'coredump'에 해당하는 글 1건

GDB, TUI mode,

카테고리 없음 2012. 7. 19. 19:23

전엔 몰랐던 기능들... 우연히 아래의 주소에서  읽게되었다.

출처 : http://beej.us/guide/bggdb/



Using Coredumps for Postmortem Analysis

Let's say you build and run a program, and it dumps core on you for some reason or another:

$ cc -g -o foo foo.c
$ ./foo
Segmentation fault (core dumped)

This means that a core file (with a memory snapshot from the time of the crash) has been created with the name "core". If you're not getting a core file (that is, it only says "Segmentation fault" and no core file is created), you might have your ulimit set too low; try typing ulimit -c unlimited at your shell prompt.

You can fire up gdb with the -c option to specify a core file:

$ gdb -tui -c core foo

And, if in TUI mode, you'll be greeted with a screen of information, telling you why the program exited ("signal 11, Segmentation fault"), and the highlight will be on the offending line. (In dumb terminal mode, the offending line is printed out.)

In this example, I print the variable that's causing the problem. Indeed it is NULL:

Even if you don't have all the source code, it's often useful to get a backtrace from the point the program crashed.

Window Functions

In TUI mode, you can get a list of existing windows with the info win command. You can then change which window has focus with the focus (or fs) command. focus takes either a window name, or "prev" or "next" as an argument. Valid window names are "SRC" (source window), "CMD" (command window), "REGS" (registers window), and "ASM" (assembly window). See the next section for how to use these other windows.

Note that when the SRC window has focus, the arrow keys will move the source code, but when the CMD window has focus, the arrow keys will select the previous and next commands in the command history. (For the record, the commands to move the SRC window single lines and single pages are +, -, <, and >.)

(gdb) info win
        SRC     (36 lines)  <has focus>
        CMD     (18 lines)
(gdb) fs next
Focus set to CMD window.
(gdb) info win
        SRC     (36 lines)
        CMD     (18 lines)  <has focus>
(gdb) fs SRC
Focus set to SRC window.
(gdb)

(Window names are case in-sensitive.)

The winheight (or wh) command sets the height of a particular window, but I've had bad luck with this working well.

Display Registers and Assembly

In TUI mode, the layout command controls which windows you see. Additionally, the tui reg allows control of the register window, and will open it if it's not already open.

The commands are:
layout srcStandard layout—source on top, command window on the bottom
layout asmJust like the "src" layout, except it's an assembly window on top
layout splitThree windows: source on top, assembly in the middle, and command at the bottom
layout regOpens the register window on top of either source or assembly, whichever was opened last
tui reg generalShow the general registers
tui reg floatShow the floating point registers
tui reg systemShow the "system" registers
tui reg nextShow the next page of registers—this is important because there might be pages of registers that aren't in the "general", "float", or "system" sets

Here's a nifty screenshot to whet your appetite, showing source and assembly in "split" mode:

Assembly code comes in two flavors on Intel machines: Intel and AT&T. You can set which one appears in the disassembly window with set disassembly-flavor. Valid values are "intel" and "att". If you already have the assembly window open, you'll have to close it and reopen it (layout src followed by layout split, for example.)

To display registers in dumb terminal mode, type info registers for the integer registers, or info all-registers for everything.

Writing a Front-End

You're thinking, "Wow, this is pretty cool, but I could write a killer front-end for this thing that worked so much better! How do I do it?"

GDB supports what it calls the "machine interface interpreter", or GDB/MI. The interpreter is selected on the gdb command line with the --interpreter switch.

Basically you'll launch gdb and read commands and results to and from it (probably using pipes). Pretty straightforward.

See the GDB documentation for all the details.

Quick Reference

Command parameters are in italics. Optional parameters are in square brackets. All commands can be abbreviated until they become ambiguous.

This list is very very incomplete, and only shows things talked about in this tutorial!

Help Commands
help commandGet help on a certain command
apropos keywordSearch help for a particular keyword
Starting and Quitting
gdb [-tui] [-c core] [exename](Unix Command) Start gdb on an executable or standalone; specify "-tui" to start the TUI GUI; specify "-c" with a corefile name to see where a crash occurred
run [arg1] [arg2] [...]Run the currently loaded program with the given command line arguments
quitExit the debugger
file exenameLoad an executable file by name
Breakpoints and Watchpoints
break locationSet a breakpoint at a location, line number, or file (e.g. "main", "5", or "hello.c:23")
watch expressionBreak when a variable is written to
rwatch expressionBreak when a variable is read from
awatch expressionBreak when a variable is written to or read from
info breakDisplay breakpoint and watchpoint information and numbers
info watchSame as info break
clear locationClear a breakpoint from a location
delete numDelete a breakpoint or watchpoint by number
Stepping and Running
nextRun to the next line of this function
stepStep into the function on this line, if possible
stepiStep a single assembly instruction
continueKeep running from here
CTRL-CStop running, wherever you are
finishRun until the end of the current function
advance locationAdvance to a location, line number, or file (e.g. "somefunction", "5", or "hello.c:23")
jump locationJust like continue, except jump to a particular location first.
Examining and Modifying Variables
display expressionDisplay the value of a variable or expression every step of the program—the expression must make sense in the current scope
info displayShow a list of expressions currently being displayed and their numbers
undisplay numStop showing an expression identified by its number (see info display)
print expressionPrint the value of a variable or expression
printf formatstr expressionlistDo some formatted output with printf() e.g. printf "i = %d, p = %s\n", i, p
set variable expressionSet a variable to value, e.g. set variable x=20
set (expression)Works like set variable
Window Commands
info winShows current window info
focus winnameSet focus to a particular window bby name ("SRC", "CMD", "ASM", or "REG") or by position ("next" or "prev")
fsAlias for focus
layout typeSet the window layout ("src", "asm", "split", or "reg")
tui reg typeSet the register window layout ("general", "float", "system", or "next")
winheight valSet the window height (either an absolute value, or a relative value prefaced with "+" or "-")
whAlias for winheight
set disassembly-flavor flavorSet the look-and-feel of the disassembly. On Intel machines, valid flavors are intel and att
Misc Commands
RETURNHit RETURN to repeat the last command
backtraceShow the current stack
btAlias for backtrace
attach pidAttach to an already-running process by its PID
info registersDump integer registers to screen
info all-registersDump all registers to screen



WRITTEN BY
RootFriend
개인적으로... 나쁜 기억력에 도움되라고 만들게되었습니다.

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