Re: [kvm-unit-tests PATCH v4 11/17] powerpc/ppc64: add hcall support and putchar

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Feb 15, 2016 at 02:49:20PM +0100, Andrew Jones wrote:
> Add broken sc1 detection and patching and an hcall for putchar,
> to use in puts. That, along with a couple more lines in start to
> prepare for C code, and a branch to main(), gets us "hello world".
> Run with
> 
> qemu-system-ppc64 -M pseries            \
>         -bios powerpc/boot_rom.bin      \
>         -display none -serial stdio     \
>         -kernel powerpc/selftest.elf
> 
> (We're still not relocating yet, that comes in a later patch. Thus,
>  testing hello-world at this point requires a hacked QEMU and linking
>  the unit test at QEMU's kernel load address.)
> 
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> Tested-by: Laurent Vivier <lvivier@redhat.com>
> ---
>  lib/powerpc/asm/hcall.h | 46 ++++++++++++++++++++++++++++
>  lib/powerpc/hcall.c     | 79 +++++++++++++++++++++++++++++++++++++++++++++++++
>  lib/powerpc/io.c        | 15 ++++++++--
>  lib/ppc64/asm/hcall.h   |  1 +
>  powerpc/Makefile.common |  2 ++
>  powerpc/cstart64.S      | 21 +++++++++++++
>  6 files changed, 162 insertions(+), 2 deletions(-)
>  create mode 100644 lib/powerpc/asm/hcall.h
>  create mode 100644 lib/powerpc/hcall.c
>  create mode 100644 lib/ppc64/asm/hcall.h
> 
> diff --git a/lib/powerpc/asm/hcall.h b/lib/powerpc/asm/hcall.h
> new file mode 100644
> index 0000000000000..f861287ac2083
> --- /dev/null
> +++ b/lib/powerpc/asm/hcall.h
> @@ -0,0 +1,46 @@
> +#ifndef _ASMPOWERPC_HCALL_H_
> +#define _ASMPOWERPC_HCALL_H_
> +/*
> + * Copyright (C) 2016, Red Hat Inc, Andrew Jones <drjones@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU LGPL, version 2.
> + */
> +
> +#define SC1			0x44000022
> +#define SC1_REPLACEMENT		0x7c000268
> +
> +#define H_SUCCESS		0
> +#define H_HARDWARE		-1
> +#define H_FUNCTION		-2
> +#define H_PRIVILEGE		-3
> +#define H_PARAMETER		-4
> +
> +#define H_SET_DABR		0x28
> +#define H_PUT_TERM_CHAR		0x58
> +
> +#ifndef __ASSEMBLY__
> +#include <libcflat.h>
> +
> +/*
> + * hcall_have_broken_sc1 checks if we're on a host with a broken sc1.
> + * Returns true if we are.
> + */
> +extern bool hcall_have_broken_sc1(void);
> +
> +/*
> + * hcall_patch_broken_sc1 patches hcall's sc1 instruction, if needed,
> + * allowing all hypercalls built on it to work.
> + */
> +extern void hcall_patch_broken_sc1(void);
> +
> +/*
> + * hcall is the hypercall wrapper function. unittests may do what
> + * they like, but the framework should make all hypercalls through
> + * here to ensure they use a working sc1 instruction, and properly
> + * handle clobbered registers. @nr is the hypercall number.
> + */
> +extern unsigned long
> +hcall(unsigned long nr, unsigned long *in, unsigned long *out);
> +
> +#endif /* !__ASSEMBLY__ */
> +#endif /* _ASMPOWERPC_HCALL_H_ */
> diff --git a/lib/powerpc/hcall.c b/lib/powerpc/hcall.c
> new file mode 100644
> index 0000000000000..db99949352133
> --- /dev/null
> +++ b/lib/powerpc/hcall.c
> @@ -0,0 +1,79 @@
> +/*
> + * Hypercall helpers
> + *
> + * broken_sc1 probing/patching inspired by SLOF, see
> + *   SLOF:lib/libhvcall/brokensc1.c
> + *
> + * hcall() implementation inspired by Linux's epapr_hypercall, see
> + *   arch/powerpc/include/asm/epapr_hcalls.h
> + *
> + * Copyright (C) 2016, Red Hat Inc, Andrew Jones <drjones@redhat.com>
> + *
> + * This work is licensed under the terms of the GNU LGPL, version 2.
> + */
> +#include <libcflat.h>
> +#include <asm/hcall.h>
> +
> +static u32 sc1[];
> +
> +bool hcall_have_broken_sc1(void)
> +{
> +	register unsigned long r3 asm("r3") = H_SET_DABR;
> +	register unsigned long r4 asm("r4") = 0;
> +
> +	asm volatile("sc 1"
> +	: "=r" (r3)
> +	: "r" (r3), "r" (r4)
> +	: "r5", "r6", "r7", "r8", "r9", "r10", "r11", "r12");
> +	return r3 == (unsigned long)H_PRIVILEGE;
> +}
> +
> +void hcall_patch_broken_sc1(void)
> +{
> +	if (!hcall_have_broken_sc1())
> +		return;
> +	sc1[0] = SC1_REPLACEMENT;
> +}
> +
> +unsigned long hcall(unsigned long nr, unsigned long *in, unsigned long *out)
> +{
> +	register unsigned long r3 asm("r3") = nr;
> +	register unsigned long r4 asm("r4") = in[0];
> +	register unsigned long r5 asm("r5") = in[1];
> +	register unsigned long r6 asm("r6") = in[2];
> +	register unsigned long r7 asm("r7") = in[3];
> +	register unsigned long r8 asm("r8") = in[4];
> +	register unsigned long r9 asm("r9") = in[5];
> +	register unsigned long r10 asm("r10") = in[6];
> +	register unsigned long r11 asm("r11") = in[7];
> +
> +	asm volatile("bl sc1"
> +		: "=r"(r3), "=r"(r4), "=r"(r5), "=r"(r6), "=r"(r7),
> +		  "=r"(r8), "=r"(r9), "=r"(r10), "=r"(r11)
> +		: "r"(r3), "r"(r4), "r"(r5), "r"(r6), "r"(r7),
> +		  "r"(r8), "r"(r9), "r"(r10), "r"(r11)
> +		: "r12", "memory", "lr");
> +
> +	out[0] = r4;
> +	out[1] = r5;
> +	out[2] = r6;
> +	out[3] = r7;
> +	out[4] = r8;
> +	out[5] = r9;
> +	out[6] = r10;
> +	out[7] = r11;
> +
> +	return r3;

