frame unwinding patches

Ulf Hermann
Tue Apr 4 08:25:00 GMT 2017

>> - In the example above, the address points into and as
>> such not compiled by my colleague but rather provided by NVidia as a binary
>> blob. When you only got a binary blob and have to make do with it, you cannot
>> tell people to "just fix the compiler invocation".
> This is their problem they support a vendor who cripples usage of their
> products.  There is also Intel and AMD.

Sorry, but I cannot tell everybody with binary-only graphics drivers 
that they cannot use perfparser. That's probably the majority of 
embedded devices and a large number of desktops.

>> - Some JIT compilers, like QV4, actually embed frame pointers into their
>> dynamic code, but do not go the extra mile for generating DWARF data or
>> asynchronous unwind tables. That is another case where the patches by Ulf
>> excel and make elfutils much more useful.
> In such case elfutils could provide some workaround with a new eu-stack option:
> 	--please-workaround-a-completely-broken-compiler-i-still-have-not-fixed

Frame pointers are the easiest way to include unwinding information into 
a binary and they require less work from the compiler than other 
methods. With JIT compilers, compile time matters much more than with 
ahead of time compilers. Also, adding extra code to the compiler has to 
be justified in that case as the compiler is shipped inside the 
libQt5Qml binary and loaded into memory whenever you run some QML.

So, I think frame pointers are a perfectly valid option for unwinding 
and should be supported.

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