C语言 C 中对“main”的未定义引用

undefined reference to `main' in C

提问by sanforyou

Hi I am getting below error while compiling a c code using gcc

嗨，我在使用 gcc 编译 ac 代码时遇到以下错误

/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../lib64/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: ld returned 1 exit status

I am trying to import the fftw()function into SystemVerilog. Here is my code

我正在尝试将该fftw()函数导入SystemVerilog。这是我的代码

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <math.h>
#include <fftw3.h> 

void fftw(double FFT_in[],int size)
{

    double *IFFT_out;
    int i;

    fftw_complex *middle;

    fftw_plan fft;
    fftw_plan ifft;
    middle = (fftw_complex*) fftw_malloc(sizeof(fftw_complex)*size);
    IFFT_out = (double *) malloc(size*sizeof(double));

    fft = fftw_plan_dft_r2c_1d(size, FFT_in, middle, FFTW_ESTIMATE);  //Setup fftw plan for fft (real 1D data)
    ifft = fftw_plan_dft_c2r_1d(size, middle, IFFT_out, FFTW_ESTIMATE);   //Setup fftw plan for ifft

    fftw_execute(fft);
    fftw_execute(ifft);

    printf("Input:    \tFFT_coefficient[i][0]      \tFFT_coefficient[i][1]   \tRecovered Output:\n");

    for(i=0;i<size;i++)
        printf("%f\t%f\t\t\t%f\t\t\t%f\n",FFT_in[i],middle[i][0],middle[i][1],IFFT_out[i]/size);

    fftw_destroy_plan(fft);
    fftw_destroy_plan(ifft);
    fftw_free(middle);
    free(IFFT_out);

    //return IFFT_out;
}

Here is a system Verilog code from where I am trying to call fftw

这是我试图调用 fftw 的系统 Verilog 代码

module top;
import "DPI-C" function void fftw(real FFT_in[0:11], int size);
real j [0:11];
integer i,size;
real FFT_in [0:11]; 

initial begin
    size = 12;
    FFT_in[0] = 0.1;
     FFT_in[1] = 0.6;
     FFT_in[2] = 0.1;
     FFT_in[3] = 0.4;
     FFT_in[4] = 0.5;
     FFT_in[5] = 0.0;
     FFT_in[6] = 0.8;
     FFT_in[7] = 0.7;
     FFT_in[8] = 0.8;
     FFT_in[9] = 0.6;
     FFT_in[10] = 0.1;
     FFT_in[11] = 0.0;

    $display("Entering in SystemVerilog Initial Block\n");
    #20
     fftw(FFT_in,size);

    $display("Printing recovered output from system verilog\n"); 
    //for(i=0;i<size;i++)
        //$display("%f\t\n",(j[i])/size);

    $display("Exiting from SystemVerilog Initial Block");
    #5 $finish;

end

endmodule

Here is an irun command to compile both systemverilg and C files

这是一个编译 systemverilg 和 C 文件的 irun 命令

# Compile the SystemVerilog files
fftw_test.sv 
-access +rwc
# Generate a header file called _sv_export.h
-dpiheader _sv_export.h
# Delay compilation of fftw_test.c until after elaboration
#-cpost fftw_test_DPI.c -end
-I/home/fftw/local/include -L/home/ss69/fftw/local/lib fftw_test_DPI.c -lfftw3 -lm 
# Redirect output of ncsc_run to a log file called ncsc_run.log
-log_ncsc_run ncsc_run.log

while running this command give below error: building library run.so ld: /home/fftw/local/lib/libfftw3.a(mapflags.o): relocation R_X86_64_32 against `.rodata' can not be used when making a shared object; recompile with -fPIC /homefftw/local/lib/libfftw3.a: could not read symbols: Bad value collect2: ld returned 1 exit status make: *[/home/ss69/DPI/./INCA_libs/irun.lnx8664.12.20.nc/librun.so] Error 1 ncsc_run: *E,TBBLDF: Failed to build test library /home/DPI/./INCA_libs/irun.lnx8664.12.20.nc/librun.so

运行此命令时出现以下错误：构建库 run.so ld: /home/fftw/local/lib/libfftw3.a(mapflags.o): relocation R_X86_64_32 against `.rodata' can not be used when making a shared object; 使用 -fPIC /homefftw/local/lib/libfftw3.a 重新编译：无法读取符号：错误值 collect2：ld 返回 1 个退出状态 make：*[/home/ss69/DPI/./INCA_libs/irun.lnx8664.12.20。 nc/librun.so] 错误 1 ​​ncsc_run: *E,TBBLDF: 无法构建测试库 /home/DPI/./INCA_libs/irun.lnx8664.12.20.nc/librun.so

irun: *E,CCERR: Error during cc compilation (status 1), exiting.

irun: *E,CCERR: cc 编译期间出错（状态 1），正在退出。

When I simply try to compile C using gcc with below command:
gcc -g -Wall -Werror -I/home/fftw/local/include -L/home/ss69/fftw/local/lib \ fftw_test_DPI.c -lfftw3 -lm -o fftw_test_DPI

当我简单地尝试使用带有以下命令的
gcc编译 C 时：gcc -g -Wall -Werror -I/home/fftw/local/include -L/home/ss69/fftw/local/lib \ fftw_test_DPI.c -lfftw3 -lm -o fftw_test_DPI

I get this error:

我收到此错误：

/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../lib64/crt1.o: In function _start': (.text+0x20): undefined reference tomain' collect2: ld returned 1 exit status

/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../lib64/crt1.o：在函数_start': (.text+0x20): undefined reference tomain'collect2中：ld返回1个退出状态

回答by HymanCColeman

Exactly how are you using the function void fftw(double FFT_in[],int size)from your comments it sounds like you are coding routine that is called as DLL or as part of a static library.

