dns
glibc
Our great sponsors
dns | glibc | |
---|---|---|
8 | 45 | |
7,740 | 1,203 | |
- | 4.6% | |
7.7 | 9.8 | |
6 days ago | 4 days ago | |
Go | C | |
BSD 3-clause "New" or "Revised" License | GNU General Public License v3.0 or later |
Stars - the number of stars that a project has on GitHub. Growth - month over month growth in stars.
Activity is a relative number indicating how actively a project is being developed. Recent commits have higher weight than older ones.
For example, an activity of 9.0 indicates that a project is amongst the top 10% of the most actively developed projects that we are tracking.
dns
-
Wrote a CLI tool to check DNS configurations quickly (an alternative to dig)
The heavylifting is done by this package: https://github.com/miekg/dns.
-
Why do clients ask the authoritive nameserver what is NS-records are?
Apart from `dig`, clients like https://github.com/miekg/dns show the same behavior.
-
Book recommendations for network programming
For the DNS i wrote a PiHole clone, which on the core it uses github.com/miekg/dns, to upstream queries and also to handle the custom entries, i've been wanting to publish that project but haven't done so cause the code is a bit messy since i did it as a PoC mostly, when comparing it to pihole it has the advantage that its really resource light mostly on the admin features, the dns resolving performs pretty much the same.
- DNS Library in Go
-
fastdns - fast dns server for go (alpha stage)
coredns uses github.com/miekg/dns under the hood
-
How to unit test net.Resolver?
You can do the same with net.Resolver, either by just setting it's Dial function (and PreferGo=true). You can use https://pkg.go.dev/golang.org/x/net/dns/dnsmessage or https://github.com/miekg/dns to implement an in-process server, either over TCP/UDP or skipping real networking completely, just like you can do with https://golang.org/pkg/net/http/httptest
-
Go 1.16 will make system calls through Libc on OpenBSD
Had a similar problem a couple years ago where I needed to use alternative DNS libraries to troubleshoot issues in a company's infrastructure.
Golang's rules for what implementation to use are found here: https://golang.org/pkg/net/#hdr-Name_Resolution
A really solid alternative DNS client implementation can be found here: https://github.com/miekg/dns. Real easy to read and vet compared to a few other libraries I ran into when working on this problem.
glibc
- I cut GTA Online loading times by 70% (2021)
-
Cray-1 performance vs. modern CPUs
I wonder if you’re using a different definition of ‘vectorized’ from the one I would use. For example glibc provides a vectorized strlen. Here is the sse version: https://github.com/bminor/glibc/blob/master/sysdeps/x86_64/m...
It’s pretty simple to imagine how to write an unoptimized version: read a vector from the start of the string, compare it to 0, convert that to a bitvector, test for equal to zero, then loop or clz and finish.
I would call this vectorized because it operates on 16 bytes (sse) at a time.
There are a few issues:
1. You’re still spending a lot of time in the scalar code checking loop conditions.
2. You’re doing unaligned reads which are slower on old processors
3. You may read across a cache line forcing you to pull a second line into cache even if the string ends before then.
4. You may read across a page boundary which could cause a segfault if the next page is not accessible
So the fixes are to do 64-byte (ie cache line) aligned accesses which also means page-aligned (so you won’t read from a page until you know the string doesn’t end in the previous page). That deals with alignment problems. You read four vector registers at a time but this doesn’t really cost much more if the string is shorter as it all comes from one cache line. Another trick in the linked code is that it first finds the cache line by reading the first 16 bytes then merging in the next 3 groups with unsigned-min, so it only requires one test against a zero vector instead of 4. Then it finds the zero in the cache line. You need to do a bit of work in the first iteration to become aligned. With AVX, you can use mask registers on reads to handle that first step instead.
-
Setenv Is Not Thread Safe and C Doesn't Want to Fix It
That was also my thought. To my knowledge `/etc/localtime` is the creation of Arthur David Olson, the founder of the tz database (now maintained by IANA), but his code never read `/etc/localtime` multiple times unless `TZ` environment variable was changed. Tzcode made into glibc but Ulrich Drepper changed it to not cache `/etc/localtime` when `TZ` is unset [1]; I wasn't able to locate the exact rationale, given that the commit was very ancient (1996-12) and no mailing list archive is available for this time period.
