[Bug libstdc++/57920] [c++11] Linux: std::random_device reads too much from /dev/urandom
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57920 Florian Philipp gnu at binarywings dot net changed: What|Removed |Added CC||gnu at binarywings dot net --- Comment #9 from Florian Philipp gnu at binarywings dot net --- Created attachment 32110 -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=32110action=edit Patch without POSIX I/O I find the original patch as applied to mainline unnecessarily complicated. You can achieve the same just with std I/O by deactivating buffering with std::setbuf. Basically a one line change when applied to the original version.
[Bug libstdc++/57920] [c++11] Linux: std::random_device reads too much from /dev/urandom
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57920 --- Comment #5 from Frank Heckenbach f.heckenb...@fh-soft.de --- (In reply to Paolo Carlini from comment #1) Note that in 4.8.x and mainline for modern x86 and x86_64 targets we don't use /dev/urandom at all, we use __x86_rdrand. In general, the idea is that more targets should use hardware support for random numbers and /dev/urandom become just a fall back. I'm not sure changing fread to read it's worth the trouble, and the change, since we are not talking about a regression, would not go in 4.7.x branch anyway. Are you on x86 / x86_64 or something else? I use an AMD (Thuban) in 32 bit mode. This processor core is ~3 years old and AFAICS it doesn't support rdrand. So even if newer AMDs do supports it (which I don't know), I guess it's fair to say that for some more years there will be processors around which don't, and in this case I assume gcc falls back to /dev/urandom.
[Bug libstdc++/57920] [c++11] Linux: std::random_device reads too much from /dev/urandom
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57920 --- Comment #6 from Frank Heckenbach f.heckenb...@fh-soft.de --- (In reply to Paolo Carlini from comment #3) I'm going to attach a patchlet which does the trick (fread - read) for me. Note I'm on purpose disabling the use of __builtin_ia32_rdrand32_step on my x86_64 machine, the undef would not be in the committed patch of course. It would be great if you could test the change on your machines (in 4.7.x just change random.h, no need to rebuild) and confirm that everything is fine. I did the equivalent change to /usr/include/c++/4.7/bits/random.h and it works for me, thanks.
[Bug libstdc++/57920] [c++11] Linux: std::random_device reads too much from /dev/urandom
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57920 --- Comment #7 from Paolo Carlini paolo.carlini at oracle dot com --- Agreed, let's just commit the improvement. If/when you become aware of ways to extend the use of builtins to other CPUs / targets, please let me know, thanks.
[Bug libstdc++/57920] [c++11] Linux: std::random_device reads too much from /dev/urandom
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57920 Paolo Carlini paolo.carlini at oracle dot com changed: What|Removed |Added Status|ASSIGNED|RESOLVED Resolution|--- |FIXED Target Milestone|--- |4.9.0 --- Comment #8 from Paolo Carlini paolo.carlini at oracle dot com --- Done.
[Bug libstdc++/57920] [c++11] Linux: std::random_device reads too much from /dev/urandom
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57920 --- Comment #1 from Paolo Carlini paolo.carlini at oracle dot com --- Note that in 4.8.x and mainline for modern x86 and x86_64 targets we don't use /dev/urandom at all, we use __x86_rdrand. In general, the idea is that more targets should use hardware support for random numbers and /dev/urandom become just a fall back. I'm not sure changing fread to read it's worth the trouble, and the change, since we are not talking about a regression, would not go in 4.7.x branch anyway. Are you on x86 / x86_64 or something else?
[Bug libstdc++/57920] [c++11] Linux: std::random_device reads too much from /dev/urandom
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57920 --- Comment #2 from Paolo Carlini paolo.carlini at oracle dot com --- I mean we use __builtin_ia32_rdrand32_step ;)
[Bug libstdc++/57920] [c++11] Linux: std::random_device reads too much from /dev/urandom
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57920 Paolo Carlini paolo.carlini at oracle dot com changed: What|Removed |Added Status|UNCONFIRMED |ASSIGNED Last reconfirmed||2013-07-21 Assignee|unassigned at gcc dot gnu.org |paolo.carlini at oracle dot com Ever confirmed|0 |1 --- Comment #3 from Paolo Carlini paolo.carlini at oracle dot com --- I'm going to attach a patchlet which does the trick (fread - read) for me. Note I'm on purpose disabling the use of __builtin_ia32_rdrand32_step on my x86_64 machine, the undef would not be in the committed patch of course. It would be great if you could test the change on your machines (in 4.7.x just change random.h, no need to rebuild) and confirm that everything is fine.
[Bug libstdc++/57920] [c++11] Linux: std::random_device reads too much from /dev/urandom
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57920 --- Comment #4 from Paolo Carlini paolo.carlini at oracle dot com --- Created attachment 30534 -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=30534action=edit Draft mainline patch
