Please merge b20ab412bf838a8a87e5cc1c8c6399c3c9255354 to release/10.x #73
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cherry-pick: b20ab41 |
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branch: issue-73-pr |
tstellar
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Nov 4, 2023
…vg (llvm#70914) This removes explicit invalidation of vg and svg that was done in `GDBRemoteRegisterContext::AArch64Reconfigure`. This was in fact covering up a bug elsehwere. Register information says that a write to vg also invalidates svg (it does not unless you are in streaming mode, but we decided to keep it simple and say it always does). This invalidation was not being applied until *after* AArch64Reconfigure was called. This meant that without those manual invalidates this happened: * vg is written * svg is not invalidated * Reconfigure uses the written vg value * Reconfigure uses the *old* svg value I have moved the AArch64Reconfigure call to after we've processed the invalidations caused by the register write, so we no longer need the manual invalidates in AArch64Reconfigure. In addition I have changed the order in which expedited registers as parsed. These registers come with a stop notification and include, amongst others, vg and svg. So now we: * Parse them and update register values (including vg and svg) * AArch64Reconfigure, which uses those values, and invalidates every register, because offsets may have changed. * Parse the expedited registers again, knowing that none of the values will have changed due to the scaling. This means we use the expedited registers during the reconfigure, but the invalidate does not mean we throw all of them away. The cost is we parse them twice client side, but this is cheap compared to a network packet, and is limited to AArch64 targets only. On a system with SVE and SME, these are the packets sent for a step: ``` (lldb) b-remote.async> < 803> read packet: $T05thread:p1f80.1f80;name:main.o;threads:1f80;thread-pcs:000000000040056c<...>a1:0800000000000000;d9:0400000000000000;reason:trace;#fc intern-state < 21> send packet: $xfffffffff200,200#5e intern-state < 516> read packet: $e4f2ffffffff000000<...>#71 intern-state < 15> send packet: $Z0,400568,4#4d intern-state < 6> read packet: $OK#9a dbg.evt-handler < 16> send packet: $jThreadsInfo#c1 dbg.evt-handler < 224> read packet: $[{"name":"main.o","reason":"trace","registers":{"161":"0800000000000000",<...>}],"signal":5,"tid":8064}]]#73 ``` You can see there are no extra register reads which means we're using the expedited registers. For a write to vg: ``` (lldb) register write vg 4 lldb < 37> send packet: $Pa1=0400000000000000;thread:1f80;#4a lldb < 6> read packet: $OK#9a lldb < 20> send packet: $pa1;thread:1f80;#29 lldb < 20> read packet: $0400000000000000#04 lldb < 20> send packet: $pd9;thread:1f80;#34 lldb < 20> read packet: $0400000000000000#04 ``` There is the initial P write, and lldb correctly assumes that SVG is invalidated by this also so we read back the new vg and svg values afterwards.
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https://llvm.org/PR45316
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