On Sun, Jun 4, 2023 at 6:15 AM Lorenzo <plore...@disroot.org> wrote: > > On Sat, 03 Jun 2023 12:14:47 +0200 > John Paul Adrian Glaubitz <glaub...@physik.fu-berlin.de> wrote: > > > Hello! > > > > On Sat, 2023-06-03 at 11:29 +0200, Lorenzo wrote: > > > There is a bug in mplayer [1] that could be fixed by building a > > > variant of mplayer without altivec, however I can't tell if such > > > bug can still be triggered nowadays. The ppc port is gone right? > > > Are cpus without altivec still usable on one of Debian's powerpc > > > ports? > > > > No, Debian for 32-bit PowerPC is still maintained as an unofficial > > port: > > > > > https://cdimage.debian.org/cdimage/ports/snapshots/2023-05-28/debian-12.0.0-powerpc-NETINST-1.iso > > > > As for Altivec support in mplayer: Have you tried the latest version? > > It might be possible there is proper runtime detection these days. > > According to mplayer upstream [1] "AltiVec runtime detection never > worked reliably" and "the way it was detected in libavcodec was an > unacceptable hack".. that was in back in 2007, I'll check if upstream > still consider runtime detection unfeasible. > > [...] > > [1]https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=448105
Altivec detection on Linux is relatively easy nowadays using getauxval(). From https://github.com/weidai11/cryptopp/blob/master/cpu.cpp#L1210 : inline bool CPU_QueryAltivec() { #if defined(__linux__) && defined(PPC_FEATURE_HAS_ALTIVEC) if ((getauxval(AT_HWCAP) & PPC_FEATURE_HAS_ALTIVEC) != 0) return true; #elif defined(_AIX) if (__power_6_andup() != 0) return true; #elif ... #endif return false; } Botan uses similar runtime detection via getauxval() at https://github.com/randombit/botan/blob/master/src/lib/utils/cpuid/cpuid_ppc.cpp. OpenSSL performs runtime probes in https://github.com/openssl/openssl/blob/master/crypto/ppccap.c. But instead of using a query via getauxval(), OpenSSL does a runtime probe by executing an Altivec instruction. If a SIGILL is encountered, then Altivec is false. The tricky machines are Apple running MacOS 9 and OS X. You have to be careful of runtime probes and SIGILLs. On Apple machines, memory corruption happens with runtime CPU probes. Jeff
