Reland "[lldb] Implement basic support for reverse-continue" (#123906)" (#123945) This reverts commit 22561cfb443267905d4190f0e2a738e6b412457f and fixes b7b9ccf44988edf49886743ae5c3cf4184db211f (#112079). The problem is that x86_64 and Arm 32-bit have memory regions above the stack that are readable but not writeable. First Arm: ``` (lldb) memory region --all <...> [0x00000000fffcf000-0x00000000ffff0000) rw- [stack] [0x00000000ffff0000-0x00000000ffff1000) r-x [vectors] [0x00000000ffff1000-0xffffffffffffffff) --- ``` Then x86_64: ``` $ cat /proc/self/maps <...> 7ffdcd148000-7ffdcd16a000 rw-p 00000000 00:00 0 [stack] 7ffdcd193000-7ffdcd196000 r--p 00000000 00:00 0 [vvar] 7ffdcd196000-7ffdcd197000 r-xp 00000000 00:00 0 [vdso] ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0 [vsyscall] ``` Compare this to AArch64 where the test did pass: ``` $ cat /proc/self/maps <...> ffffb87dc000-ffffb87dd000 r--p 00000000 00:00 0 [vvar] ffffb87dd000-ffffb87de000 r-xp 00000000 00:00 0 [vdso] ffffb87de000-ffffb87e0000 r--p 0002a000 00:3c 76927217 /usr/lib/aarch64-linux-gnu/ld-linux-aarch64.so.1 ffffb87e0000-ffffb87e2000 rw-p 0002c000 00:3c 76927217 /usr/lib/aarch64-linux-gnu/ld-linux-aarch64.so.1 fffff4216000-fffff4237000 rw-p 00000000 00:00 0 [stack] ``` To solve this, look up the memory region of the stack pointer (using https://lldb.llvm.org/resources/lldbgdbremote.html#qmemoryregioninfo-addr) and constrain the read to within that region. Since we know the stack is all readable and writeable. I have also added skipIfRemote to the tests, since getting them working in that context is too complex to be worth it. Memory write failures now display the range they tried to write, and register write errors will show the name of the register where possible. The patch also includes a workaround for a an issue where the test code could mistake an `x` response that happens to begin with an `O` for an output packet (stdout). This workaround will not be necessary one we start using the [new implementation](https://discourse.llvm.org/t/rfc-fixing-incompatibilties-of-the-x-packet-w-r-t-gdb/84288) of the `x` packet. --------- Co-authored-by: Pavel Labath <pavel@labath.sk>
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