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On aarch64 the kernel ignores the tag in the top byte of the address of mprotect(), pkey_mprotect(), munmap() and madvise() and of mremap()'s old address, and of the pointers that syscalls access once the thread enables the tagged address ABI. rr updated its model of the tracee's memory with the tagged address, which is outside every mapping, so e.g. a page made writable through a tagged pointer stayed read-only in the model. And it read and wrote tracee memory at the tagged address, which for tags of 0x80 and above is a negative /proc/<pid>/mem offset that pread() and pwrite() reject, so rr asserted. Untag these addresses. Test: arm/tagged_addr_syscalls. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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[Encountered, debugged, test, patch by AI]
On aarch64 the kernel ignores the tag in the top byte of the address of mprotect(), pkey_mprotect(), munmap() and madvise() and of mremap()'s old address, and of the pointers that syscalls access once the thread enables the tagged address ABI. rr updated its model of the tracee's memory with the tagged address, which is outside every mapping, so e.g. a page made writable through a tagged pointer stayed read-only in the model. And it read and wrote tracee memory at the tagged address, which for tags of 0x80 and above is a negative /proc//mem offset that pread() and pwrite() reject, so rr asserted. Untag these addresses.
Test: arm/tagged_addr_syscalls.