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, 44 insertions, 0 deletions

diff --git a/gdb/symtab.c b/gdb/symtab.c
index 7b4444c..8a551f1 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -6261,6 +6261,50 @@ symbol_set_symtab (struct symbol *symbol, struct symtab *symtab)
   symbol->owner.symtab = symtab;
 }
 
+/* See symtab.h.  */
+
+CORE_ADDR
+get_symbol_address (const struct symbol *sym)
+{
+  gdb_assert (sym->maybe_copied);
+  gdb_assert (SYMBOL_CLASS (sym) == LOC_STATIC);
+
+  const char *linkage_name = SYMBOL_LINKAGE_NAME (sym);
+
+  for (objfile *objfile : current_program_space->objfiles ())
+    {
+      bound_minimal_symbol minsym
+	= lookup_minimal_symbol_linkage (linkage_name, objfile);
+      if (minsym.minsym != nullptr)
+	return BMSYMBOL_VALUE_ADDRESS (minsym);
+    }
+  return sym->ginfo.value.address;
+}
+
+/* See symtab.h.  */
+
+CORE_ADDR
+get_msymbol_address (struct objfile *objf, const struct minimal_symbol *minsym)
+{
+  gdb_assert (minsym->maybe_copied);
+  gdb_assert ((objf->flags & OBJF_MAINLINE) == 0);
+
+  const char *linkage_name = MSYMBOL_LINKAGE_NAME (minsym);
+
+  for (objfile *objfile : current_program_space->objfiles ())
+    {
+      if ((objfile->flags & OBJF_MAINLINE) != 0)
+	{
+	  bound_minimal_symbol found
+	    = lookup_minimal_symbol_linkage (linkage_name, objfile);
+	  if (found.minsym != nullptr)
+	    return BMSYMBOL_VALUE_ADDRESS (found);
+	}
+    }
+  return (minsym->value.address
+	  + ANOFFSET (objf->section_offsets, minsym->section));
+}
+
 
 
 void