[Qemu-devel] ARM/system mode/stdin

[Qemu-devel] ARM/system mode/stdin

[Christophe LYON]

Hello,

I am trying to use qemu-system-arm (0.12.3) to execute an ARM bare 
machine program (not a Linux kernel), and I have some trouble when the 
program in question tries to read from stdin.

The program does use ARM semihosting to communicate with the host.

Here is the sample code:
======================
#include <stdio.h>
int main() {
   int i, j;
   char tab[81];
   printf("enter a number\n");
   scanf("%d", &i);
   printf("enter a string (max: 80 char)\n");
   scanf("%80s", tab);
   printf("enter a number\n");
   scanf("%d", &j);

   printf("You entered:\n%d\n%s\n%d\n", i, tab, j);

   return 0;
}
=======================
(compiled with arm-none-eabi-gcc -O0 -mcpu=cortex-a9)

To execute it, I use:
$ qemu-system-arm -semihosting -cpu cortex-a9 -nographic -kernel ./input.exe
In this case, it does not wait for me to type something:
enter a number
enter a string (max: 80 char)
enter a number
You entered:
134217720

1

Now, if
$ cat data
4 hello 5
$ qemu-system-arm -semihosting -cpu cortex-a9 -nographic -kernel 
./input.exe < data
enter a number
enter a string (max: 80 char)
enter a number
You entered:
134217720
ello
5

as you can see, the first 3 chars of 'data' have been changed/swallowed.

If I remove
     fcntl(0, F_SETFL, O_NONBLOCK);
from term_init() (qemu-char.c), then I get expected behaviour when I 
don't redirect stdin, but this has no effect on the latter case.


What should I do/patch to achieve the behaviour I'd like?

Thanks!

Christophe.

Re: [Qemu-devel] ARM/system mode/stdin

[Christophe LYON]

Hi all,

After more investigation, I am wondering whether there is a conflict 
between 2 entities reading for stdin:
- one is initialized by qemu_chr_open_stdio() (in qemu-char.c)
- the 2nd one is the handling of SYS_READ in arm-semi.c

After some debug/tracing, I have noticed that a few chars a swallowed 
from stdin by calls to stdio_read() because the stdin FD is monitored by 
the select() call in main_loop_wait().

This seems to be in conflict with the ARM semihosting support for 
SYS_READ which also tries to read FD 0.

If I remove the call to
      qemu_set_fd_handler2(0, stdio_read_poll, stdio_read, NULL, chr);
in qemu_chr_open_stdio() then my sample test works, but I wonder what I 
might have broken?

Thanks and best regards,

Christophe.

Re: [Qemu-devel] ARM/system mode/stdin

[Paul Brook]

> $ qemu-system-arm -semihosting -cpu cortex-a9 -nographic -kernel
> ./input.exe

-nographic implies -monitor stdio -serial stdio. Don't do that if you want to 
access stdio via semihosting.

Paul

Re: [Qemu-devel] ARM/system mode/stdin

[Christophe LYON]

On 18.06.2010 18:52, Paul Brook wrote:
>> $ qemu-system-arm -semihosting -cpu cortex-a9 -nographic -kernel
>> ./input.exe
>
> -nographic implies -monitor stdio -serial stdio. Don't do that if you want to
> access stdio via semihosting.
>

Indeed, using either
-monitor null -serial none -nographic
or
-monitor vc -serial vc -nographic -kernel

achieves what I want. (probably other values too, not sure which is optimal)

Thanks!

Christophe.