[native] Replace the bundled properties map with a linked list

[simonrozsival]

Part of the drop-libc++ work for CoreCLR.

AndroidSystem::bundled_properties was an std::unordered_map<std::string, std::string> and the only user of <unordered_map> in the CoreCLR host.

A sorted static array + binary search isn't an option here: bundled properties are read from the environment override files at run time, so the set isn't known at build time. But the map isn't buying us anything either — the entries are added once during startup, looked up a handful of times, and there are only a few of them.

So this uses the same malloc'd singly linked list that MonoVM has always used for exactly this purpose (BundledProperty), keeping the two runtimes consistent:

struct BundledProperty
{
	BundledProperty *next;
	char            *name;
	char            *value;
	size_t           value_len;
};

The name is allocated together with the node (one allocation covers both); the value is allocated separately so that setting the same property twice can replace it. Allocation failure aborts, as elsewhere in this stack.

This also fixes a real bug

The lookup returned the map key instead of the value:

value_len = prop_iter->second.length ();   // the value's length
return prop_iter->first.c_str ();          // ...but the *name*

So in Debug builds every bundled property resolved to its own name, reported with the value's length. When the value is longer than the name that's an over-read past the end of the name's buffer. This is pre-existing on main, and falls out of the rewrite for free.

Results

This code is #if defined (DEBUG) only, so Release builds are completely unaffected — I verified the undefined-libc++-symbol list per object file is byte-for-byte identical before and after (58 both ways).

The win is in Debug builds. Compiling android-system.cc with the real build flags plus -DDEBUG:

	before	after
undefined libc++ symbols	13	12
object size	83,400	77,984 (−5,416)

The symbol that disappears is std::__ndk1::__next_prime() — the bucket-count helper that is unordered_map's only out-of-line dependency.

Testing

• CoreCLR and MonoVM Release builds are clean.
• The Debug path was compile-checked with the real build flags plus -DDEBUG, and I confirmed via llvm-nm that the new code is genuinely being compiled (find_bundled_property and add_system_property are present in the object) rather than silently skipped.

[Copilot]

Copilot review overview

Review tier: Lite
Findings: 1

New issues introduced by this change (1)

Severity	Finding
	src/​native/​clr/​runtime-base/​android-system.cc — 💡 suggestion (performance/alloc churn) — add_system_property() always allocates a new value…

What changed in this PR

This PR updates the CoreCLR host’s debug-only bundled system property storage to remove the last std::unordered_map usage (and its <unordered_map> dependency), aligning the implementation with MonoVM’s long-standing BundledProperty singly linked list approach. It also corrects a pre-existing debug-only lookup bug where the property name was returned instead of the value, which could cause buffer over-reads.

Changes:

• Replace AndroidSystem::bundled_properties from std::unordered_map<std::string, std::string> to a malloc’d BundledProperty singly linked list (DEBUG-only).
• Add AndroidSystem::find_bundled_property() helper for linear lookup in the linked list.
• Fix debug-only property lookup to return the correct value pointer and length.

File	Description
src/​native/​clr/​runtime-base/​android-system.cc	Implements linked-list storage and correct lookup of bundled properties in DEBUG builds.
src/​native/​clr/​include/​runtime-base/​android-system.hh	Removes <unordered_map> and introduces the DEBUG-only BundledProperty definition + storage pointer.