[LLDB] Fix ambiguous alias for register X8 in RISC-V

[kper]

This is a follow-up issue based on the PR #124475 and issue #124023.

After defining the aliases for the RISCV's registers, it turned out that reading the register X8 does not work. The reason might be that X8 has two aliases s0 and fp. For more details see comment https://github.com/llvm/llvm-project/pull/124475/files#diff-deac7d69803ab75bbc0e97d7635cd8cfbdf54da14e5f98d5573ce4b9673d34d2R776

[llvmbot]

@llvm/issue-subscribers-backend-risc-v

Author: None (kper)

This is a follow-up issue based on the PR https://github.com//pull/124475 and issue https://github.com//issues/124023.

After defining the aliases for the RISCV's registers, it turned out that reading the register X8 does not work. The reason might be that X8 has two aliases s0 and fp. For more details see comment https://github.com/llvm/llvm-project/pull/124475/files#diff-deac7d69803ab75bbc0e97d7635cd8cfbdf54da14e5f98d5573ce4b9673d34d2R776

[llvmbot]

@llvm/issue-subscribers-lldb

Author: None (kper)

This is a follow-up issue based on the PR https://github.com//pull/124475 and issue https://github.com//issues/124023.

After defining the aliases for the RISCV's registers, it turned out that reading the register X8 does not work. The reason might be that X8 has two aliases s0 and fp. For more details see comment https://github.com/llvm/llvm-project/pull/124475/files#diff-deac7d69803ab75bbc0e97d7635cd8cfbdf54da14e5f98d5573ce4b9673d34d2R776

[DavidSpickett]

Fixing this will mean extending the alt_name field of:

llvm-project/lldb/include/lldb/lldb-private-types.h

Line 37 in dc326d0

struct RegisterInfo {

As this structure has to be trivially constructable, you'll have to update a whole bunch of macros and files in the process if you change what alt_name is, or add a new field.

When I did this to add register field information, I did this first part as its own change just setting the new field to null. Then the follow up PR actually used the field, which made it a lot easier to review.

[labath]

Are you sure you need the extra alias? LLDB already has a concept called "generic register names". The string fp is one of those names, and it is already used when looking up a register by name, so I think things should work (and if not, they could probably be made to work) by setting the two available fields for your register to the two other names (x8 and s0) and marking the register as LLDB_REGNUM_GENERIC_FP.