78d6a7e98c
This is a patch in preparation to upcoming patches enabling SME support. It attempts to simplify the gdb/gdbserver shared interface used to read/write SVE registers. Where the current code makes use of unique_ptr, allocating a new buffer by hand and passing a buffer around, this patch makes that code use gdb::byte_vector and passes a reference to this byte vector to the functions, allowing the functions to have ready access to the size of the buffer. It also shares a bit more code between gdb and gdbserver, in particular around handling of ptrace get/set requests for SVE. I think gdbserver could be refactored to handle register reads/writes more like gdb's native layer as opposed to letting the generic linux-low layer do the ptrace calls. This is not very flexible and assumes one size for the responses. If you have something like NT_ARM_SVE, where you can have either FPSIMD or SVE contents, it doesn't work that well. I didn't want to change that interface right now as it is a bit too much work and touches all the targets, some of which I can't easily test. Hence the reason why the buffer the generic linux-now passes down to linux-aarch64-low is unused or ignored. No user-visible changes should happen as part of this refactor other than a slightly reworded warning message. While doing the refactor, I also noticed what seems to be a mistake in checking if the register cache contains active (non-zero) SVE data. For instance, the original code did something like this in aarch64_sve_regs_copy_from_reg_buf: has_sve_state |= reg_buf->raw_compare (AARCH64_SVE_Z0_REGNUM + i reg, sizeof (__int128_t)); "reg" is a zeroed-out buffer that we compare the Z register contents past the first 128 bits. The problem here is that raw_compare returns 1 if the contents compare the same, which means has_sve_state will be true. But if we compared the Z register contents to 0, it means we *do not* have SVE state, and therefore has_sve_state should be false. The consequence of this mistake is that we convert the initial FPSIMD-formatted data we get from ptrace for the NT_ARM_SVE register set to a SVE-formatted one. In the end, this doesn't cause user-visible differences because the values of both the Z and V registers will still be the same. But the logic is not correct. I used the opportunity to fix this, and it gets tested later on by the additional SME tests. I do plan on submitting some SVE-specific tests to make sure we have a bit more coverage in GDB's testsuite. Regression-tested on aarch64-linux Ubuntu 22.04/20.04. Reviewed-by: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
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