Invalid reads / valgrind errors

[danpovey]

I am getting a lot of Valgrind errors with OpenBLAS right now. They appear to relate to reading past the end of allocated memory, e.g.:

==18705== Invalid read of size 8
==18705== at 0x52754C4: saxpy_k (axpy_sse.S:801)

This is reading past the end of a block which is not a multiple of 8,, e.g.

==18705== Address 0x7768a48 is 5,096 bytes inside a block of size 5,100 alloc'd

Is it expected that I should allocate memory in multiples of 8 or 16 bytes? I do already align it to 16 byte boundaries.

Also in
==18705== at 0x5276FC1: sdot_k (dot_sse.S:735)
==18705== at 0x5275FE8: scopy_k (copy_sse.S:411)

I am on x86_64 architecture.

[xianyi]

Hi Dan,

I have read the codes of axpy_sse.S around line 801.

To use movaps aligned accessing instruction, OpenBLAS must load 4 SP numbers to 128-bit register in line 801 which may past the end. However, I think it doesn't use the dirty number.

Thank you

Xianyi

[juliantaylor]

However, I think it doesn't use the dirty number.

it may be fine for axpy but dot uses horizontal operations, I'm not so sure about them not being used (e.g. via NaN * 0 = NaN)
quite likely that this is the cause of gh-189

[xianyi]

Hi @ juliantaylor,

This may have a risk in dot. I need to check the source code.

Xianyi