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diff --git a/Documentation/powerpc/elf_hwcaps.rst b/Documentation/powerpc/elf_hwcaps.rst new file mode 100644 index 000000000..3366e5b18 --- /dev/null +++ b/Documentation/powerpc/elf_hwcaps.rst @@ -0,0 +1,231 @@ +.. _elf_hwcaps_powerpc: + +================== +POWERPC ELF HWCAPs +================== + +This document describes the usage and semantics of the powerpc ELF HWCAPs. + + +1. Introduction +--------------- + +Some hardware or software features are only available on some CPU +implementations, and/or with certain kernel configurations, but have no other +discovery mechanism available to userspace code. The kernel exposes the +presence of these features to userspace through a set of flags called HWCAPs, +exposed in the auxiliary vector. + +Userspace software can test for features by acquiring the AT_HWCAP or +AT_HWCAP2 entry of the auxiliary vector, and testing whether the relevant +flags are set, e.g.:: + + bool floating_point_is_present(void) + { + unsigned long HWCAPs = getauxval(AT_HWCAP); + if (HWCAPs & PPC_FEATURE_HAS_FPU) + return true; + + return false; + } + +Where software relies on a feature described by a HWCAP, it should check the +relevant HWCAP flag to verify that the feature is present before attempting to +make use of the feature. + +HWCAP is the preferred method to test for the presence of a feature rather +than probing through other means, which may not be reliable or may cause +unpredictable behaviour. + +Software that targets a particular platform does not necessarily have to +test for required or implied features. For example if the program requires +FPU, VMX, VSX, it is not necessary to test those HWCAPs, and it may be +impossible to do so if the compiler generates code requiring those features. + +2. Facilities +------------- + +The Power ISA uses the term "facility" to describe a class of instructions, +registers, interrupts, etc. The presence or absence of a facility indicates +whether this class is available to be used, but the specifics depend on the +ISA version. For example, if the VSX facility is available, the VSX +instructions that can be used differ between the v3.0B and v3.1B ISA +versions. + +3. Categories +------------- + +The Power ISA before v3.0 uses the term "category" to describe certain +classes of instructions and operating modes which may be optional or +mutually exclusive, the exact meaning of the HWCAP flag may depend on +context, e.g., the presence of the BOOKE feature implies that the server +category is not implemented. + +4. HWCAP allocation +------------------- + +HWCAPs are allocated as described in Power Architecture 64-Bit ELF V2 ABI +Specification (which will be reflected in the kernel's uapi headers). + +5. The HWCAPs exposed in AT_HWCAP +--------------------------------- + +PPC_FEATURE_32 + 32-bit CPU + +PPC_FEATURE_64 + 64-bit CPU (userspace may be running in 32-bit mode). + +PPC_FEATURE_601_INSTR + The processor is PowerPC 601. + Unused in the kernel since f0ed73f3fa2c ("powerpc: Remove PowerPC 601") + +PPC_FEATURE_HAS_ALTIVEC + Vector (aka Altivec, VMX) facility is available. + +PPC_FEATURE_HAS_FPU + Floating point facility is available. + +PPC_FEATURE_HAS_MMU + Memory management unit is present and enabled. + +PPC_FEATURE_HAS_4xxMAC + The processor is 40x or 44x family. + +PPC_FEATURE_UNIFIED_CACHE + The processor has a unified L1 cache for instructions and data, as + found in NXP e200. + Unused in the kernel since 39c8bf2b3cc1 ("powerpc: Retire e200 core (mpc555x processor)") + +PPC_FEATURE_HAS_SPE + Signal Processing Engine facility is available. + +PPC_FEATURE_HAS_EFP_SINGLE + Embedded Floating Point single precision operations are available. + +PPC_FEATURE_HAS_EFP_DOUBLE + Embedded