[Dwarf-Discuss] .debug_frame and the base address

Greg Clayton clayborg at gmail.com
Mon Sep 24 08:59:57 PDT 2018



> On Sep 24, 2018, at 8:44 AM, Robert Harris <robert.m.harris at oracle.com> wrote:
> 
> 
> 
>> On 24 Sep 2018, at 15:33, Greg Clayton <clayborg at gmail.com> wrote:
>> 
>> 
>> 
>>> On Sep 24, 2018, at 7:15 AM, Robert Harris via Dwarf-Discuss <dwarf-discuss at lists.dwarfstd.org> wrote:
>>> 
>>> I'd like some clarification regarding what precisely needs to be relocated relative to
>>> the object load address when interpreting .debug_frame.  I'm interested in versions
>>> 2, 3 and 4.
>>> 
>>> I think the only explicit mention of relocation in DWARF 4 is § 6.4.1:
>>> 
>>> 	Abstractly, this mechanism describes a very large table...
>>> 	...
>>> 	The first column indicates an address for every location that contains
>>> 	code in a program. (In shared objects, this is an object-relative offset.)
>>> 
>>> Thus adjustments need to be made to only
>>> 
>>> 	An FDE's initial_location field
>>> 	DW_CFA_set_loc's operand
>>> 
>>> Have I missed anything?  I see some ambiguity in the definition of
>>> DW_CFA_def_cfa_expression and it's making me wonder if there are any
>>> other occasions when a result would require relocation.
>> 
>> Any DWARF expression can contain a DW_OP_addr, which has an address argument, and would need to be relocated.
> 
> Do you mean that DW_OP_addr's argument should be relocated in all instances
> of a DWARF expression, i.e. in other .debug_ sections, or just in the context of
> .debug_frame?

I was specifically talking about DWARF expressions in any .debug_frame info. But in general, yes, any DWARF expression that contains a DW_OP_addr might need a relocation for its address argument.

Greg
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