[RFA] Set language for Ada minimal symbols.

[Joel Brobecker <brobecker at adacore dot com>]

Hello,

This helps with the following issue: Given an Ada program defining
a global variable:

    package Pck is
       Watch : Integer := 1974;
    end Pck;

When printing the address of this variable, GDB also tries to print
the associated symbol name:

    (gdb) p watch'address
    $1 = (access integer) 0x6139d8 <pck__watch>
                                       ^^
                                       ||

The problem is that GDB prints the variable's linkage name, instead
of its natural name. This is because the language of the associated
minimal symbol never really gets set.

This patch adds handling for Ada symbols in symbol_find_demangled_name.
After this patch, we now get:

    (gdb) p watch'address
    $1 = (access integer) 0x6139d8 <pck.watch>
                                       ^
                                       |

gdb/ChangeLog:

        * symtab.c (symbol_find_demangled_name): Add handling of
        Ada symbols.

gdb/testsuite/ChangeLog:

        * gdb.ada/int_deref.exp: Add test verifying that we print
        the decoded symbol name when printing the address of Ada
        symbols.

I've added a large comment explaining why we do what we do. I hope
it's all acceptable. Tested on x86_64-linux.

OK to commit?

Thank you,
-- 
Joel

---
 gdb/symtab.c                        | 37 +++++++++++++++++++++++++++++++++++++
 gdb/testsuite/gdb.ada/int_deref.exp |  5 +++++
 2 files changed, 42 insertions(+)

diff --git a/gdb/symtab.c b/gdb/symtab.c
index 8fac0be..aa1e14b 100644
--- a/gdb/symtab.c
+++ b/gdb/symtab.c
@@ -60,6 +60,7 @@
 #include "solist.h"
 #include "macrotab.h"
 #include "macroscope.h"
+#include "ada-lang.h"
 
 #include "psymtab.h"
 #include "parser-defs.h"
@@ -692,6 +693,42 @@ symbol_find_demangled_name (struct general_symbol_info *gsymbol,
      symbols).  Just the mangling standard is not standardized across compilers
      and there is no DW_AT_producer available for inferiors with only the ELF
      symbols to check the mangling kind.  */
+
+  /* Check for Ada symbols last.  See comment below explaining why.  */
+
+  if (gsymbol->language == language_auto)
+   {
+     const char *demangled = ada_decode (mangled);
+
+     if (demangled != mangled && demangled != NULL && demangled[0] != '<')
+       {
+	 /* Set the gsymbol language to Ada, but still return NULL.
+	    Two reasons for that:
+
+	      1. For Ada, we prefer computing the symbol's decoded name
+		 on the fly rather than pre-compute it, in order to save
+		 memory (Ada projects are typically very large).
+
+	      2. There are some areas in the definition of the GNAT
+		 encoding where, with a bit of bad luck, we might be able
+		 to decode a non-Ada symbol, generating an incorrect
+		 demangled name (Eg: names ending with "TB" for instance
+		 are identified as task bodies and so stripped from
+		 the decoded name returned).
+
+		 Returning NULL, here, helps us get a little bit of
+		 the best of both worlds.  Because we're last, we should
+		 not affect any of the other languages that were able to
+		 demangle the symbol before us; we get to correctly tag
+		 Ada symbols as such; and even if we incorrectly tagged
+		 a non-Ada symbol, which should be rare, any routing
+		 through the Ada language should be transparent (Ada
+		 tries to behave much like C/C++ with non-Ada symbols).  */
+	 gsymbol->language = language_ada;
+	 return NULL;
+       }
+   }
+
   return NULL;
 }
 
diff --git a/gdb/testsuite/gdb.ada/int_deref.exp b/gdb/testsuite/gdb.ada/int_deref.exp
index 7b8f426..ea61d4a 100644
--- a/gdb/testsuite/gdb.ada/int_deref.exp
+++ b/gdb/testsuite/gdb.ada/int_deref.exp
@@ -26,6 +26,11 @@ clean_restart ${testfile}
 set bp_location [gdb_get_line_number "Pck.Watch" ${testdir}/foo.adb]
 runto "foo.adb:$bp_location"
 
+# Hijack a bit this testcase, to verify that name decoding works
+# when doing symbolic address printing.
+gdb_test "print watch'address" \
+         " = \\(system\\.address\\) $hex <pck\\.watch>"
+
 gdb_test "print *long_integer(watch'address)" \
          " = 4874"
 
-- 
1.8.1.2