[1] https://github.com/bminor/glibc/commit/68dbb3a69e78e24a778c6...
-
CTF Writeup: Abusing select() to factor RSA
That's not really what the problem is. The actual code is fine.
The issue is that the definition of `fd_set` has a constant size [1]. If you allocate the memory yourself, the select() system call will work with as many file descriptors as you care to pass to it. You can see that both glibc [2] and the kernel [3] support arbitrarily large arrays.
[1] https://github.com/bminor/glibc/blob/master/misc/sys/select....
[2] https://github.com/bminor/glibc/blob/master/sysdeps/unix/sys...
[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...
-
How are threads created in Linux x86_64
The source code for that is here.
-
Using Uninitialized Memory for Fun and Profit (2008)
Expanding macro gives three GCC function attributes [2]: `__attribute__ ((malloc))`, `__attribute__ ((alloc_size(1)))` and `__attribute__ ((warn_unused_result))`. They are required for GCC (and others recognizing them) to actually ensure that they behave as the standard dictates. Your own malloc-like functions won't be treated same unless you give similar attributes.
[1] https://github.com/bminor/glibc/blob/807690610916df8aef17cd1...
[2] https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attribute...
-
“csinc”, the AArch64 instruction you didn’t know you wanted
IFunc relocations is what enables glibc to dynamically choose the best memcpy routine to use at runtime based on the CPU.
see https://github.com/bminor/glibc/blob/glibc-2.31/sysdeps/x86_...
-
memmove() implementation in strictly conforming C -- possible?
memmove can be very well implemented in pure C, libc implementations usually have a "generic" (meaning, architecture independent) fallback. Here is musl generic implementation and its x86-64 assembly implementation. For glibc, implementation is a bit more complex, having multiple architectures implemented, but you could find a generic implementation with these two files: memmove.c and generic/memcopy.h.
-
Fedora 38 LLVM vs. Team Fortress 2
Yeah, looks like the Q_strcat(pszContentPath, "/"); is invalid, as glibc has only allocated exactly enough to fit the path in the buffer returned by realpath().
Interestingly, the open group spec says that a null argument to realpath is "Implementation defined" [0]
And the linux (glibc) man pages say it allocates a buffer "Up to PATH_MAX" [1]
I guess "strlen(path)" is "Up to PATH_MAX", but the man page seems unclear - you could read that as implying the buffer is always allocated to PATH_MAX size, but that's not what seems to be happening, just effectively calling strdup() [2]. I have no idea how to feed back to the linux man pages, but might be worth clarifying there.
[0] https://pubs.opengroup.org/onlinepubs/009696799/functions/re...
[1] https://linux.die.net/man/3/realpath
[2] https://github.com/bminor/glibc/blob/0b9d2d4a76508fdcbd9f421...
-
Method implementations
For the actual sources you will have to look at one of the mirrors of the C standard library, such as https://github.com/bminor/glibc/tree/master/sysdeps/ieee754/dbl-64
What are some alternatives?
gopacket - Provides packet processing capabilities for Go
musl - Unofficial mirror of etalabs musl repository. Updated daily.
arp - Package arp implements the ARP protocol, as described in RFC 826. MIT Licensed.
cosmopolitan - build-once run-anywhere c library
llb
0.30000000000000004 - Floating Point Math Examples
ftp - FTP client package for Go
json-c - https://github.com/json-c/json-c is the official code repository for json-c. See the wiki for release tarballs for download. API docs at http://json-c.github.io/json-c/
quic-go - A QUIC implementation in pure Go
degasolv - Democratize dependency management.
kcptun - A Stable & Secure Tunnel based on KCP with N:M multiplexing and FEC. Available for ARM, MIPS, 386 and AMD64。N:M 多重化と FEC を備えた KCP に基づく安定した安全なトンネル。 N:M 다중화 및 FEC를 사용하는 KCP 기반의 안정적이고 안전한 터널입니다. Un tunnel stable et sécurisé basé sur KCP avec multiplexage N:M et FEC.
wepoll - wepoll: fast epoll for windows 🎭