Stream: git-wasmtime

Topic: wasmtime / Issue #1518 Support of DWARF transformation fo...

view this post on Zulip Wasmtime GitHub notifications bot (Apr 15 2020 at 21:41):

yurydelendik opened Issue #1518:

C global variables (such as double s = 0;) are compiled to WebAssembly as locations in the memory. The produced DWARF describes them as DIEs with DW_AT_location attribute that points to that memory address, e.g.:

0x00000072:   DW_TAG_variable
                DW_AT_name  ("s")
                DW_AT_type  (0x00000083 "double")
                DW_AT_external  (true)
                DW_AT_decl_file ("/Users/yury/Work/wasmtime/t.c")
                DW_AT_decl_line (11)
                DW_AT_location  (DW_OP_addr 0x410)

The wasmtime does not attempt to transform such locations since it needs "vmctx". In https://github.com/bytecodealliance/wasmtime/pull/1482 , we used some global state, accessible to debugger, to resolve pointers. It is possible to do the same for DW_OP_addr in static variables expression: user sets current vmctx in some global memory and a debugger gets it in DWARF expressions (in crates/debug/transform/expression.rs). Though we need to able to relocate the data in the DWARF expression written by gimli to make this work.

The similar approach can be used for transformation of DW_OP_Wasm_location wasm-global operation.

Last updated: Dec 23 2024 at 12:05 UTC