[RFA/commit/Win64] Remove new extra leading underscore in symbol name

[Joel Brobecker <brobecker@adacore.com>]

For any Ada program, the debugger no longer finds the right routine as
the main subprogram when using the "start" command.  For instance:

    % gdb simple_main
    (gdb) start
    [...]
    Temporary breakpoint 1, main (argc=1, argv=(system.address) 0x232470, [...]
                            ^^^^

The expected behavior is to stop in the Ada main program:

    (gdb) start
    [...]
    Temporary breakpoint 1, simple_main () at simple_main.adb:4
    4           simple.test_simple;

The problem was introduced, I believe, by a patch in bfd causing
the names in the symbol table to now have a leading underscore:

    Adjust calling convention of x64 windows to non-leading underscore
    http://www.sourceware.org/ml/binutils/2010-04/msg00354.html

In the case of the "start" command, the search for the name of the
main subprogram requires GDB to find the __gnat_ada_main_program_name
symbol.  But since the patch above got applied, GDB now sees that
(minimal) symbol as ___gnat_ada_main_program_name (extra leading
underscore).

Other consequences of that change of behavior:

  - Ada tasking support is broken, since it relies on other known
    symbol names;

  - minimal symbol and symbols from debug info has non-matching names;
    I would think that some parts of GDB's code make the assumption
    that these names match, at least for C, but I might be unnecessarily
    pessimistic.

This patch changes the COFF reader such that, for COFF/PE64, we discard
the leading underscore.

2010-06-17  Joel Brobecker  <brobecker@adacore.com>

        gdb/
        * coffread.c (getsymname): Skip the leading underscore on pe64.

Tested on x64-windows with AdaCore's testsuite (we do a MinGW build).
I'd like to commit a fix before 7.2.

Kai's input would be greatly appreciated, as he probably knows Windows
a thousand times better than I do.

---
 gdb/coffread.c |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/gdb/coffread.c b/gdb/coffread.c
index 52417b2..4ab0640 100644
--- a/gdb/coffread.c
+++ b/gdb/coffread.c
@@ -1256,6 +1256,9 @@ getsymname (struct internal_syment *symbol_entry)
 {
   static char buffer[SYMNMLEN + 1];
   char *result;
+  const char *target = bfd_get_target (symfile_bfd);
+  const int is_pe64 = (strcmp (target, "pe-x86-64") == 0
+                       || strcmp (target, "pei-x86-64") == 0);
 
   if (symbol_entry->_n._n_n._n_zeroes == 0)
     {
@@ -1269,6 +1272,17 @@ getsymname (struct internal_syment *symbol_entry)
       buffer[SYMNMLEN] = '\0';
       result = buffer;
     }
+
+  /* On x64-windows, an extra leading underscore is usually added to
+     the symbol name.  However, the name provided in the associated
+     debug information does not include that underscore.  So remove it
+     now, to make the two names match.
+
+     This is also useful for code that searches the minimal symbols
+     for a specific symbol whose name should be target-independent.  */
+  if (is_pe64 && result[0] == '_')
+    result++;
+
   return result;
 }
 
-- 
1.7.1