[MPlayer-dev-eng] [PATCH] Disable additional optimization if compiler doesn't support __attribute__((used))

[Loren Merritt]

On Sun, 10 Jun 2007, Guillaume POIRIER wrote:
>
> BTW, I always wondered what MANGLE was supposed to do. What you just
> wrote makes me think that MANGLE is a way to access, within an ASM
> block, variables that aren't in the IN/OUT/Clobber list of the ASM
> block.
> Considering that GCC 2.95 allows only a limited amount of IN/OUT, I
> can understand why such a "hack" (it's a hack, right?) has been used.

To access a static const variable in an asm block, you don't need any 
asm constraints. Just write the variable name literally in the asm. But 
this is where mangling comes in: The name that the compiler uses for a 
variable or function is not necessarily identical to the name you wrote 
in the sourcecode. Some C ABIs prepend a "_", and some don't (C++ gets 
more complicated, but we don't care about that). So the name that you 
write in the asm block has to match the name that the compiler generated 
for the variable, and MANGLE performs that translation.
I wouldn't call it a hack. It is the only way to access static/global 
variables if you're writing pure asm files, and it doesn't get any less 
valid just because gcc inline asm provides another way.

--Loren Merritt