[NativeAOT] Add printf gref logging

[jonathanpeppers]

Dependency

Depends on #12211 and targets its jonathanpeppers-finish-gc-bridge-printf branch.

Part of #12139.

Design

Adds a non-exported printf-style OSBridge::_monodroid_gref_logf() path for the shared CoreCLR/NativeAOT GC bridge. It formats directly to logcat with log_writev() and to the gref file with vfprintf(), using va_copy() so both sinks can consume the arguments without allocating or transferring ownership.

The existing exported _monodroid_gref_log(const char*) entry point, P/Invoke registration, managed callers, and MonoVM implementation remain unchanged.

Scope

Migrates only the three intentionally deferred std::format calls in src/native/clr/host/bridge-processing.cc that feed the gref file/logcat pipeline.

Behavior preservation

• Retains the existing Logger::gref_log(), Logger::gref_to_logcat(), LOG_GREF, and gc_spew_enabled() gates and surrounding control flow.
• Preserves message text, punctuation, newlines, source locations, and sink flushing.
• Uses explicit 0x prefixes with PRIxPTR/uintptr_t so handles retain lowercase pointer-width hexadecimal output, including 0x0 for null handles.
• Keeps the existing null-message handling on the exported string API; the new internal format argument is also null-safe.
• Borrows format strings and arguments only for the duration of the call and introduces no returned or transferred ownership.

Non-goals

• Does not change the managed/native ABI or add a new P/Invoke symbol.
• Does not modify MonoVM-only gref logging.
• Does not migrate unrelated formatting outside the NativeAOT-reachable shared GC bridge.

Validation

Prerequisites initialized in the fresh worktree:

• dotnet build build-tools\xa-prep-tasks\xa-prep-tasks.csproj -v:minimal
• dotnet build build-tools\Xamarin.Android.Tools.BootstrapTasks\Xamarin.Android.Tools.BootstrapTasks.csproj -v:minimal
• git submodule update --init -- external/libunwind

Validation run:

• dotnet build src\native\native-nativeaot.csproj -p:AndroidSupportedTargetJitAbis=arm64-v8a -p:AndroidSupportedTargetAotAbis=arm64 -v:minimal
• dotnet build src\native\native-clr.csproj -p:AndroidSupportedTargetJitAbis=arm64-v8a -p:AndroidSupportedTargetAotAbis=arm64 -v:minimal
• rg "std::format" src\native\clr\host\bridge-processing.cc (no matches)
• git diff --check

No focused existing test target covers this internal OSBridge formatting boundary.

[Copilot]

Pull request overview

Adds an internal printf-style gref logging helper for the shared CoreCLR/NativeAOT GC bridge, and migrates the remaining std::format-based gref messages in bridge-processing.cc to avoid libc++ formatting dependencies while preserving existing gref logging behavior.

Changes:

• Introduce OSBridge::gref_logf(const char* format, ...) which logs to logcat via log_writev() and to the gref file via vfprintf(), using va_copy() for dual-sink consumption.
• Replace three std::format call sites in src/native/clr/host/bridge-processing.cc with gref_logf() and PRIxPTR-based pointer formatting.
• Add <cinttypes> include to support PRIxPTR.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/native/clr/include/host/os-bridge.hh	Declares new internal OSBridge::gref_logf() printf-style gref logging API.
src/native/clr/host/os-bridge.cc	Implements gref_logf() to write to logcat and the gref file without allocating intermediate strings.
src/native/clr/host/bridge-processing.cc	Migrates three gref log messages from std::format to gref_logf() with pointer-width hex output.

[jonathanpeppers]

/review

[github-actions]

✅ Android PR Reviewer completed successfully!

[github-actions]

🤖 Android PR Review — ✅ LGTM (with 1 minor suggestion)

Clean, well-scoped port of three std::format gref-logging calls to the new printf-style OSBridge::_monodroid_gref_logf() path for the shared CoreCLR/NativeAOT GC bridge.

Verified

• Logcat gating preserved. The original _monodroid_gref_log() gated logcat on Logger::gref_to_logcat() and delegated the log_categories & LOG_GREF check to log_debugf(). Since log_writev() does not perform that internal check, the new function correctly replicates it inline via (log_categories & LOG_GREF) != 0. Net behavior is identical. ✅
• File-sink behavior preserved. The gref-file write remains ungated by log_categories (only null-checked), matching the original. Caching Logger::gref_log() in a local is a nice small cleanup. ✅
• va_copy correctness. Each sink consumes its own va_list (logcat_args copied for log_writev, original args for vfprintf), with matching va_end on every path including the null-format case. ✅
• Format output. 0x%" PRIxPTR on uintptr_t reproduces the lowercase 0x-prefixed pointer-width hex of {:#x}, including 0x0 for null handles — and using uintptr_t avoids the signed -0x... rendering {:#x} would produce for high addresses. ✅
• Text/punctuation/newlines on all three call sites match the originals (trailing \n retained where present, omitted for the "collected by a Java GC" message). ✅
• Attribute format (printf, 1, 2) is correct for a static member function (no implicit this). ✅
• <cinttypes> include added for PRIxPTR. ✅

Notes

• CI shows no completed checks yet (status pending) — merge should wait for the pipeline to go green.
• One 💡 consistency suggestion posted inline (optional use of optional_string).

No bugs, safety, or performance concerns found.

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