Your message dated Wed, 26 Apr 2023 08:50:50 +0200
with message-id <[email protected]>
and subject line gcc-6 has been removed from Debian
has caused the Debian Bug report #860823,
regarding gcc-6: sqrt x64 intrinsic broken with -O3 and -ffast-math
to be marked as done.
This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.
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--
860823: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=860823
Debian Bug Tracking System
Contact [email protected] with problems
--- Begin Message ---
Package: gcc-6
Version: 6.3.0-12
Severity: normal
After being "hit" by unexplained division by 0 related crashes of an
application, the
following simple test code shows the issue:
****
#include <cmath>
#include <cstdlib>
void TestSqrt(const float *Src,float *Dest,size_t Size,float &Gain)
{
while (Size--)
{
float G,X;
G=sqrt(X=*Src++);
if (G)
{
Gain=Gain*0.9f+1/G*0.1f;
X*=Gain;
}
*Dest++=X;
}
}
****
The compile and listing generating where done using:
****
gcc -O3 -m64 -ffast-math -c -o sqrt.o sqrt.cpp
objdump -M intel -S -r -C sqrt.o > sqrt.lst
****
The "sqrt" coresponding piece of code looks like:
****
30: f3 0f 10 0c 87 movss xmm1,DWORD PTR [rdi+rax*4]
35: f3 0f 52 d1 rsqrtss xmm2,xmm1
39: 0f 28 c2 movaps xmm0,xmm2
3c: 0f 2f cb comiss xmm1,xmm3
3f: f3 0f 59 c1 mulss xmm0,xmm1
43: f3 0f 59 c2 mulss xmm0,xmm2
47: f3 0f 59 d4 mulss xmm2,xmm4
4b: f3 0f 58 c5 addss xmm0,xmm5
4f: f3 0f 59 c2 mulss xmm0,xmm2
53: 74 18 je 6d <TestSqrt(float const*, float*,
unsigned long, float&)+0x6d>
55: f3 0f 10 11 movss xmm2,DWORD PTR [rcx]
59: f3 0f 59 c6 mulss xmm0,xmm6
5d: f3 0f 59 d7 mulss xmm2,xmm7
61: f3 0f 58 c2 addss xmm0,xmm2
65: f3 0f 59 c8 mulss xmm1,xmm0
69: f3 0f 11 01 movss DWORD PTR [rcx],xmm0
6d: f3 0f 11 0c 86 movss DWORD PTR [rsi+rax*4],xmm1
72: 48 83 c0 01 add rax,0x1
76: 48 39 c2 cmp rdx,rax
79: 75 b5 jne 30 <TestSqrt(float const*, float*,
unsigned long, float&)+0x30>
****
The generated code is not handling in any way the case of 0 as input value. As
per Intel spec,
rsqrtss has an +/-INF result when the input is 0 and the final results of the
test code is
unpredictable, while 0 is a perfect valid input value for sqrt.
Regards,
Catalin
-- System Information:
Debian Release: 9.0
APT prefers testing
APT policy: (500, 'testing')
Architecture: amd64 (x86_64)
Kernel: Linux 4.9.0-2-amd64 (SMP w/2 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
Versions of packages gcc-6 depends on:
ii binutils 2.28-3
ii cpp-6 6.3.0-12
ii gcc-6-base 6.3.0-12
ii libc6 2.24-9
ii libcc1-0 6.3.0-12
ii libgcc-6-dev 6.3.0-12
ii libgcc1 1:6.3.0-12
ii libgmp10 2:6.1.2+dfsg-1
ii libisl15 0.18-1
ii libmpc3 1.0.3-1+b2
ii libmpfr4 3.1.5-1
ii libstdc++6 6.3.0-12
ii zlib1g 1:1.2.8.dfsg-5
Versions of packages gcc-6 recommends:
ii libc6-dev 2.24-9
Versions of packages gcc-6 suggests:
pn gcc-6-doc <none>
pn gcc-6-locales <none>
pn gcc-6-multilib <none>
pn libasan3-dbg <none>
pn libatomic1-dbg <none>
pn libcilkrts5-dbg <none>
pn libgcc1-dbg <none>
pn libgomp1-dbg <none>
pn libitm1-dbg <none>
pn liblsan0-dbg <none>
pn libmpx2-dbg <none>
pn libquadmath0-dbg <none>
pn libtsan0-dbg <none>
pn libubsan0-dbg <none>
-- no debconf information
--- End Message ---
--- Begin Message ---
Version: 6.5.0-2+rm
src:gcc-6 was last released with Debian 9 (stretch)
in June 2017 and was removed from the Debian archive afterwards.
It has been superseded by newer versions.
See https://bugs.debian.org/920171 for details on the removal.
After regular security support for stretch ended in July 2020 and LTS
support ended in July 2022, I'm closing the remaining bug reports now.
In case the bug is still present in recent releases, please reopen and
reassign it.
Andreas
--- End Message ---
