This patch adds a requirement that the number of outgoing arguments for a
function is at least 8 bytes when using stack-clash protection and alloca.
By using this condition we can avoid a check in the alloca code and so have
smaller and simpler code there.
A simplified version of the AArch64 stack frames is:
+-----------------------+
| |
| |
| |
+-----------------------+
|LR |
+-----------------------+
|FP |
+-----------------------+
|dynamic allocations | ---- expanding area which will push the outgoing
+-----------------------+ args down during each allocation.
|padding |
+-----------------------+
|outgoing stack args | ---- safety buffer of 8 bytes (aligned)
+-----------------------+
By always defining an outgoing argument, alloca(0) effectively is safe to probe
at $sp due to the reserved buffer being there. It will never corrupt the stack.
This is also safe for alloca(x) where x is 0 or x % page_size == 0. In the
former it is the same case as alloca(0) while the latter is safe because any
allocation pushes the outgoing stack args down:
|FP |
+-----------------------+
| |
|dynamic allocations | ---- alloca (x)
| |
+-----------------------+
|padding |
+-----------------------+
|outgoing stack args | ---- safety buffer of 8 bytes (aligned)
+-----------------------+
Which means when you probe for the residual, if it's 0 you'll again just probe
in the outgoing stack args range, which we know is non-zero (at least 8 bytes).
gcc/
PR target/86486
* config/aarch64/aarch64.h (STACK_CLASH_MIN_BYTES_OUTGOING_ARGS,
STACK_DYNAMIC_OFFSET): New.
* config/aarch64/aarch64.c (aarch64_layout_frame):
Update outgoing args size.
(aarch64_stack_clash_protection_alloca_probe_range,
TARGET_STACK_CLASH_PROTECTION_ALLOCA_PROBE_RANGE): New.
gcc/testsuite/
PR target/86486
* gcc.target/aarch64/stack-check-alloca-1.c: New.
* gcc.target/aarch64/stack-check-alloca-10.c: New.
* gcc.target/aarch64/stack-check-alloca-2.c: New.
* gcc.target/aarch64/stack-check-alloca-3.c: New.
* gcc.target/aarch64/stack-check-alloca-4.c: New.
* gcc.target/aarch64/stack-check-alloca-5.c: New.
* gcc.target/aarch64/stack-check-alloca-6.c: New.
* gcc.target/aarch64/stack-check-alloca-7.c: New.
* gcc.target/aarch64/stack-check-alloca-8.c: New.
* gcc.target/aarch64/stack-check-alloca-9.c: New.
* gcc.target/aarch64/stack-check-alloca.h: New.
* gcc.target/aarch64/stack-check-14.c: New.
* gcc.target/aarch64/stack-check-15.c: New.
From-SVN: r264751
