[committed] amdgcn: Handle early debug info in mkoffload

[Andrew Stubbs]

On 17/07/2020 07:20, Thomas Schwinge wrote:
>> --- a/gcc/config/gcn/mkoffload.c
>> +++ b/gcc/config/gcn/mkoffload.c
>> @@ -33,31 +33,53 @@
>>   #include <libgen.h>
>>   #include "collect-utils.h"
>>   #include "gomp-constants.h"
>> +#include "simple-object.h"
>> +#include "elf.h"
>> +
>> +/* These probably won't be in elf.h for a while.  */
>> +#ifndef EM_AMDGPU
> 
> Nope, it already is.  ;-P
[...]
> I've got the canary 'EM_AMDGPU', but not the other '#define's.

Oops, I've committed this patch to fix it.

The code now assumes only that the relocations are defined as a block. 
The rest are undefined and redefined individually.

This matches the usage we've previously had in gcn-run.c and 
plugin-gcn.c (actually, those can be cleaned up now, but that's another 
patch).

>> -/* Files to unlink.  */
>> -static const char *gcn_s1_name;
>> -static const char *gcn_s2_name;
>> -static const char *gcn_o_name;
>> -static const char *gcn_cfile_name;
>>   static const char *gcn_dumpbase;
>> +static struct obstack files_to_cleanup;
> 
> (Good idea; should do similar in the other 'mkoffload's.)

Actually, I think the original code was more readable, but now we have a 
(potentially) variable number of files to clean up I needed something 
more general.

>> +uint32_t elf_arch = EF_AMDGPU_MACH_AMDGCN_GFX803;  // Default GPU architecture.
> 
> For easier later maintenance, shouldn't this be a '#define' (or similar)
> done next to where the GCC back end defines its default?

I thought of this, but I don't think there's actually a problem. The 
default is defined via OPTION_DEFAULT_SPECS, so there ought to be an 
explicit option passed to mkoffload at all times. If that's not the case 
I think the problem lies elsewhere.

In practice, a mismatch here will not fail silently, so we'll know to 
fix it.

The way simple_object is supposed to work is to clone (or merge) the ELF 
headers from an existing binary. Unfortunately, the way mkoffload is 
currently coded we don't have any to clone from until too late. We could 
separate the assemble and link steps, but I chose not to go that way at 
this time.

Andrew
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