Why there is no debug info loaded after I add -g parameter - makefile

Question

I think I have added the -g option in the makefile. The makefile is like this:
C=edgelist.c geometry.c heap.c main.c memory.c output.c voronoi.c
O=edgelist.o geometry.o heap.o main.o memory.o output.o voronoi.o
tt: voronoi t
./voronoi -t <t >tt
voronoi: $O
cc -g -o voronoi $O -lm
$O:vdefs.h
voronoi.tar : $C vdefs.h Makefile Doc t
tar -cf voronoi.tar $C vdefs.h Makefile Doc t
mailable: $C vdefs.h Makefile t
bundle $C vdefs.h Makefile t > mailable
When gdb runs the program:
jack#ubuntu:~/下载/voronoi$ gdb ./voronoi
GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2) 7.4-2012.04
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-linux-gnu".
For bug reporting instructions, please see:
<http://bugs.launchpad.net/gdb-linaro/>...
Reading symbols from /home/jack/下载/voronoi/voronoi...(**no debugging symbols found**)...done.
(gdb)
What's the problem?

Answer 1

Each of the object files has to be created with -g, and the executable has to be linked with -g. At the moment, you are linking with -g but not compiling with -g.
Given the structure of your makefile, the simplest fix is probably:
$O: vdefs.h
gcc -g -c $*.c
However, ideally, you should set things up so that you use CC and CFLAGS. For example:
CFLAGS = -g -Wall -Wextra -Werror
CC = gcc # May be unnecessary
LDLIBS = -lm
Then you don't need the gcc line after $O: vdefs.h. Your linking line should become:
${CC} -o $# ${CFLAGS} $O ${LDFLAGS} ${LDLIBS}
or thereabouts.