Date: Fri, 4 Apr 2014 18:50:18 -0400 From: Morten Welinder <mwelinder@...il.com> To: musl@...ts.openwall.com Subject: Re: printf issues > Were you able to determine what data it clobbers (in practice; > obviously this is compiler-specific) and whether the clobber > has any observable effects? It clobbers uninitialized parts of "big". If you add for (i = 0; i < sizeof(big)/sizeof(big); i++) big[i] = 12345678; then it will consistently print "1.23E+16" which is a bit off, :-) If you instead initialize like this: for (i = 0; i < sizeof(big)/sizeof(big); i++) big[i] = 999999999; then I get "1E+15939" which is fairly impressive. Also, in this case it will clobber whatever happened to come before "big". Morten On Fri, Apr 4, 2014 at 5:08 PM, Rich Felker <dalias@...ifal.cx> wrote: > On Fri, Apr 04, 2014 at 04:22:46PM -0400, Morten Welinder wrote: >> Another printf issue has shown up, this time with memory corruption. >> >> printf ("%.3E\n", 999999999.0); >> >> The rounding test correctly decides that it needs to round this value >> up to 1E+09. It is, however, utterly unprepared for having nowhere to >> put the carry. It happily accesses and changes one or more elements >> before the one that held 999999999. > > I suspect this may be true; if so, it's a very nice catch. Were you > able to determine what data it clobbers (in practice; obviously this > is compiler-specific) and whether the clobber has any observable > effects? > > Rich
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