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Update gdb.Value.__str__ to iterate through, and return, children val… #21

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Update gdb.Value.__str__ to iterate through, and return, children val…
cmtice Sep 6, 2024
e718017
Fix some issues with initial version. Also fix a small bug in
cmtice Sep 11, 2024
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6 changes: 6 additions & 0 deletions gdb/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -640,6 +640,12 @@ def __str__(self) -> str:
if type_flags & lldb.eTypeIsPointer:
return "0x%x" % self._as_number()

# Check for synthetic children.
if (t.GetTypeClass() == lldb.eTypeClassStruct):
valstr = str(self._sbvalue_object.GetSyntheticValue())
if (valstr != "No value" and
valstr.find("$1") == -1):
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@slackito slackito Sep 11, 2024

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Would SBValue.IsValid() work here instead of checking the string against "No value"?

What is the check against "$1" supposed to do? If possible, we should replace this with some API call that tests some property of the SBValue rather than pattern-matching the stringified version. If this is not possible, is it always "$1" or is this the kind of convenience variable that depends on how many expressions you've evaluated before? Can it ever be "$2" or "$3"?

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@cmtice cmtice Sep 12, 2024

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The problem comes from 'address.test'. There is a part of the text that specifically does not want to use a synthetic value (but there is a valid one). The Check line is
CHECK: Pretty s = pretty MyStruct

What my code returns, without the '$1' test is:
Pretty s = (MyStruct) $1 = pretty MyStruct

I don't really like the '$1' hack, but I'm not sure how to handle/fix this particular case?

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@cmtice cmtice Sep 12, 2024

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Using IsValid does work, allowing me to not text for "No Value"

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@slackito slackito Sep 12, 2024

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I've been trying some stuff and it looks like lldb is pretty inflexible about what str(sbvalue) does. It will always generate a string with the following format

(${val.GetType().GetName()}) ${val.GetName()} = ${val.GetSummary()} {
  children
  ...
}

In this case, the "$1" comes from SBValue.GetName(). If we want to match what gdb does, I'm afraid we'll need to implement the logic to generate the string ourselves without relying on str(val).

Or we could live with (MyStruct) $1 = pretty MyStruct and relax address.test to match that output.

return valstr
valstr = self._sbvalue_object.GetSummary()
if not valstr:
valstr = self._sbvalue_object.GetValue()
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7 changes: 6 additions & 1 deletion test/lit/print_elements.test
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Expand Up @@ -7,7 +7,7 @@ RUN: %lldb -b -o 'command script import print_elements' %t | FileCheck %s
Check target.max-children-count values are correctly translated to "print
elements" values.

CHECK: gdb.parameter('print elements'): None
CHECK: gdb.parameter('print elements'): 256
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@slackito slackito Sep 11, 2024

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The behavior where a negative number means "no limit" was recently removed by llvm/llvm-project#105460. I think it would be better to just remove this CHECK, I don't see a need to check for a specific default value and it makes the test brittle in case lldb decides to change the default.

If you want, you could also simplify the parameter function around line 950 to

def parameter(s: str) -> Any:
    # gdb's 'print elements' is used for number of array elements to print and
    # also max number of chars in a string. lldb has 'target.max-children-count'
    # and 'target.max-string-summary-length', but max-children-count seems like
    # a closer match.
    if s == "print elements":
        return int(_GetSetting('target.max-children-count'))
    return None

but we can also do that as a follow-up if you prefer.

CHECK: gdb.parameter('print elements'): 0
CHECK: gdb.parameter('print elements'): 10

Expand All @@ -20,3 +20,8 @@ yield child 10. So check that we don't yield 11.

CHECK: yielding child 10
CHECK-NOT: yielding child 11


CHECK: yielding child 10
CHECK: A TestStruct of size 100
CHECK-NOT: yielding child 11
4 changes: 3 additions & 1 deletion test/lit/print_elements/__init__.py
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Expand Up @@ -34,7 +34,7 @@ def __lldb_init_module(debugger, internal_dict):
gdb.printing.register_pretty_printer(gdb.current_objfile(), printer)

# lldb treats all negative values here as 'unlimited'.
# gdb.parameter('print elements') returns None in this case.
# gdb.parameter('print elements') returns 256 in this case.
debugger.HandleCommand('settings set -- target.max-children-count -99')
print("gdb.parameter('print elements'):", gdb.parameter('print elements'))
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@slackito slackito Sep 11, 2024

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Same here, please remove the negative number test case.


Expand All @@ -51,3 +51,5 @@ def __lldb_init_module(debugger, internal_dict):
print("gdb.parameter('print elements'):", gdb.parameter('print elements'))

debugger.HandleCommand('p s')

debugger.HandleCommand("script print(gdb.parse_and_eval('s'))")