[RFA/commit] Improve gdb_realpath for Windows hosts

[Joel Brobecker <brobecker@adacore.com>]

Hello,

I noticed that inserting a breakpoint on Windows hosts
often does not work when the linespec involves a filename
with its full path. For instance:

    (gdb) b c:/some/double/slashes/dir/foo.c:4
    No source file named c:/some/double/slashes/dir/foo.c:4.
    (gdb) b c:\some\double\slashes\dir\foo.c:4
    No source file named c:\some\double\slashes\dir\foo.c:4.

The problem in this case comes from the fact that the compiler
produced some debugging info where the filename had double
backslaces (weird), as in `c:\\some\\double\\slashes\\dir'.

On Unix platforms, this wouldn't be a problem, because gdb_realpath
takes care of normalizing the path.  But on windows, the implementation
is just an xstrdup.

This fixes the problem by enhancing gdb_realpath on Windows hosts.
The code is inspired from libiberty's lrealpath. I decided to
continue duplicating part of lrealpath rather than replacing
everything by a call to lrealpath because I think that we actually
want something slightly different: after normalizing the path,
lrealpath then lowercases it. This is not idea of GDB, because
it prevents us from displaying filenames using the correct casing.

gdb/ChangeLog:

        * utils.c (gdb_realpath): Add better support for Windows hosts.

Tested on x86-windows. Any objection to this? There is a performance
cost, but this is just on par with what we do on Unix hosts, so
I assume it's OK.

Thanks,
-- 
Joel

---
 gdb/utils.c |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/gdb/utils.c b/gdb/utils.c
index 16405d1..d55e6f1 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -3341,6 +3341,25 @@ gdb_realpath (const char *filename)
   }
 #endif
 
+  /* The MS Windows method.  If we don't have realpath, we assume we
+     don't have symlinks and just canonicalize to a Windows absolute
+     path.  GetFullPath converts ../ and ./ in relative paths to
+     absolute paths, filling in current drive if one is not given
+     or using the current directory of a specified drive (eg, "E:foo").
+     It also converts all forward slashes to back slashes.  */
+  /* The file system is case-insensitive but case-preserving.
+     So we do not lowercase the path.  Otherwise, we might not
+     be able to display the original casing in a given path.  */
+#if defined (_WIN32)
+  {
+    char buf[MAX_PATH];
+    DWORD len = GetFullPathName (filename, MAX_PATH, buf, NULL);
+
+    if (len > 0 && len < MAX_PATH)
+      return xstrdup (buf);
+  }
+#endif
+
   /* This system is a lost cause, just dup the buffer.  */
   return xstrdup (filename);
 }
-- 
1.7.1