llvm dev - Feb 2014 - [LLVMdev] [cfe-dev] Unwind behaviour in Clang/LLVM

I assume this "CantUnwind table" is not the same as

Unwind table index '.ARM.exidx' at offset 0x818 contains 4 entries:
0x5d4 <main>: 0x1 [cantunwind]

because the latter prevent any unwinding, breaking
debuggers/profilers/sanitizers.

As I understand, the right way to enable basic unwind through any
function (without emitting landing pands etc, unless they are needed
for something else) is -funwind-tables. I'm going to add that in the
driver for all sanitizers then.


On Tue, Feb 11, 2014 at 6:20 PM, Renato Golin <renato.golin at linaro.org>
wrote:
> On 11 February 2014 14:12, Rafael Espíndola <rafael.espindola at
gmail.com> wrote:
>> Why fails? I would read a "generate a CantUnwind table" as a
table
>> that a debugger or profiler can use, but lacks information to allow an
>> exception to be handled.
>
> Right, I was assuming CantUnwind was interpreted as is by debug and
> profilers. If CantUnwind is *only* blocking EH, than it looks good.
>
> Let Keith's patch go in and I'll have a go trying to merge the two.
>
> Thanks,
> --renato
>
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On 13 February 2014 11:35, Evgeniy Stepanov <eugenis at google.com>
wrote:
> Unwind table index '.ARM.exidx' at offset 0x818 contains 4 entries:
> 0x5d4 <main>: 0x1 [cantunwind]
This is exactly what I meant.

> because the latter prevent any unwinding, breaking
> debuggers/profilers/sanitizers.
In that case, my argument stands again.

> As I understand, the right way to enable basic unwind through any
> function (without emitting landing pands etc, unless they are needed
> for something else) is -funwind-tables. I'm going to add that in the
> driver for all sanitizers then.
-funwind-tables are not yet understood by ARM, but it is for Dwarf EH.
I plan on moving ARM to the same style as Dwarf, so you can assume it
is correct.

cheers,
--renato

On Thu, Feb 13, 2014 at 5:39 PM, Renato Golin <renato.golin at linaro.org>
wrote:
> On 13 February 2014 11:35, Evgeniy Stepanov <eugenis at google.com>
wrote:
>> Unwind table index '.ARM.exidx' at offset 0x818 contains 4
entries:
>> 0x5d4 <main>: 0x1 [cantunwind]
>
> This is exactly what I meant.
>
>
>> because the latter prevent any unwinding, breaking
>> debuggers/profilers/sanitizers.
>
> In that case, my argument stands again.
>
>
>> As I understand, the right way to enable basic unwind through any
>> function (without emitting landing pands etc, unless they are needed
>> for something else) is -funwind-tables. I'm going to add that in
the
>> driver for all sanitizers then.
>
> -funwind-tables are not yet understood by ARM, but it is for Dwarf EH.
> I plan on moving ARM to the same style as Dwarf, so you can assume it
> is correct.
Hm, I see that -funwind-tables on arm-linux-androideabi target
replaces this "cantunwind" with a proper unwind table.
Hence http://llvm-reviews.chandlerc.com/D2762.