Re: [PATCH 5/5] gdb: native target invalid architecture detection

[Luis Machado <luis.machado@arm.com>]

On 6/7/22 19:42, Pedro Alves wrote:
> On 2022-06-07 12:03, Luis Machado via Gdb-patches wrote:
> 
>> Yeah, sorry for the poor experience. I can confirm your procedure is
>> correct, and that you built GDB correctly. Unfortunately this part of
>> the AArch64 port seems to have rotted away given it is a less common
>> execution scenario.
> 
> This is actually covered by the testsuite, since:
> 
> ~~~~~
> commit 71be1fdc3655a170f4b14d795e5c9e81fcea06ef
> Author:     Yao Qi <yao.qi@linaro.org>
> AuthorDate: Tue Jul 7 16:58:19 2015 +0100
> Commit:     Yao Qi <yao.qi@linaro.org>
> CommitDate: Tue Jul 7 16:58:19 2015 +0100
> 
>      Adjust gdb.multi tests for aarch64
>      
>      Multi-arch related tests under gdb.multi are to compile programs with
>      the same compiler but different compiler options (-m64 vs -m32).  However,
>      different compilers are needed to compile both aarch64 program and
>      arm (aarch32) program.  This patch is to adjust these test cases to
>      compile programs in different modes with different compiler.
>      
>      When we use gcc for arm-linux target, its file name can be different,
>      arm-linux-gnueabihf-gcc, arm-linux-gnueabi-gcc, or arm-none-linux-gnueabi-gcc,
>      so I add a variable ARM_CC_FOR_TARGET, so that user can set the name
>      of gcc for arm-linux target on aarch64, like:
>      
>       $ make check RUNTESTFLAGS='ARM_CC_FOR_TARGET=arm-linux-gnueabihf-gcc multi-arch.exp'
>      
>      gdb/testsuite:
>      
>      2015-07-07  Yao Qi  <yao.qi@linaro.org>
>      
>              * gdb.multi/multi-arch-exec.exp: Set march1 and march2 to "" if target
>              is aarch64.  If target is aarch64, set compiler=${ARM_CC_FOR_TARGET}
>              if it exists.
>              * gdb.multi/multi-arch.exp: Likewise.
> 
> ~~~~~
> 
> I guess the issue is that nobody ever remembers to set ARM_CC_FOR_TARGET, or even
> knows about it.

Yeah. As a general comment, I always have to stop and think about the list of things that need
to be installed in order for GDB's testsuite to run all/most of the tests.

If you're missing something, most of the time things show up as UNTESTED/UNSUPPORTED. It
would be nice to have a stable list of things we need to have complete (as much as possible)
testsuite coverage.

Having to set these options by hand is quite obscure as well.

> 
> IWBN if the aarch64 bots people have access to tested with ARM_CC_FOR_TARGET, if they
> aren't already.

I think it is a less common scenario. Yes, this is supported, but my feeling is that people
seldom use this. Which explains why nobody complained, and some are surprised this even works.

> 
> Maybe it would be possible to come up with a way to default ARM_CC_FOR_TARGET to
> something that works for most people when testing aarch64, somehow.
The problem is that a compiler is not enough to make things run fine. If you have an aarch64
Ubuntu, for example, you'd need to add armhf as an architecture option and install both the
compiler and the libraries (libc6:armhf mostly).

Another problem is that not every processor/kernel supports running a 32-bit process in a
64-bit environment. This makes things more complicated.