[PATCH] D142654: [LiveDebugValues] Allow EntryValue with OP_deref expressions

[Felipe de Azevedo Piovezan via Phabricator via llvm-commits]

fdeazeve added a comment.

In D142654#4085122 <https://reviews.llvm.org/D142654#4085122>, @djtodoro wrote:

> Hello. I am wondering, have you checked how both ```GDB``` and ```LLDB``` act with this example?

I believe we don't have much to check in this example, as there are no callers for the function here.
However, the test `lldb/test/API/functionalities/param_entry_vals/basic_entry_values/` has a function with this exact behaviour (see func15).
It  produces this dwarf for the callee:

  0x0000065f:   DW_TAG_subprogram
                  DW_AT_low_pc	(0x00000000000001f8)
                  DW_AT_high_pc	(0x0000000000000228)
                  DW_AT_frame_base	(DW_OP_reg29 W29)
                  DW_AT_call_all_calls	(true)
                  DW_AT_linkage_name	("_Z6func1537StructPassedViaPointerToTemporaryCopy")
                  DW_AT_name	("func15")
                  DW_AT_decl_file	("lldb/test/API/functionalities/param_entry_vals/basic_entry_values/main.cpp")
                  DW_AT_decl_line	(157)
                  DW_AT_external	(true)
  
  0x00000678:     DW_TAG_formal_parameter
                    DW_AT_location	(0x000003ef: 
                       [0x00000000000001f8, 0x0000000000000204): DW_OP_breg0 W0+0
                       [0x0000000000000204, 0x0000000000000228): DW_OP_entry_value(DW_OP_reg0 W0))
                    DW_AT_name	("S")
                    DW_AT_decl_file	("lldb/test/API/functionalities/param_entry_vals/basic_entry_values/main.cpp")
                    DW_AT_decl_line	(157)
                    DW_AT_type	(0x00000749 "StructPassedViaPointerToTemporaryCopy")

And then, on the caller's side (main):

  0x0000093d:     DW_TAG_call_site
                    DW_AT_call_origin	(0x0000065f)
                    DW_AT_call_return_pc	(0x00000000000002dc)
  
  0x0000094a:       DW_TAG_call_site_parameter
                      DW_AT_location	(DW_OP_reg0 W0)
                      DW_AT_call_value	(DW_OP_breg31 WSP+8)

LLDB is able -- in fact this is what the test is testing -- to recover the parameter with those two pieces of information.

I have not checked whether GDB has support for this dwarf OP.


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https://reviews.llvm.org/D142654