RFR: 8131483 : aarch64: illegal stlxr instructions (original) (raw)

Andrew Dinn adinn at redhat.com
Thu Jul 16 09:50:59 UTC 2015

The fix looks ok to me (I checked places where this code gets called and it is safe to clobber rscratch2).

regards,

Andrew Dinn

Senior Principal Software Engineer Red Hat UK Ltd Registered in UK and Wales under Company Registration No. 3798903 Directors: Michael Cunningham (USA), Matt Parson (USA), Charlie Peters (USA), Michael O'Neill (Ireland)

On 16/07/15 10:25, Edward Nevill wrote:

Hi,

http://cr.openjdk.java.net/~enevill/8131483/webrev Fixes an issue reported by one of our partners where the aarch64 port is generating illegal instructions on their HW. The instruction in question is stlxr(rscratch1, end, rscratch1) According to the ARM ARM this is unpredictable and an implementation may treat this as undefined which our partners HW does. The relevant section from the ARM ARM is:- STLXR For a description of this instruction and the encoding, see STLXR on page C6-702. CONSTRAINED UNPREDICTABLE behavior If s == t || (pair && s == t2), then one of the following behaviors can occur: The instruction is UNDEFINED. The instruction executes as a NOP. The instruction performs the store to the specified address, but the value stored is UNKNOWN. If s == n && n != 31 then one of the following behaviors can occur: The instruction is UNDEFINED. The instruction executes as a NOP. The instruction performs the store to an UNKNOWN address. Thanks for the review, Ed.

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