[Bug symtab/31427] New: DWARF expression evaluation misconception

[Bug symtab/31427] New: DWARF expression evaluation misconception

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31427

            Bug ID: 31427
           Summary: DWARF expression evaluation misconception
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: symtab
          Assignee: unassigned at sourceware dot org
          Reporter: tromey at sourceware dot org
  Target Milestone: ---

This comes from:

https://lists.dwarfstd.org/pipermail/dwarf-discuss/2024-February/002375.html
https://dwarfstd.org/issues/181205.1.html

gdb should reset the DWARF expression stack after a piece operation.
Apparently nobody noticed this text in 2.6.1 "Single Location Descriptions":

Each simple location description that is a DWARF expression is
evaluated independently of any others.

Also an empty first piece is ok.

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug symtab/31427] DWARF expression evaluation misconception

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31427

--- Comment #1 from Tom Tromey <tromey at sourceware dot org> ---
I'm not sure there's a valid expression that would give
a different result if values were left on the stack
between pieces.

Maybe it can only be done in the situation where an initial
value must be pushed.  Presumably in the pieced case,
the initial value must be pushed before each piece is
evaluated.

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug symtab/31427] DWARF expression evaluation misconception

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31427

--- Comment #2 from Tom Tromey <tromey at sourceware dot org> ---
The empty first piece part works, according to a test
case I wrote:

(gdb) print s1
$1 = {a = <optimized out>, b = 23}

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug symtab/31427] DWARF expression evaluation misconception

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31427

--- Comment #3 from Tom Tromey <tromey at sourceware dot org> ---
(In reply to Tom Tromey from comment #1)

> Maybe it can only be done in the situation where an initial
> value must be pushed.  Presumably in the pieced case,
> the initial value must be pushed before each piece is
> evaluated.

It's hard to imagine this even being useful, as the cases
where a value is pushed on the stack aren't really ones
where a pieced result would be useful or expected.
I'll attach my test case here but I think this bug
is probably only of pedantic interest; and the bug
in the rust support pointed out in those links is,
I think, a problem in rust-lang.c.  I'll file a separate
bug for that.

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug symtab/31427] DWARF expression evaluation misconception

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31427

--- Comment #4 from Tom Tromey <tromey at sourceware dot org> ---
Created attachment 15382
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15382&action=edit
test case

-- 
You are receiving this mail because:
You are on the CC list for the bug.