Assembler templates, asmSymbolicName and "error: expected string-literal" - gcc

Question

I'm trying to use GCC's extended ASM like Microsoft's assembler. Under Microsoft's MASM, we can do the following, where __FUNC is a C variable:
mov eax, __FUNC
According to Extended Asm - Assembler Instructions with C Expression Operands, § 6.44.3.1 Input Operands:
Operands are separated by commas. Each operand has this format:
[ [asmSymbolicName] ] constraint (cexpression)
asmSymbolicName
Specifies a symbolic name for the operand. Reference the name in the assembler template by enclosing it in square brackets (i.e. ‘%[Value]’). The scope of the name is the asm statement that contains the definition. Any valid C variable name is acceptable, including names already defined in the surrounding code...
When I try and use it in code:
unsigned int func = 1;
...
__asm__ __volatile__ (
"movl %[__FUNC], %%eax"
...
:
: __FUNC "" (func)
);
It results in:
cpu.cpp:148:5: error: expected string-literal before ‘__FUNC’
: __FUNC "" (func)
^
cpu.cpp:148:5: error: expected ‘(’ before ‘__FUNC’
cpu.cpp:148:17: error: ‘__FUNC’ was not declared in this scope
...
The best I can tell, I am using __FUNC according to the manual and its description of asmSymbolicName. But obviously I am not since there's an error.
What am I doing wrong?
I also tried the following because the manual told me I could use variable names in surrounding code, but it did not work either:
"movl %[func], %%eax"
...
:
: func "" (func)
And:
"movl %[func], %%eax"
...
:
: func (func)
...

Answer 1

This is correct:
Operands are separated by commas. Each operand has this format:
[ [asmSymbolicName] ] constraint (cexpression)
However [asmSymbolicName] means asmSymbolicName is literally surrounded by square brackets [ and ] (The outside brackets say that it is an optional parameter). You might have been going for this:
uint32_t func = 1;
uint32_t result;
__asm__ __volatile__ (
"movl %[func], %[result]"
: [result]"=a"(result)
: [func]"g"(func)
);
This takes an input parameter of func makes it available as a symbolic name called func within the assembler template. Output parameter is eax (writable) with a symbolic name of result and eax will be stored in the C variable result when finished. I chose "g" since any immediate value, memory address, or register would be appropriate for the source in movl . You could pass an immediate value rather than a "C" variable with:
: [func]"g"(42)