Floating Point double precision operations are available. + +PPC_FEATURE_NO_TB + The timebase facility (mftb instruction) is not available. + This is a 601 specific HWCAP, so if it is known that the processor + running is not a 601, via other HWCAPs or other means, it is not + required to test this bit before using the timebase. + Unused in the kernel since f0ed73f3fa2c ("powerpc: Remove PowerPC 601") + +PPC_FEATURE_POWER4 + The processor is POWER4 or PPC970/FX/MP. + POWER4 support dropped from the kernel since 471d7ff8b51b ("powerpc/64s: Remove POWER4 support") + +PPC_FEATURE_POWER5 + The processor is POWER5. + +PPC_FEATURE_POWER5_PLUS + The processor is POWER5+. + +PPC_FEATURE_CELL + The processor is Cell. + +PPC_FEATURE_BOOKE + The processor implements the embedded category ("BookE") architecture. + +PPC_FEATURE_SMT + The processor implements SMT. + +PPC_FEATURE_ICACHE_SNOOP + The processor icache is coherent with the dcache, and instruction storage + can be made consistent with data storage for the purpose of executing + instructions with the sequence (as described in, e.g., POWER9 Processor + User's Manual, 4.6.2.2 Instruction Cache Block Invalidate (icbi)):: + + sync + icbi (to any address) + isync + +PPC_FEATURE_ARCH_2_05 + The processor supports the v2.05 userlevel architecture. Processors + supporting later architectures DO NOT set this feature. + +PPC_FEATURE_PA6T + The processor is PA6T. + +PPC_FEATURE_HAS_DFP + DFP facility is available. + +PPC_FEATURE_POWER6_EXT + The processor is POWER6. + +PPC_FEATURE_ARCH_2_06 + The processor supports the v2.06 userlevel architecture. Processors + supporting later architectures also set this feature. + +PPC_FEATURE_HAS_VSX + VSX facility is available. + +PPC_FEATURE_PSERIES_PERFMON_COMPAT + The processor supports architected PMU events in the range 0xE0-0xFF. + +PPC_FEATURE_TRUE_LE + The processor supports true little-endian mode. + +PPC_FEATURE_PPC_LE + The processor supports "PowerPC Little-Endian", that uses address + munging to make storage access appear to be little-endian, but the + data is stored in a different format that is unsuitable to be + accessed by other agents not running in this mode. + +6. The HWCAPs exposed in AT_HWCAP2 +---------------------------------- + +PPC_FEATURE2_ARCH_2_07 + The processor supports the v2.07 userlevel architecture. Processors + supporting later architectures also set this feature. + +PPC_FEATURE2_HTM + Transactional Memory feature is available. + +PPC_FEATURE2_DSCR + DSCR facility is available. + +PPC_FEATURE2_EBB + EBB facility is available. + +PPC_FEATURE2_ISEL + isel instruction is available. This is superseded by ARCH_2_07 and + later. + +PPC_FEATURE2_TAR + TAR facility is available. + +PPC_FEATURE2_VEC_CRYPTO + v2.07 crypto instructions are available. + +PPC_FEATURE2_HTM_NOSC + System calls fail if called in a transactional state, see + Documentation/powerpc/syscall64-abi.rst + +PPC_FEATURE2_ARCH_3_00 + The processor supports the v3.0B / v3.0C userlevel architecture. Processors + supporting later architectures also set this feature. + +PPC_FEATURE2_HAS_IEEE128 + IEEE 128-bit binary floating point is supported with VSX + quad-precision instructions and data types. + +PPC_FEATURE2_DARN + darn instruction is available. + +PPC_FEATURE2_SCV + The scv 0 instruction may be used for system calls, see + Documentation/powerpc/syscall64-abi.rst. + +PPC_FEATURE2_HTM_NO_SUSPEND + A limited Transactional Memory facility that does not support suspend is + available, see Documentation/powerpc/transactional_memory.rst. + +PPC_FEATURE2_ARCH_3_1 + The processor supports the v3.1 userlevel architecture. Processors + supporting later architectures also set this feature. + +PPC_FEATURE2_MMA + MMA facility is available. |