[Qemu-devel] [Bug 1821444] Re: qemu-ppc (user) incorrectly translates float32 arithmetics

[Sergei Trofimovich]

My native system is x86_64-pc-linux-gnu with a few binfmt_misc handlers wired.
Checking other targets I have locally I get the following:

affected targets:
- powerpc
- powerpc64
- powerpc64le
unaffected targets:
- arm
- arm64
- hppa
- sparc
probably unaffected:
- alpha (maybe it's ok as alpha is not quite an IEEE754 platform)

Raw log:

$ for gcc in /usr/bin/*-gcc; do rm -f a; $gcc -O2 a.c -Wall -o a -fno-
strict-aliasing -fno-stack-protector 2>/dev/null && ./a 2>/dev/null &&
echo -n "$gcc: " && file a; done | sort

0x1 = 1.401298e-45 : /usr/bin/aarch64-unknown-linux-gnu-gcc: a: ELF 64-bit LSB 
pie executable, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter 
/lib/ld-linux-aarch64.so.1, for GNU/Linux 3.7.0, not stripped
0x1 = 1.401298e-45 : /usr/bin/aarch64_be-unknown-linux-gnu-gcc: a: ELF 64-bit 
MSB pie executable, ARM aarch64, version 1 (SYSV), dynamically linked, 
interpreter /lib/ld-linux-aarch64_be.so.1, for GNU/Linux 3.7.0, not stripped
0x1 = 1.401298e-45 : /usr/bin/afl-gcc: a: ELF 64-bit LSB pie executable, 
x86-64, version 1 (SYSV), dynamically linked, interpreter 
/lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, with debug_info, not stripped
0x1 = 1.401298e-45 : /usr/bin/armv6j-unknown-linux-gnueabihf-gcc: a: ELF 32-bit 
LSB pie executable, ARM, EABI5 version 1 (SYSV), dynamically linked, 
interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 3.2.0, not stripped
0x1 = 1.401298e-45 : /usr/bin/armv7a-unknown-linux-gnueabihf-gcc: a: ELF 32-bit 
LSB pie executable, ARM, EABI5 version 1 (SYSV), dynamically linked, 
interpreter /lib/ld-linux-armhf.so.3, for GNU/Linux 3.2.0, not stripped
0x1 = 1.401298e-45 : /usr/bin/hppa-unknown-linux-gnu-gcc: a: ELF 32-bit MSB pie 
executable, PA-RISC, 1.1 version 1 (GNU/Linux), dynamically linked, interpreter 
/lib/ld.so.1, for GNU/Linux 3.2.0, with debug_info, not stripped
0x1 = 1.401298e-45 : /usr/bin/hppa2.0-unknown-linux-gnu-gcc: a: ELF 32-bit MSB 
pie executable, PA-RISC, 1.1 version 1 (GNU/Linux), dynamically linked, 
interpreter /lib/ld.so.1, for GNU/Linux 3.2.0, with debug_info, not stripped
0x1 = 1.401298e-45 : /usr/bin/m68k-unknown-linux-gnu-gcc: a: ELF 32-bit MSB pie 
executable, Motorola m68k, 68020, version 1 (SYSV), dynamically linked, 
interpreter /lib/ld.so.1, for GNU/Linux 3.2.0, not stripped
0x1 = 1.401298e-45 : /usr/bin/mips64-unknown-linux-gnuabin64-gcc: a: ELF 64-bit 
MSB pie executable, MIPS, MIPS-III version 1 (SYSV), dynamically linked, 
interpreter /lib64/ld.so.1, for GNU/Linux 3.2.0, not stripped
0x1 = 1.401298e-45 : /usr/bin/riscv64-unknown-linux-gnu-gcc: a: ELF 64-bit LSB 
pie executable, UCB RISC-V, version 1 (SYSV), dynamically linked, interpreter 
/lib/ld-linux-riscv64-lp64d.so.1, for GNU/Linux 4.15.0, not stripped
0x1 = 1.401298e-45 : /usr/bin/s390x-unknown-linux-gnu-gcc: a: ELF 64-bit MSB 
pie executable, IBM S/390, version 1 (SYSV), dynamically linked, interpreter 
/lib/ld64.so.1, for GNU/Linux 3.2.0, not stripped
0x1 = 1.401298e-45 : /usr/bin/sparc-unknown-linux-gnu-gcc: a: ELF 32-bit MSB 
pie executable, SPARC32PLUS, V8+ Required, total store ordering, version 1 
(SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 
3.2.0, not stripped
0x1 = 1.401298e-45 : /usr/bin/x86_64-HEAD-linux-gnu-gcc: a: ELF 64-bit LSB pie 
executable, x86-64, version 1 (SYSV), dynamically linked, interpreter 
/lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, not stripped
0x1 = 1.401298e-45 : /usr/bin/x86_64-UNREG-linux-gnu-gcc: a: ELF 64-bit LSB pie 
executable, x86-64, version 1 (SYSV), dynamically linked, interpreter 
/lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, not stripped
0x1 = 1.401298e-45 : /usr/bin/x86_64-pc-linux-gnu-gcc: a: ELF 64-bit LSB pie 
executable, x86-64, version 1 (SYSV), dynamically linked, interpreter 
/lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, with debug_info, not stripped

