lib/posix-environ: Ensure that compiled-in strings are writable

[mogasergiu]

Previously, the elements of __init_env would be compile-in strings
that would correspond to CONFIG_LIBPOSIX_ENVIRON_ENVPx configurable
strings. This lead to these strings being placed by in the .rodata
section and making them unmodifiable.

Unfortunately, Redis represents an application whose code may want to
modify such data (see
commit 6356cf6808be ("Set process name in ps output to make operations safer.").
Therefore, to appease such actions, make sure that this data is placed
in a modifiable section such as .data by using statically declared
global variables containing these very strings as an indirection.

To make it look somewhat nicer, do so with the help of two basic helper
macros: DECLARE_LIBPOSIX_ENVIRON_ENV_VAR to transparently declare such
variables and LIBPOSIX_ENVIRON_ENV_VAR to transparently access them.

Signed-off-by: Sergiu Moga sergiu@unikraft.io

Prerequisite checklist

• Read the contribution guidelines regarding submitting new changes to the project;
• Tested your changes against relevant architectures and platforms;
• Ran the checkpatch.uk on your commit series before opening this PR;
• Updated relevant documentation.

Base target

• Architecture(s): [All]
• Platform(s): [All]
• Application(s): [All]

Additional configuration

Description of changes

[michpappas]

Looks good to me. One minor point is the leading underscore in the variable name. Unless there is a strong reason to be there it should be changed to something in compliance with our guidelines.

[mogasergiu]

Looks good to me. One minor point is the leading underscore in the variable name. Unless there is a strong reason to be there it should be changed to something in compliance with our guidelines.

I noticed that @skuenzer likes using those 😝.

[skuenzer]

Looks good to me. One minor point is the leading underscore in the variable name. Unless there is a strong reason to be there it should be changed to something in compliance with our guidelines.

I noticed that @skuenzer likes using those 😝.

I have to admit that this is true. I liked them for things to mark them as "do not touch", especially when they are part of a system declared in the file/library. But since we have our convention, we can change it. In this sense @michpappas is right that we should be a good example for other contributors.

[michpappas]

Reviewed-by: Michalis Pappas michalis@unikraft.io

[unikraft-bot]

⚠️ Checkpatch passed with warnings

Beep boop! I ran Unikraft's checkpatch.pl support script on your pull request but it encountered warnings:

SHA	commit	checkpatch
97918b2	lib/posix-environ: Ensure that compiled-in strings are writable	⚠️

Truncated logs starting from first warning 97918b2:

WARNING:COMMIT_LOG_LONG_LINE: Possible unwrapped commit description (prefer a maximum 75 chars per line)
#14: 
commit 6356cf6808be ("Set process name in ps output to make operations safer.")).

total: 0 errors, 1 warnings, 98 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

/tmp/build/a53d4c5b/patches/0001-lib-posix-environ-Ensure-that-compiled-in-strings-ar.patch has style problems, please review.

NOTE: Ignored message types: ASSIGN_IN_IF FILE_PATH_CHANGES NEW_TYPEDEFS OBSOLETE

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.

---

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[skuenzer]

Thanks a lot for these changes!

Approved-by: Simon Kuenzer simon@unikraft.io