Implement GetCommandLineArgs fallback on Unix

[am11]

#128545

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[agocke]

I don't see a good reason why this, or really much of anything else in the file, needs to be written in C. I think we could use standard platform pinvokes (or even just opening the proc fs in this case) from C#.

[am11]

There are number of varied syscalls for each platform; it'd require exposing them all to managed side just to move the implementation there as opposed to having it here next to getexepath.c (which also uses approximately same syscalls) with a single P/Invoke.

[jkotas]

We have most of the required syscalls exposed in managed code already. I do not think it would be too bad to expose the rest.

However, I agree with your point that moving the whole implementation to C# would just be more complicated. We had faced similar tradeoff in the native shims. https://github.com/dotnet/runtime/blob/main/docs/coding-guidelines/interop-guidelines.md touches on it: "At first, it seemed that we'd want to use 1:1 names throughout, but it turns out there are many cases where being strictly 1:1 isn't practical."

having it here next to getexepath.c (which also uses approximately same syscalls)

It is similar code, but it is not a good general-purpose functionality that the minipal should be about. I do not think we would expose it at all if we were starting from scratch. The reason for fixing the linked issue is combination of:

• it works on Windows for historic reasons
• parity between OSes is good
• introducing breaking change on Windows to achieve the parity is not worth it

I think it would be better for this to live in the System.Native shim directly as I have mentioned in the other comment.

[Copilot]

Pull request overview

Implements a Unix/WASI/browser fallback path for Environment.GetCommandLineArgs() when Environment.s_commandLineArgs isn’t initialized (hosted-library scenario), by adding a System.Native entrypoint that retrieves argv via a new minipal_getcmdline helper and wiring it into CoreLib’s GetCommandLineArgsNative().

Changes:

• Add minipal_getcmdline and expose it via SystemNative_GetCommandLine / SystemNative_FreeCommandLine.
• Update CoreLib Unix/Browser implementation to call the new System.Native interop and remove the prior stubbed-out implementation.
• Broaden the fallback test coverage beyond “Windows CoreCLR only” (still excluding Mono).

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/native/minipal/getcmdline.h	New minipal helper that attempts to obtain argv across multiple Unix-like targets (plus WASI/browser).
src/native/libs/System.Native/pal_process.h	Declares new SystemNative_GetCommandLine / SystemNative_FreeCommandLine exports.
src/native/libs/System.Native/pal_process.c	Implements the new exports by delegating to minipal_getcmdline.
src/native/libs/System.Native/pal_process_wasi.c	Implements the new exports for WASI builds.
src/native/libs/System.Native/entrypoints.c	Registers the new exports for System.Native DllImport dispatch.
src/libraries/Common/src/Interop/Unix/System.Native/Interop.GetCommandLine.cs	Adds LibraryImport declarations for SystemNative_GetCommandLine / SystemNative_FreeCommandLine.
src/libraries/System.Private.CoreLib/src/System/Environment.UnixOrBrowser.cs	Adds a Unix/Browser GetCommandLineArgsNative() implementation that calls the new interop.
src/libraries/System.Private.CoreLib/src/System/Environment.Unix.cs	Removes the old stub GetCommandLineArgsNative() implementation.
src/libraries/System.Private.CoreLib/src/System/Environment.Browser.cs	Removes the old Browser stub for GetCommandLineArgsNative().
src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems	Includes the new interop source file in CoreLib build items.
src/libraries/System.Runtime/tests/System.Runtime.Extensions.Tests/System/Environment.GetCommandLineArgs.cs	Updates conditions so fallback tests run on non-Mono (and parser tests run on Windows non-Mono).

Suppressed comments (1)

src/native/minipal/getcmdline.h:83

• The /proc/self/cmdline reader doesn't check whether the initial malloc succeeded, and it doesn't handle read() returning -1 (including EINTR). As written, a read error after partial data can silently return a truncated/invalid argv buffer, and a NULL buf would be dereferenced.

    size_t bufSize = 1024;
    char* buf = (char*)malloc(bufSize);
    size_t totalBytes = 0;
    ssize_t bytesRead;