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diff --git a/docs/dwarf.md b/docs/dwarf.md new file mode 100644 index 00000000000..ac400bb8d07 --- /dev/null +++ b/docs/dwarf.md @@ -0,0 +1,21 @@ +# Line number information + +Line number information maps between machine code instructions and the source level location. + +## Encoding + +The line number information is stored in the `.debug_line` section for ELF and `__debug_line` +section of the `__DWARF` segment for Mach-O object files. The line number information contains a +header followed by the line program. The line program is a program for a virtual machine with +instructions like set line number for the current machine code instruction and advance the current +machine code instruction. + +## Tips + +You need to set either `DW_AT_low_pc` and `DW_AT_high_pc` **or** `DW_AT_ranges` of a +`DW_TAG_compilation_unit` to the range of addresses in the compilation unit. After that you need +to set `DW_AT_stmt_list` to the `.debug_line` section offset of the line program. Otherwise a +debugger won't find the line number information. On macOS the debuginfo relocations **must** be +section relative and not symbol relative. +See [#303 (comment)](https://github.com/bjorn3/rustc_codegen_cranelift/issues/303#issuecomment-457825535) +for more information. |