I'm running a program that does processing on a file.
I want to be able to supply the program with several files, and by attaching to it with gdb, I want to get a memory dump at a certain point in the code for each of the files. I want the dump for each file to go to a file with the same filename as the input file (maybe after formatting it a little, say adding a suffix)
So suppose I have a function called HereIsTheFileName(char* filename), and another function called DumpThisMemoryRegion(void* startAddr, void* endAddr), I want to do something like the following:
To get the file name to an environment variable:
break HereIsTheFileName
commands 1
set $filename = malloc(strlen(filename) + 1)
call memcpy($filename, filename, strlen(filename) + 1)
end
Then to dump the memory to the filename I saved earlier:
break DumpThisMemoryRegion
commands 2
append binary memory "%s.memory"%$filename startAddr endAddr
end
(I would even settle for the filename as it is, without formatting, if that turns out to be the difficult part)
However, I couldn't get gdb to accept anything except an exlicit file name for the append/dump commands. when I ran "append binary memory $filename ..." I got the output in the file "/workdir/$filename".
Is there any way to make gdb choose the file name at runtime?
Thanks!
I don't know how to make append accept a runtime filename, but you can always cheat a bit by writing the whole thing to a file and then sourcing that file, using logging.
By putting this in your ~/.gdbinit
define reallyappend
printf "using gdbtmp.log to dump memory to file %s\n", $arg0
set logging file gdbtmp.log
set logging overwrite on
set logging redirect on
set logging on
printf "append binary memory %s 0x%x 0x%x", $arg0, $arg1, $arg2
set logging off
set logging redirect off
set logging overwrite off
source gdbtmp.log
end
you can use the function reallyappend instead, for example with
(gdb) set $filename = "somethingruntimegenerated"
(gdb) reallyappend $filename startAddr endAddr
I don't know if logging works ok in an "commands" environment, but you can give it a shot at least.
Yeah, you can't use a variable here for the filename argument.
The best suggestion I can offer is to write a script that will
set all the breakpoints and set up the "append" commands, and
use text editing or awk and sed to set up the filenames in the
script.
Related
So trying to finish a very simple script that has given me a unbelievably hard time. It's supposed to iterate through specified directories and open all text files in them and append them all with the same specified string.
The issue is it's not doing anything to the files at all. Using print to test my logic I've replaced lines 10 and 11 with print f (the write and close functions), and get the following output:
<open file '/Users/russellculver/documents/testfolder/.DS_Store', mode 'a+' at
So I think it is storing the correct files in the f variable for the write function, however I am not familiar with how Mac's handle DS_STORE or the exact role it plays in temporary location tracking.
Here is the actual script:
import os
x = raw_input("Enter the directory path here: ")
def rootdir(x):
for dirpaths, dirnames, files in os.walk(x):
for filename in files:
try:
with open(os.path.join(dirpaths, filename), 'a+') as f:
f.write('new string content')
f.close()
except:
print "Directory empty or unable to open file."
return x
rootdir(x)
And the exact return in Terminal after execution:
Enter the directory path here: /Users/russellculver/documents/testfolder
Exit status: 0
logout
[Process completed]
Yet nothing written to the .txt files in the provided directory.
The way the indentation is in the question, you return from the function right after writing the first file; either of the for-loops never finish. Which is relatively easy to surmise from the fact that you only get one output file printed.
Since you're not doing anything with the result of the rootdir function, I would just remove the return statement entirely.
An aside: there is no need to use f.close() when you open a file with the with statement: it will automatically be closed (even upon an exception). That is in fact what the with statement was introduced for (see the pep on context managers if necessary).
To be complete, here's the function the way I would have (roughly) written it:
def rootdir(x):
for dirpaths, dirnames, files in os.walk(x):
for filename in files:
path = os.path.join(dirpaths, filename)
try:
with open(path, 'a+') as f:
f.write('new string content')
except (IOError, OSError) as exc:
print "Directory empty or unable to open file:", path
(Note that I'm catching only the relevant I/O errors; any other exceptions (though unlikely) will not be caught, as they are likely not to be related to non-existing/unwritable file.)
Return was indented wrong, ending the iteration after a single loop. Wasn't even necessary so was removed entirely.
A program generates a text file after every 15 iterations. It overwrites the output.txt (formed at 15th step) with a new output.txt (formed at 30th step), due to using the same name. I can't modify the file name within the program. Can I run some script concurrently with the program on my Ubuntu system that monitors my directory and moves the output.txt file to a desired directory when it is formed or changes the output file name?
I can't modify the file name within the program.
(I take this to mean you are required to not change the file name, not that you don't know how.)
You've marked this posting as C++.
While it is possible to run some script to monitor a directory, coordinating the name change and running a thread or another process (from C++) can be much more challenging than other choices.
How about a simpler approach:
I suggest using std::stringstream to generate a unique pfn (path-file-name) for each time you want to write a file. For instance, an incrementing number can be appended to the unmodifiable-file-name.
Something like:
std::string uniqueFileName(void)
{
std::stringstream ss;
// vvvvvvvvvv -- unmodifiable-file-name is not changed
ss << "output.txt" << ++fileCount;
uniqueFileName = ss.str();
return(uniqueFileName);
}
Good luck.
PS
If you feel you must write the file first in the correct file name, and then change the file name to something unique ... yes, you can rename the file from within this program (i.e. trivial synchronization)
I would use popen() as I feel it provides more feedback, and I've used it before.
