Kconfig-induced build errors: CONFIG_PAGE_OFFSET

[Atish Patra]

On Wed, Jan 27, 2021 at 7:18 PM Randy Dunlap <rdunlap at infradead.org> wrote:
>
> Hi,
>
> I took a riscv-32 .config from kernel test robot (it was for a clang build)
> and did a "make olddefconfig" (using gcc tools) and got build errors
> due to this config item from arch/riscv/Kconfig;
>
>
> config PAGE_OFFSET
>         hex
>         default 0xC0000000 if 32BIT && MAXPHYSMEM_1GB
>         default 0x80000000 if 64BIT && !MMU
>         default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB
>         default 0xffffffe000000000 if 64BIT && MAXPHYSMEM_128GB
>
> PAGE_OFFSET is undefined for the case of 32BIT && MAXPHYSMEM_2GB.

Because, RV32 doesn't support 2GB physical memory yet.

The compilation errors can be fixed by not allowing MAXPHYSMEM_2GB for RV32 and
MAXPHYSMEM_1GB for RV64. How about this ?

--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -253,8 +253,10 @@ choice
        default MAXPHYSMEM_128GB if 64BIT && CMODEL_MEDANY

        config MAXPHYSMEM_1GB
+               depends on 32BIT
                bool "1GiB"
        config MAXPHYSMEM_2GB
+               depends on 64BIT && CMODEL_MEDLOW
                bool "2GiB"
        config MAXPHYSMEM_128GB
                depends on 64BIT && CMODEL_MEDANY


> That causes lots of errors when _AC() is used to paste
> CONFIG_PAGE_OFFSET to "UL", like these:
>
> In file included from ../include/vdso/const.h:5,
>                  from ../include/linux/const.h:4,
>                  from ../include/linux/bits.h:5,
>                  from ../include/linux/bitops.h:6,
>                  from ../include/linux/kernel.h:11,
>                  from ../init/do_mounts_initrd.c:3:
> ../arch/riscv/include/asm/uaccess.h: In function '__access_ok':
> ../arch/riscv/include/asm/page.h:34:46: error: 'UL' undeclared (first use in this function)
>    34 | #define PAGE_OFFSET  _AC(CONFIG_PAGE_OFFSET, UL)
>       |                                              ^~
> ../include/uapi/linux/const.h:20:23: note: in definition of macro '__AC'
>    20 | #define __AC(X,Y) (X##Y)
>       |                       ^
> ../arch/riscv/include/asm/page.h:34:22: note: in expansion of macro '_AC'
>    34 | #define PAGE_OFFSET  _AC(CONFIG_PAGE_OFFSET, UL)
>       |                      ^~~
> ../arch/riscv/include/asm/pgtable.h:26:27: note: in expansion of macro 'PAGE_OFFSET'
>    26 | #define VMALLOC_START    (PAGE_OFFSET - VMALLOC_SIZE)
>       |                           ^~~~~~~~~~~
> ../arch/riscv/include/asm/pgtable.h:41:24: note: in expansion of macro 'VMALLOC_START'
>    41 | #define VMEMMAP_START (VMALLOC_START - VMEMMAP_SIZE)
>       |                        ^~~~~~~~~~~~~
> ../arch/riscv/include/asm/pgtable.h:50:26: note: in expansion of macro 'VMEMMAP_START'
>    50 | #define PCI_IO_END       VMEMMAP_START
>       |                          ^~~~~~~~~~~~~
> ../arch/riscv/include/asm/pgtable.h:51:27: note: in expansion of macro 'PCI_IO_END'
>    51 | #define PCI_IO_START     (PCI_IO_END - PCI_IO_SIZE)
>       |                           ^~~~~~~~~~
> ../arch/riscv/include/asm/pgtable.h:53:26: note: in expansion of macro 'PCI_IO_START'
>    53 | #define FIXADDR_TOP      PCI_IO_START
>       |                          ^~~~~~~~~~~~
> ../arch/riscv/include/asm/pgtable.h:59:27: note: in expansion of macro 'FIXADDR_TOP'
>    59 | #define FIXADDR_START    (FIXADDR_TOP - FIXADDR_SIZE)
>       |                           ^~~~~~~~~~~
> ../arch/riscv/include/asm/pgtable.h:471:19: note: in expansion of macro 'FIXADDR_START'
>   471 | #define TASK_SIZE FIXADDR_START
>       |                   ^~~~~~~~~~~~~
> ../arch/riscv/include/asm/uaccess.h:56:17: note: in expansion of macro 'TASK_SIZE'
>    56 |  return size <= TASK_SIZE && addr <= TASK_SIZE - size;
>
>
> I suppose that it wants something like this, but someone else can
> fix/use the correct default value here:
>
> ---
>
> From: Randy Dunlap <rdunlap at infradead.org>
>
> Provide a default value for PAGE_OFFSET for the case of
> 32BIT and MAXPHYSMEM_2GB.
>
> Fixes many build errors.
>
> Signed-off-by: Randy Dunlap <rdunlap at infradead.org>
> ---
>  arch/riscv/Kconfig |    1 +
>  1 file changed, 1 insertion(+)
>
> --- linux-next-20210125.orig/arch/riscv/Kconfig
> +++ linux-next-20210125/arch/riscv/Kconfig
> @@ -143,6 +143,7 @@ config PA_BITS
>  config PAGE_OFFSET
>         hex
>         default 0xC0000000 if 32BIT && MAXPHYSMEM_1GB
> +       default 0x80000000 if 32BIT && MAXPHYSMEM_2GB
>         default 0x80000000 if 64BIT && !MMU
>         default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB
>         default 0xffffffe000000000 if 64BIT && MAXPHYSMEM_128GB
>
>
>
> --
> ~Randy
> Reported-by: Randy Dunlap <rdunlap at infradead.org>
>
>
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-- 
Regards,
Atish