RFR: 8163014: Mysterious/wrong value for "long" frame local variable on 64-bit
max.ockner at oracle.com
Tue Sep 6 21:33:51 UTC 2016
Please review this multi-platform fix for the stack walk API.
In 64 bits, long values can fit into a single slot, but two slots are
still used. The high slot contains garbage. This normally wouldn't
matter since it is never read from but the stack walk API expects to
display useful information. This is an issue when displaying longs from
local variables, so this means we can kill any garbage off by zeroing it
when it is pushed to the stack in the previous frame. This solution
zeroes the high byte of a long value when it is being pushed to the
stack (in push_l).
This applies to x86, aarch64, and sparc. This change does not apply to
ppc, though the bug almost certainly does affect it. I have left ppc
untouched since I don't have access to the hardware required to
reproduce the bug and test the fix.
I have adapted the reproducer from the bug into a test. It is curently
sitting in runtime/locallong, but I believe there must be a better place
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