确切地说，您如何void fftw(double FFT_in[],int size)从您的评论中使用该函数，听起来您正在编写称为 DLL 或作为静态库一部分的例程。

If this is the case then adding main()isn't going to help, at all.

如果是这种情况，那么添加main()根本无济于事。

What you have written is ABSOLUTELY 100% OK, if it is to be used as a callable routine.

如果要将其用作可调用例程，则您编写的内容绝对 100% 可以。

What you might need to do is compile this routine into a library, even a static lib. is probably ok. If this is the case then consult your GCC documentation on how to create a static or dynamic lib.

您可能需要做的是将这个例程编译成一个库，甚至是一个静态库。大概没问题。如果是这种情况，请查阅您的 GCC 文档，了解如何创建静态或动态库。

Finally, I have written Verilog code myself, so you can also provide any lines or references to Verilog documentation that you have read and whose instructions you are following. I assume that at some point you are invoking Verilog and supplying it with a list of libraries it can/should use. Your lib should be included in that list.

最后，我自己编写了 Verilog 代码，因此您还可以提供您阅读过的 Verilog 文档的任何行或引用，以及您遵循的说明。我假设在某个时候您正在调用 Verilog 并向它提供它可以/应该使用的库列表。您的库应该包含在该列表中。

Am including comments from jxhper his request: To import the function into SystemVerilog, you need to compile your function into a shared object. Then, you would point SystemVerilog at the shared object. (I don't use SystemVerilog, but that is what I gather from its web page.)

根据他的要求，包括jxh 的评论：要将函数导入 SystemVerilog，您需要将函数编译为共享对象。然后，您将 SystemVerilog 指向共享对象。（我不使用 SystemVerilog，但这是我从它的网页上收集到的。）

gcc -shared -fPIC -g -Wall -Werror \
-I/home/ss69/fftw/local/include -L/home/ss69/fftw/local/lib \
fftw_test_DPI.c -lfftw3 -lm -o libfftw_test_DPI.so

回答by Greg

• Your are missing #include "svdpi.h"in the fftwc.c file (or maybe you are not showing it because it is in fftwc.h). This include is needed for DPI.
• You are compiling a DPI library to be used with a SystemVerilog simulator. Therefore, you do not need a main()method.
• I prefer to always compile all DPI methods outside of the SystemVerilog compiler. The include the DPI library to the simulation phase. My flow looks something like the following:
  

• 您#include "svdpi.h"在 fftwc.c 文件中丢失了（或者您没有显示它，因为它在 fftwc.h 中）。DPI 需要这包括。
• 您正在编译要与 SystemVerilog 模拟器一起使用的 DPI 库。因此，您不需要main()方法。
• 我更喜欢总是在 SystemVerilog 编译器之外编译所有 DPI 方法。将 DPI 库包含到模拟阶段。我的流程如下所示：
  

${SVTOOL} -compile -f svfiles.f -dpi_header gen_dpi_header.h
gcc -fPIC -pipe -O2 -c -g \
    -I${SVTOOL_PATH}/include -Imy_dpi_dir -I. \
    -o fftw_test_DPI.o \
    fftw_test_DPI.c
gcc -shared -o libdpi.so \
    fftw_test_DPI.o [other object files]
# then call ${SVTOOL} again for simulation with libdpi.so

If you cannot get past the first gcc stage then your issue is clearly on the C side.

如果您无法通过第一个 gcc 阶段，那么您的问题显然是在 C 方面。

I do not have access to the fftw3 library at the moment. I'm wondering your void fftw(double FFT_in[],int size)might be clobbering a library function. Try renaming it void dpi_fftw(double FFT_in[],int size)

我目前无法访问 fftw3 库。我想知道您void fftw(double FFT_in[],int size)可能正在破坏库函数。尝试重命名void dpi_fftw(double FFT_in[],int size)

回答by Magn3s1um

You have no main function. Every binary must define main. If it doesn't, you don't have a null region of memory that _start defines in the binary, which means your program can't start!

您没有主要功能。每个二进制文件都必须定义 main。如果没有，您就没有 _start 在二进制文件中定义的空内存区域，这意味着您的程序无法启动！

Add a function:

添加一个函数：

int main(){

   fftw(doubleArgumentsArray, intArgument); //Or whatever function calls this function
   return 1; //Needed for C89, C99 will automatically return 1
}

回答by HymanCColeman

Have found the following tutorial on Dynamic Programming Interface (DPI) :

找到了以下关于动态编程接口 (DPI) 的教程：

    http://www.doulos.com/knowhow/sysverilog/tutorial/dpi/

Specifically, scroll down to the "Including Foreign Language Code".

具体来说，向下滚动到“包括外语代码”。

It should help with background information about how to construct a C modules for SystemVerilog.

它应该有助于了解有关如何为 SystemVerilog 构建 C 模块的背景信息。

Also, the tutorial has the following importstatement:

此外，本教程还有以下import声明：

  import "DPI" function void slave_write(input int address, input int data);

This SystemVerilog statement obviously has inputdefs on the parameters, is this required? Your importdoes NOT identify input vs. output??

这个 SystemVerilog 语句显然input对参数有定义，这是必需的吗？你import不识别输入与输出？

回答by user3716072

I believe this is an issue with some gcc linkers. I added the following linker flag:

我相信这是一些 gcc 链接器的问题。我添加了以下链接器标志：

irun ... -Wld,-B/usr/lib/x86_64-linux-gnu

And it fixed the issue.

它解决了这个问题。