Fix register regression in DWARF evaluator

On an internal test case, using an arm-elf target, commit ba5bc3e5a92
("Make DWARF evaluator return a single struct value") causes a
regression.  (It doesn't happen for any of the other cross targets
that I test when importing upstream gdb.)

I don't know if there's an upstream gdb test case showing the same
problem... I can only really run native tests with dejagnu AFAIK.

The failure manifests like this:

    Breakpoint 1, file_1.export_1 (param_1=<error reading variable: Unable to access DWARF register number 64>, str=...) at [...]/file_1.adb:5

Whereas when it works it looks like:

    Breakpoint 1, file_1.export_1 (param_1=99.0, str=...) at [...]/file_1.adb:5

The difference is that the new code uses the passed-in gdbarch,
whereas the old code used the frame's gdbarch, when handling
DWARF_VALUE_REGISTER.

This patch restores the use of the frame's arch.

diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 85088e9a07ac44bb94db887cf0f33541f525176b..0e62de22affb9cc0144c598011158a08eb35a9a0 100644 (file)
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -927,9 +927,11 @@ dwarf_expr_context::fetch_result (struct type *type, struct type *subobj_type,
        {
        case DWARF_VALUE_REGISTER:
          {
+           gdbarch *f_arch = get_frame_arch (this->m_frame);
            int dwarf_regnum
              = longest_to_int (value_as_long (this->fetch (0)));
-           int gdb_regnum = dwarf_reg_to_regnum_or_error (arch, dwarf_regnum);
+           int gdb_regnum = dwarf_reg_to_regnum_or_error (f_arch,
+                                                          dwarf_regnum);
 
            if (subobj_offset != 0)
              error (_("cannot use offset on synthetic pointer to register"));