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SubjectRe: [PATCH 7/7] DWARF: add the config option
On Fri, May 19, 2017 at 04:29:13PM -0500, Josh Poimboeuf wrote:
> > How are you handling control flow?
>
> Control flow of what?
>
> > > Here's the struct in its current state:
> > >
> > > #define UNDWARF_REG_UNDEFINED 0
> > > #define UNDWARF_REG_CFA 1
> > > #define UNDWARF_REG_SP 2
> > > #define UNDWARF_REG_FP 3
> > > #define UNDWARF_REG_SP_INDIRECT 4
> > > #define UNDWARF_REG_FP_INDIRECT 5
> > > #define UNDWARF_REG_R10 6
> > > #define UNDWARF_REG_DI 7
> > > #define UNDWARF_REG_DX 8
> > >
> >
> > Why only those registers? Also, if you have the option I would really
> > suggest using the actual x86 register numbers (ax, ex, dx, bx, sp, bp,
> > si, di, r8-r15 in that order.)
>
> Those are the only registers which are ever needed as the base for
> finding the previous stack frame. 99% of the time it's sp or bp, the
> other registers are needed for aligned stacks and entry code.
>
> Using the actual register numbers isn't an option because I don't need
> them all and they need to fit in a small number of bits.
>
> This construct might be useful for other arches, which is why I called
> it "FP" instead of "BP". But then I ruined that with the last 3 :-)

BTW, here's the link to the unwinder code if you're interested:

https://github.com/jpoimboe/linux/blob/undwarf/arch/x86/kernel/unwind_undwarf.c

--
Josh

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