V3 patches of stack-clash mitigation should land tomorrow after another
round of testing completes. Key changes this iteration:
1. For constant sized dynamic allocations we'll allocate/probe up to 4
STACK_CLASH_PROTECTION_PROBE_INTERVAL regions inline and unrolled.
2. For larger constant sized dynamic allocations we rotate the loop,
saving a compare/jump.
3. blockage insns added to prevent scheduler reordering, particularly
in the inline/unrolled loop case.
4. PARAMs to control the assumed size of the guard and the probing
interval. Both default to 4k. Note that the backends may not
support all possible values for these PARAMs.
a. The size of the guard helps determine how big of a local static
frame can be allocated without probing on targets that have an
implicit probe in the caller
b. The interval determines how often we probe once we decide
probing is required.
c. Backends can override the default values. aarch64 for example
overrides the guard size
5. More aarch64 improvements based on discussions with Wilco, Richard
and Ramana.
a. Support for a probing interval > 4k.
b. Assume guard of 64k, with 1k for outgoing arglist. Thus frames
less than 63k require no probing.
6. Additional tests for the unrolled inline dynamic case, rotated
loop case and use of a large guard value to avoid probing
(x86 and ppc only)
Jeff
