Re: [PATCH 04/24] 32-bit userspace ABI: introduce ARCH_32BIT_OFF_T config option

From: Palmer Dabbelt
Date: Fri Jun 08 2018 - 18:34:03 EST


On Fri, 08 Jun 2018 10:32:07 PDT (-0700), catalin.marinas@xxxxxxx wrote:
On Wed, May 16, 2018 at 11:18:49AM +0300, Yury Norov wrote:
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?