NASM: copying a pointer from a register to a buffer in .data

I am new to asm. I am trying to copy a pointer from a register to a .data variable using NASM, on linux 64-bit.

Concider this program:

    section .data
ptr: dq 0

    section .text
    global _start

_start:
    mov [ptr], rsp

    mov rax, 60
    mov rdi, 0
    syscall

Here I try to copy the current stack pointer to ptr. ptr is declared as a quadword. Neither nasm nor the linker complains, but when debugging the program with gdb, I can see that both addresses are different:

gdb ./test.s
+(gdb) break _start
Breakpoint 1 at 0x4000b0
+(gdb) run
Starting program: test
Breakpoint 1, 0x00000000004000b0 in _start ()
+(gdb) nexti
0x00000000004000b8 in _start ()
+(gdb) info registers
...
rsp            0x7fffffffe460   0x7fffffffe460
...
+(gdb) x ptr
0xffffffffffffe460: Cannot access memory at address 0xffffffffffffe460

From what I understand, mov should copy all 64 bits from rsp to [ptr], but it seems that the most significant 0s are not copied and/or that there is some kind of sign extension, as if only the least significant bits were copied.

Best How To :

The problem is, you don't have debug info for the ptr type, so gdb treats it as integer. You can examine its real contents using:

(gdb) x/a &ptr
0x600124 <ptr>: 0x7fffffffe950
(gdb) p/a $rsp
$3 = 0x7fffffffe950

Of course I have a different value for rsp than you, but you can see that ptr and rsp match.

What are correct permissions for Linux Apache2 PHP 5.3 log file?

php,linux,apache,logging,permissions

I'd simply set its owner to apache user. This will give you the name of apache user : ps aux | grep httpd In my case (CentOS), it's 'apache' but sometimes it's 'www-data'... chown apache:apache /var/log/httpd/php_errors.log chmod 600 /var/log/httpd/php_errors.log ...

ret_from_syscall source code and when it is called

linux,linux-kernel,kernel,linux-device-driver,system-calls

The ret_from_syscall symbol will be in architecture-specific assembly code (it does not exist for all architectures). I would look in arch/XXX/kernel/entry.S. It's not actually a function. It is part of the assembly code that handles the transition from user-space into kernel-space for a system call. It's simply a label to...

Extra backslash when storing grep in a value

linux,bash

The output from set -x uses single quotes. So the outer double quotes were replaced with single quotes but you can't escape single quotes inside a single quoted string so when it then replaced the inner double quotes it needed, instead, to replace them with '\'' which ends the single...

Java read bytes from Socket on Linux

linux,windows,sockets,network-programming,raspberry-pi

InputStream input = client.getInputStream(); BufferedReader in = new BufferedReader(new InputStreamReader(input)); Your problem is here. You can't use multiple inputs on a socket when one or more of them is buffered. The buffered input stream/reader will read-ahead and 'steal' data from the other stream. You need to change your protocol so...

Bash modify CSV to change a field

linux,bash,awk

Please save following awk script as awk.src: function date_str(val) { Y = substr(val,0,4); M = substr(val,5,2); D = substr(val,7,2); date = sprintf("%s-%s-%s",Y,M,D); return date; } function time_str(val) { h = substr(val,9,2); m = substr(val,11,2); s = substr(val,13,2); time = sprintf("%s:%s:%s",h,m,s); return time; } BEGIN { FS="|" } # ## MAIN...

How does the kernel separate threads from processes

linux,multithreading,linux-kernel

Unlike Windows, Linux does not have an implementation of "threads" in the kernel. The kernel gives us what are sometimes called "lightweight processes", which are a generalization of the concepts of "processes" and "threads", and can be used to implement either. It may be confusing when you read kernel code...

What does it indicate if /proc/PID/maps shows zero for all addresses?

linux,linux-kernel

I found the discussion in Valgrind mail list when someone had the same problem. The issue was that the kernel have been patched with PaX patches, one of which doesn't allow to look at the /proc/pid/maps. The quote about the patch from wikipedia The second and third classes of attacks...

AWK write to new column base on if else of other column

linux,bash,shell,awk,sed

You can use: awk -F, 'NR>1 {$0 = $0 FS (($4 >= 0.7) ? 1 : 0)} 1' test_file.csv ...

Error: Junk at EOL, first unrecognised character is '('

assembly,gas,quake

The assembly file is meant to be run through the C preprocessor before being sent to the assembler. This should result in the C macro being properly expanded, assuming that the macro been defined in the one of the other files that are included by the #include lines. To have...

