[llvm-dev] Exceptions not getting caught on bare-metal target

[Dominik Montada via llvm-dev]

Hi,

We're working on adding exception handling support for a downstream 
bare-metal target. I read through the LLVM exception handling docs [1] 
and went through some patches from other backends to understand what 
parts we need to implement.

We're now at a point were it feels like it should work, but 
unfortunately exceptions are still not getting caught. Our target uses 
DWARF unwinding.

The problem seems to be that findFDE cannot find a CIE which covers the 
given PC. We're not sure why this is though. From [2] and other backend 
implementations we gathered that unw_getcontext saves the PC of the 
call-site, i.e. the return address of unw_getcontext and that is that we 
are doing as well.

Is there some other target hook in LLVM or libunwind that we need to 
implement in order to get this to work? Or are we not emitting 
enough/correct CFI instructions (currently we only emit .cfi_def_cfa in 
the prolog, we don't have any callee-saved registers).

Speaking of calling conventions: our target is special in that registers 
are automatically pushed to a special save area upon executing a call, 
and automatically restored when executing a return instruction. I assume 
we need to implement some target specific code in stepWithDwarf to 
handle this?

Any help in this regard would be highly appreciated!

Cheers,

Dominik

[1] https://llvm.org/docs/ExceptionHandling.html
[2] https://www.nongnu.org/libunwind/man/unw_getcontext(3).html

-- 
----------------------------------------------------------------------
Dominik Montada                   Email: dominik.montada at hightec-rt.com
HighTec EDV-Systeme GmbH          Phone: +49 681 92613 19
Europaallee 19                    Fax:   +49-681-92613-26
D-66113 Saarbrücken               WWW: http://www.hightec-rt.com

Managing Director: Vera Strothmann
Register Court: Saarbrücken, HRB 10445, VAT ID: DE 138344222

This e-mail may contain confidential and/or privileged information. If
you are not the intended recipient please notify the sender immediately
and destroy this e-mail. Any unauthorised copying, disclosure or
distribution of the material in this e-mail is strictly forbidden.
---

-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/x-pkcs7-signature
Size: 6822 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20200703/b05bfe3e/attachment.bin>