I'm not sure there's much advantage to having this in C, rather than
folding this and the sc1 symbol into a single asm implemented hcall
function.

Doing it that way might more easily allow you to avoid packing the
arguments into an array, before unpacking them into registers again,
which seems a bit perverse.

> +}
> +
> +void putchar(int c)
> +{
> +	unsigned long in[8], out[8];
> +
> +	in[0] = 0; /* default vty */
> +	in[1] = 1; /* just 1 byte */
> +	in[2] = (unsigned long)c << 56;
> +
> +	hcall(H_PUT_TERM_CHAR, in, out);
> +}
> diff --git a/lib/powerpc/io.c b/lib/powerpc/io.c
> index 0af45742fc900..5e1fa8dd96ab6 100644
> --- a/lib/powerpc/io.c
> +++ b/lib/powerpc/io.c
> @@ -6,15 +6,26 @@
>   * This work is licensed under the terms of the GNU LGPL, version 2.
>   */
>  #include <libcflat.h>
> +#include <asm/spinlock.h>
> +
> +extern void halt(int code);
> +extern void putchar(int c);
> +
> +static struct spinlock uart_lock;
>  
>  void io_init(void)
>  {
>  }
>  
> -void puts(const char *s __unused)
> +void puts(const char *s)
>  {
> +	spin_lock(&uart_lock);

The name uart_lock isn't really accurate, since it's a hypervisor
console rather than serial.

> +	while (*s)
> +		putchar(*s++);
> +	spin_unlock(&uart_lock);
>  }
>  
> -void exit(int code __unused)
> +void exit(int code)
>  {
> +	halt(code);
>  }
> diff --git a/lib/ppc64/asm/hcall.h b/lib/ppc64/asm/hcall.h
> new file mode 100644
> index 0000000000000..daabaca510cd4
> --- /dev/null
> +++ b/lib/ppc64/asm/hcall.h
> @@ -0,0 +1 @@
> +#include "../../powerpc/asm/hcall.h"
> diff --git a/powerpc/Makefile.common b/powerpc/Makefile.common
> index 0c3eaba0d3aab..89610b525f0c1 100644
> --- a/powerpc/Makefile.common
> +++ b/powerpc/Makefile.common
> @@ -21,6 +21,7 @@ CFLAGS += -ffreestanding
>  CFLAGS += -Wextra
>  CFLAGS += -O2
>  CFLAGS += -I lib -I lib/libfdt
> +CFLAGS += -Wa,-mregnames
>  
>  asm-offsets = lib/$(ARCH)/asm-offsets.h
>  include scripts/asm-offsets.mak
> @@ -29,6 +30,7 @@ cflatobjs += lib/util.o
>  cflatobjs += lib/alloc.o
>  cflatobjs += lib/devicetree.o
>  cflatobjs += lib/powerpc/io.o
> +cflatobjs += lib/powerpc/hcall.o
>  
>  libgcc := $(shell $(CC) $(machine) --print-libgcc-file-name)
>  start_addr := $(shell printf "%x\n" $$(( $(phys_base) + $(kernel_offset) )))
> diff --git a/powerpc/cstart64.S b/powerpc/cstart64.S
> index f90828dee1c19..623fd693b02d1 100644
> --- a/powerpc/cstart64.S
> +++ b/powerpc/cstart64.S
> @@ -7,13 +7,34 @@
>   */
>  #define __ASSEMBLY__
>  
> +#define LOAD_REG_IMMEDIATE(reg,expr)		\
> +	lis	reg,(expr)@highest;		\
> +	ori	reg,reg,(expr)@higher;		\
> +	rldicr	reg,reg,32,31;			\
> +	oris	reg,reg,(expr)@h;		\
> +	ori	reg,reg,(expr)@l;
> +
> +#define LOAD_REG_ADDR(reg,name)			\
> +	ld	reg,name@got(r2)
> +
>  .section .init
>  
>  .globl start
>  start:
> +	LOAD_REG_IMMEDIATE(r1, stackptr)
> +	LOAD_REG_IMMEDIATE(r2, tocptr)
> +	bl	hcall_patch_broken_sc1

Come to that, is there any point putting hcall_patch_broken_sc1 in C,
rather than just doing it inline here.

> +	bl	main
> +	bl	exit
>  	b	halt
>  
>  .text
> +.align 3
> +
> +.globl sc1
> +sc1:
> +	sc	1
> +	blr
>  
>  .globl halt
>  halt:

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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