On Fri, Jun 08, 2018 at 03:33:51PM -0700, Palmer Dabbelt wrote:

On Fri, 08 Jun 2018 10:32:07 PDT (-0700), catalin.marinas@arm.com wrote:

quoted

On Wed, May 16, 2018 at 11:18:49AM +0300, Yury Norov wrote:

quoted

diff --git a/arch/Kconfig b/arch/Kconfig
index 76c0b54443b1..ee079244dc3c 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig

@@ -264,6 +264,21 @@ config ARCH_THREAD_STACK_ALLOCATOR
 config ARCH_WANTS_DYNAMIC_TASK_STRUCT
 	bool

+config ARCH_32BIT_OFF_T
+	bool
+	depends on !64BIT
+	help
+	  All new 32-bit architectures should have 64-bit off_t type on
+	  userspace side which corresponds to the loff_t kernel type. This
+	  is the requirement for modern ABIs. Some existing architectures
+	  already have 32-bit off_t. This option is enabled for all such
+	  architectures explicitly. Namely: arc, arm, blackfin, cris, frv,
+	  h8300, hexagon, m32r, m68k, metag, microblaze, mips32, mn10300,
+	  nios2, openrisc, parisc32, powerpc32, score, sh, sparc, tile32,
+	  unicore32, x86_32 and xtensa. This is the complete list. Any
+	  new 32-bit architecture should declare 64-bit off_t type on user
+	  side and so should not enable this option.

Do you know if this is the case for riscv and nds32, merged in the
meantime? If not, I suggest you drop this patch altogether and just
define force_o_largefile() for arm64/ilp32 as we don't seem to stick to
"all new 32-bit architectures should have 64-bit off_t".

We (RISC-V) don't have support for rv32i in glibc yet, so there really isn't
a fixed ABI there yet.  From my understanding the rv32i port as it currently
stands has a 32-bit off_t (via __kernel_off_t being defined as long), so
this change would technically be a kernel ABI break.

Since we don't have rv32i glibc yet I'm not fundamentally opposed to an ABI
break.  Is there a concrete advantage to this?

One obvious advantage is manipulating large files - if file is greater than
2G, you cannot easily mmap(), lseek() etc with 32-bit offset.

Another point is unification of layuots for structures like struct
stat between 32- and 64-bit worlds.

On glibc side it helps to unify 32-bit and 64-bit versions of syscalls.
Refer, for example this commit:
3c7f1f59cd161 (Consolidate lseek/lseek64/llseek implementations).

Yury