Handle copy relocations

In ELF, if a data symbol is defined in a shared library and used by
the main program, it will be subject to a "copy relocation".  In this
scenario, the main program has a copy of the symbol in question, and a
relocation that tells ld.so to copy the data from the shared library.
Then the symbol in the main program is used to satisfy all references.

This patch changes gdb to handle this scenario.  Data symbols coming
from ELF shared libraries get a special flag that indicates that the
symbol's address may be subject to copy relocation.

I looked briefly into handling copy relocations by looking at the
actual relocations in the main program, but this seemed difficult to
do with BFD.

Note that no caching is done here.  Perhaps this could be changed if
need be; I wanted to avoid possible problems with either objfile
lifetimes and changes, or conflicts with the long-term (vapor-ware)
objfile splitting project.

gdb/ChangeLog
2019-10-02  Tom Tromey  <tromey@adacore.com>

	* symmisc.c (dump_msymbols): Don't use MSYMBOL_VALUE_ADDRESS.
	* ada-lang.c (lesseq_defined_than): Handle
	LOC_STATIC.
	* dwarf2read.c (dwarf2_per_objfile): Add can_copy
	parameter.
	(dwarf2_has_info): Likewise.
	(new_symbol): Set maybe_copied on symbol when
	appropriate.
	* dwarf2read.h (dwarf2_per_objfile): Add can_copy
	parameter.
	<can_copy>: New member.
	* elfread.c (record_minimal_symbol): Set maybe_copied
	on symbol when appropriate.
	(elf_symfile_read): Update call to dwarf2_has_info.
	* minsyms.c (lookup_minimal_symbol_linkage): New
	function.
	* minsyms.h (lookup_minimal_symbol_linkage): Declare.
	* symtab.c (get_symbol_address, get_msymbol_address):
	New functions.
	* symtab.h (get_symbol_address, get_msymbol_address):
	Declare.
	(SYMBOL_VALUE_ADDRESS, MSYMBOL_VALUE_ADDRESS): Handle
	maybe_copied.
	(struct symbol, struct minimal_symbol) <maybe_copied>:
	New member.

1 files changed, 11 insertions, 0 deletions

diff --git a/gdb/minsyms.h b/gdb/minsyms.h
index ce4b83d..0a19f0b 100644
--- a/gdb/minsyms.h
+++ b/gdb/minsyms.h
@@ -205,6 +205,17 @@ struct bound_minimal_symbol lookup_bound_minimal_symbol (const char *);
 struct bound_minimal_symbol lookup_minimal_symbol_text (const char *,
 							struct objfile *);
 
+/* Look through the minimal symbols in OBJF (and its separate debug
+   objfiles) for a global (not file-local) minsym whose linkage name
+   is NAME.  This is somewhat similar to lookup_minimal_symbol_text,
+   only data symbols (not text symbols) are considered, and a non-NULL
+   objfile is not accepted.  Returns a bound minimal symbol that
+   matches, or an "empty" bound minimal symbol otherwise.  */
+
+extern struct bound_minimal_symbol lookup_minimal_symbol_linkage
+  (const char *name, struct objfile *objf)
+  ATTRIBUTE_NONNULL (1) ATTRIBUTE_NONNULL (2);
+
 /* Look through all the current minimal symbol tables and find the
    first minimal symbol that matches NAME and PC.  If OBJF is non-NULL,
    limit the search to that objfile.  Returns a pointer to the minimal