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Date: Thu, 18 Oct 2018 16:57:52 +0800 From: Guo Ren <ren_guo@...ky.com> To: Arnd Bergmann <arnd@...db.de> Cc: Andrew Morton <akpm@...ux-foundation.org>, Daniel Lezcano <daniel.lezcano@...aro.org>, David Miller <davem@...emloft.net>, gregkh <gregkh@...uxfoundation.org>, Christoph Hellwig <hch@...radead.org>, Marc Zyngier <marc.zyngier@....com>, Mark Rutland <mark.rutland@....com>, Peter Zijlstra <peterz@...radead.org>, Rob Herring <robh@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>, DTML <devicetree@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>, c-sky_gcc_upstream@...ky.com Subject: Re: [PATCH V9 21/21] csky: support dword access for get_user_size() On Thu, Oct 18, 2018 at 10:34:00AM +0200, Arnd Bergmann wrote: > On Thu, Oct 18, 2018 at 5:41 AM Guo Ren <ren_guo@...ky.com> wrote: > > > > On Wed, Oct 17, 2018 at 05:44:17PM +0200, Arnd Bergmann wrote: > > > On Tue, Oct 16, 2018 at 5:33 AM Guo Ren <ren_guo@...ky.com> wrote: > > > > > > > > Support dword access for get_user_size and redesign put_user_size with > > > > the same style of get_user_size. It's Ok to use xxx_user_asm_common for > > > > all size of variable with ldb, ldh, ldw, ld.d > > > > > > > > ld.d rx, (addr, 0) could "rx <= addr" "and r(x+1) <= addr+4" and this also > > > > follow abiv2 gcc ABI for dword access. > > > > > > Are you sure this is correct for this? > > > > > > static inline u32 get_64_to_32(__u64 __user *p) > > > { > > > u32 ret; > > > get_user(ret, p); > > > return ret; > > > } > > > > > > If I read __get_user_asm_common() right, the ld.d would overwrite > > > two registers, but the caller only expects one, so it clobbers one > > > that might be in use. > > Ah... BUG! I only consider the get_user(u64, u64 *) :P > > > > Change to: > > case 8: \ > > __get_user_asm_dword((x), ptr, "ld.d", retval); \ > > break; > > > > #define __get_user_asm_dword(x, ptr, err) \ > > do { \ > > u64 tmp; \ > > __get_user_asm_common(tmp, ptr, "ld.d", err); \ > > x = typeof(x) tmp; \ > > } while(0) > > > > #define __put_user_asm_dword(x, ptr, err) \ > > do { \ > > u64 tmp = (u64) x; \ > > __put_user_asm_common(tmp, ptr, "st.d", err); \ > > } while(0) > > > > I think this will cause warnings for code that passes a pointer. > > The 64-bit __get_user() is really hard, and most 32-bit architectures don't > implement it at all. If you really want to add it, have a look at what > x86 and arm do. IIRC they both use __builtin_choose_expr(), Thx for the tips and I'll drop the patch first for the upstream. I want to implement it because of make allmodconfig and drivers/android/binder.c need it. I'll learn __builtin_choose_expr() and prepare patch next. Best Regards Guo Ren
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