Hi Masahiro,

On 18/02/2020 00:37, Masahiro Yamada wrote:

Hi,

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Could you please elaborate a bit more?

I am just not familiar with this usage of /dev/zero.

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The behavior of /dev/null is clear.

The read/write to /dev/null is described in the standard:
https://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap10.html

I just do not know whether the write to /dev/zero is
the defined-behavior or not.

Even if /dev/null is more common for this use, in linux /dev/zero has the same
behavior for what concerns the write operation. In particular all write
operations to /dev/zero succeed with no other effects.

You do not find it at the link you provided because existence of /dev/zero is
not required by POSIX as far as I know, but the behavior is standardized by
Linux ABI hence I do not think it is going to change.

Please have a look at drivers/char/mem.c +818 where the operation is defined.

Based on this I propose to put a comment on why we are not using /dev/null in
this case accordingly with what you stated in your previous email, but to leave
the rule as is.

Masahiro Yamada

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Does this work?

as-option = $(success, cat /dev/null | $(CC) $(CLANG_FLAGS) $(1) -c -x
assembler -o /dev/null -)

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-- 
Regards,
Vincenzo