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Fix a getauxval comment and expand the Krait idiv workaround (#206)

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* Fix getauxval comment (API 18 not 20)

getauxval is available in Android starting with API 18, not 20.

The comment about __ANDROID_API__ appears to have been copied from the
NDK's cpufeatures, which always uses dlopen/dlsym and doesn't assume it
can directly call getauxval, even if __ANDROID_API__ is new enough.
With this project, though, when __ANDROID_API__ is 18 or up, the
CMakeLists.txt file would detect that getauxval is available and define
HAVE_STRONG_GETAUXVAL.

* Broaden Qualcomm Krait idiv workaround

Some Qualcomm Krait CPUs have IDIV support but the kernel doesn't
report it. Previously, this code looked for two CPUs:
 - 0x510006F2 (0x51/'Q', variant 0, part 0x06f, rev 2)
 - 0x510006F3 (0x51/'Q', variant 0, part 0x06f, rev 3)

This check misses my 2013 Nexus 7 device, which has this CPU ID:
 - 0x511006f0 (0x51/'Q', variant 1, part 0x06f, rev 0)

My Nexus 7 device doesn't report idiv through AT_HWCAP or through
/proc/cpuinfo (AT_HWCAP is 0x1b0d7).

Expand the check to anything with:
 - implementer 0x51
 - architecture 7
 - part 0x4d or 0x6f

Part 0x4d appears to be a dual-core Krait (e.g. see
https://crbug.com/341598#c43).

This new matching behavior is a subset of what the upstream kernel
does (patch[1] contributed by CodeAurora), and also closely matches the
behavior of pytorch/cpuinfo.

[1] 120ecfafab
This commit is contained in:
Ryan Prichard
2022-02-01 08:25:05 -08:00
committed by GitHub
parent f1801f0ca1
commit 5f5e6d620f
3 changed files with 27 additions and 14 deletions
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18
test/cpuinfo_arm_test.cc
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@ -327,6 +327,24 @@ CPU revision : 3)");
EXPECT_EQ(GetArmCpuId(&info), 0x510006f3);
}
// The 2013 Nexus 7 (Qualcomm Krait) kernel configuration forgets to report IDIV
// support.
TEST(CpuinfoArmTest, Nexus7_2013_0x511006f0) {
ResetHwcaps();
auto& fs = GetEmptyFilesystem();
fs.CreateFile("/proc/cpuinfo",
R"(CPU implementer : 0x51
CPU architecture: 7
CPU variant : 0x1
CPU part : 0x06f
CPU revision : 0)");
const auto info = GetArmInfo();
EXPECT_TRUE(info.features.idiva);
EXPECT_TRUE(info.features.idivt);
EXPECT_EQ(GetArmCpuId(&info), 0x511006f0);
}
// The emulator-specific Android 4.2 kernel fails to report support for the
// 32-bit ARM IDIV instruction. Technically, this is a feature of the virtual
// CPU implemented by the emulator.