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I am trying very hard to understand how to use a linker file, but my brain is apparently not getting it at all. I am using an STM32L476, which has two RAM regions, RAM and RAM2 (memory definition below). I would like to put a buffer into RAM2, but there is no section for RAM2 in the default linker script that is generated by Cube. Seems like a good exercise for me. I really thought that the following would do the trick, where all I've added is the .sensor_buffer section:

I'm doing an assignment for Assembly programming, and I can't get past this problem. The task is to write a program, in which user types a password, console shows '*' instead of typed letters. After typing said password user presses ENTER which "sets" the password, and requires the user to type the same password again to check if it's the same as set before.

I got this code to work which reads keystrokes, saves typed password and then writes it in the console. But I can't get it to stop on pressed ENTER. (it is set to register only 12 letters now)

Are we enclosing the variable or register in brackets to specify a pointer in assembly?

Example1;

Background information:

1. I'm using 64 bit Arch on an x86 system.

2. I'm not using libc or any language that depends on libc. I'm using a proprietary research language. I am making my syscalls through inline assembly.

3. I'm writing an experimental custom allocator for a research project, so a portable solution is a nice-to-have, but not a requirement.

4. My programs are statically linked and I am willing and able to rewrite the libraries I'm using to account for a given solution.

According to this SO post: Where is the stack memory allocated from for a Linux process? A program's virtual address space is organized like this:

Edit: Still No answer works, the output is:

Update: Writing this out allowed me to spot where I was going wrong, but not why. I am obviously calling fgets in the wrong way, because after five calls I get to the address 0x221000 which is where the mmapped memory is - I am writing at higher addresses - but I don't know why that that is happening. Could someone explain?

This is a bit complex and I'm at a loss to see why this behaviour is seen: I don't know if I have got the basics wrong or if it's a feature of Spike/PK.

To note: the libc here is provided by newlib and the code is compiled as riscv64-unknown-elf.

Short version I have input code written in RISC-V assembly that previously ran smoothly, but since I introduced a system call to mmap it crashes the fifth time it is executed. Is the problem because I have got the wrong sequence of calls or possibly an issue with the Spike emulator and PK proxy kernel?

Long explanation

I am writing a Forth-like threaded interpreted language. It is currently targeted at the PK proxy kernel on the Spike emulator, but hopefully soon to run on 'real' hardware. The code is at https://github.com/mcmenaminadrian/riscyforth

The TIL implements an endless loop to pick up input calling, in sequence, a routine to get the filepointer for standard input and then a routine to get the input.

To get the standard input filepointer (which is stored on the stack):

I am writing a Forth-like language for RISC-V and naturally that means I need to have a way to allow the users to define new words and execute them.

But I am struggling to find a way that will allow users to execute dynamically generated code without using privileged instructions to change a page's status. Is there any way to do this - for example, can I define a large empty section in .text (as opposed to .bss which is what I am currently doing)?

Or do I have to write an explicit trap handler?

Update: I am using the pk proxy kernel with Spike. I am executing an mprotect system call against either a buffer created in the .bss section or an allocation in the .text section.

In either case the mprotect call fails - returning -EACCES. (So using the .bss version fails on any attempt to execute the new code and using the .text version fails when I attempt to write the new code.)

It seems I cannot mark a page as R/W/X - and this might be fundamental. Is there a way round this (there surely must be!)

By default, different threads also have different stacks. Is it possible to make them share the same thread? For example: I want to call a function in thread A, but the argument for that function call was pushed onto the stack in thread B. Since those threads do not share a stack, the function call in thread A will fail.

example code:

edit: I added an image of the error shown in gdb I am having a problem with my assembly code. This code once worked for me and it gave out the right outputs that I need (mainly string1 as I need to change its vowel characters to some other character). A few hours later, however, it stopped working and is now dumping a segmentation fault.