> > In a more complicated example, I'm trying to position uncommonly used
> > code in a separate memory region for better cache locality. One of the
> > inline assembly statements I'm using is not produced. This results in
> > not changing back to the ".text" section, resulting in further assembler
> > problems as described in:
>
> Use an attribute to set the section.
>
> extern void foobar (void) __attribute__ ((section ("bar")));
>
> puts the function `foobar' in the `bar' section.
This definition method is not granular enough. I don't want the entire
function in the 'bar' section. I want the entire function in the 'text'
section but in some cases in the function where there is an if-statement
like this:
if (something) {
/* body /*
}
...I want to place the body, which is written in C, in the 'bar'
section. And everything after the if-statement should remain in the
'text' section.
I'm currently producing
if (something) {
relocate_pre("if_something");
/* body */
relocate_post();
}
And then defining:
#define relocate_pre(name) \
asm volatile ( "jmp 1f\n\t" \
".subsection 2\n\t" \
".section .bar\n" \
"hcu_uncommon_section_" name ":\n\t" \
"1:\n\t" );
#define relocate_post() \
asm volatile( "jmp 1f\n\t" \
".text\n\t" \
"1:\n" );
The problems begin when I hit a case like:
if (something) {
relocate_pre("if_something");
/* parts of the body */
goto somewhere_else;
relocate_post();
}
or
if (something) {
relocate_pre("if_something");
/* parts of the body */
return;
relocate_post();
}
relocate_post() seems to be eliminated, hence I don't get the switch
back to the ".text" section.
>
> If you really need naked assembly code, do it *outside* a function:
>
> asm ("\nfoo:\t\n"
> "\t# wibble");
>
> int main(void)
> {
> return 0;
> }
The problem with using naked assembly code outside a function is that
after such code I may need to execute additional code written in C, and
presently there's no way to write such code in C outside a function. I
requested a feature like this in the past, but it was not accepted:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12118
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12284
I'm applying an automated transformation to 3rd-party source code to
produce such uncommon code in separate memory regions. Certainly,
interpreting the body of if-statements as C code and automatically
producing the corresponding naked assembly outside a function image
seems like something the compiler or assembler should be doing. It
shouldn't be hand written.
I can't help but feel that the compiler should be helping here.
