[LLVMdev] [lld] Handling a whole bunch of readers

[Shankar Easwaran]

On 10/10/2013 5:00 PM, Rui Ueyama wrote:
> On Thu, Oct 10, 2013 at 9:16 AM, Shankar Easwaran
> <shankare at codeaurora.org>wrote:
>
>> On 10/9/2013 11:19 PM, Rui Ueyama wrote:
>>
>>> Isnt having a YAML file starting with the below better, so that you dont
>>> need to go through file extensions.
>>>
>>> magic :
>>> arch:
>>>
>>> I guess we will use a fixed file extension anyway (we probaly don't want
>>> to
>>> use .txt for YAML object file for example), so what do you think is the
>>> benefit of depending on special file magic compared to using file
>>> extension?
>>>
>>>
>>>   I would like to support usecases like this.
>> (a)
>> $ cat simple.s
>>           .text
>>           .global _start
>>           .type _start, at function
>> _start:
>>           callq bar
>>           ret
>>
>> clang simple.s -c- -o- | lld -flavor gnu -target x86_64
>> --output-filetype=yaml -r - | lld -flavor gnu -target x86_64 -
>>
>> Which is certainly not doable because you dont have a file created on the
>> filesystem.
>>
> This is an interesting example but I doubt the actual value of doing that,
> especially because it cannot handle multiple input files. An alternative
> command line would be
>
>    lld -flavor gnu -target x86_64 <(clang simple.s -c- -o- | lld -flavor gnu
> -target x86_64 --output-filetype=yaml -r -)
>
> which could handle multiple inputs, but it works only on bash and may be
> too tricky.
>
> The compiler usually depends on the file extension to distinguish file
> type, and your file has a non standard file extension, you can explicitly
> specify the language type by -x*language* option. Adding a similar option
> to the linker would be an option for us too.
>
> Even if we go with a magic, I'd like to make it a simple magic comment,
> such as "#!obj" at the beginning of a file. A magic string which is valid
> as a YAML, such as "magic:" is IMO less flexible and should be avoided.
YAML only allows key-value pairs. #!obj are all invalid characters for 
YAML files.
>
>> PS: This has been snipped from an earlier discussion with Tim.
>>
>> (b)
>>
>> lld -flavor gnu -target x86_64 input.o --output-filetype=yaml -o
>> atoms.objtxt (Create a atom file using x86_64 target)
>> lld -flavor gnu -target hexagon atoms.objtxt (use it with hexagon)
>>
>> You can create yaml files from each flavor and pass it to the wrong
>> flavor, too.
>>
>> If we have the magic and arch in the yaml file (or) one entry combined
>> triple(that combines flavor, operating system and target) this would work
>> and there is no need to create new types of extensions.
>>
>>
>> Thanks
>>
>> Shankar Easwaran
>>
>> -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
>> hosted by the Linux Foundation
>>
>>


-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation