Don't check os_major on Linux

[yan12125 (Chih-Hsuan Yen)]

I've just upgrade my server from Linux kernel 4.18.16 to kernel 5.1.2, and the port command refuses to work:

Error: Current platform "linux 5" does not match expected platform "linux 4"
Error: If you upgraded your OS, please follow the migration instructions: https://trac.macports.org/wiki/Migration
OS platform mismatch
    while executing
"mportinit ui_options global_options global_variations"
Error: /opt/local/bin/port: Failed to initialize MacPorts, OS platform mismatch

This check is not necessary on Linux IMO as programs compiled on Linux 4.x should work just fine on Linux 5.x. Need to change this line: ​https://github.com/macports/macports-base/blob/v2.5.4/src/macports1.0/macports.tcl#L703

[raimue (Rainer Müller)]

Changing just this one line will not help much, as the installed ports also store the platform information in the registry and will all be considered outdated. I guess the real fix would be not to store the Linux kernel version in os_major, but I am also not sure what else to use.

[yan12125 (Chih-Hsuan Yen)]

Ah, great reminder!

The actual version to use might be much more complicated. For each Linux executable file, there is a tag .note.ABI-tag indicating the minimum compatible kernel version. For example on my machine readelf --notes /opt/local/libexec/macports/bin/tclsh8.5 gives the following info: (excerpted)

Displaying notes found in: .note.ABI-tag
  Owner                 Data size	Description
  GNU                  0x00000010	NT_GNU_ABI_TAG (ABI version tag)
    OS: Linux, ABI: 3.2.0

There are some challenges:

1. The ABI tag version might be lower than the running kernel. For example I got 3.2.0 even if I built macports on kernel 4.x.
2. Different executables can have different version tags. For example, programmers can specify it via an assembly file (1).

Maybe the most accurate approach needs scanning files. That sounds too complicated. I would prefer a simpler way - change most (if not all) checks around os_major from != to >= for Linux.

(1) ​https://github.com/qt/qtbase/blob/5.12/src/corelib/global/minimum-linux.S

[mojca (Mojca Miklavec)]

Unless we provide accurate information and implement this properly (which is unlikely to happen), we could either disable version checks, remove the version from Linux altogether (this is probably used in way too many places to get them all correct), or always set the version to "1".

I don't know all the details, but kernel version sounds a pretty useless metric, it's usually glibc that governs compatibility, and portfiles cannot do any sane checks on linux version anyway..

[Satryaji Aulia <satraul@…>]

In d7cbf171c1994066f68d4d10548bc44731959f62/macports-base (master):

Only check OS/platform on MacOS

Temporary fix for Linux not working

References: #58497

[yan12125 (Chih-Hsuan Yen)]

Thank you Satryaji Aulia! Just wondering - is there a reason to call the commit "temporary"?

[mojca (Mojca Miklavec)]

At the moment one probably still needs two different portindex files to be generated on the server, and it might be that all ports will be rebuilt as they contain a hardcoded version in the binary archives. So maybe this needs to be changed at other locations, or handled in some different way.