Linux-wget command

linux,shell,wget

Try this to create a string variable n, with no leading whitespace (thanks @011c): n="10.0.0.135.527" wget http://infamvn:8081/nexus/content/groups/LDM_REPO_LIN64/com/infa/com.infa.products.ldm.ingestion.server.scala/"$n"-SNAPSHOT/com.infa.products.ldm.ingestion.server.scala-"$n"-20150622.210643-1-sources.jar ...

Extract minor version from kernel to bash variable

linux,bash,sed,cut

The problem is you are using -c to cut. Don't do that. Use the -f and -d flags instead to control the delimiter and fields to output. Or use awk -F . '{print $2}' <<< "$(uname -r)". Or use IFS=. read -r _ minor _rest <<< "$(uname -r)"; echo "$minor"...

Calling find more than once on the same folder tree

linux,bash,shell,unix,find

Try this: find . -mmin +35 -or -mmin -25 find supports several logical operators (-and, -or, -not). See the OPERATORS section of the man pages for more details. ==================== EDIT: In response to the question about processing the two matches differently, I do not know of a way to do...

ARM assembly cannot use immediate values and ADDS/ADCS together

gcc,assembly,arm,instructions

Somewhat ironically, by using UAL syntax to solve the first problem you've now hit pretty much the same thing, but the other way round and with a rather more cryptic symptom. The only Thumb encodings for (non-flag-setting) mov with an immediate operand are 32-bit ones, however Cortex-M0 doesn't support those,...

AWK count number of times a term appear with respect to other columns

linux,shell,command-line,awk,sed

Almost same as the other answer, but printing 0 instead of blank. AMD$ awk -F, 'NR>1{a[$2]+=$3;b[$2]++} END{for(i in a)print i, a[i], b[i]}' File pear 1 1 apple 2 3 orange 0 1 peach 0 1 Taking , as field seperator. For all lines except the first, update array a. i.e...

Syncing Vagrant VMs across different physical servers

linux,vagrant,backup,virtual-machine,sync

Vagrant doesn't inherently support this, since it's intended audience is really development environments. It seems like you're looking for something more like what VMWare vSphere does.

sed string with special character New

linux,sed,special-characters

Escape / with \: sed -i 's/mrm.fr.mycompany.com/10.70.89.40:8081\/artifactory/' config.xml Or use this: sed -i 's|mrm.fr.mycompany.com|10.70.89.40:8081/artifactory|' config.xml ...

How to look at the top 30 lines (or head) of all files inside a directory?

linux

You can use globbing: head -n 10 *.cpp > all_headers.txt The above command exports the first 10 lines of all cpp files in a folder into all_headers.txt. According to Aereaux's comment you should also use the -q option of head since otherwise head would print the file name before the...

fread(), solaris to unix portability and use of uninitialised values

c,linux,memory,stack,portability

Q 1. why is ch empty even after fread() assignment? (Most probably) because fread() failed. See the detailed answer below. Q 2.Is this a portability issue between Solaris and Linux? No, there is a possible issue with your code itself, which is correctly reported by valgrind. I cannot quite...

Shell script to loop over files with same names but different extensions

linux,bash,shell

anubhava's solution is excellent if, as they do in your example, the extensions sort into the right order. For the more general case, where sorting cannot be relied upon, we can specify the argument order explicitly: for f in *.ext1 do program "$f" "${f%.ext1}.ext2" done This will work even if...

storing array from user and accessing it

arrays,assembly,input,user,mips

Some mistake I found is: In GETLIST: sw $v0,0($a2) #store in array add $a0,$a0,4 #next number <= instead write 'add $a2,$a2,4' if you want don't want to overwrite it. Also the problem in printing list is that you are adding $a2 to store the number in the array. But, you...

Force linux to use php as php55

php,linux,fedora

You can create an alias: alias php="php55" Now if you type php it uses php55...

make error during building webkitgtk

linux,makefile,cmake,make

as you see, in Edit1, you (make) try to run JavaScriptCore-4.0.gir instead of compile it with g-ir-compiler; I tried on my pc and my command is: cd /home/davide/src/webkitgtk-2.8.3/build/Source/JavaScriptCore && \ /usr/bin/g-ir-compiler /home/davide/src/webkitgtk-2.8.3/build/JavaScriptCore-4.0.gir \ -o /home/davide/src/webkitgtk-2.8.3/build/JavaScriptCore-4.0.typelib as a workaround, you cand edit: build/Source/JavaScriptCore/CMakeFiles/JavascriptCore-4-gir.dir/build here's the lines on my file (the last...

