fix(runtime): segmentation fault when calling interface private methods cross-package

[luoliwoshang]

Fixes #1370 #1357

Problem

LLGo previously used an optimization to pre-filter methods before itab matching:

mthds := methods(u, inter.PkgPath_)

func methods(u *abi.UncommonType, from string) []abi.Method {
    if u.PkgPath_ == from {
        return u.Methods()          // All methods if same package
    }
    return u.ExportedMethods()      // Only exported if different package
}

This optimization attempted to improve itab filling performance by filtering out private methods when the interface and type are from different packages.

However, this optimization relies on interfaceType.PkgPath being set to the interface definition package. Currently, interfaceType.PkgPath is set to the
package where the interface is used (where the interface conversion happens) rather than the package where the interface is defined. This causes private
methods to be incorrectly filtered out, leaving itab slots as NULL and causing segmentation faults.

Solution

Remove the pre-filtering optimization entirely. Since method names (Name_) already contain package path information:

• Exported methods: "MethodName"
• Unexported methods: "package/path.methodName"

When Name_ matches, the method is guaranteed to be the correct one. The additional package checks are redundant, and comparing all methods is safe without
risk of adding unexpected functions.

This PR removes the methods() filtering function and directly uses u.Methods() for matching, bypassing the interfaceType.PkgPath issue entirely.

Impact

✅ Fixes segfaults for:

• Standard library: go/types.Object, go/ast.Expr, etc.
• User-defined interfaces with private methods
• Cross-package interface conversions returning concrete type pointers

All test cases in the issue now pass.

[gemini-code-assist]

Summary of Changes

Hello @luoliwoshang, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request primarily refactors the LLVM backend's handling of Go interfaces, focusing on their representation and method lookup mechanisms. The changes streamline how interface types are generated in LLVM IR by omitting explicit package path strings during runtime.Interface calls. Additionally, the method visibility logic has been enhanced to support retrieving all methods when a package path is not specified. The PR also includes new demonstration code for Go's token and types packages and a new interface-related test case to ensure correctness.

Highlights

• Go Interface Representation: The way Go interfaces are represented and initialized in the generated LLVM IR has been updated. Specifically, the package path string is no longer passed to the runtime.Interface function, instead using a zero-initialized string.
• Method Visibility Logic: The logic for retrieving methods from an UncommonType has been refined. The methods function in the runtime now returns all methods (not just exported ones) if the from package path is an empty string.
• New Go Tooling Demos: New demonstration files have been added for the go/token and go/types packages, showcasing their functionalities related to tokenizing, parsing, and type information in Go.
• Interface Test Case: A new test case (geometry1370) has been introduced to validate the updated interface handling, including a Go interface, a struct implementing it, and its corresponding LLVM IR output.

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[gemini-code-assist]

Code Review

This pull request correctly fixes an issue with cross-package interface conversions, particularly when interfaces contain unexported methods. The core of the fix is in ssa/abitype.go, where anonymous interfaces are now correctly generated with an empty package path. This is supported by a change in runtime/internal/runtime/z_face.go to adjust method visibility checks for such interfaces. The new test case interface1370 effectively demonstrates and validates the fix. The PR also includes updates to numerous LLVM IR output files, which are consistent with the logic changes, and adds new comprehensive demo/test files for the go/token and go/types packages. The changes are correct and well-implemented.

[xgopilot]

Documentation: Consider adding a comment explaining why unexported methods need fully qualified names:

// For unexported methods, use the fully qualified name with package path
// to distinguish methods with the same name from different packages
if !token.IsExported(mName) {
    mName = abi.FullName(m.Pkg(), mName)
}

This helps maintainers understand the cross-package interface method resolution logic.

[xgopilot]

Code Review Summary

This PR correctly fixes PkgPath handling for interface methods, particularly for anonymous interfaces and cross-package conversions. The implementation is solid with well-structured demo programs.

Key findings:

• One security issue in ssa/interface.go:255 regarding potential out-of-bounds access
• Documentation could be improved to explain cross-package interface method resolution
• No performance regressions introduced
• Comprehensive test coverage with excellent demo programs

Overall: Good work. Please address the validation issue in Imethod function.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.98%. Comparing base (d2a2225) to head (4e374a9).
⚠️ Report is 37 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1387      +/-   ##
==========================================
+ Coverage   90.18%   90.98%   +0.79%     
==========================================
  Files          43       43              
  Lines       12752    11287    -1465     
==========================================
- Hits        11501    10269    -1232     
+ Misses       1092      859     -233     
  Partials      159      159              

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[visualfc]

Name_ 本身格式为 Name 或者是 pkg.Name ( 不导出时 ）所以如果 Name_ 相同，最后两个判断也一定是相同的。

[luoliwoshang]

明白，那么基于当前的匹配逻辑来说，把所有abi.Type对应的Method都进入对比是安全的，并不会额外添加一些不预期的函数。当前的 mthds := methods(u, inter.PkgPath_) 是提高itab 填充func数组效率的一个方式，但是由于当前interfaceType.PkgPath 设定为了使用包，而非定义包，导致这个优化过程把应该保留的私有方法过滤了，当前Pr将移除当前提前过滤private methods的过程。

[luoliwoshang]

@xushiwei