I want to define a assembly to read register from arm64. Code is like the following:
asm volatile(
"str <reg> [%0]\n"
:
: "r"(value)
: "memory"
);
how to use a macro to define such code. <reg> is in a string literal and the behaviour of macros make me confused when I use # and ##
I tried to define even in the following way, it still causes an error.
#define STR_x0 "str x0 [%0]\n"
#define STR_x1 "str x1 [%0]\n"
...
#define STR_REG(reg) STR_##reg
#define ASM_READ_REG(reg) \
asm volatile( \
STR_REG(reg) \
: \
: "r"(value) \
: "memory" \
)
Answer
Try this corrected approach,
#define STR_x0 "str x0, [%0]\n"
#define STR_x1 "str x1, [%0]\n"
// your other registers
#define STR_REG(reg) STR_##reg
#define ASM_READ_REG(reg) \
asm volatile( \
STR_REG(reg) \
: \
: "r"(value) \
: "memory" \
)
Issues for you to fix:
the arm64 assembly syntax requires a comma after the register name:
str x0, [%0]notstr x0 [%0]the way you're trying to use marcos is correct, but there is issues with how you're invoking them.
this is the another approarch
#define ASM_READ_REG(reg) \
asm volatile( \
"str " #reg ", [%0]\n" \
: \
: "r"(value) \
: "memory" \
)
with this kind of appraoch you can call it like
ASM_READ_REG(x0);
ASM_READ_REG(x1);
The # operator in the macro convers the parameter to a string literal, that is what you need for assembly a code, this avoids the need for the intermediate STR_REG and STR_x0 macros.
I HOPE IT WORKS FOR YOU! <3