dietlibc; build path issue on ARM despite -fdebug-prefix-map

Christian Seiler christian at
Sat Nov 5 11:29:40 UTC 2016

Thanks for your quick response!

On 11/05/2016 12:09 PM, Ximin Luo wrote:
> If you set a -fdebug-prefix-map=. option and it still doesn't apply
> it to those FILE entries, I would guess that is probably a GCC bug.

Ok, good that you think we're in agreement. :)

> You should either file it upstream or submit a patch to them.
> I'm unfortunately not familiar with what is supposed to happen on ARM
> to suggest exactly which file to edit, to affect the final FILE
> entry. But for DWARF2 entries, the logic is in gcc/final.c
> (remap_debug_filename) and gcc/dwarf2out.c (the places where it calls
> remap_debug_filename).

Thanks for the pointers, I'll take a look. Although I'm not sure
whether it'll be feasible for me to actually test this, because
I don't have access to ARM hardware and compiling in qemu-user
emulation is very, very slow - and gcc is a large project. (Just
for comparison: dietlibc compiles in ~35s without unit tests
natively on amd64 with -j4, in qemu-user with armhf as arch it
takes > 10 minutes, also with -j4.) Maybe I'll see if the cross
compiler is also affected, and if that's the case, I'll have an

> If the FILE entry is technically "not debugging output"

I do believe it is though, because if you look at the diffoscope
output on, the path entry is moved
to the split debug info of the executables and is not present in
the executables itself anymore.


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