EOF is not detected, when semihosting is reading from stdin

Host environment

• Operating system: Ubuntu 22.04.3 LTS
• OS/kernel version: Linux 6.2.0-34-generic #34~22.04.1-Ubuntu
• Architecture: x86_64
• QEMU flavor: qemu-system-arm
• QEMU version: 8.1.50 (v8.1.0-2161-ga9526048)
• QEMU command line:

  echo -n 1234 | ~/local/qemu/git/bin/qemu-system-arm -M mps2-an385 -cpu cortex-m3 -chardev stdio,mux=on,id=stdio0 -semihosting-config enable=on,chardev=stdio0 -monitor none -serial none -nographic -device loader,file=test-stdin,cpu-num=0

Emulated/Virtualized environment

• Operating system: bare metal
• OS/kernel version: bare metal
• Architecture: arm

Description of problem

QEMU hangs.

Steps to reproduce

1. Run the program with stdin from a pipe.

Additional information

The code is compiled from this source:

#include <stdio.h>

int main(int argc, char** argv) {
    int i = -1;
    int result = scanf("%d", &i);
    printf("result = %d, i = %d\n", result, i);
    return 0;
}

compiled with GCC and picolibc:

arm-none-eabi-gcc --specs=picolibc.specs -march=armv7-m ~/sources/picolibc/git/test-stdin.c -o test-stdin -lc -lsemihost --crt0=hosted -O0 -g

test-stdin The execution hangs at semihosting SYS_READC(0x7) call:

	movs r0, #7
(...)
	bkpt #0xab