Allow memfd_create to be used with older glibc (<2.27) #2146
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LizardWizzard
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Are you trying to create a dylib target? If so, your trouble should be fixed by #2049 . |
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Thanks for quick response! No, I’m building a binary target |
Do you mean an executable? Ordinary Rust executables should not have a problem with this, as I understand, unless you're using a very old compiler or something. Is there anything unusual in your setup, and have you tested with the lastest Nix release? |
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Sorry for long response
Yes
The only unusual thing here is old glibc. I've prepared a reproducer that gives the same error: https://github.com/LizardWizzard/nix_memfd_create_repro it uses latest nix version available on crates io (0.27.1) and latest stable release of rustc (1.72.1) My exact conditions are a bit different, but this is a small reproducer that shows the same problem. See code that triggers the problem here: https://github.com/LizardWizzard/nix_memfd_create_repro/blob/master/pure_nix_repro/src/main.rs docker image I use is a default centos:7 with some installed packages. To run the example in this repo only call to Thank you! |
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I rebased the patch on top of current master to resolve conflict in changelog. All pipelines that failed have this error message: |
The memfd_create() function is available in glib >= 2.27, but Rust supports glibc >= 2.17. In order to keep compatibility with old glibc versions, this performs a memfd_create syscall directly. This syscall is available in the Linux kernel >= 3.17. There is currently a pull request nix-rust/nix#2146 in the nix crate that will use the syscall with all the glibc versions, in order to account for older glibc versions, while calling the libc function in other libc's such as musl where the function has existed from the beginning. When this pull request is merged, this change can be undone and memfd_create() from nix can be called instead. Signed-off-by: Daniel Estévez <[email protected]>
LizardWizzard
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Hey @SteveLauC! Sorry for the ping, will you have some time to take a look at the PR? Thanks in advance! |
No worry about the ping, feel free to do so when needed:)
Different from the problem #2049 tries to solve, the author actually uses the To address this issue, we should either:
For solution 2, this is actually what |
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Yeah, I briefly looked at weak stuff. Apparently it has a bigger scope compared to reverting to raw syscalls, because I havent seen weak being already used anywhere in nix. If there are no objections option 1 looks ok to me. Otherwise probably weak needs to be introduced separately and then used here and maybe in other API's |
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@SteveLauC what do you think if we merge this one? Do you have any objections? |
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I do tend to use the libc wrapper as syscalls are inherently unsafe, so I prefer approach 2 cc @asomers, thoughts on this? |
Hi! Thank you for your great work!
What does this PR do
While upgrading to more recent version of nix I've faced an issue on a system that has older glibc.
Since this commit nix started to refer to
memfd_createsymbol instead of using a syscall. Glibc started to export this symbol since 2.27 and lowest version supported by rust project is now 2.17, so it would be nice to keep compatibility on a similar level if possible. See comments in code.Found that there was similar issue in libsystemd-rs: lucab/libsystemd-rs#144
Thanks in advance!
Checklist:
CONTRIBUTING.md