[Mingw-users] [GDB] v6.0 and program's I/O

[Manu <ma...@wa...>]

I've noticed a different behavior between MinGW's GDB 5.2.1
and GDB 6.0 when running a console program.

The 5.2.1 creates a console window, the program's output goes to
that console, which seems correct.
The 6.0 doesn't show a console, worse, the program's output doesn't
show up at the right time, but just before the program exits.

0/ Sample program:
--------------------
/********************************************************
* A simple Hello World.
*
* The stdio header declares standard input/output routines like printf.
* The main() procedure is the program entry point.
*
********************************************************/
#include <stdio.h>

int main(){
 /* Writes a string in the DOS box. */
 printf("Hello world !");
 return 0; /* Program termination. */
}


1/ Sample session with gdb 5.2.1:
----------------------------------
Manu@TBIRD1000 /c/Dev/Visual-MinGW/Projects/Samples/Console/Hello
$ gdb50201 -nw -q -f "C:\Dev\Visual-MinGW\Projects\Samples\Console\Hello\hello.
exe"
(gdb) b main.c:11
Breakpoint 1 at 0x4012fc: file main.c, line 11.
(gdb) run
Starting program: C:\Dev\Visual-MinGW\Projects\Samples\Console\Hello\hello.exe 

Breakpoint 1, main () at main.c:12
C:/Dev/Visual-MinGW/Projects/Samples/Console/Hello/main.c:12:349:beg:0x4012fc

(gdb) info terminal
Inferior's terminal status (currently saved by GDB):
File descriptor flags = O_RDONLY
^^^^^^ GDB has saved a terminal info.

(gdb) s
^^^^^^ The "Hello world!" outputs in the console window, which is correct.

C:/Dev/Visual-MinGW/Projects/Samples/Console/Hello/main.c:13:376:beg:0x40130c
(gdb) s
C:/Dev/Visual-MinGW/Projects/Samples/Console/Hello/main.c:14:415:beg:0x401311
(gdb) s
0x0040122d in __mingw_CRTStartup ()
(gdb) s
Single stepping until exit from function __mingw_CRTStartup, 
which has no line number information.

Program exited normally.
(gdb) q


2/ Sample session with gdb 6.0:
----------------------------------
Manu@TBIRD1000 /c/Dev/Visual-MinGW/Projects/Samples/Console/Hello
$ gdb -nw -q -f "C:\Dev\Visual-MinGW\Projects\Samples\Console\Hello\hello.exe"
(gdb) b main.c:11
Breakpoint 1 at 0x4012fc: file main.c, line 11.
(gdb) run
Starting program: C:\Dev\Visual-MinGW\Projects\Samples\Console\Hello\hello.exe 

Breakpoint 1, main () at main.c:12
C:/Dev/Visual-MinGW/Projects/Samples/Console/Hello/main.c:12:349:beg:0x4012fc

(gdb) info terminal
This GDB does not control a terminal.
^^^^^^ well, well well.

(gdb) s
^^^^^^ nothing outputs after the printf() at line 12.

C:/Dev/Visual-MinGW/Projects/Samples/Console/Hello/main.c:13:376:beg:0x40130c
(gdb) s
C:/Dev/Visual-MinGW/Projects/Samples/Console/Hello/main.c:14:415:beg:0x401311
(gdb) s
0x0040122d in __mingw_CRTStartup ()
(gdb) s
Single stepping until exit from function __mingw_CRTStartup, 
which has no line number information.

Hello world !
^^^^^^ Thanks, but a bit too late!!!

Program exited normally.
(gdb) q


The same behavior is observed within MSYS and Visual-MinGW.
(redirected GDB I/O)

Any information about the way GDB is supposed to process
programs' I/O is greatly welcome.
Thanks.

Manu.