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When inserting hw watchpoints, we take care of masking off the top byte of the address (and sign-extending it if needed). This guarantees we won't pass tagged addresses to the kernel via ptrace. However, from the kernel documentation on tagged pointers... "Non-zero tags are not preserved when delivering signals. This means that signal handlers in applications making use of tags cannot rely on the tag information for user virtual addresses being maintained for fields inside siginfo_t. One exception to this rule is for signals raised in response to watchpoint debug exceptions, where the tag information will be preserved." So the stopped data address after a hw watchpoint hit can be potentially tagged, and we don't handle this in GDB at the moment. This results in GDB missing a hw watchpoint hit and attempting to step over an unsteppable hw watchpoint, causing it to spin endlessly. The following patch fixes this by adjusting the stopped data address and adds some tests to expose the problem. gdb/ChangeLog: 2020-12-16 Luis Machado <luis.machado@linaro.org> * aarch64-linux-nat.c (aarch64_linux_nat_target::stopped_data_address): Handle the TBI. gdbserver/ChangeLog: 2020-12-16 Luis Machado <luis.machado@linaro.org> * linux-aarch64-low.cc (address_significant): New function. (aarch64_target::low_stopped_data_address): Handle the TBI. gdb/testsuite/ChangeLog: 2020-12-16 Luis Machado <luis.machado@linaro.org> * gdb.arch/aarch64-tagged-pointer.c (main): Add a few more pointer-based memory accesses. * gdb.arch/aarch64-tagged-pointer.exp: Exercise additional hw watchpoint cases.
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