gdb linux環境でC言語のデバッグ

 [root@linux1 test]# gdb gdbsample
GNU gdb (GDB) Red Hat Enterprise Linux 8.2-20.el8
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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Reading symbols from gdbsample...done.
(gdb) break main
Breakpoint 1 at 0x40060e: file ./gdbsample.c, line 11.
(gdb) run
Starting program: /work/sakag/routine/modify_original/test/gdbsample
Breakpoint 1, main () at ./gdbsample.c:11
11              char buf[] = {"a1       b2      c3"};
Missing separate debuginfos, use: yum debuginfo-install glibc-2.28-236.el8.7.x86_64 libgcc-8.5.0-20.el8.x86_64 libstdc++-8.5.0-20.el8.x86_64
(gdb) l
6       #include        <string.h>
7
8       #define M_SEPARATE      '\t'
9
10      int main() {
11              char buf[] = {"a1       b2      c3"};
12              char *p = buf;
13              char *tmp = NULL;
14
15              printf("buf=%s\n",buf);
(gdb) s
12              char *p = buf;
(gdb) s
13              char *tmp = NULL;
(gdb) print p
$1 = 0x7fffffffe317 "a1\tb2\tc3"
(gdb) s
15              printf("buf=%s\n",buf);
(gdb) s
buf=a1  b2      c3
16              while(*p != NULL) {
(gdb) break 16
Breakpoint 2 at 0x400648: file ./gdbsample.c, line 16.
(gdb) s
17                      tmp = strchr(buf, M_SEPARATE);
(gdb) s
18                      if (tmp != NULL) {
(gdb) p tmp
$2 = 0x7fffffffe319 "\tb2\tc3"
(gdb) c
Continuing.
Breakpoint 2, main () at ./gdbsample.c:16
16              while(*p != NULL) {
(gdb) l
11              char buf[] = {"a1       b2      c3"};
12              char *p = buf;
13              char *tmp = NULL;
14
15              printf("buf=%s\n",buf);
16              while(*p != NULL) {
17                      tmp = strchr(buf, M_SEPARATE);
18                      if (tmp != NULL) {
19                              *tmp = ',';
20                      }
(gdb) clear 16
Deleted breakpoint 2
(gdb) b 17
Breakpoint 3 at 0x400653: file ./gdbsample.c, line 17.
(gdb) s
Breakpoint 3, main () at ./gdbsample.c:17
17                      tmp = strchr(buf, M_SEPARATE);
(gdb) p buf
$3 = "a1,b2\tc3"
(gdb) c
Continuing.
Breakpoint 3, main () at ./gdbsample.c:17
17                      tmp = strchr(buf, M_SEPARATE);
(gdb) c
Continuing.
Breakpoint 3, main () at ./gdbsample.c:17
17                      tmp = strchr(buf, M_SEPARATE);
(gdb) s
18                      if (tmp != NULL) {
(gdb) p tmp
$4 = 0x0
(gdb) p buf
$5 = "a1,b2,c3"
(gdb) c
Continuing.
Breakpoint 3, main () at ./gdbsample.c:17
17                      tmp = strchr(buf, M_SEPARATE);
(gdb) clear
Deleted breakpoint 3
(gdb) c
Continuing.
buf changed=a1,b2,c3
[Inferior 1 (process 11940) exited normally]
(gdb) quit
[root@lnux1 test]#

command:

->省略形

break main ->b main

run ->r

break 120 ->b 120

list ->l

continue ->c

step ->s

clear(clear breakpoint) ->cl

quit(quit) ->q

info break(info breakpoints) -> i b

info local: ローカル変数の一覧を表示

watch global_var : グローバル変数が更新されたときに通知する

finish:現在の関数を最後まで実行

until: loopを抜ける

record：recordを始める

reverse-step：stepを1つ戻す

reverse-continue：continueを1つ戻す

reverse-finish：finishを1つ戻す

record stop : recordを止める

# cat gdbsample.mk

SRCDIR     = .

OBJDIR     = .

LIBDIR     = .

TARGETDIR  = .

TARGETLIB  = $(LIBDIR)/gdbsample

TARGETOBJ  = $(OBJDIR)/gdbsample.o

TARGETSRC  = $(SRCDIR)/gdbsample.c

CC = g++

CCOPTIONS = -c -g -O0 -fPIC -Wno-deprecated -m64 -mtune=generic -mcmodel=small

### gdb needs -g -O0 options

### gdb needs -g3 -O0 options for macro debugging

LIBCC = $(CC)

LDOPTIONS = -m64

.SUFFIXES: .c .o

# -------------------------------

# rules

# -------------------------------

all: $(TARGETLIB)

$(TARGETLIB): $(TARGETOBJ)

        $(LIBCC) $(LDOPTIONS) $(TARGETOBJ) -o $(TARGETLIB)

$(TARGETOBJ): $(TARGETSRC)

        $(CC) $(CCOPTIONS) $(TARGETSRC) -o $(TARGETOBJ)

clean:

        @rm -f $(TARGETOBJ) $(TARGETLIB)

install:

        @cp -p $(TARGETLIB) $(TARGETDIR)

# -------------------------------

# end of makefile

# -------------------------------

[root@linux1 test]#

# cat gdbsample.c

// test program for gdb to debug codes

// gdbsample.c

//

#include        <stdio.h>

#include        <stdlib.h>

#include        <string.h>

#define M_SEPARATE      '\t'

int main() {

        char buf[] = {"a1       b2      c3"};

        char *p = buf;

        char *tmp = NULL;

        printf("buf=%s\n",buf);

        while(*p != NULL) {

                tmp = strchr(buf, M_SEPARATE);

                if (tmp != NULL) {

                        *tmp = ',';

                }

                p++;

        }

        printf("buf changed=%s\n",buf);

        return 0;

}

MACROのdebugには、-g3 optionでコンパイルする。

#define M_SEPARATE              '\t'

(gdb) s

17                      tmp = strchr(buf, M_SEPARATE);

(gdb) print M_SEPARATE

$1 = 9 '\t'

(gdb) s

18                      if (tmp != NULL) {

(gdb) print tmp

$2 = 0x7fffffffe329 "\tb2\tc3"

(gdb)