How to open a new terminal from my working terminal with same directory in Linux?

linux,unix,ssh

if you connect to your remote server via ssh -x [host] now run gnome-terminal & this will open a terminal with the same ssh connection. is this what your were after?...

Ignore first few lines and last few lines in a file Linux

linux,awk

awk cannot look ahead so you'll have to save the lines. awk 'NR>2{if(z!="")print z;z=y;y=x;x=$0}' file Practically zero memory overhead...

How to check which symbols on my shared library have non-position independent code (PIC)?

linux,gcc,debian,powerpc

To find which symbols made your elf non-PIC/PIE (Position Independent Code/Executable), use scanelf from pax-utils package (on ubuntu, install it with sudo apt-get install pax-utils): $ scanelf -qT /usr/local/lib/libluajit-5.1.so.2.1.0 | head -n 3 libluajit-5.1.so.2.1.0: buf_grow [0x7694] in (optimized out: previous lj_BC_MODVN) [0x7600] libluajit-5.1.so.2.1.0: buf_grow [0x769C] in (optimized out: previous lj_BC_MODVN)...

sed and PHP tags

regex,linux,sed

.* is greedy: it matches all possible characters. This way, even sed 's/<?php.*//' file will also delete all the content in your file. To prevent this greediness of .*, say "everything but a ?" -> [^?]*: sed 's/<?php[^?]*?><?php[^?]*?>//' file Test $ cat a <?php echo 'first' ?><?php echo 'second' ?><?php...

assembly function with C segfault

c,assembly,x86,sse,fpu

You have forgotten to cleanup the stack. In the prologue you have: pushl %eax pushl %ecx pushl %edx pushl %ebp movl %esp, %ebp You obviously need to undo that before you ret, such as: movl %ebp, %esp popl %ebp popl %edx popl %ecx popl %eax ret PS: I have already...

Django MySQLClient pip compile failure on Linux

python,linux,django,gcc,pip

It looks like you're missing zlib; you'll want to install it: apt-get install zlib1g-dev I also suggest reading over the README and confirming you have all other dependencies met: https://github.com/dccmx/mysqldb/blob/master/README Also, I suggest using mysqlclient over MySQLdb as its a fork of MySQLdb and what Django recommends....

Get system startup time (without reading /proc/uptime)

php,linux

You don't need the -s flag to determine the uptime. If you do something like this you have the time the server is running: $tmp = explode(' ', exec('uptime')); $uptime = $tmp[2]; // something like 2:14 (hh:mm) nb: an alternative would be to use the who -b command, which will...

How to extract single-/multiline regex-matching items from an unpredictably formatted file and put each one in a single line into output file?

linux,shell,unix,replace,grep

Assuming that your document is well-formed, i.e. opening tags always match with a closing tag, then this may be what you need: sed 's@<[/]\?b>@\n&\[email protected]' path/to/input.txt | awk 'BEGIN {buf=""} // {Y=1; buf=""} /<\/b>/ {Y=0; print buf""} Y {buf = buf$0} ' | tr -s ' ' Output: data1...

Linux - sh script - download multiple files from FTP

linux,ftp,sh

wget expect can be tricky to work with so I'd prefer to use GNU Wget as an alternative. The following should work as long as you don’t have any spaces in any of the arguments. for v in "${files_to_download[@]}" do ftp_file="${v}.bz2" wget --user=${USER} --password=${PASSWD} ${HOST}/${ftp_file} done Request multiple resources using...

linux running command as root from c code that run as normal user

c++,linux

A workaround is to modify the sudoers file and remove the requirement of a password from your user ID for a particular script to have sudo privileges. Enter sudo visudo After this, add the details in the following manner. username ALL=(ALL) NOPASSWD: /path/to/script Another method would be to pipe the...

Git post-receive hook is not executed

linux,git,githooks,git-post-receive

The hook file is incorrectly named post-reveive.

Delete some lines from text using Linux command

linux,shell,sed,grep,pattern-matching

The -v option to grep inverts the search, reporting only the lines that don't match the pattern. Since you know how to use grep to find the lines to be deleted, using grep -v and the same pattern will give you all the lines to be kept. You can write...

Finding the average of a column excluding certain rows using AWK

linux,bash,awk,scripting

Through awk, $ awk '$5!="99999"{sum+=$5}END{print sum}' file 227.5 Explanation: $5!="99999" if 5th column does not contain 99999, then do {sum+=$5} adding the value of 5th column to the variable sum. Likewise it keeps adding the value of 5th column when awk see's the record which satisfies the given condition. Finally...

