Bison + Flex段故障无回溯 [英] Bison+Flex segfault no backtrace

问题描述

我正在尝试调试Bison + Flex生成的代码(真是太高兴了！).它的段错误非常严重，以致gdb甚至没有可用的堆栈信息.有什么方法可以使这种组合生成更可调试的代码?

I'm trying to debug code generated by Bison + Flex (what a joy!). It segfaults so badly that there isn't even stack information available to gdb. Is there any way to make this combination generate code that's more debuggable?

请注意，我正在尝试编译可重入的词法分析器和解析器(这本身就是一个巨大的痛苦).

Note that I'm trying to compile a reentrant lexer and parser (which is in itself a huge pain).

下面是尝试使用yyparse的程序:

Below is the program that tries to use the yyparse:

int main(int argc, char** argv) {
    int res;
    if (argc == 2) {
        yyscan_t yyscanner;
        res = yylex_init(&yyscanner);
        if (res != 0) {
           fprintf(stderr, "Couldn't initialize scanner\n");
           return res;
        }
        FILE* h = fopen(argv[1], "rb");

        if (h == NULL) {
            fprintf(stderr, "Couldn't open: %s\n", argv[1]);
            return errno;
        }
        yyset_in(h, yyscanner);
        fprintf(stderr, "Scanner set\n");
        res = yyparse(&yyscanner);
        fprintf(stderr, "Parsed\n");
        yylex_destroy(&yyscanner);
        return res;
    }
    if (argc > 2) {
        fprintf(stderr, "Wrong number of arguments\n");
    }
    print_usage();
    return 1;
}

尝试运行此操作会得到:

Trying to run this gives:

(gdb) r
Starting program: /.../program 
[Inferior 1 (process 3292) exited with code 01]

注意2:我要将-d传递给flex，将-t传递给bison.

Note 2: I'm passing -d to flex and -t to bison.

在对代码进行混排之后，我能够获得回溯.但是...看来，传递-t的效果与*.y文件中的%debug指令一样为零.获取跟踪的唯一方法是在代码中设置yydebug = 1.

After shuffling the code around I was able to get backtrace. But... it appears that passing -t has zero effect as does %debug directive in *.y file. The only way to get traces is to set yydebug = 1 in your code.

推荐答案

您正在通过将yyscanner的地址而不是其值传递给yyparse来破坏堆栈.以这种方式覆盖堆栈后，即使gdb也将无法提供准确的回溯.

You are clobbering the stack by passing the address of yyscanner instead of its value to yyparse. Once the stack has been overwritten in that fashion, even gdb will be unable to provide accurate backtraces.

-d和%debug指令使bison发出执行调试跟踪所需的代码. (这会使解析器代码稍大一些，并且稍慢一些，因此默认情况下未启用.)这是跟踪工作所必需的，但是您仍然必须通过将yydebug设置为非零值来请求跟踪.

The -d and %debug directives cause bison to emit the code necessary to perform debugging traces. (This makes the parser code somewhat larger and a tiny bit slower, so it is not enabled by default.) That is necessary for tracing to work, but you still have to request traces by setting yydebug to a non-zero value.

在《野牛手册》部分跟踪 :(添加了重点)

8.4.1启用跟踪

8.4.1 Enabling Traces

有几种方法启用编译功能:

稍晚一点:

使用跟踪工具编译程序后，请求跟踪的方法是将非零值存储在变量yydebug中.您可以通过使C代码做到这一点(也许主要是这样做)来完成此操作，也可以使用C调试器更改该值.

Once you have compiled the program with trace facilities, the way to request a trace is to store a nonzero value in the variable yydebug. You can do this by making the C code do it (in main, perhaps), or you can alter the value with a C debugger.

除非您是在资源极为有限的环境中工作，否则建议您始终使用-t选项，就像Bison作者一样:

Unless you are working in an extremely resource-constrained environment, I suggest you always use the -t option, as do the Bison authors:

我们建议您始终启用跟踪选项，以便始终可以进行调试.

We suggest that you always enable the trace option so that debugging is always possible.

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