kandi X-RAY | PDoS Summary
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QUESTION
i have cloned the xv6-public repository in ubuntu virtual box and i have used the commands
...ANSWER
Answered 2022-Mar-02 at 09:23I've learned this solution from somebody named Amrollahi.
Try these steps, if your current step works, don't try the rest of it.
QUESTION
In "Packrat Parsing: a Practical Linear-Time Algorithm with Backtracking" on page 30 the author states that the context-free grammar (CFG):
...ANSWER
Answered 2022-Jan-11 at 23:02You just didn't test enough. Try inputs consisting of an odd number of as. All match the grammar but PEG only accepts those of length 2k−1 for some integer k.
QUESTION
In the user/usys.S here a fragment which is generate by the usys.pl script
ANSWER
Answered 2021-Dec-22 at 19:20Let's just talk about sleep. In one of your earlier questions, you posted a link to the user.h header file.
That header file tells your C compiler what arguments the function takes and what the function returns, on this line:
QUESTION
In the user.h
https://github.com/mit-pdos/xv6-riscv/blob/a1da53a5a12e21b44a2c79d962a437fa2107627c/user/user.h#L6
exit is only syscall defined this way
int exit(int) __attribute__((noreturn));
why this is needed for the exit function declaration?
ANSWER
Answered 2021-Dec-21 at 18:50I don't think the noreturn attribute is strictly required, but it helps.
The noreturn attribute tells the compiler that the exit function will never return. In theory, this allows the compiler to better understand the possible code paths of any code that calls exit, so it can display more accurate warnings and optimize the code better.
QUESTION
What is the use of the stat.h header in cat.c?
Here you have the cat.c
https://github.com/mit-pdos/xv6-riscv/blob/riscv/user/cat.c
Here you have the stat.h
https://github.com/mit-pdos/xv6-riscv/blob/riscv/kernel/stat.h
I do not see any direct use of the stat struct in the cat.c so I wonder if there is an indirect one.
ANSWER
Answered 2021-Dec-19 at 13:38It was added in this commit probably because user.h uses the struct stat * datatype
QUESTION
Despite consulting the documentation, I still can't understand this line:swtch(&c->scheduler, &p->context);.
My question: I know this line is to switch p->context, including save registers and restore registers, but I can't understand the pc change in this process, that is what execution order of this code? After theswtch(&c->scheduler, &p->context); is executed, is it immedidate to execute c->proc = 0;, then the effect of executing c->proc=p; disappears? I am confused now.
code link: https://github.com/mit-pdos/xv6-riscv/blob/riscv/kernel/proc.c line 456
...ANSWER
Answered 2021-Jun-04 at 13:21This is literally the code that was so confusing that its original authors wrote "You are not expected to understand this" in the comments, so don't feel bad for not understanding it.
The key thing you may have missed is that p->context contains an address where swtch is to resume execution of process p. It's set up, for instance, here:
QUESTION
I was wondering how fetchAll of PDO is actually implemented to get an Idea how to map the result from the database including a GROUP_CONCAT() comma separated list string to an array property.
Having a sql like
$query = "Select a.id, GROUP_CONCAT(b.name) AS referencingNames FROM a JOIN b on (a.id = b.id_a)"
Will return something like
id (int) referencingNames (srting) 1 Mark, Mona, Sam 2 Jim, Tom, Sara, Mike 3 ...My Object to map to looks like this
...ANSWER
Answered 2021-May-24 at 15:09As the name of the column you are loading is part of the class, it's setting that value anyway without having to call the __set method. So one way (seems to work) is to add a column alias which doesn't exist in the class - nameList in this example...
QUESTION
I am a Laravel and Eloquent noob.
I'm trying to do a simple foreign key in a "checklist items" table that takes the primary ID from the "users" table as a foreign key.
Here are my two database migrations:
users:
...ANSWER
Answered 2021-May-04 at 12:44Replace your items migration with the following code:
QUESTION
I'm using VMware Workstation 15 Pro on Windows 10. The guest OS is Linux 18.04.5 LTS. In guest Linux, I downloaded xv6 using command: git clone git://github.com/mit-pdos/xv6-public.git. After building xv6 using make, I run make qemu-nox-gdb. However, the xv6 freezes inside qemu. No prompt printed out. No response to any key input. But if I remove gdb, everything works well.
output image
PS: I have update and upgrade everything in Linux, including qemu, git, gdb, nasm, etc.
...ANSWER
Answered 2021-Mar-29 at 18:07That QEMU commandline tells QEMU "don't run anything, instead, stop and wait for a connection from gdb". The makefile printed a message for you: "Now run 'gdb'". Have you run gdb and connected it to QEMU? (Probably there should be some tutorial or other info with xv6 that explains more about how to do this.)
QUESTION
I'm trying to set up xv6 on Ubuntu 18.04.5 but there is an error during make qemu:
ANSWER
Answered 2021-Mar-20 at 12:23Everything went right after I upgraded Ubuntu to version 20.04.2 :)
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