Eric Botcazou <botca...@adacore.com> writes: > Hi, > > this changes the stack checking method (that of -fstack-check) used on Linux > from the traditional model (probe then move SP) to the model implemented for > -fstack-clash-protection (probe while moving SP). The rationale is that the > latter is in widespread use on Linux and thus thought to be more robust. > > This entails doing a couple of things: defining STACK_CHECK_MOVING_SP to 1: > > -- Macro: STACK_CHECK_MOVING_SP > An integer which is nonzero if GCC should move the stack pointer > page by page when doing probes. This can be necessary on systems > where the stack pointer contains the bottom address of the memory > area accessible to the executing thread at any point in time. In > this situation an alternate signal stack is required in order to be > able to recover from a stack overflow. The default value of this > macro is zero
This part I followed :) > and replacing tests on flag_stack_clash_protection by calls to a new wrapper > routine do_stack_clash_protection in the back-end [the implementation is the > same as the one present in the i386 back-end]. But I'm not sure I understand this part. It seems like it's using the stack-clash mechanism and stack-clash thresholds for allocating static parts of the frame while still using the stack-check mechanism for dynamic alloctions. Is that right? If so, don't the two have different assumptions about which part needs to be probed? I wasn't sure why we continued to use PROBE_INTERVAL for dynamic allocations but switched to stack_clash_probe_interval for static ones (if I followed the code correctly). Thanks, Richard > > -fstack-check is mainly used for Ada and AdaCore has been using this method > in > its Aarch64/Linux compilers for some time. > > Bootstrapped/regtested on Aarch64/Linux, OK for the mainline? > > > 2024-10-01 Eric Botcazou <ebotca...@adacore.com> > > * config/aarch64/aarch64-linux.h (STACK_CHECK_MOVING_SP): Define to 1. > * config/aarch64/aarch64-protos.h (do_stack_clash_protection): Declare. > * config/aarch64/aarch64.h (STACK_DYNAMIC_OFFSET): Replace > flag_stack_clash_protection with call to do_stack_clash_protection. > * config/aarch64/aarch64.cc (aarch64_output_probe_stack_range): > Likewise. > (aarch64_output_probe_sve_stack_clash): Likewise. > (aarch64_layout_frame): Likewise. > (aarch64_get_separate_components): Likewise. > (aarch64_allocate_and_probe_stack_space): Likewise. > (aarch64_expand_prologue): Likewise. And do not check the stack prior > to establishing the frame if STACK_CHECK_MOVING_SP is 1. > (aarch64_expand_epilogue): Likewise. > (do_stack_clash_protection): New predicate.