Others prefer something like system() (there are about 6 of these).
In either case, use the command to rename the existing file (to each you provide a bash command, like mv fromPfn toPfn, or maybe you'll need cp.
For each, your code must not proceed until the command has completed.
The problem I am trying to solve is that I want to dynamically compute the length of an instruction given its address (from within GDB) and set that length as the value of a variable. The challenge is that I don't want any extraneous output printed to the console (e.g. disassembled instructions, etc.).
My normal approach to this is to do x/2i ADDR, then subtract the two addresses. I would like to achieve the same thing automatically; however, I don't want anything printed to the console. If I could disable console output then I would be able to do this by doing x/2i ADDR, followed by $_ - ADDR.
I have not found a way to disable the output of a command in GDB. If you know such a way then please tell me! However, I have discovered interpreter-exec and GDB/MI. A quick test shows that doing x/2i works on GDB/MI, and the value of $_ computed by the MI interpreter is shared with the console interpreter. Unfortunately, this approach also spits out a lot of output.
Does anyone know a way to either calculate the length of an instruction without displaying anything, or how to disable the output of interpreter-exec, thus allowing me to achieve my goal? Thank you.
I'll give an arguably cleaner and more extensible solution that's not really shorter. It implements $instn_length() as a new GDB convenience function.
Save this to instn-length.py
import gdb
def instn_length(addr_expr):
t = gdb.execute('x/2i ' + addr_expr, to_string=True)
return long(gdb.parse_and_eval('$_')) - long(gdb.parse_and_eval(addr_expr))
class InstnLength(gdb.Function):
def __init__(self):
super(InstnLength, self).__init__('instn_length')
def invoke(self, addr):
return instn_length(str(long(addr)))
InstnLength()
Then run
$ gdb -q -x instn-length.py /bin/true
Reading symbols from /usr/bin/true...Reading symbols from /usr/lib/debug/usr/bin/true.debug...done.
done.
(gdb) start
Temporary breakpoint 1 at 0x4014c0: file true.c, line 59.
Starting program: /usr/bin/true
Temporary breakpoint 1, main (argc=1, argv=0x7fffffffde28) at true.c:59
59 if (argc == 2)
(gdb) p $instn_length($pc)
$1 = 3
(gdb) disassemble /r $pc, $pc + 4
Dump of assembler code from 0x4014c0 to 0x4014c4:
An alternative implementation of instn_length() is to use the gdb.Architecture.disassemble() method in GDB 7.6+:
def instn_length(addr_expr):
addr = long(gdb.parse_and_eval(addr_expr))
arch = gdb.selected_frame().architecture()
return arch.disassemble(addr)[0]['length']
I have found a suitable solution; however, shorter solutions would be preferred. This solution sets a logging file to /dev/null, sets to to be overridden if it exists, and then redirects the console output to the log file temporarily.
define get-in-length
set logging file /dev/null
set logging overwrite on
set logging redirect on
set logging on
x/2i $arg0
set logging off
set logging redirect off
set logging overwrite off
set $_in_length = ((unsigned long) $_) - ((unsigned long) $arg0)
end
This solution was heavily inspired by another question's answer: How to get my program name in GDB when writting a "define" script?.
I would like to know if in Fortran it is possible to use just a single command (with options/specifiers) to do the following:
open a file if it exists and append some data
(this can be done with: open(unit=40,file='data.data',Access = 'append',Status='old') but if the file does not exist a runtime error is issued)
create the file if it does not exist and write some data.
I am currently using inquire to check whether the file exist or not but then I still have to use the open statement to append or write data.
As far as I am aware of, the only safe solution is to do the way you're already doing it, using different open statements for the different cases:
program proba
implicit none
logical :: exist
inquire(file="test.txt", exist=exist)
if (exist) then
open(12, file="test.txt", status="old", position="append", action="write")
else
open(12, file="test.txt", status="new", action="write")
end if
write(12, *) "SOME TEXT"
close(12)
end program proba
You may be interested in my Fortran interface library to libc file system calls (modFileSys), which could at least spare you the logical variable and the inquire statement by querying the file status directly:
if (file_exists("test.txt")) then
...
else
...
end if
but of course you can program a similar function easily yourself, and especially it won't save you from the two open statements...
open(61,file='data.txt',action='write',position='append')
write(61,*) 'hey'
close(61)
This will append to an existing file, otherwise create and write. Adding status='unknown' would be equivalent.
if you replace the status from 'old' to 'unknown' then you will not get the run time error if the file exists or now.
Thanks
In open statement add the attribute access as follows;
Open(unit=031,file='filename.dat',form='formatted',status='unknown',access='append')
The above statement will open the file without destroying old data and write command will append the new lines in the file.
The simplest solution for fortran 90.
How can I save all the input(cin) and output(cout, cerr) from a program whose input is taken from file(using "<")? I would like the input and output to be in order(so each input is followed by corresponding output as if I were typing the input in myself).
I tried ">" to output everything to a file, but that only saves standard output(no input/cerr), and just plainly copying the command line output still only gives the output without the input(because of how "<" works).
Is there a way to write everything(output+input) to file in order?
EDIT: edited for clarity
EDIT2: I just realized that it's impossible to do what I'm trying to do since the console does not know anything about when the commands would actually be entered. I'll have to manually enter commands and use the "script" command to actually log all input/output.
You need to add cerr to the stream
command > file 2&>1
This means put 2 (stderr) to 1 (stdout) as well.