|
|
|
|
|
if (line[1] == 'j' && line[2] != 'm' && R(100) < inst_ratio) {
|
|
|
|
|
|
fprintf(outf, use_64bit ? trampoline_fmt_64 : trampoline_fmt_32,
|
|
|
R(MAP_SIZE));
|
|
|
|
|
|
ins_lines++;
|
|
|
|
|
|
}
|
|
|
|
|
|
continue;
|
|
|
|
|
|
}
|
|
|
|
|
|
/* Label of some sort. This may be a branch destination, but we need to
|
|
|
tread carefully and account for several different formatting
|
|
|
conventions. */
|
|
|
|
|
|
#ifdef __APPLE__
|
|
|
|
|
|
/* Apple: L<whatever><digit>: */
|
|
|
//处理标签。
|
|
|
//如果当前行是标签（如 .L0: 或 LBB0_0:），则根据需要设置 instrument_next，表示后续需要插桩
|
|
|
if ((colon_pos = strstr(line, ":"))) {
|
|
|
|
|
|
if (line[0] == 'L' && isdigit(*(colon_pos - 1))) {
|
|
|
|
|
|
#else
|
|
|
|
|
|
/* Everybody else: .L<whatever>: */
|
|
|
|
|
|
if (strstr(line, ":")) {
|
|
|
|
|
|
if (line[0] == '.') {
|
|
|
|
|
|
#endif /* __APPLE__ */
|
|
|
|
|
|
/* .L0: or LBB0_0: style jump destination */
|
|
|
|
|
|
#ifdef __APPLE__
|
|
|
|
|
|
/* Apple: L<num> / LBB<num> */
|
|
|
|
|
|
if ((isdigit(line[1]) || (clang_mode && !strncmp(line, "LBB", 3)))
|
|
|
&& R(100) < inst_ratio) {
|
|
|
|
|
|
#else
|
|
|
|
|
|
/* Apple: .L<num> / .LBB<num> */
|
|
|
|
|
|
if ((isdigit(line[2]) || (clang_mode && !strncmp(line + 1, "LBB", 3)))
|
|
|
&& R(100) < inst_ratio) {
|
|
|
|
|
|
#endif /* __APPLE__ */
|
|
|
|
|
|
/* An optimization is possible here by adding the code only if the
|
|
|
label is mentioned in the code in contexts other than call / jmp.
|
|
|
That said, this complicates the code by requiring two-pass
|
|
|
processing (messy with stdin), and results in a speed gain
|
|
|
typically under 10%, because compilers are generally pretty good
|
|
|
about not generating spurious intra-function jumps.
|
|
|
|
|
|
We use deferred output chiefly to avoid disrupting
|
|
|
.Lfunc_begin0-style exception handling calculations (a problem on
|
|
|
MacOS X). */
|
|
|
|
|
|
if (!skip_next_label) instrument_next = 1; else skip_next_label = 0;
|
|
|
|
|
|
}
|
|
|
|
|
|
} else {
|
|
|
|
|
|
/* Function label (always instrumented, deferred mode). */
|
|
|
|
|
|
instrument_next = 1;
|
|
|
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
}
|
|
|
//在所有插桩完成后，插入主插桩代码
|
|
|
if (ins_lines)
|
|
|
fputs(use_64bit ? main_payload_64 : main_payload_32, outf);
|
|
|
//关闭文件并输出插桩结果。
|
|
|
//如果没有插桩目标，则输出警告；否则输出插桩的详细信息
|
|
|
if (input_file) fclose(inf);
|
|
|
fclose(outf);
|
|
|
|
|
|
if (!be_quiet) {
|
|
|
|
|
|
if (!ins_lines) WARNF("No instrumentation targets found%s.",
|
|
|
pass_thru ? " (pass-thru mode)" : "");
|
|
|
else OKF("Instrumented %u locations (%s-bit, %s mode, ratio %u%%).",
|
|
|
ins_lines, use_64bit ? "64" : "32",
|
|
|
getenv("AFL_HARDEN") ? "hardened" :
|
|
|
(sanitizer ? "ASAN/MSAN" : "non-hardened"),
|
|
|
inst_ratio);
|
|
|
|
|
|
}
|
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
/* Main entry point */
|
|
|
//程序的主入口点。处理命令行参数，设置随机种子，调用edit_params来编辑参数
|
|
|
//根据环境变量AFL_INST_RATIO设置instrumentation概率
|
|
|
//然后调用add_instrumentation来添加instrumentation代码，并最终执行as
|
|
|
int main(int argc, char** argv) {
|
|
|
|
|
|
s32 pid; //用于存储 fork 后的子进程 ID
|
|
|
u32 rand_seed; //用于存储随机种子
|
|
|
int status; //用于存储子进程的退出状态
|
|
|
