On Sunday, 2 March 2014 at 15:36:01 UTC, Johannes Pfau wrote:
To make sure that libgcc
is built correctly for Cortex-M4 you have to specify
"--with-arch=armv7e-m --with-cpu=cortex-m4 --with-mode=thumb
--with-tune=" when configuring gcc/gdc.
(And I don't see these flags mentioned in
https://bitbucket.org/timosi/minlibd/src/691c76aa2b543998bb573e6ce6d96951a80817bd/README.gdc?at=default)
Gcc build fails with these. It will take time to check them one
by one. Also enable/disable-multilib may affect to this.
Then I updated my host binutils and gcc to latest head and with
these I compiled cross binutils and gcc/gdc from head. I used my
current settings. Now my own code and minlibd do not have any blx
instructions but libgcc has some.
Sounds strange, I don't think we could cause this in the gdc
frontend.
I am not saying it is a gdc bug. It may very well be a side
effect of a flag that is related to maybe umwinding or
relocation. I do have two kind of object files now in my
executable and I just like to know what is the difference between
them.
I guess binutils generates blx if thumb code calls arm code or
the
other way round. So I'd verify which libraries are really
picked up by
ld (ld --verbose) then check if the entry points are in thumb
or arm
mode:
http://stackoverflow.com/a/15931232
This sounds a lot as if calls to the same library/object file
generate
bl instructions as the code is in the same mode, but functions
in
external libraries are in a different mode and therefore
generate blx.
Yes, I think blx is for this. M4 does not have arm mode and there
is no this instruction, so it should be a linker error if the
user try to mix objects with different modes.
As I mentioned, I pass manually everything, including libgcc.
Nothing is picked by default. The multilib thing should be just
because of this. There are 4 variants of libgcc. If I pick the
m4-fpu library it should be already compiled with the right
flags. If it is not, I think that is a gcc bug.
How can I check from the library which modes/flags is has?
I'm not sure but I still don't think we could cause this. This
low-level stuff is usually part of the backend, the frontend
doesn't
know much about thumb/arm.
Yes, this is going a little off-topic now
