Update Ubuntu (and therefore Qemu) Version #557
Description
Currently, on images provided by cross v0.2.1, we get the following after loading into the image:
Cross Information:
$ cross --version
cross 0.2.1
cargo 1.51.0 (43b129a20 2021-03-16)Image Information
$ $ docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
rustembedded/cross powerpc-unknown-linux-gnu-0.2.1 e18a73ede16f 10 months ago 752MB
$ docker run -it e18a73ede16f /bin/bash
# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 16.04.6 LTS
Release: 16.04
Codename: xenial
# qemu-img --version
qemu-img version 3.0.1
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developersThe latest LTS version for Ubuntu is 20.04, which has newer versions of important dependencies, such as Qemu.
$ docker run -it ubuntu:20.04 /bin/bash
# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 20.04.2 LTS
Release: 20.04
Codename: focal
# qemu-img --version
qemu-img version 4.2.1 (Debian 1:4.2-3ubuntu6.16)
Copyright (c) 2003-2019 Fabrice Bellard and the QEMU Project developersIssue
This actually matters, as numerous bugs, such as for float-point emulation, have been fixed in newer Qemu versions:
In addition, here's a sample code snippet that fails on Qemu 3.0.1 but works on Qemu 4.2.1:
#include <inttypes.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>
double dn1() {
double num = 1303.0;
double den = 1e-20;
return num * den;
}
double dn2() {
double num = 1303.0;
double den = 1e20;
return num / den;
}
float fn1() {
float num = 1303.0;
float den = 1e-20;
return num * den;
}
float fn2() {
float num = 1303.0;
float den = 1e20;
return num / den;
}
int main() {
float f = fn1();
uint32_t bf;
memcpy(&bf, &f, 8);
printf("%u\n", bf);
f = fn2();
memcpy(&bf, &f, 8);
printf("%u\n", bf);
double d = dn1();
uint64_t bd;
memcpy(&bd, &d, 8);
printf("%" PRIu64 "\n", bd);
d = dn2();
memcpy(&bd, &d, 8);
printf("%" PRIu64 "\n", bd);
return 0;
}If we run the above using Qemu 3.0.1, we get:
# qemu-ppc --version
qemu-ppc version 3.0.1
Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers
# qemu-ppc ./main-ppc
594566255
594566255
4354430593920867240
4354430593920867241If we run the above using Qemu 4.2.1, we get:
# qemu-ppc --version
qemu-ppc version 4.2.1 (qemu-4.2.1-1.fc32)
Copyright (c) 2003-2019 Fabrice Bellard and the QEMU Project developers
# qemu-ppc ./main-ppc
594566255
594566255
4354430593920867240
4354430593920867240In short, we have a rounding error of 1 ULP due to cross using outdated Ubuntu (and therefore Qemu) versions. Ideally, we'd use version 6.0.1 or v5.0.0 (the latter requiring the following PPA, the former requiring compiling from source).