[Lldb-commits] [PATCH] D79699: Add ptrace register access for AArch64 SVE registers

[Muhammad Omair Javaid via Phabricator via lldb-commits]

omjavaid marked 3 inline comments as done.
omjavaid added inline comments.


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Comment at: lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_arm64.cpp:240
+  // Update SVE registers in case there is change in configuration.
+  ConfigureRegisterContext();
+
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labath wrote:
> What's the relationship of this function and the `InvalidateAllRegisters` function we added (for arm64 benefit) a couple of reviews back? Can we just have one of them?
Both InvalidateAllRegisters and ConfigureRegisterContext are inter related.

The idea is to maintain a cache of SVE register configurations created after thread stop on first call to ReadRegister/WriteRegister, using ConfigureRegisterContext. This configuration cache is maintained unless we do register write or we issue a step or resume.

InvalidateAllRegisters is called before resume and it will invalidate all cached register data including SVE configuration thus forcing us to do ConfigureRegisterContext on stop.

There is also a case where we need to reconfigure register context when we write vector granule register and need to update register sizes and offsets and sync them up between LLDB client and server. That case is handled by the child revisions of this patch.


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Comment at: lldb/source/Plugins/Process/Linux/NativeRegisterContextLinux_arm64.h:22
+#define INCLUDE_LINUX_PTRACE_DEFINITIONS_FOR_SVE_ARM64
+#include "Plugins/Process/Utility/LinuxPTraceDefines_arm64sve.h"
+#endif
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labath wrote:
> At this point, that header is sufficiently different from the asm/ptrace.h implementation (names of all structs and fields are different) that I don't think it makes sense to use it as an optional replacement. It makes it very likely things will not build in one of the modes.
> 
> This should either use the system version (and then only build when the system has the appropriate headers), or we should use the in-house version unconditionally (which may require renaming/namespacing the rest of the file so that it does not conflict with the real `asm/ptrace.h`).
Ack.


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Comment at: lldb/test/API/commands/register/register/aarch64_sve_registers/rw_access_static_config/main.c:2-4
+  asm volatile("ptrue p0.s\n\t");
+  asm volatile("fcpy  z0.s, p0/m, #5.00000000\n\t");
+  return 0; // Set a break point here.
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labath wrote:
> In our newer register tests we use the pattern where the debugger sets the register values, which are then read back through the inferior (and vice versa). I thing this is a good thing as it avoids the possibility of making symmetrical bugs in the read/write code, which will then appear to modify the register successfully, but they won't actually change the value observed by the inferior process.
In this test we are also doing the same please have a look at TestSVERegisters.py:140-142.

The code in main.c is used to make sure we enable SVE mode. AArch64 SVE mode is enabled by Linux kernel on first execution of SVE code.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D79699/new/

https://reviews.llvm.org/D79699