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Correct value of ARM Cortex-A8 MVFR1 register.

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The value of the MVFR1 (Media and VFP Feature Register 1) register for
the Cortex-A8 appears to be incorrect (according to the TRM, DDI0344K),
with the "full denormal arithmetic" and "propagation of NaN" fields
holding both 0 instead of both 1.

I had a go tracing the history of the use of this value, and it seems
it's always just been wrong in QEMU: maybe it was derived from early
documentation, or guessed based on the use of a "VFP Lite" implementation
in the Cortex-A8.

Depending on the startup/early-boot code in use, this can manifest as
failure to perform denormal arithmetic properly: in our case, selecting
a Cortex-A8 CPU when using QEMU as an instruction-set simulator for
bare-metal GCC testing caused tests using denormal arithmetic to
fail. Problems might be masked (or not occur) when using a full OS kernel
with suitable trap handlers (I'm not sure).

Backports commit 0f1944735b6bac810b067e8a7a5154744536fd59 from qemu
This commit is contained in:
Julian Brown 2018-03-01 11:07:01 -05:00 committed by Lioncash
parent fcc05dc1ce
commit 86670028f7
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GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 1 additions and 1 deletions
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2
qemu/target-arm/cpu.c
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@ -919,7 +919,7 @@ static void cortex_a8_initfn(struct uc_struct *uc, Object *obj, void *opaque)
cpu->midr = 0x410fc080; cpu->midr = 0x410fc080;
cpu->reset_fpsid = 0x410330c0; cpu->reset_fpsid = 0x410330c0;
cpu->mvfr0 = 0x11110222; cpu->mvfr0 = 0x11110222;
cpu->mvfr1 = 0x00011100; cpu->mvfr1 = 0x00011111;
cpu->ctr = 0x82048004; cpu->ctr = 0x82048004;
cpu->reset_sctlr = 0x00c50078; cpu->reset_sctlr = 0x00c50078;
cpu->id_pfr0 = 0x1031; cpu->id_pfr0 = 0x1031;