Counter not working after jumps - assembly language

loops,assembly,counter,increment

The fault is caused because the mouse interrupt 33h function AX=0003h returns the mouse position in CX and DX. This overwrites your "counter" in register CX. It is always a dangerous game to keep values in registers throughout a program. Better to have a memory variable location. You could also...

How to append entry the end of a multi-line entry using any of stream editors like sed or awk

linux,bash,awk,sed,sh

Here's a sed version: /^Host_Alias/{ # whenever we match Host_Alias at line start : /\\$/{N;b} # if backslash, append next line and repeat s/$/,host25/ # add the new host to end of line } If you need to add your new host to just one of the host aliases, adjust...

Change a Script to a For Do Done Loop

linux,bash,for-loop,awk

Turns out the code wasn't invalid (had to correct some quoting issues) but that the folder was corrupt when i tried to use it in the bash script. Here is the working code with the correct double quotes around the directory variables. #!/bin/bash #file location XMLDIR='/home/amoore19/XML/00581-001/scores' NEWXML='/home/amoore19/XML/00581-001' #this gives me...

how to modify an array value with given index?

arrays,linux,bash

You don't need the quotes. Just use ${i}, or even $i: pomme[${i}]="" Or pomme[$i]="" ...

BASH - conditional sum of columns and rows in csv file

linux,bash,csv,awk

This awk program will print the modified header and modify the output to contain the sums and their division: awk 'BEGIN {FS=OFS=";"} (NR==1) {$10="results/time"; print $0} (NR>1 && NF) {sum8[$10]+=$8; sum9[$10]+=$9; other[$10]=$0} END {for (i in sum8) {$0=other[i]; $8=sum8[i]; $9=sum9[i]; $10=(sum9[i]?sum8[i]/sum9[i]:"NaN"); print}}' which gives: Date;dbms;type;description;W;D;S;results;time;results/time Mon Jun 15 14:22:20 CEST...

How could I simulate a lack of file descriptor?

c,linux,file-descriptor

You can limit the number of file descriptors a process can open under Linux using ulimit. Executing ulimit -n 3 before running your C program should make it an error to open any more files, since stdin, stdout, and stderr take up the first 3 descriptors. An example: $ ulimit...

How to extract first letters of dashed separated words in a bash variable?

linux,string,bash,shell,variables

This isn't the shortest method, but it doesn't require any external processes. IFS=- read -a words <<< $MY_TEXT for word in "${words[@]}"; do MY_INITIALS+=${word:0:1}; done ...

NASM: copying a pointer from a register to a buffer in .data

linux,assembly,nasm,x86-64

The problem is, you don't have debug info for the ptr type, so gdb treats it as integer. You can examine its real contents using: (gdb) x/a &ptr 0x600124 <ptr>: 0x7fffffffe950 (gdb) p/a $rsp $3 = 0x7fffffffe950 Of course I have a different value for rsp than you, but you...

debian 8: deb command not found. How can i fix it? [closed]

linux,debian,deb

The instruction is Add "contrib" and "non-free" components to /etc/apt/sources.list, for example I.e., you're supposed to add that line to the given file with a text editor. You are not supposed to execute it on a command line....

How can I resolve the “Could not fix timestamps in …” “…Error: The requested feature is not implemented.”

linux,build,f#

This is usually a sign that you should update your mono. Older mono versions have issues with their unzip implementation

Declaring Variables in the .data Versus on the Stack - ASM

assembly

Variables created in the .data section are directly accessable from every procedure. LOCAL variables are only present in the specific procedure and getting popped from the stack as soon as the procedure ends. What do you mean exactly with "end up with a random value"?

Using an ad-hoc libc with a tool which is an argument of another tool

linux,shared-libraries

You can achieve that by using the env utility: timeout 10 /usr/bin/env LD_LIBRARY_PATH=/path/to/mod/libc/ cp a b Env will set the environment variable and exec the other utility with that environment....

While loop in bash using variable from txt file

linux,bash,rhel

As indicated in the comments, you need to provide "something" to your while loop. The while construct is written in a way that will execute with a condition; if a file is given, it will proceed until the read exhausts. #!/bin/bash file=Sheetone.txt while IFS= read -r line do echo sh...

How to make new line when using echo to write a file in C

c,linux,file,echo,system

There is one new line, which is to be expected. The echo command prints all its arguments on a single line separated by spaces, which is the output you see. You need to execute the result of: echo "$(ls %s)" to preserve the newlines in the ls output. See Capturing...