Resolving Linker Errors: Multiple Definition of `yylloc` in Embedded Linux

Resolving Linker Errors: Multiple Definition of <span>yylloc</span>

When compiling the Device Tree Compiler (DTC) tool, developers often encounter the following linker error:

/usr/bin/ld: scripts/dtc/dtc-parser.tab.o:(.bss+0x20): multiple definition of `yylloc';
scripts/dtc/dtc-lexer.lex.o:(.bss+0x0): first defined here

This error indicates that the linker has found a duplicate definition of the global variable <span>yylloc</span> in <span>dtc-parser.tab.o</span> and <span>dtc-lexer.lex.o</span>. This article will analyze the reasons behind this issue and provide solutions.

🔍 Error Analysis

  1. Variable Definition Conflict:

  • <span>yylloc</span> is a global variable shared by Bison (the <span>.y</span> file parser) and Flex (the <span>.l</span> file lexer) used to store lexical analysis location information.
  • When both Bison-generated <span>dtc-parser.tab.c</span> and Flex-generated <span>dtc-lexer.lex.c</span> define this variable, a conflict occurs during the linking stage.

  • Missing Header File Declaration:

    • In standard Bison/Flex collaboration, <span>yylloc</span> should be defined in the Bison-generated parser (via <span>%locations</span> or <span>%define api.location.type</span> directives).
    • The Flex-generated lexer should declare <span>extern YYLTYPE yylloc;</span> by including <span>#include "dtc-parser.tab.h"</span>.

  • Generated Files Not Properly Synchronized:

    • If the Flex file does not include the Bison-generated header file, or if Bison is not configured to handle location information, Flex may generate its own definition of <span>yylloc</span>.

    🛠️ Solutions

    Method 1: Modify the Lexer (Recommended)

    // File: scripts/dtc/dtc-lexer.lex.c
extern YYLTYPE yylloc;  // Add extern declaration

    Steps:

    1. Open <span>scripts/dtc/dtc-lexer.lex.c</span>
    2. Add <span>extern YYLTYPE yylloc;</span> in the global variable area
    3. Save and recompile

    Method 2: Ensure Header File Inclusion

    Include the Bison-generated header file at the beginning of the Flex file (<span>.l</span>):

    %{
#include "dtc-parser.tab.h"  // Explicitly include parser header file
%}

    Method 3: Configure Bison to Generate Location Support

    Add configuration directives in the Bison file (<span>.y</span>):

    %locations    // Enable location tracking
%define api.location.type {YYLTYPE}  // Explicitly define location type

    ✅ Verification and Considerations

    1. Clean Build: 
      make clean &amp;&amp; make
    2. Regenerate Files:
    • After modifying <span>.y</span> or <span>.l</span> files, re-run Bison/Flex.
  • Version Compatibility:
    • Ensure compatibility of Bison (≥3.0) and Flex (≥2.6) versions.

    Permanent Fix Suggestion: Automatically patch generated files in the project build script using <span>sed</span><code><span>:</span>

    sed -i 's/YYLTYPE yylloc;/extern YYLTYPE yylloc;/' scripts/dtc/dtc-lexer.lex.c

    📚 Summary

    Key Points Description
    Nature of the Error Duplicate definition of global variable
    Root Cause Improper collaboration between Flex and Bison generated files
    Solution Add <span>extern</span> declaration or include header files
    Preventive Measures Explicitly configure Bison location support

    By explicitly declaring <span>yylloc</span> as an external variable, linker conflicts can be eliminated. Understanding the collaboration mechanism between Bison and Flex can effectively prevent such issues and ensure a smooth compilation process.

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