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How do I access Dev MEM?
To start with, open dev/mem device file and map the phys address we are interested in. Note that the phys address should be page-aligned. Depending on request, read or write value to the mapped address. To avoid a code sequence optimization from compiler, use volatile when you read or write.
Can kernel access physical address?
Yes at OS level you have access to the physical memory. a boot loader (like GRUB) usually boots you into a protected mode environment where paging is off, which means there is no virtual memory setup yet which means you are using the physical memory directly.
How does MMAP work in Linux?
mmap works by manipulating your process’s page table, a data structure your CPU uses to map address spaces. The CPU will translate “virtual” addresses to “physical” ones, and does so according to the page table set up by your kernel. When you access the mapped memory for the first time, your CPU generates a page fault.
Is the addressing for DD if = / Dev / Mem different?
Is the addressing for dd if=/dev/mem different than for devmem ? If your devmem is from busybox, it uses /dev/mem to read and write values, so you should get the same results.
When to use devmem to access physical memory?
Recently, when debugging, physical memory needs to be accessed at the user level, and it is found that the application layer can use devmem tools to access physical addresses. Looking at the source code is actually an operation on / dev/mem.
What do you do with a / Dev / Mem file?
/dev/mem is a character device file that is an image of the main memory of the computer. It may be used, for example, to examine (and even patch) the system.
Can you use DD in place of devmem?
But, while devmem works great, that dd invocation gives me a segfault. For many other bs,skip combinations (found by accident during my attempt to figure this out) dd successfully returns, but the data is nothing like what I’m expecting.