https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115179
Bug ID: 115179
Summary: Capture method address with inline asm in PIC mode?
Product: gcc
Version: 11.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: paul_robinson at playstation dot sony.com
Target Milestone: ---
Is there a way to capture a method address in inline asm that works in
-fPIC mode? Specifically I want to capture the address of a static
method that's in a class that's local to a function. I'm able to do it
in non-PIC mode but not PIC mode.
```
__asm__(
".pushsection .init_array" "\n"
".quad %c0" "\n"
".popsection" "\n"
: : "p"(Helper::myfunc));
```
I've run through all the combinations of %0, %a0, %c0 as the operand,
and constraints i, m, o, p. %c0 with either i or p works in non-PIC
mode, but nothing works in PIC mode. %0 with "p" compiles without
error but prefixes the mangled name with $ which then can't be
resolved at link time. Other combinations error out with "impossible
constraint" or "invalid constraint", or suffix the mangled name with
(%rip) which isn't much use in a .quad directive.
I can't use __attribute__((constructor)) because it's not allowed on
methods of local classes. (FTR, the documentation doesn't say that.)
I can't allocate the pointer directly in a custom section because that
doesn't always work (see bug 41091 and friends). (If that worked, I
wouldn't need the .init_array hack.)
Generating asm and editing it to remove the $ or (%rip) isn't practical.
I'm hoping there's some combination of asm operands/constraints that
isn't obvious from the docs that will work here.
