e7cd4979be
This patch rolls the main .debug_info DWARF section from version 4 to version 5, and also introduces machinery in the Go compiler and linker for taking advantage of the DWARF5 ".debug_addr" section for subprogram DIE "high" and "low" PC attributes. All functionality is gated by GOEXPERIMENT=dwarf5. For the compiler portion of this patch, we add a new DIE attribute form "DW_FORM_addrx", which accepts as an argument a function (text) symbol. The dwarf "putattr" function is enhanced to handle this format by invoking a new dwarf context method "AddIndirectTextRef". Under the hood, this method invokes the Lsym method WriteDwTxtAddrx, which emits a new objabi.R_DWTXTADDR_* relocation. The size of the relocation is dependent on the number of functions in the package; we pick a size that is just big enough for the largest func index. In the linker portion of this patch, we now switch over to writing out a version number of 5 (instead of 4) in the compile unit header (this is required if we want to use addrx attributes). In the parallel portion of DWARF gen, within each compilation unit we scan subprogram DIEs to look for R_DWTXTADDR_* relocations, and when we find such a reloc, we assign a slot in the .debug_addr section for the func targeted. After the parallel portion is complete, we then walk through all of the compilation units to assign a value to their DW_AT_addr_base attribute, which points to the portion of the single .debug_addr section containing the text addrs for that compilation unit. Note that once this patch is in, programs built with GOEXPERIMENT=dwarf5 will have broken/damaged DWARF info; in particular, since we've changed only the CU and subprogram DIEs and haven't incorported the other changes mandated by DWARF5 (ex: .debug_ranges => .debug_rnglists) a lot of the variable location info will be missing/incorrect. This will obviously change in subsequent patches. Note also that R_DWTXTADDR_* can't be used effectively for lexical scope DIE hi/lo PC attrs, since there isn't a viable way to encode "addrx + constant" in the attribute value (you would need a new entry for each attr endpoint in .debug_addr, which would defeat the point). Updates #26379. Change-Id: I2dfc45c9a8333e7b2a58f8e3b88fc8701fefd006 Reviewed-on: https://go-review.googlesource.com/c/go/+/635337 LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: David Chase <drchase@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com> |
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