[Bug c/105576] New: x86: Support a machine constraint to get raw symbol name

[i at maskray dot me via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105576

            Bug ID: 105576
           Summary: x86: Support a machine constraint to get raw symbol
                    name
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: i at maskray dot me
  Target Milestone: ---

An raw symbolic operand is useful in inline asm (e.g. in C++ to get the mangled
name, or in C to let the compiler do some asm checking). In aarch64 and riscv,
there is a documented (supported) approach.
documented on
https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html#Machine-Constraints

extern int var;
void *addr(void) { return &var; }
void addr_via_asm(void) {
  asm (".pushsection .xxx,\"aw\"; .dc.a %0; .popsection" :: "S"(addr)); //
supported on aarch64 and riscv
  asm (".pushsection .xxx,\"aw\"; .dc.a %0; .popsection" :: "S"(&var)); //
supported on aarch64
}

On x86, it is unclear which should be preferred. It seems that the operand
modifier 'p' can be used for a function,
but not a variable.

asm (".pushsection .xxx,\"aw\"; .dc.a %p0; .popsection" :: "m"(addr));