Recording of register saves in DWARF2 CFI

Andrew Haley
Mon Apr 21 12:41:00 GMT 2008

James Molloy wrote:
> Hi,
> I'm attempting to write a cross-platform debugger for a hobby kernel,
> and as part of which I use DWARF-2's CFI stack unwinding functionality.
> This works perfectly, however I would also like to obtain the parameters
> given to each function call on the stack. I can do this easily in x86 as
> all the parameters are passed via stack, however on x64 and MIPS I'm
> having difficulty, as the first X parameters are passed via register.
> The DWARF-2 specification makes allowance for this - the CFI system is
> capable of determining the value of any and every register at the start
> of any stack frame - but I have noticed that GCC doesn't record
> unwinding rules for many registers (seemingly any register not essential
> to the finding of the CFA or return address).
> Is there any flag available to enable recording of every register, or,
> even better, certain registers, for every stack frame? I've grepped the
> manual to no avail.

Surely this is in the debuginfo, not the unwinder data.  Aren't
you looking in the wrong place?


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