René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Fix incorrect pinned maps handling and missing userspace setup code","articleBody":"When using the `pin` keyword with map declarations (e.g., `pin var cpu_counters : array\u003c...\u003e`), the current implementation faces two primary issues that prevent the maps from being correctly pinned to the BPF filesystem.\n\n### The Problems\n\n1. **Incorrect Treatment as Global Variables**: The IR generator incorrectly creates both an IR map definition and an IR global variable for pinned maps. This causes the userspace codegen to treat the map as a \"pinned global variable,\" looking for a non-existent `__pinned_globals` map and resulting in the error: `Failed to find pinned globals map in eBPF object`.\n2. **Missing Setup Code**: Setup and pinning logic for maps is only generated if the userspace code explicitly performs map operations. However, pinned maps require setup (pinning to `/sys/fs/bpf/...`) even if they are only accessed within the eBPF program itself.\n3. **Variable Redefinition**: If multiple pinned maps exist, the generated C code uses the same variable name (`existing_fd`) for all of them, leading to compilation errors.\n4. **Missing Directory Creation**: The generated code fails to pin maps if the parent directory (e.g., `/sys/fs/bpf/\u003cproject\u003e/maps/`) does not already exist.\n\n### Proposed Changes\n\nThe provided patch addresses these issues with the following logic:\n\n* **IR Generator**: Modified `ir_generator.ml` to ensure that map-type global declarations only produce map definitions, not global variable entries.\n* **Userspace Codegen**:\n* Updated `userspace_codegen.ml` to trigger map setup and FD declarations if any pinned maps are detected (`has_pinned_maps`), regardless of whether they are used in userspace C code.\n* Implemented unique variable naming (e.g., `%s_existing_fd`) to prevent C redefinition errors.\n* Added a C helper function `ensure_bpf_dir` to recursively create the necessary BPF filesystem directories before pinning.\n* Included necessary headers (`\u003csys/stat.h\u003e`, `\u003csys/types.h\u003e`) when pinning is required.\n\n[fix_pin_var_map.patch](https://github.com/user-attachments/files/25742537/fix_pin_var_map.patch)\n\n### Verification\n\nTesting with `examples/maps_demo.ks` confirms:\n\n* The \"Failed to find pinned globals map\" error is resolved.\n* Maps are correctly pinned to `/sys/fs/bpf/maps_demo/maps/`.\n* Userspace programs compile and run correctly with multiple pinned maps.\n","author":{"url":"https://github.com/SiyuanSun0736","@type":"Person","name":"SiyuanSun0736"},"datePublished":"2026-03-04T14:01:23.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/12/kernelscript/issues/12"}