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id = 2462
title = "QEMU SIFIVE reading from stdin hangs"
state = "closed"
created_at = "2024-07-27T13:19:31.620Z"
closed_at = "2024-08-13T02:30:02.602Z"
labels = ["target: riscv"]
url = "https://gitlab.com/qemu-project/qemu/-/issues/2462"
host-os = "Ubuntu23"
host-arch = "x86"
qemu-version = "git from july26, 2024"
guest-os = "n/a"
guest-arch = "n/a"
description = """I have a simple test program (C and ASM) that reads from stdin. When i was using the qemu provided by Ubuntu, QEMU emulator version 8.0.4 (Debian 1:8.0.4+dfsg-1ubuntu3.23.10.5), my test was working, and was able to read bytes from stdin.
Using the latest Qemu from git, breaks my test. I can still print, but now reading hangs, like its always waiting for input but never getting it.
My guess is that this commit breaks my code:
https://github.com/qemu/qemu/commit/6ee7ba1b8a10bd8eb1d3b918eaaf9f832a51adb4
Before the above commit, `qemu_chr_fe_set_handlers` was being called, and that is what allowed the default behavior of reading from stdin is on by default?
from sifive_uart.c
```
qemu_chr_fe_set_handlers(&s->chr, sifive_uart_can_rx, sifive_uart_rx,
sifive_uart_event, sifive_uart_be_change, s,
NULL, true);
```"""
reproduce = """1. compile simple C program that calls `read` reading a single byte from stdin
2. do not initialize UART options
3. run in QEMU, send input, hangs."""
additional = """Other examples online, like riscv-probe, use a uart init function like below:
```
static void sifive_uart_init()
{
uart = (int *)(void *)getauxval(SIFIVE_UART0_CTRL_ADDR);
uint32_t uart_freq = getauxval(UART0_CLOCK_FREQ);
uint32_t baud_rate = getauxval(UART0_BAUD_RATE);
uint32_t divisor = uart_freq / baud_rate - 1;
uart[UART_REG_DIV] = divisor;
uart[UART_REG_TXCTRL] = UART_TXEN;
uart[UART_REG_RXCTRL] = UART_RXEN;
uart[UART_REG_IE] = 0;
}
```
However, when I was using QEMU 8.0.4, i did not have to write a function like above to init UART, because stdin and stdout were working out of the box.
Below is my C and ASM:"""
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