How does Linux start a process

https://iq.thc.org/how-does-linux-start-a-process

by 10xJobs_net • 3 years ago

276 18 3 years ago

iq.thc.org

bluetomcat2• 3 years ago

A good walkthrough, but it doesn't mention how the ELF headers are interpreted and how the corresponding file sections (code, data, rodata) are mapped into the virtual address space of the process. It only covers the setup of the stack and the invocation of main.

22SAS• 3 years ago

Any good resources to learn about that?

duped• 3 years ago

The book "Linkers an Loaders" by Levine is the Bible on the subject

bluetomcat2• 3 years ago

"man 5 elf" should be the ultimate source of truth :-)

yrro• 3 years ago

I've found that searching for stories with ELF in the title then trawling through the comments for the links is really informative.

mimimi31• 3 years ago

There's a great summary from LWN[1] with lots of references and links to other articles for further reading.

[1] https://lwn.net/Articles/631631

emidln• 3 years ago

The source code to the kernel's elf "binfmt"[0] is very readable. The elf binfmt is registered (along with a few others like `binfmt_misc`) and you get dispatched there via `exec_binprm`[1] which is invoked by the `execve` syscall[2]. When loading a shared library, you also dispatch to a binfmt via the `uselib`[3] syscall.

[0] https://github.com/torvalds/linux/blob/9fdfb15a3dbf818e06be5...

[1] https://github.com/torvalds/linux/blob/9fdfb15a3dbf818e06be5...

[2] https://github.com/torvalds/linux/blob/9fdfb15a3dbf818e06be5...

[3] https://github.com/torvalds/linux/blob/9fdfb15a3dbf818e06be5...

proto_lambda• 3 years ago

If you're interested in or already comfortable with Rust, Amos (fasterthanlime) has a nice long-form series that goes into this, basically building a custom ELF loader in the end. The writing style isn't everyone's cup of tea, but maybe you like it: https://fasterthanli.me/series/making-our-own-executable-pac...

dharmab• 3 years ago

CPU Land is an accessible introduction. This chapter covers ELF https://cpu.land/becoming-an-elf-lord

mananaysiempre• 3 years ago

The first thing I thought of when I saw the article title here was “How programs get run”[1], a series on LWN; the second installment[2] describes the ELF parts of the story.

(The exposition in his two-parter “Anatomy of a system call”[3,4] is similarly brilliant.)

If all you want is a non-Linux-specific description of how to write a static ELF loader (which is surprisingly simple), you can also take a look at the description on the OSDev Wiki[5] (but be mindful of the somewhat uneven code quality on that website) and at Libelf by example[6] (but libelf may be a bit too much abstraction than you really need if you’re trying to understand the format itself).

[1] https://lwn.net/Articles/630727/

[2] https://lwn.net/Articles/631631/

[3] https://lwn.net/Articles/604287/

[4] https://lwn.net/Articles/604515/

[5] https://wiki.osdev.org/ELF

[6] https://sourceforge.net/projects/elftoolchain/files/Document...

i4k• 3 years ago

Instead of only hiding the arguments, is it also possible to change them? and even change argv[0]?

hakre• 3 years ago

see exec builtin in the bash shell. otherwise man execvp etc.

abhishekjha• 3 years ago

No reference to fork anywhere?

CodeL• 3 years ago

This could be deliberate. Either to not derail focus from `execve` or perhaps the author assumed that the readers are already well-versed with `fork`.

How does Linux start a process

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