Software :: Accessing Memory Address Outside Standard Memory
Nov 22, 2009
I am writing an application that wants to access periphals registers outside the standard (allowed) memory area.
Doing so gets me "segmentation fault".
I know, this is natural behaviour.
One way of getting around this is writing the module which has to be loaded by linux. I will consider this some time later.
For now, I want to come to some quick result and allow linux or gcc compiler to write to those memory areas of periphals. Is there a direct way to do so?
I am using malloc and frees a lot in my program. It shows its allocated but when i remove it doesnt show as the memory is removed(I am using the top command to view VIRT memory usage). If this continously grows what would happen to my program (Will it go out of memory?)
When I try to access at physical address (0xD0000), we known that it is necessary to convert physical address to virtual address using function IOREMAP(0xD0000, 1024) and return me 0xC00D0000.
Now our doubt is when I have a board with I/O in address 0x150, is it necessary to convert this address to other virtual address??? or with inb(0x150) return me state of I/O in this address? How can I known where is this I/O address in my map memory?
I am looking to buy some memory for my netbook. Currently I have 1 GB of DDR3 memory. However, the specification says that 2 GB of memory is the max. However, when I do the following it says that 4GB is the max:
I have a computer with 16GB of ram. At the moment, top shows all the RAM is taken, (NOT by cache), but the RAM used by the various processes is very far from 16GB.I have seen this problem several times, but I don't understand what is happening.My only remedy so far has been to reboot the machine.
I am looking for free database that has low memory usage and innodb and memory like engins that has C API and support trigger and client/server support for using in embedded linux systems.
I am new to C and linux. My code below does arbitary writes but I cant figure out where or how it does it.
I am calling the insertNode() function with seq = 'MISSISSPPI$' and alphabets = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ$'
Code:
Weird behaviour I should mention is that when I check for NULL pointer in node->child[index], the unassigned values are not null anymore, they point to arbitary memory.
we found that if we use 'top' to show the memory usage of a server (SuSe Linux 10), we can get virtual memory usage as well as 'Resident memory' usage. For virtual mem or a particular process, it is around 1.1GB, which is large but for resident memory, it only consumes 300MB. Are there anyone who knows what the differences are? I would also like to know whether the difference (1.1GB - 300MB) = 800MB are actually available for use by other applications in the system.
I am monitoring physical memory in a server I administer, and my hardware provider told me they had increased physical memory size to 4Gb... However, using several tools (free -m; top; dmesg | grep Memory; grep MemTotal /proc/meminfo I discovered that I actually have 3Gb, not 4... But, my doubt comes from the fact that dmesg | grem Memory tells me I have 3103396k/4194304k available The first number is effectively 3Gb, but the second one, is 4! so, why I am looking at this two different numbers?
I have had a fresh install of Ubuntu 9.10 and installed some software after that.Since third some, some process is eating half of my memory.I have checked processes running in system manager but everything is normal.Maximum is consumed by compiz which is about 26 mb, seems very normal.I did restarted my computer several times, and in the start for 5 mins, its fine after that again my cpu fans runs at very fast speed and my one cpu is used up 95 % (I have dual core).Please help me out, this invisible thing is driving me crazy.I am attaching my htop screen shot (sorted by cpu %), now the cpu is not used by completely but fan is still struggling hard and fast.
Is that possible that SHM shared memory is counted as cache memory on Linux with kernel 2.6.18?If find it really odd since this memory is not file backed, but I have a piece of code that loads data using shm_open+mmap, and it generates an amount of cache memory in /proc/meminfo that corresponds exactly to the amount of shared memory (I load that data from a file but I am using posix_fadvise(fd,0,0,POSIX_FADV_DONTNEED) to ensure this file is not cached and I made sure that it is working as expected). As far as I know SHM memory was not tagged as cache memory with kernel 2.6.9.If it is the case it is really unfortunate since normally cache memory can be considered to be part of the "available" memory since it can be flushed promptly but this is clearly not the case with SHM memory... Is there an easy way to get the total amount of used SHM memory on a system?
So I'll try to be brief and to the point here: I've got a couple of C / C++ apps that communicate with one another via shared memory. These worked completely fine until.. well, about twenty minutes ago when I finished making some network card changes and suddenly, I've got a weird problem going on. At one point, Parent app waits for Child app to set a boolean indicating it's finished initialization. This worked fine the last time I ran this app up (a few days ago). But right now, the shared flag never seems to get triggered (I've added a printf("Waiting..."); in Parent app until the flag is set). All the code leading up to it being set in Child app seem to be running smoothly, so I tried spitting out the addresses of the shared memory locations. The addresses mapped by Parent app and Child app are different; this seemed odd, so I went back and wrote a simple miniature app that just opened a shared structure on my own box, and I get the same thing - different addresses - but the miniature apps work just fine.
Is it normal for a shared memory space to be mapped to two different addresses across two processes?
If so, does anyone have any idea what might be the issue at hand with my Parent / Child app scenario? The Child creates the shared memory, the Parent has a wait before it opens it, and if it doesn't exist should fail (opening with PROT_READ | PROT_WRITE)... it doesn't fail so it's evidently there.
All of this worked until literally just a few hours ago and I made some changes to my network cards, and I can't even imagine how that could have changed whether or not shared memory mapping worked...