0x1 = 2.652494e-315 : /usr/bin/alpha-unknown-linux-gnu-gcc: a: ELF
64-bit LSB pie executable, Alpha (unofficial), version 1 (SYSV),
dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 3.2.0,
not stripped

0x1 = 2.802597e-45 : /usr/bin/powerpc-unknown-linux-gnu-gcc: a: ELF 32-bit MSB 
pie executable, PowerPC or cisco 4500, version 1 (SYSV), dynamically linked, 
interpreter /lib/ld.so.1, for GNU/Linux 3.2.0, not stripped
0x1 = 2.802597e-45 : /usr/bin/powerpc64-unknown-linux-gnu-gcc: a: ELF 64-bit 
MSB pie executable, 64-bit PowerPC or cisco 7500, version 1 (SYSV), dynamically 
linked, interpreter /lib64/ld64.so.1, for GNU/Linux 3.2.0, not stripped
0x1 = 2.802597e-45 : /usr/bin/powerpc64le-unknown-linux-gnu-gcc: a: ELF 64-bit 
LSB pie executable, 64-bit PowerPC or cisco 7500, version 1 (SYSV), dynamically 
linked, interpreter /lib64/ld64.so.2, for GNU/Linux 3.10.0, not stripped

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1821444

Title:
  qemu-ppc (user) incorrectly translates float32 arithmetics

Status in QEMU:
  New

Bug description:
  I'm using qemu-3.1.0 (Gentoo).

  When I was running regression test suite via qemu-ppc for GHC I
  noticed a few uint32_t<->float32 failures I did not expect to
  encounter.

  Here is an example

  $ cat a.c
  #include <stdio.h>
  #include <stdint.h>

  int main() {
      volatile uint32_t i = 1;
      printf("0x1 = %e\n", *(volatile float*)&i);
  }

  $ powerpc-unknown-linux-gnu-gcc -O2 a.c -Wall -o a -fno-strict-aliasing 
-fno-stack-protector -static && ./a
  0x1 = 2.802597e-45

  $ scp a timberdoodle.ppc64.dev.gentoo.org:~/
  a                                                                             
                          100%  826KB 102.0KB/s   00:08    

  $ ssh timberdoodle.ppc64.dev.gentoo.org ./a
  0x1 = 1.401298e-45
  $ qemu-ppc ./a
  0x1 = 2.802597e-45

  Looks like off-by-one bit somewhere. I'm not sure if it's FPU
  instruction or some internals of printf() that are emulated
  incorrectly.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1821444/+subscriptions