On 06/09/2023 03:40, bot crack wrote:
Hi
1. I want to add some register definitions.
2. I want to know why #define CNTPCT_EL0 SYSREG_64(0, c14) in arm64
*has only two arguments*, but it can be expanded into assembly "MRS
X0, #3, c14, c0, #1"
oh yeah, that's finest macro magic!
#define CNTPCT_EL0 SYSREG_64(0, c14)
#define SYSREG_64(...) 64, __VA_ARGS__
leads to the equivalent:
#define CNTPCT_EL0 64, 0, c14
Usage of CNTPCT_EL0:
arm_read_sysreg(CNTPCT_EL0, pct64);
with
#define arm_read_sysreg(...) _arm_read_sysreg(__VA_ARGS__)
So here, we, in fact, have
_arm_read_sysreg(64, 0, c14, pct64)
Which is defined as:
#define _arm_read_sysreg(size, ...) arm_read_sysreg_ ## size(__VA_ARGS__)
So we get
arm_read_sysreg_64(0, c14, pct64)
which is defined as:
#define arm_read_sysreg_64(op1, crm, val) \
asm volatile ("mrrc p15, "#op1", %Q0, %R0, "#crm"\n" \
: "=r" ((u64)(val)))
The rest is done by the assembler.
3. I didn’t understand the definition in
inmates/lib/arm64/include/asm/sysregs.h because I couldn’t find how
to expand the macro definition SYSREG_64
#define SYSREG_64(...) 64, __VA_ARGS__
SYSREG_64(1,2,foo) => 64, 1, 2, foo
These can be used as arguments in further macros.
4. For example, I want to add a new CNTVCT_EL0 (op0=0b11, op1=0b011,
CRn=0b1110, CRm=0b0, op2=b010) register. How should I do it?
I don't know, but have a look at the Linux kernel to see how others did
it in a pretty similar way:
https://elixir.bootlin.com/linux/latest/source/arch/arm/include/asm/vdso/cp15.h#L32
HTH,
Ralf
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