On Sat, 12 Mar 2016, Piotr Henryk Dabrowski wrote: > Currently there is no way of disabling CPU features reported by the CPUID > instruction. Which sometimes turn out to be broken [1] or undesired [2]. ... > * The kernel takes a command line parameter (cpu-=...) allowing for an easy way > to disable any of the known CPUID capability bits [3]. Plus the kernel may > disable certain features by itself as well. > * Then the kernel provides a system call for obtaining the adjusted data [4] > (SYS_cpuid, to be used instead of the __cpuid* macros from GCC's cpuid.h). Wouldn't it be better to (finally) extend the AT_HWCAP ELF stuff properly on x86 for the missing cpuid levels? Basically, get every cpuid leaf that contributes to the /proc/cpuinfo "flags" field into new AT_HWCAPx ELF fields? Some arches already have AT_HWCAP2, for example. x86 would need more than just AT_HWCAP2, though. https://lwn.net/Articles/519085/ http://man7.org/linux/man-pages/man3/getauxval.3.html AT_HWCAP is not only useful for LDSO tricks to load flag-optimized versions of libraries, it is directly accessible to the process, so it could also be used as an alternate source of cpuid() information that the kernel can modify through quirks. > Since the cpuid instruction is available from the user-space, use of SYS_cpuid > cannot be enforced on programmers. But it can be encouraged. And having a Indeed. Well, we already have it, but it is stuck in the past and gathering cowebs. -- "One disk to rule them all, One disk to find them. One disk to bring them all and in the darkness grind them. In the Land of Redmond where the shadows lie." -- The Silicon Valley Tarot Henrique Holschuh -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
