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0 pointsmatheusmoreira5mo ago0 comments

Let's systematize this.

Compilers build for target triples such as x86_64-linux-gnu. It is of the form isa-kernel-userspace. If kernel is linux, the builtin can be used. The isa determines the code generated by the compiler, both in general and for the builtin. The userspace can be anything at all, including none. Sometimes compilers build for target quadruples which also include a vendor, and that information is also irrelevant.

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17186274405mo ago

I am not sure you understand my point. Inlining libc definitions for syscalls is fine when you only care about Debian 12 commit hash ####. It will break as soon as you think your machine is running Debian 12 and you updated it, so surely it includes the latest userspace-patches. It will also break when a user uses the OS configuration to change the behaviour of some OS functionality, but your code is oblivious to that matter, because your code bypasses the OS version of libc.

Modifying the OS is fine, if this is what you want to do, but it comes with tradeoffs.

----

You wrote earlier:

> actually tried to hack a linux_system_call builtin into GCC at some point. [...] The maintainers didn't seem too convinced in the mailing list so I didn't bother rewriting it.

I am not sure what exactly this means. There is syscall(2) in the libc, if you want to do this. If you want to inline the wrappers you can pass -static to the compiler invocation.

matheusmoreiraOP5mo ago

> It will break

If it ever breaks, it's a bug in the Linux kernel.

> It will also break when a user uses the OS configuration to change the behaviour of some OS functionality

Can you give concrete examples of this?

> There is syscall(2) in the libc, if you want to do this.

I know. I've written my own syscall(), as well. The idea is to put it in the compiler as a builtin so there's no need to even write it.

17186274405mo ago

> If it ever breaks, it's a bug in the Linux kernel.

No, your program will still instruct the kernel to do the same. It will just cause conflicts with the other OS internals.

> Can you give concrete examples of this?

Adding another encoding as a gconv module. The DNS issues everyone is talking about.

I don't know what that gets you compared to using syscall(2) and -static. When you want your program to depend on the kernel API instead of the OS API, then you should really link libc statically.

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17186274405mo ago

Modifying the OS is fine, if this is what you want to do, but it comes with tradeoffs.

----

You wrote earlier:

> actually tried to hack a linux_system_call builtin into GCC at some point. [...] The maintainers didn't seem too convinced in the mailing list so I didn't bother rewriting it.

I am not sure what exactly this means. There is syscall(2) in the libc, if you want to do this. If you want to inline the wrappers you can pass -static to the compiler invocation.

matheusmoreiraOP5mo ago

> It will break

If it ever breaks, it's a bug in the Linux kernel.

> It will also break when a user uses the OS configuration to change the behaviour of some OS functionality

Can you give concrete examples of this?

> There is syscall(2) in the libc, if you want to do this.

I know. I've written my own syscall(), as well. The idea is to put it in the compiler as a builtin so there's no need to even write it.

17186274405mo ago

> If it ever breaks, it's a bug in the Linux kernel.

No, your program will still instruct the kernel to do the same. It will just cause conflicts with the other OS internals.

> Can you give concrete examples of this?

Adding another encoding as a gconv module. The DNS issues everyone is talking about.

I don't know what that gets you compared to using syscall(2) and -static. When you want your program to depend on the kernel API instead of the OS API, then you should really link libc statically.

1 more reply

j / k navigate · click thread line to collapse