Running programs on aarch64 simulator

[Simon Marchi]

On 2020-05-08 12:57 p.m., Joel Sherrill wrote:
> On all the elf/eabi targets I have tried over the years, CPU-elf-gcc produced an a.out that was linked with the installed libgloss. I randomly had an sh-elf toolchain laying around and it worked like "sh-elf-gcc m.c" and then both sh-elf-gdb and sh-elf-run could run it on the gdb simulator.
> 
> The aarch64-elf toolchain installs 4 .specs files from libgloss but adding -specs XXX and trying each with the gdb simulator (via aarch64-elf-run) all fail.
> 
> home/joel/test-gcc/install-master/aarch64-elf/lib/aem-validation.specs
> /home/joel/test-gcc/install-master/aarch64-elf/lib/aem-ve.specs
> /home/joel/test-gcc/install-master/aarch64-elf/lib/nosys.specs
> /home/joel/test-gcc/install-master/aarch64-elf/lib/rdimon.specs

Ok, I am not familiar with that.

Well, it did work for me to build with:

$ aarch64-none-elf-gcc test.c -g3 -O0 -o test -specs=nosys.specs

I didn't have to provide my own _exit.  According to the DWARF info, the _exit now
included in my program comes from:

  /tmp/dgboter/bbs/rhev-vm1--rhe6x86_64/buildbot/rhe6x86_64--aarch64-none-elf/build/src/newlib-cygwin/libgloss/libnosys/_exit.c

> 
> This seems to be an odd case where there is a simulator in the source tree and there is no clear way to use it. Assuming it works.

It's also possible to run it directly like this:

$ ./sim/aarch64/run gdb/test
core: 8 byte write to unmapped address 0xfffffff0 at 0x0
program stopped with signal 11 (Segmentation fault).

The result is the same as when I ran it through GDB.  I have no idea if it's the sim that
is faulty, or the binary needs to be compiled differently.

> 
>     Program received signal SIGSEGV, Segmentation fault.
>     0x0000000000000000 in ?? ()
> 
> 
> That matches what luck I had on master. I suspect that is a mismatch between
> the address map of the simulator and whatever the default linker script does.

Perhaps.  With the ARM simulator, when I do "starti" in GDB, I see that it starts
executing at the ELF file's entry point.  With the AArch64 simulator, it starts
at 0 (the entry point of the ELF is not 0).  So I also suspect that the initial
PC is not right.

> 
>     I did not push the investigation further.
> 
> 
> I think Nick may be the key to getting an answer here. 

Added him in CC, we'll see :).

Simon