This is my first post in these forums. I'm still quite new to Linux (using Mint 9) so please bear with my not-very-articulate question(s)When I boot up and open up a tty terminal I get a message saying "Memory corruption detected in low memory." I've done an extensive google search about the issue and it seems not uncommon. I ran a memtest with no errors returned, so I'm sure that there's nothing really wrong with the memory; apparently it's a bug in the kernel that's causing this.
I found from command 'top' that 8GB memory are used. However, using command 'ps' with some options to grep the running processes and then summing up the memory used by the running processes are less than 2 GB. Where has the used memory gone ?
I have been setting up a vps I got out with bhost.net, with CentOS installed. I've been learning and have set up everying I need with the exception of ftp/sftp.
Using yum I installed vsftpd and ran into problems, thinking it was something I might of done I did a fresh install of CentOS and I still recieve the same problem on a fresh install so it is nothing I have done to the server.
The problem is when connecting via a sftp client I get an out of memory error. This error is listed in the putty faq ( url ) under A.7.5, there is a brief explaintion of the cure under A.7.6.
there is mention of a login script but I don't know where this is located. I'm a novice at Linux but by no means incompotent when it comes to computing.
A process is trying one access to memory, for example through an array (ex.: vect[0]=123. What happens?
Here below what I guess but I'm not sure and accept any comment (please, distinguish between "the system" and "the CPU" in case).
Let's suppose swapping to disk disbled.
We have two scenarios: without and with cache.
If no cache is present in the system: 1. The CPU must discover the phys addr of vect[0] virtual addr. To do that, has to read from 3 (or 2 depending on the system?) pages tables, stored in memory as well. 2. The CPU writes to the final address.
These mean 4 memory accesses.
If cache is present: 1. Like above but, if the pages tables are in cache, we have 3 accesses to that. 2. If the req. page is not in cache, it's reads from ram and transferred to it. Afterwards, cache is written. In the best case we have 4 cache accesses.
This GDB was configured as "i486-slackware-linux".
Code:
What could the cause of the message output by gdb possibly be? Reading some tutorials, I've learn the flat memory model is used in linux. So, in particular, I needn't care about the DS segment register.
Also, line 7 in the listing above, suggests nasm is assuming 32-bit addressing and so, I think it is using the flat memory model.
how to calculate (if possible) the end address of an image file in a flash memory. I'm trying to create a checksum and checkheader function and the info that I got is the file's offset, how many sector it consumes and its size. I kinda need the end address, sad thing is, I don't know how to calculate it.test.img's start address is 0, the size is 0x20000 and consumes 3 sectors.
I am writing a game in C with SDL. I can successfully display one image on the screen and animate it. However, I am having a lot of issues getting the background to display using the same method. I was asking for help on SDL related forums, but I determined that the issue is not SDL related, and it is actually a pointer issue. However, I can't find where I'm going wrong.
I allocated a chunk of memory using kmalloc in a Device Driver. Kmalloc provides a pointer to the allocated memory. This is one of my first few drivers.
I assume that the address returned is a Virtual address. I need to find the physical address of the memory location. I am working on an Intel 64 bit Fedora machine. I used the virt_to_phys() routine present in <asm/io_64.h>. I found that this routine returns an unsigned long value (32 bit) instead of an unsigned long long value (64 bit). Moreover, it seems that it simply returns the address - OFFSET instead of extracting the value in the page tables.
So is there any function / system call in Linux which will allow me to see the actual physical address on the Intel 64 arch.
I'm running an embedded Linux kernel, and I want to obtain a real memory address from user space. After goggeling a little, I found that the only way was to use mmap to access /dev/mem. But I never used mmap. I want to load a program in memory, in order to make it available from another processor, that has access to the DDR, but not to the flash memory where program is stored. Here is the code I use:
Code: // Open file and get its size FILE* program = fopen(argv[3],"rb"); fseek(program, 0, SEEK_END); long program_size = ftell(program); fseek(program, 0, SEEK_SET); // Prepare memory to copy it in void* program_address = malloc(program_size+1); FILE* memory_stream = fmemopen(program_real_address, program_size + 1, "wb"); [Code]....
If i have a shell script to run on a Linux unit, which has a command to Reset(or say upgrade) the unit in between the script.Is it possible to find out the memory address of the next waiting command so that i can store the address to any environment variable in flash , then after Reset will continue Run from the stored address.
As i undertsand - out of 1GB of the virtual Address space for Kernel from 3GB to 4GB of the process address space, Kernel image (code, data, bss, stack, heap) resides staring @0x0 address. Vmalloc area starts either at the end of Physical ram size or at 896M. This 896M cap is mandated to ensure that minimum of 128MB is reserved as vmalloc_reserve for vmalloc,kmap etc.
Is the understanding correct? Now trying to map Physical Zones into this 1GB address space
Initial 16MB is mapped to ZONE_DMA 16MB - 896MB is mapped to ZONE_NORMAL 896MB - 1024MB is mapped to ZONE_HIGHMEM
Does this mean that Kernel image is residing in ZONE_DMA area? Any call to vmalloc() in kernel code will return address beyond 896M? insmod of any LKM will internally invoke vmalloc() to obtain contiguous area - where will this code physically located along with rest of kernel code in ZONE_DMA or in ZONE_HIGHMEM?
I have a query regarding top & virtual memory. When we run top it show VIRT (Virtual Mem), RES (Resident Mem) & SHR (Shared Memory). The total virtual memory of my machine is 4 GBs (2 GB RAM + 2 GB Swap), but still I am able to see a process showing 4000m virtual memory column. what it means, as its show VIRT Mem more than actual available VIRT memory
