On 11/27/2015 11:02 PM, Bernd Edlinger wrote:
Hi,
I just found this in the docs:
The compiler copies the assembler instructions in a basic @code{asm}
verbatim to the assembly language output file, without
processing dialects or any of the @samp{%} operators that are available with
extended @code{asm}. This results in minor differences between basic
@code{asm} strings and extended @code{asm} templates. For example, to refer to
registers you might use @samp{%eax} in basic @code{asm} and
@samp{%%eax} in extended @code{asm}.
So it might be good to warn about % in asm statements too, because changing
anything on the asm syntax can be is quite dangerous.
There are a few differences to be aware of between basic and extended,
and yes that is one of them.
I'm putting together a "How to convert basic asm to extended asm"
guide. Not quite sure where to put it yet. Doesn't really belong in
the User Guide, but I worry no one would ever see it in the wiki.
And I wonder what the exact equivalence of asm("") is
in extended asm ("":::) or asm volatile ("":::) ?
From the docs: "asm statements that have no output operands, including
asm goto statements, are implicitly volatile." In other words, those 2
are the same.
Well, I start to think that Jeff is right, and we should treat a asm ("") as if
it
were asm volatile ("" ::: )
I believe Segher is already looking at this:
https://gcc.gnu.org/ml/gcc/2015-11/msg00196.html
but if the asm ("nonempty with optional %") we should
treat it as asm volatile ("nonempty with optional %%" ::: "memory").
Our docs should say that explicitly, and the implementation should follow that
direction.
Bernd.