Re: [patch V4 part 5 13/31] x86/irq: Convey vector as argument and not in ptregs

Lai Jiangshan
2020-05-10T02:45:05Z

On Tue, May 5, 2020 at 10:23 PM Thomas Gleixner <tglx@linutronix.de> wrote:

> +/*
> + * ASM code to emit the common vector entry stubs where each stub is
> + * packed into 8 bytes.
> + *
> + * Note, that the 'pushq imm8' is emitted via '.byte 0x6a, vector' because
> + * GCC treats the local vector variable as unsigned int and would expand
> + * all vectors above 0x7F to a 5 byte push. The original code did an
> + * adjustment of the vector number to be in the signed byte range to avoid
> + * this. While clever it's mindboggling counterintuitive and requires the
> + * odd conversion back to a real vector number in the C entry points. Using
> + * .byte achieves the same thing and the only fixup needed in the C entry
> + * point is to mask off the bits above bit 7 because the push is sign
> + * extending.
> + */
> + .align 8
> +SYM_CODE_START(irq_entries_start)
> + vector=FIRST_EXTERNAL_VECTOR
> + .rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)
> + UNWIND_HINT_IRET_REGS
> + .byte 0x6a, vector
> + jmp common_interrupt
> + .align 8
> + vector=vector+1
> + .endr
> +SYM_CODE_END(irq_entries_start)

Hello, tglx

Using ".byte 0x6a, vector" is somewhat ugly.

I hope it should be " pushq $(s8_to_s64(vector))", which can also
help to reduce bunches of comments about ".byte 0x6a, vector".

However, I don't know how to implement s8_to_s64() here. But at
least the following code works (generates the same two-byte machine
code as ".byte 0x6a, vector" does):

.if vector < 128
pushq $(vector)
.else
pushq $(0xffffffffffffff00+vector)
.endif

Thanks,
Lai