程序 C 错误 valgrind 分段错误

Question

I compiled this C program and generated the executable but starting it gives me segmentation error. I debugged with valgrind and it gives me error on this line of strcpy code (ctfilename, app_data.ct_path) where app_data is a typedef struct of extern.h and ct_path is its variable. Valgrind's error is this:

== 27435 == Invalid read of size 1
== 27435 == at 0x4840094: strcpy (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
== 27435 == by 0x11CD49: GetColors (color.c: 304)
== 27435 == by 0x10C0F7: main (main.c: 162)
== 27435 == Address 0x0 is not stack'd, malloc'd or (recently) free'd

Anyone know how I can get it?

I attach the link with the sources on my google drive https://drive.google.com/file/d/10o66Xu20Maw_aD9Sc7yXWKRsJqeUhApQ/view?usp=sharing

Answer 1

First. Do NOT use strcpy . Use a function which you can pass size as an argument, it can cause memory-safety problems like stack-based buffer overflows or heap-based buffer overflows.

strcpy is just "valid" when statically-defined strings are used as source data.

But anyway it is not a good practice.

And about the specific problem you are facing on valgrind:

typedef struct {
    char * seq_directory;
    char  * sequence_name;
    char * colortable;
    char * fltctable;
    char * difftable;
    char * bitmap_path;
    char  * ct_path;
    char * pbm_path;
    XColor lforeground;
    XColor cursorcolor;
} AppData, *AppDataPtr;

Your AppData struct, defined as a global with name app_data in globals.c .

line of code where the SIGSEGV is triggered: strcpy (ctfilename, app_data.ct_path);

It appears that app_data.ct_path is NULL for some reason, and couldn't be accessed.

$ grep -r 'app_data.ct_path'
color.c:    strcpy (ctfilename, app_data.ct_path);

And the only time app_data.ct_path is present is when you are trying to copy it's content to your stack buffer.

Why didn't you assign dynamic memory to the pointer?