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Replace movaps with movups

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objdump on my system and code snippet in blog agree - problem is caused
by `movups` not `movaps`. Fix surrounding text and doc link to reflect
this.
This commit is contained in:
William Orr
2016-05-02 11:18:15 -07:00
committed by Philipp Oppermann
parent 301859a4b9
commit a9f41d7303
1 changed files with 2 additions and 2 deletions
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blog/post/2015-09-02-set-up-rust.md
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@@ -271,12 +271,12 @@ So let's look at the first exception: `old:0xffffffff` means that the CPU wasn't
> objdump -D build/kernel-x86_64.bin | grep "10018a:"
10018a: 0f 10 05 c7 01 00 00 movups 0x1c7(%rip),%xmm0 ...
```
Through `objdump -D` we disassemble our whole kernel and `grep` picks the relevant line. The instruction at `0x10018a` seems to be a valid `movaps` instruction. It's a [SSE] instruction that moves 128 bit between memory and SSE-registers (e.g. `xmm0`). But why the `Invalid Opcode` exception? The answer is hidden behind the [movaps documentation][movaps]: The section _Protected Mode Exceptions_ lists the conditions for the various exceptions. The short code of the `Invalid Opcode` is `#UD`. An `#UD` exception occurs:
Through `objdump -D` we disassemble our whole kernel and `grep` picks the relevant line. The instruction at `0x10018a` seems to be a valid `movups` instruction. It's a [SSE] instruction that moves 128 bit between memory and SSE-registers (e.g. `xmm0`). But why the `Invalid Opcode` exception? The answer is hidden behind the [movups documentation][movups]: The section _Protected Mode Exceptions_ lists the conditions for the various exceptions. The short code of the `Invalid Opcode` is `#UD`. An `#UD` exception occurs:
> If an unmasked SIMD floating-point exception and OSXMMEXCPT in CR4 is 0. If EM in CR0 is set. If OSFXSR in CR4 is 0. If CPUID feature flag SSE is 0.
[SSE]: https://en.wikipedia.org/wiki/Streaming_SIMD_Extensions
[movaps]: http://www.c3se.chalmers.se/Common/VTUNE-9.1/doc/users_guide/mergedProjects/analyzer_ec/mergedProjects/reference_olh/mergedProjects/instructions/instruct32_hh/vc181.htm
[movups]: http://www.c3se.chalmers.se/Common/VTUNE-9.1/doc/users_guide/mergedProjects/analyzer_ec/mergedProjects/reference_olh/mergedProjects/instructions/instruct32_hh/vc206.htm
The rough translation of this cryptic definition is: _If SSE isn't enabled_. So apparently Rust uses SSE instructions by default and we didn't enable SSE before. To fix this, we can either disable SSE instructions in the compiler or enable SSE in our kernel. We do the latter, as it's easier.