[Bug testsuite/14531] New: gdb.base/dprintf.exp fails in newlib environment

["yufeng.zhang at arm dot com" <sourceware-bugzilla@sourceware.org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14531

             Bug #: 14531
           Summary: gdb.base/dprintf.exp fails in newlib environment
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: testsuite
        AssignedTo: unassigned@sourceware.org
        ReportedBy: yufeng.zhang@arm.com
    Classification: Unclassified


I have seen the following failures in a bare-metal environment with newlib:

set dprintf-function fprintf^M
(gdb) PASS: gdb.base/dprintf.exp: Set dprintf function
set dprintf-channel stderr^M
(gdb) PASS: gdb.base/dprintf.exp: Set dprintf channel
jump *start^M
Line 0 is not in `foo'.  Jump anyway? (y or n) y^M
Continuing at 0x400178.^M
^M
Breakpoint 2, main (argc=1, argv=0x2041bfe0) at
gdb/testsuite/gdb.base/dprintf.c:33^M
33        int loc = 1234;^M
(gdb) continue^M
Continuing.^M
kickoff 1234^M
also to stderr 1234^M
No symbol "stderr" in current context.^M
(gdb) FAIL: gdb.base/dprintf.exp: 1st dprintf, fprintf
continue^M
Continuing.^M
No symbol "stderr" in current context.^M
(gdb) FAIL: gdb.base/dprintf.exp: 2nd dprintf, fprintf
---------------------- CUT ----------------------

The reason of the failure is because that 'stderr' in the newlib has the
following definition:

#ifndef _REENT_ONLY
#define stdin   (_REENT->_stdin)
#define stdout  (_REENT->_stdout)
#define stderr  (_REENT->_stderr)
#else /* _REENT_ONLY */
#define stdin   (_impure_ptr->_stdin)
#define stdout  (_impure_ptr->_stdout)
#define stderr  (_impure_ptr->_stderr)
#endif /* _REENT_ONLY */

while in the GNU/Linux env, there are 'stderr's defined as both the macro and
variable:

/* Standard streams.  */
extern struct _IO_FILE *stdin;          /* Standard input stream.  */
extern struct _IO_FILE *stdout;         /* Standard output stream.  */
extern struct _IO_FILE *stderr;         /* Standard error output stream.  */
#ifdef __STDC__
/* C89/C99 say they're macros.  Make them happy.  */
#define stdin stdin
#define stdout stdout
#define stderr stderr
#endif

This is probably why this test doesn't fail in GNU/Linux but newlib.  I think
we need a more robust way to test 'dprintf' with 'set dprintf-function fprintf'
and 'set dprintf-channel stderr'.  The C standard has specified that 'stderr'
is just a macro.

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