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authorTom Tromey <tom@tromey.com>2017-07-06 06:44:38 -0600
committerTom Tromey <tom@tromey.com>2017-11-17 14:34:14 -0700
commit71a3c36949407eafea744bf00334c4e0c136f927 (patch)
tree2449b4419ef190f549e5bd0f4bbc1c210b67076f /gdb/symfile.h
parent7468702dcb37013edbbbc62e247e23c4b2632379 (diff)
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Handle dereferencing Rust trait objects
In Rust, virtual tables work a bit differently than they do in C++. In C++, as you know, they are connected to a particular class hierarchy. Rust, instead, can generate a virtual table for potentially any type -- in fact, one such virtual table for each trait (a trait is similar to an abstract class or to a Java interface) that a type implements. Objects that are referenced via a trait can't currently be inspected by gdb. This patch implements the Rust equivalent of "set print object". gdb relies heavily on the C++ ABI to decode virtual tables; primarily to make "set print object" work; but also "info vtbl". However, Rust does not currently have a specified ABI, so this approach seems unwise to emulate. Instead, I've changed the Rust compiler to emit some DWARF that describes trait objects (previously their internal structure was opaque), vtables (currently just a size -- but I hope to expand this in the future), and the concrete type for which a vtable was emitted. The concrete type is expressed as a DW_AT_containing_type on the vtable's type. This is a small extension to DWARF. This patch adds a new entry to quick_symbol_functions to return the symtab that holds a data address. Previously there was no way in gdb to look up a full (only minimal) non-text symbol by address. The psymbol implementation of this method works by lazily filling in a map that is added to the objfile. This avoids slowing down psymbol reading for a feature that is likely to not be used too frequently. I did not update .gdb_index. My thinking here is that the DWARF 5 indices will obsolete .gdb_index soon-ish, meaning that adding a new feature to them is probably wasted work. If necessary I can update the DWARF 5 index code when it lands in gdb. Regression tested on x86-64 Fedora 25. 2017-11-17 Tom Tromey <tom@tromey.com> * symtab.h (struct symbol) <is_rust_vtable>: New member. (struct rust_vtable_symbol): New. (find_symbol_at_address): Declare. * symtab.c (find_symbol_at_address): New function. * symfile.h (struct quick_symbol_functions) <find_compunit_symtab_by_address>: New member. * symfile-debug.c (debug_qf_find_compunit_symtab_by_address): New function. (debug_sym_quick_functions): Link to debug_qf_find_compunit_symtab_by_address. * rust-lang.c (rust_get_trait_object_pointer): New function. (rust_evaluate_subexp) <case UNOP_IND>: New case. Call rust_get_trait_object_pointer. * psymtab.c (psym_relocate): Clear psymbol_map. (psym_fill_psymbol_map, psym_find_compunit_symtab_by_address): New functions. (psym_functions): Link to psym_find_compunit_symtab_by_address. * objfiles.h (struct objfile) <psymbol_map>: New member. * dwarf2read.c (dwarf2_gdb_index_functions): Update. (process_die) <DW_TAG_variable>: New case. Call read_variable. (rust_containing_type, read_variable): New functions. 2017-11-17 Tom Tromey <tom@tromey.com> * gdb.rust/traits.rs: New file. * gdb.rust/traits.exp: New file.
Diffstat (limited to 'gdb/symfile.h')
-rw-r--r--gdb/symfile.h8
1 files changed, 8 insertions, 0 deletions
diff --git a/gdb/symfile.h b/gdb/symfile.h
index 3472aa0..e742984 100644
--- a/gdb/symfile.h
+++ b/gdb/symfile.h
@@ -270,6 +270,14 @@ struct quick_symbol_functions
(struct objfile *objfile, struct bound_minimal_symbol msymbol,
CORE_ADDR pc, struct obj_section *section, int warn_if_readin);
+ /* Return the comp unit from OBJFILE that contains a symbol at
+ ADDRESS. Return NULL if there is no such comp unit. Unlike
+ find_pc_sect_compunit_symtab, any sort of symbol (not just text
+ symbols) can be considered, and only exact address matches are
+ considered. This pointer may be NULL. */
+ struct compunit_symtab *(*find_compunit_symtab_by_address)
+ (struct objfile *objfile, CORE_ADDR address);
+
/* Call a callback for every file defined in OBJFILE whose symtab is
not already read in. FUN is the callback. It is passed the file's
FILENAME, the file's FULLNAME (if need_fullname is non-zero), and