I also found the gcc docs for asm to be very limited, so I have been
re-writing them.
For example, I have documented a number of the modifiers (see
www.LimeGreenSocks.com/gcc/Extended-Asm.html#i386Operandmodifiers).
Because of concerns expressed in some of gcc's bug reports re asm, I
have tried to limit the number of modifiers I doc to those I believe are
essential, and commonly useful. I haven't doc'ed %a. Perhaps %c will
do what you need?
I haven't had much (actually any) response from the gcc doc people about
this effort. But perhaps someday these updates can be rolled back into
the docs.
Note: This documentation has not been reviewed for technical accuracy by
the gcc team. It should be considered a work in progress.
dw
On 12/16/2013 3:29 AM, Luchezar Belev wrote:
Hello,
Sometimes one needs to pass an immediate operand to asm statement that
should not be prefixed with dollar sign (e.g. for doing custom things
with assembly directives).
After much search in the internet i managed to find the way to do it:
when the operand is used in the assembly string, it must have the 'a'
modifier. (e.g. ".equ name, %a0" instead of ".equ name, %0".
My question is: why is this feature not mentioned anywhere in the GCC
documentation and is so extremely hard to find info about? Does this
mean that it is planned for removal or deprecation? Can one rely on
it's presence in future GCC versions?
(I think it is extremely useful for some specific tasks, please don't
remove it!)
