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std: One more cpuid fix 

Don't read from stale eax value, rework the logic a bit so that's clear
what's going on.
master
LemonBoy 2020-03-08 10:55:00 +01:00 committed by Andrew Kelley
parent 9e60c89601
commit 2b1316954f
1 changed files with 19 additions and 7 deletions
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26
lib/std/zig/system/x86.zig
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@ -2,6 +2,12 @@ const std = @import("std");
const Target = std.Target;
const CrossTarget = std.zig.CrossTarget;
const XCR0_XMM = 0x02;
const XCR0_YMM = 0x04;
const XCR0_MASKREG = 0x20;
const XCR0_ZMM0_15 = 0x40;
const XCR0_ZMM16_31 = 0x80;
fn setFeature(cpu: *Target.Cpu, feature: Target.x86.Feature, enabled: bool) void {
const idx = @as(Target.Cpu.Feature.Set.Index, @enumToInt(feature));
@ -12,6 +18,10 @@ inline fn bit(input: u32, offset: u5) bool {
return (input >> offset) & 1 != 0;
}
inline fn hasMask(input: u32, mask: u32) bool {
return (input & mask) == mask;
}
pub fn detectNativeCpuAndFeatures(arch: Target.Cpu.Arch, os: Target.Os, cross_target: CrossTarget) Target.Cpu {
var cpu = Target.Cpu{
.arch = arch,
@ -309,7 +319,6 @@ fn detectNativeFeatures(cpu: *Target.Cpu, os_tag: Target.Os.Tag) void {
leaf = cpuid(1, 0);
setFeature(cpu, .cx8, bit(leaf.edx, 8));
setFeature(cpu, .cx8, bit(leaf.edx, 8));
setFeature(cpu, .cmov, bit(leaf.edx, 15));
setFeature(cpu, .mmx, bit(leaf.edx, 23));
@ -327,11 +336,13 @@ fn detectNativeFeatures(cpu: *Target.Cpu, os_tag: Target.Os.Tag) void {
setFeature(cpu, .aes, bit(leaf.ecx, 25));
setFeature(cpu, .rdrnd, bit(leaf.ecx, 30));
// If the CPU supports XSAVE/XRESTORE (bit 27) and AVX (bit 28) also check
// if the AVX registers are saved & restored on context switch
const has_avx_save = bit(leaf.ecx, 27) and
bit(leaf.ecx, 28) and
((getXCR0() & 0x6) == 0x6);
const has_xsave = bit(leaf.ecx, 27);
const has_avx = bit(leaf.ecx, 28);
// Make sure not to call xgetbv if xsave is not supported
const xcr0_eax = if (has_xsave and has_avx) getXCR0() else 0;
const has_avx_save = hasMask(xcr0_eax, XCR0_XMM | XCR0_YMM);
// LLVM approaches avx512_save by hardcoding it to true on Darwin,
// because the kernel saves the context even if the bit is not set.
@ -355,7 +366,7 @@ fn detectNativeFeatures(cpu: *Target.Cpu, os_tag: Target.Os.Tag) void {
// set right now.
const has_avx512_save = switch (os_tag.isDarwin()) {
true => true,
false => has_avx_save and ((leaf.eax & 0xE0) == 0xE0),
false => hasMask(xcr0_eax, XCR0_MASKREG | XCR0_ZMM0_15 | XCR0_ZMM16_31),
};
setFeature(cpu, .avx, has_avx_save);
@ -530,6 +541,7 @@ fn cpuid(leaf_id: u32, subid: u32) CpuidLeaf {
[leaf_ptr] "r" (&cpuid_leaf)
: "eax", "ebx", "ecx", "edx"
);
return cpuid_leaf;
}