system-calls

问题 How can I see which system calls my Java program is making? Is there a tool that will do this on Linux? 回答1: Use strace: strace java your_program 回答2: Use strace. But there is is trick for my case. Option -f is needed. For example, the following code: public class Foo { public static void main (String [] args) { System.out.println("XXX"); } } After running javac Foo.java to compile it, strace java Foo 2>&1 | grep write print nothing. But strace -f java Foo 2>&1 | grep write prints: [pid 11655

问题 If a close(2) system call fails with EIO, will the file descriptor still be deleted? If yes, is it not possible to handle a spurious IO error by retrying later? If no, how should one prevent a file descriptor leak? 回答1: That's a tricky question. However, the POSIX standard does cover it in the description of close(): If close() is interrupted by a signal that is to be caught, it shall return -1 with errno set to [EINTR] and the state of fildes is unspecified. If an I/O error occurred while

问题 I'm trying to get file size wit stat syscall with assembly (nasm): section .data encodeFile db "/home/user/file" section .bss stat resb 64 struc STAT .st_dev: resd 1 .st_ino: resd 1 .st_mode: resw 1 .st_nlink: resw 1 .st_uid: resw 1 .st_gid: resw 1 .st_rdev: resd 1 .st_size: resd 1 .st_atime: resd 1 .st_mtime: resd 1 .st_ctime: resd 1 .st_blksize: resd 1 .st_blocks: resd 1 endstruc _start: mov rax, 4 mov rdi, encodeFile mov rsi, stat syscall mov eax, dword [stat + STAT.st_size] There is 0 in

问题 This question already has an answer here : What happens if you use the 32-bit int 0x80 Linux ABI in 64-bit code? (1 answer) Closed 2 years ago . I have just started to teach myself x86 assembly on linux from these video tutorials. Early on it teaches you how to use the write sys-call to print a string that is stored in the data section. Is it possible to use the write syscall to print a string that is stored on the stack. Here is the code I wrote to try and do this which doesn't seem to work.

问题 I've written a web crawler that I'd like to be able to stop via the keyboard. I don't want the program to die when I interrupt it; it needs to flush its data to disk first. I also don't want to catch KeyboardInterruptedException , because the persistent data could be in an inconsistent state. My current solution is to define a signal handler that catches SIGINT and sets a flag; each iteration of the main loop checks this flag before processing the next url. However, I've found that if the

问题 Can anybody explain the mechanism of clipboard of xwindow to me? For example, if I make a operation of open a file from gedit and copy the content of this file using ctrl+c. And then I open vim and use ctrl+v to paste the content into the new opened file. I know that it will use the buffer of xwindow to store the content. But I am curious how it works in the system level. More specifically, how the underlying linux kernel needs to do to handle this copy-paste operation? Is there any system

问题 Can anybody explain the mechanism of clipboard of xwindow to me? For example, if I make a operation of open a file from gedit and copy the content of this file using ctrl+c. And then I open vim and use ctrl+v to paste the content into the new opened file. I know that it will use the buffer of xwindow to store the content. But I am curious how it works in the system level. More specifically, how the underlying linux kernel needs to do to handle this copy-paste operation? Is there any system

问题 When a syscall returns, I get the syscall return value in %eax, however on entry I am getting -38, which is 0xFFFFFFDA in hex. This is for both write/read. What is this number? Can it be used to safely differentiate an entry from an exit? 回答1: The -38 in eax on syscall entry is apparently ENOSYS (Function not implemented), and is put there by syscall_trace_entry in arch/x86/kernel/entry_32.S. I suppose it's safe to assume that it will always be there on syscall entry, however it can also be

问题 I am using a system call and in case it fails, I need to do different things for different errnos. I need to write code that looks something like this: int res; res = systemCall(); if (res == -1) { if (errno == ENOMSG) { doSomething(); } else { doSomethingElse(); } } perror doesn't help, because it only prints the value. As for strerro - if it is what I need, I am not suer how to use it, because here it says that the actual string is not the same as the error. Quote from the man page: "(For

问题 I want to read the std output of a system call into a C/C++ string. Can I do this without using a temp file? Perl //without file io $output = `echo hello`; C++ //with file io system ("echo hello > tmp"); std::fstream file ("tmp"); std::string s; file >> s; 回答1: Using C's popen (probably the simplest solution, even if it doesn't use C++'s iostream ): FILE *p = popen("echo hello", "r"); std::string s; for (size_t count; (count = fread(buf, 1, sizeof(buf), p));) s += string(buf, buf + count);