u8* inst_ratio_str = getenv("AFL_INST_RATIO"); //从环境变量 AFL_INST_RATIO 中获取插桩比例
|
|
|
|
|
|
struct timeval tv;
|
|
|
struct timezone tz;
|
|
|
//检查是否处于 clang 模式。
|
|
|
//如果环境变量 CLANG_ENV_VAR 存在，则设置 clang_mode 为 1，否则为 0
|
|
|
clang_mode = !!getenv(CLANG_ENV_VAR);
|
|
|
//检查是否在终端运行，并输出提示信息。
|
|
|
//如果标准错误输出是终端且未设置 AFL_QUIET，则输出程序名称和版本信息；否则设置 be_quiet 为 1，表示静默模式
|
|
|
if (isatty(2) && !getenv("AFL_QUIET")) {
|
|
|
|
|
|
SAYF(cCYA "afl-as " cBRI VERSION cRST " by <lcamtuf@google.com>\n");
|
|
|
|
|
|
} else be_quiet = 1;
|
|
|
//检查命令行参数是否足够。
|
|
|
//如果参数少于 2 个，则输出帮助信息并退出程序
|
|
|
if (argc < 2) {
|
|
|
|
|
|
SAYF("\n"
|
|
|
"This is a helper application for afl-fuzz. It is a wrapper around GNU 'as',\n"
|
|
|
"executed by the toolchain whenever using afl-gcc or afl-clang. You probably\n"
|
|
|
"don't want to run this program directly.\n\n"
|
|
|
|
|
|
"Rarely, when dealing with extremely complex projects, it may be advisable to\n"
|
|
|
"set AFL_INST_RATIO to a value less than 100 in order to reduce the odds of\n"
|
|
|
"instrumenting every discovered branch.\n\n");
|
|
|
|
|
|
exit(1);
|
|
|
|
|
|
}
|
|
|
//生成并设置随机种子。
|
|
|
//使用当前时间、微秒数和进程 ID 生成随机种子，并调用 srandom 设置随机数生成器
|
|
|
gettimeofday(&tv, &tz);
|
|
|
|
|
|
rand_seed = tv.tv_sec ^ tv.tv_usec ^ getpid();
|
|
|
|
|
|
srandom(rand_seed);
|
|
|
//调用 edit_params 函数处理命令行参数。
|
|
|
//该函数会解析命令行参数并设置相关变量（如 input_file、modified_file 等）
|
|
|
edit_params(argc, argv);
|
|
|
//从环境变量 AFL_INST_RATIO 中读取插桩比例。
|
|
|
//如果插桩比例无效（不在 0 到 100 之间），则输出错误信息并终止程序
|
|
|
if (inst_ratio_str) {
|
|
|
|
|
|
if (sscanf(inst_ratio_str, "%u", &inst_ratio) != 1 || inst_ratio > 100)
|
|
|
FATAL("Bad value of AFL_INST_RATIO (must be between 0 and 100)");
|
|
|
|
|
|
}
|
|
|
//检查并设置环境变量 AS_LOOP_ENV_VAR。
|
|
|
//如果该环境变量已存在，则输出错误信息并终止程序（防止无限循环）。
|
|
|
//否则设置该环境变量为 "1"
|
|
|
if (getenv(AS_LOOP_ENV_VAR))
|
|
|
FATAL("Endless loop when calling 'as' (remove '.' from your PATH)");
|
|
|
|
|
|
setenv(AS_LOOP_ENV_VAR, "1", 1);
|
|
|
|
|
|
/* When compiling with ASAN, we don't have a particularly elegant way to skip
|
|
|
ASAN-specific branches. But we can probabilistically compensate for
|
|
|
that... */
|
|
|
//处理 ASAN 或 MSAN 模式。
|
|
|
//如果启用了 ASAN 或 MSAN，则设置 sanitizer 为 1，并将插桩比例除以 3
|
|
|
if (getenv("AFL_USE_ASAN") || getenv("AFL_USE_MSAN")) {
|
|
|
sanitizer = 1;
|
|
|
inst_ratio /= 3;
|
|
|
}
|
|
|
//调用 add_instrumentation 函数进行插桩。
|
|
|
//如果未设置 just_version，则执行插桩操作
|
|
|
if (!just_version) add_instrumentation();
|
|
|
//创建子进程并执行 as 命令。
|
|
|
//使用 fork 创建子进程，并在子进程中调用 execvp 执行 as 命令。
|
|
|
//如果执行失败，则输出错误信息并终止程序
|
|
|
if (!(pid = fork())) {
|
|
|
|
|
|
execvp(as_params[0], (char**)as_params);//传递给as的参数数组
|
|
|
FATAL("Oops, failed to execute '%s' - check your PATH", as_params[0]);
|
|
|
|
|
|
}
|
|
|
//等待子进程结束。
|
|
|
//如果 fork 失败，则输出错误信息并终止程序。
|
|
|
//使用 waitpid 等待子进程结束，并获取其退出状态
|
|
|
if (pid < 0) PFATAL("fork() failed");
|
|
|
|
|
|
if (waitpid(pid, &status, 0) <= 0) PFATAL("waitpid() failed");
|
|
|
//删除临时文件。
|
|
|
//如果未设置 AFL_KEEP_ASSEMBLY，则删除生成的临时文件
|
|
|
if (!getenv("AFL_KEEP_ASSEMBLY")) unlink(modified_file);
|
|
|
//使用 WEXITSTATUS 获取子进程的退出状态，并将其作为程序的返回值
|
|
|
exit(WEXITSTATUS(status));
|
|
|
|
|
|
}
|
|
|
|
