linux-kernel - Re: [PATCH] RISC-V: Add address map dumper

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Date:   Mon, 11 Nov 2019 22:55:28 +0100
From:   Mike Rapoport <rppt@...ux.ibm.com>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     Yash Shah <yash.shah@...ive.com>,
        "Paul Walmsley ( Sifive)" <paul.walmsley@...ive.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "palmer@...belt.com" <palmer@...belt.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "Anup.Patel@....com" <Anup.Patel@....com>,
        "ren_guo@...ky.com" <ren_guo@...ky.com>,
        "bmeng.cn@...il.com" <bmeng.cn@...il.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        Sachin Ghadi <sachin.ghadi@...ive.com>
Subject: Re: [PATCH] RISC-V: Add address map dumper

On Mon, Nov 11, 2019 at 11:14:30AM -0700, Logan Gunthorpe wrote:
> 
> 
> On 2019-11-10 10:27 p.m., Yash Shah wrote:
> > Add support for dumping the kernel address space layout to the console.
> > User can enable CONFIG_DEBUG_VM_LAYOUT to dump the virtual memory region
> > into dmesg buffer during boot-up.
> 
> Cool, I'd find this useful. Though, is there any reason we don't do this
> more generally for all architectures?

Some architectures do this, some don't. I don't think there's a particular
reason we don't do this generally, it just evolved that way :)
 
> > Signed-off-by: Yash Shah <yash.shah@...ive.com>
> > ---
> > This patch is based on Linux 5.4-rc6 and tested on SiFive HiFive Unleashed
> > board.
> > ---
> >  arch/riscv/Kconfig.debug |  9 +++++++++
> >  arch/riscv/mm/init.c     | 30 ++++++++++++++++++++++++++++++
> >  2 files changed, 39 insertions(+)
> > 
> > diff --git a/arch/riscv/Kconfig.debug b/arch/riscv/Kconfig.debug
> > index e69de29..cdedfd3 100644
> > --- a/arch/riscv/Kconfig.debug
> > +++ b/arch/riscv/Kconfig.debug
> > @@ -0,0 +1,9 @@
> > +config DEBUG_VM_LAYOUT
> > +	bool "Print virtual memory layout on boot up"
> > +	depends on DEBUG_KERNEL
> > +	help
> > +	  Say Y here if you want to dump the kernel virtual memory layout to
> > +	  dmesg log on boot up. This information is only useful for kernel
> > +	  developers who are working in architecture specific areas of the
> > +	  kernel. It is probably not a good idea to enable this feature in a
> > +	  production kernel.
> > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > index 79cfb35..fcb8144 100644
> > --- a/arch/riscv/mm/init.c
> > +++ b/arch/riscv/mm/init.c
> > @@ -55,6 +55,36 @@ void __init mem_init(void)
> >  	memblock_free_all();
> >  
> >  	mem_init_print_info(NULL);
> > +#ifdef CONFIG_DEBUG_VM_LAYOUT
> 
> Generally, it's best to avoid #ifdefs inside functions, it's even
> counter-indicated in the style guide[1].
> 
> > +#define MLK(b, t) b, t, (((t) - (b)) >> 10)
> > +#define MLM(b, t) b, t, (((t) - (b)) >> 20)
> > +#define MLK_ROUNDUP(b, t) b, t, DIV_ROUND_UP(((t) - (b)), SZ_1K)
> 
> I personally find these inline defines rather ugly. Maybe it would be
> better to have a helper function that prints a single line. Also seems
> like MLK and MLK_ROUNDUP could be the same assuming the entries in MLK
> are aligned...
> 
> > +
> > +	pr_notice("Virtual kernel memory layout:\n"
> > +			"    fixmap  : 0x%08lx - 0x%08lx   (%4ld kB)\n"
> > +			"    vmemmap : 0x%08lx - 0x%08lx   (%4ld MB)\n"
> > +			"    vmalloc : 0x%08lx - 0x%08lx   (%4ld MB)\n"
> > +			"    lowmem  : 0x%08lx - 0x%08lx   (%4ld MB)\n"
> > +			"      .init : 0x%px - 0x%px   (%4td kB)\n"
> > +			"      .text : 0x%px - 0x%px   (%4td kB)\n"
> > +			"      .data : 0x%px - 0x%px   (%4td kB)\n"
> > +			"       .bss : 0x%px - 0x%px   (%4td kB)\n",
> > +
> > +			MLK(FIXADDR_START, FIXADDR_TOP),
> > +			MLM(VMEMMAP_START, VMEMMAP_END),
> > +			MLM(VMALLOC_START, VMALLOC_END),
> > +			MLM(PAGE_OFFSET, (unsigned long)high_memory),
> > +
> > +			MLK_ROUNDUP(__init_begin, __init_end),
> > +			MLK_ROUNDUP(_text, _etext),
> > +			MLK_ROUNDUP(_sdata, _edata),
> > +			MLK_ROUNDUP(__bss_start, __bss_stop));
> > +
> > +#undef MLK
> > +#undef MLM
> > +#undef MLK_ROUNDUP
> > +#endif
> >  }
> >  
> >  #ifdef CONFIG_BLK_DEV_INITRD
> 
> Thanks,
> 
> Logan
> 
> [1]
> https://www.kernel.org/doc/html/latest/process/coding-style.html#conditional-compilation

-- 
Sincerely yours,
Mike.