I have an assignment that has me design my own system call. To do this, I would like to view the definition of the open system call. By this, I mean I would like to see how the actual open(const char*, const int) is defined, not sys_open (Since I know where the source code is and can read it).
In both xv6's documentation and files in xv6-public, I am unable to find any reference of the prototype of definition.
The theory of my friend and I is that it's defined in some asm file, or some .o file.
Would anyone happen to know where the actual source code is? I'd appreciate this greatly.
Tried a ctrl-f for open in the source documentation, and tried a grep over all files in xv6-public. Found nothing.
Well,
open is declared in user.h.
open is defined in usys.S:
Lets see:
SYSCALL(open)
Will be transformed in
.globl open;
open:
movl $SYS_ ## open, %eax;
int $T_SYSCALL;
ret
What happened?
When function open is called
register %eax is set to SYS_open (which value is 15 (see syscall.h) and SYS_open is defined in sysfile.c
interuption T_SYSCALL (64 see traps.h) is raised.
after the system call returned, open returns too.
Related
How to write function at particular memory location in flash memory? Is there any directive for that? Do i need particular linker?
If you are using keil ide you can place a function at a specific address using .ARM.__at_address as the section name. To place the function add at 0x20000, specify:
int add(int n1,int n2) __attribute__((section(".ARM.__at_0x20000")));
int add(int n1,int n2)
{
return n1+n2;
}
Do you use the keil toolchain?
If yes, perhaps http://www.keil.com/support/docs/359.htm helps.
Edit:
The .obj file is generated by the compiler. I am not sure what you mean with 'how can i configure .obj file'.
The linker mentioned above takes the obj files, links them together and places code and variables.
You should start with a project which compiles and links without errors.
Then you have:
- Some c files. One of them with your function.
- A linkfile with the settings for the linker.
- A makefile or some kind of batchfile which calls compiler and linker with the necessary arguments.
If you have that, you can look into the m51 file for the name of the symbol for your function.
The m51 file is a textfile generated by the lx51 linker with interesting information about which symbols are there and what the linker has done with them.
The keil documentation for the linker I mentioned says: The compiler creates a symbol name for the function using the following format: ?PR?function_name?file_name.
This means: You will find the names of all functions of your project in the m51 file. If your function is in file file_x and named func_x. The symbol name will be PR?func_x?file_x
In http://www.keil.com/support/man/docs/lx51/lx51_segments.htm you can find some information about the usage of the SEGMENTS directive of the lx51 linker. According to that:
SEGMENTS (PR?func_x?file_x(C:0x1234))
should place your function to address 0x1234 in code memory.
Actually I have no keil toolchain. Therefore I cannot test all that myself.
But I am sure that you can manage that yourself if you start with a simple working example, change things step by step and check what happens.
Good Luck.
Helmut
Use ORG directive.
For example, for a function to start at location 2000H
ORG 2000H
MY_FUNC:
: YOUR CODE HERE
RET
I have a C file with several macros.
The exe generated from the file crashes several times reporting events in the Windows event viewer. Upon taking a dump of the process and analyzing it using WinDbg with the correct pdb files for the symbols, we get the stacktrace and know the function which is causing the problem.
The stacktrace shows the line number of our function code which called other functions one of which led to the crash-
08 msvcr80!fwrite(void * buffer = 0x00000000`01ded180, unsigned int64 size =
0x1fff38, unsigned int64 count = 0x524fe123, struct _iobuf * stream =
0x00000000`00000000)+0x5f [f:\dd\vctools\crt_bld\self_64_amd64\crt\src\fwrite.c
# 77]
09 <function name>(void * param = 0x00000000`02d15a00)+0xb02
[<path to file> # 1516]
Our function called fwrite, which is shown to be at line 1516. However, there is no call to fwrite at 1516. (The crash happens because the stream argument to fwrite is 0x0)
I was wondering if these line numbers correspond to the source file after the macros are expanded ? What could be the reason for a possibly wrong line number ?
EDIT : The exe here is a debug build and was compiled with optimizations disabled.
I loaded the dump again in WinDbg but also linked in the source file to WinDbg itself this time. It points to line 1516 and upon viewing that in the source from WinDbg, it points to a line where there is no call to fwrite. However, there is such a call a few lines above.
Well i do not have direct answer to question here :(
But i would make a COD file. a file that maps source code to assembly code. Then see the assembly code generated for the function of interest. Specifically related to line 1516.
Am hoping that would give a fair insight as to whats going on behind the scene. You may want to give a quick try.
You just need to turn on a compiler flag to generate COD file. More can be read here
I'm running linux kernel no. 2.6.15.51 on a ubuntu system.
I created a custom system call and added it to the kernel (containing a struct), compiled, and booted into the new kernel. Now I'm trying to create a c file that calls that system call (for testing purposes). Because I have a struct declared in my system call file, I am including the header in my test file so I can use that same struct. However, when I try including my system call file (which makes a call to access_ok() method), I get an error saying asm/uaccess.h (the file where access_ok() is declared) does not exist. Any ideas why I could be having this problem? Thank you!
I'm developing something on Minix 3 and, when it comes to deal with io files, I got a problem.
In the code:
#include <stdio.h> /* If I don't call any stdio funcs compiler doesnt's complain*/
int main() {
FILE * fp; /* I get the following: " * not expected " */
return 0;
}
Already tried everything that comes to my mind, can't figure it out..
/EDIT/
From what I can tell, when I include something, if I call functions not related to structs, it's OK. Is it the structs ?
I will assume you have checked whether the Minix file is present, that it really defines the type FILE and that your include path provides the correct -Ioption to the compiler to find that file.
Depending on your environment it could happen that an environment variable INCLUDE exists and is recognized by your compiler to provide additional include paths, recognized even before the include options from the command line. In such a case it might happen to include a stdio.hfrom a different compiler. Visual Studio is known to provide such an environment variable by default, and that has bitten me once before.
EDIT: Running the preprocessor in isolation may help to find out what is really happening in any case. Verify that FILEis defined in the preprocessed version of your file.
I am seeing a strange issue while implementing the readdir() functionality in fuse. Basically when I do ls on any directory in fuse, I get an error such as:
# ls
ls: reading directory .: Input/output error
file1.c file2.c
But the strange thing is, readdir() is doing exactly what it is supposed to do. In the sense that in that particular directory, I have two files named file1.c and file2.c and it is able to read it correctly.
While debugging the issue I noticed that fuse filler function (fuse_fill_dir_t passed as an argument to readdir() ) is what may be causing this error.
This is because if I simply print the contents of the directory using a debug printf without returning the contents using the filler function, I do not see the error.
But as soon as I start using the filler function to return the contents, I start seeing this error.
I have two questions related to this:
1) Anybody have any idea as to why the filler function might be causing this problem?
2) How do I look for the definition of the code for the fuse_fill_dir_t function? I have looked through most of the fuse functions with that kind of arguments but have had no luck until now.
Any help is appreciated!
Cheers,
Vinay
Such messages may be caused by failed calls to other (possibly unimplemented) FUSE callbacks like getxattr(). Then readdir() is called and results are obtained right.
You can debug a FUSE filesystem running its executable with key -d (debug mode), - that does not daemonize process and prints detailed debug output about FUSE calls.
Also, it would be nice to know what is your platform (Linux/OS X/etc).