Fix setting-breakpoints regression on PPC64 (function descriptors)

The recent-ish commit e5f25bc5d6db ('Fix "list ambiguous_variable"')
caused a serious regression on PPC64.  See
<https://sourceware.org/ml/gdb-patches/2017-11/msg00666.html>.

Basically, after that patch, GDB sets breakpoints in function
descriptors instead of where the descriptors point to, which is
incorrect.

The problem is that GDB now only runs a minsym's address through
gdbarch_convert_from_func_ptr_addr if msymbol_is_text returns true.
However, if the symbol points to a function descriptor,
msymbol_is_text is false since function descriptors are in fact
outside the text section.

The fix is to also run a non-text address through
gdbarch_convert_from_func_ptr_addr, and if that detects that it was
indeed a function descriptor, treat the resulting address as a
function.

While implementing that directly in linespec.c:minsym_found (where the
bad msymbol_is_text check is) fixes the issue, I noticed that
linespec.c:add_minsym has some code that also basically needs to do
the same checks, however it's implemented differently.  Also,
add_minsym is calling find_pc_sect_line on non-function symbols, which
also doesn't look right.

So I introduced msymbol_is_function, so that we have a simple place to
consider minsyms and function descriptors.

And then, the only other use of msymbol_is_text is in
find_function_alias_target, which turns out to also be incorrect.
Changing that one to use msymbol_is_function, i.e., to consider
function descriptors too fixes (on PPC64):

  -FAIL: gdb.base/symbol-alias.exp: p func_alias
  -FAIL: gdb.base/symbol-alias.exp: p *func_alias()
  +PASS: gdb.base/symbol-alias.exp: p func_alias
  +PASS: gdb.base/symbol-alias.exp: p *func_alias()

And then after that, msymbol_is_text is no longer used anywhere, so it
can be removed.

Tested on x86_64 GNU/Linux, no regressions.  Tested on PPC64 GNU/Linux
and results compared to a testrun of e5f25bc5d6db^ (before the
offending commit), also no regressions.  (there's a couple new FAILs
and some new symbol name matching unit tests are crashing, but that
looks unrelated).

gdb/ChangeLog:
2017-11-29  Pedro Alves  <palves@redhat.com>

	* linespec.c (minsym_found, add_minsym): Use msymbol_is_function.
	* minsyms.c (msymbol_is_text): Delete.
	(msymbol_is_function): New function.
	* minsyms.h (msymbol_is_text): Delete.
	(msymbol_is_function): New declaration.
	* symtab.c (find_function_alias_target): Use msymbol_is_function.

1 files changed, 4 insertions, 4 deletions

diff --git a/gdb/symtab.c b/gdb/symtab.c
index 3d59367..a249a8d 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -3927,14 +3927,14 @@ skip_prologue_using_sal (struct gdbarch *gdbarch, CORE_ADDR func_addr)
 symbol *
 find_function_alias_target (bound_minimal_symbol msymbol)
 {
-  if (!msymbol_is_text (msymbol.minsym))
+  CORE_ADDR func_addr;
+  if (!msymbol_is_function (msymbol.objfile, msymbol.minsym, &func_addr))
     return NULL;
 
-  CORE_ADDR addr = BMSYMBOL_VALUE_ADDRESS (msymbol);
-  symbol *sym = find_pc_function (addr);
+  symbol *sym = find_pc_function (func_addr);
   if (sym != NULL
       && SYMBOL_CLASS (sym) == LOC_BLOCK
-      && BLOCK_START (SYMBOL_BLOCK_VALUE (sym)) == addr)
+      && BLOCK_START (SYMBOL_BLOCK_VALUE (sym)) == func_addr)
     return sym;
 
   return NULL;