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Re: [PATCH] Fix P81033 for FDEs in partitioned code.


On Tue, Aug 14, 2018 at 10:18 PM Mike Stump <mikestump@comcast.net> wrote:
>
> On Aug 14, 2018, at 4:20 AM, Iain Sandoe <iain@sandoe.co.uk> wrote:
> > When function sub-sections are enabled, Darwin’s assembler needs the FDE local start
> > label for each sub-section to follow a linker-visible one so that the FDE will be correctly
> > associated with the code of the subsection.
> >
> > The current code in final.c emits a linker-visible symbol, as needed by several targets.
> > However the local label used to define the FDE start precedes the linker-visible one
> > which, for Darwin causes it (the FDE start) to be associated with the previous linker-
> > visible symbol (or the section start if there isn’t one).  This applies regardless of the
> > actual address of the label, for toolchain assemblers that have strict interpretation of
> > the Darwin sub-sections-via-symbols ABI.
> >
> > The patch adds a new local label (analogous to the "LFBn” emitted for the regular
> > function starts) just after the linker-visible label emitted after switching text section.
> > The FDE second entry is made to point to this instead of the LcoldStartn one.  This
> > should be a no-op for targets using .cfi_ and for targets without sub-sections-via-symbols.
> >
> > Bootstrapped on x86_64 and i686 linux and on a number of Darwin platforms (from
> > i686-darwin9 to x86_64-darwin17).
> >
> > OK for trunk?
> > open branches? (although it's a regression on 8, it’s a latent wrong-code on all branches)
>
> I'm fine with the darwin aspects of it, but I think it needs review/approval by final.c/dwarf people.

The approach looks fine (though we have extra labels even for targets
that do not need it).  But,

+  fde->dw_fde_second_begin = xstrdup (label);

to me it looks like dw_fde_node is GC allocated so the above needs ggc_strdup.

Richard.


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