From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:55927) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TOL5Y-0004MT-4C for qemu-devel@nongnu.org; Wed, 17 Oct 2012 00:18:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TOL5W-00017R-S5 for qemu-devel@nongnu.org; Wed, 17 Oct 2012 00:18:36 -0400 Received: from mail-pb0-f45.google.com ([209.85.160.45]:59325) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TOL5W-00017F-M5 for qemu-devel@nongnu.org; Wed, 17 Oct 2012 00:18:34 -0400 Received: by mail-pb0-f45.google.com with SMTP id rp2so6699043pbb.4 for ; Tue, 16 Oct 2012 21:18:34 -0700 (PDT) Sender: Richard Henderson From: Richard Henderson Date: Wed, 17 Oct 2012 14:17:16 +1000 Message-Id: <1350447438-8603-3-git-send-email-rth@twiddle.net> In-Reply-To: <1350447438-8603-1-git-send-email-rth@twiddle.net> References: <1350447438-8603-1-git-send-email-rth@twiddle.net> Subject: [Qemu-devel] [PATCH 2/4] linux-user: Rewrite __get_user/__put_user with __builtin_choose_expr List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Riku Voipio The previous formuation with multiple assignments to __typeof(*hptr) falls down when hptr is qualified const. E.g. with const struct S *p, p->f is also qualified const. With this formulation, there's no assignment to any local variable. Signed-off-by: Richard Henderson --- linux-user/qemu.h | 67 ++++++++++++++++++++++++++++++------------------------- 1 file changed, 37 insertions(+), 30 deletions(-) diff --git a/linux-user/qemu.h b/linux-user/qemu.h index 5e53dca..bf0c911 100644 --- a/linux-user/qemu.h +++ b/linux-user/qemu.h @@ -287,36 +287,43 @@ static inline int access_ok(int type, abi_ulong addr, abi_ulong size) (type == VERIFY_READ) ? PAGE_READ : (PAGE_READ | PAGE_WRITE)) == 0; } -/* NOTE __get_user and __put_user use host pointers and don't check access. */ -/* These are usually used to access struct data members once the - * struct has been locked - usually with lock_user_struct(). - */ -#define __put_user(x, hptr)\ -({ __typeof(*hptr) pu_ = (x);\ - switch(sizeof(*hptr)) {\ - case 1: break;\ - case 2: pu_ = tswap16(pu_); break; \ - case 4: pu_ = tswap32(pu_); break; \ - case 8: pu_ = tswap64(pu_); break; \ - default: abort();\ - }\ - memcpy(hptr, &pu_, sizeof(pu_)); \ - 0;\ -}) - -#define __get_user(x, hptr) \ -({ __typeof(*hptr) gu_; \ - memcpy(&gu_, hptr, sizeof(gu_)); \ - switch(sizeof(*hptr)) {\ - case 1: break; \ - case 2: gu_ = tswap16(gu_); break; \ - case 4: gu_ = tswap32(gu_); break; \ - case 8: gu_ = tswap64(gu_); break; \ - default: abort();\ - }\ - (x) = gu_; \ - 0;\ -}) +/* NOTE __get_user and __put_user use host pointers and don't check access. + These are usually used to access struct data members once the struct has + been locked - usually with lock_user_struct. */ + +/* Tricky points: + - Use __builtin_choose_expr to avoid type promotion from ?:, + - Invalid sizes result in a "invalid use of void expression" error, + stemming from the fact that the return type of abort is void. + - While we eliminate byte stores with the "true" part of the first + choose, the "false" part of the first choose must remain valid + to avoid tripping over the "invalid use" error above. Thus the + use of <= 2 to keep byte stores syntactically ok in the discarded + expression. */ + +#define __put_user(x, hptr) \ +(__builtin_choose_expr(sizeof(*(hptr)) == 1, *(hptr) = (uint8_t)(x), \ + __builtin_choose_expr(sizeof(*(hptr)) <= 2, unaligned_w16, \ + __builtin_choose_expr(sizeof(*(hptr)) == 4, unaligned_w32, \ + __builtin_choose_expr(sizeof(*(hptr)) == 8, unaligned_w64, abort))) \ + ((hptr), \ + __builtin_choose_expr(sizeof(*(hptr)) <= 2, tswap16((uint16_t)(x)), \ + __builtin_choose_expr(sizeof(*(hptr)) == 4, tswap32((uint32_t)(x)), \ + __builtin_choose_expr(sizeof(*(hptr)) == 8, tswap64((uint64_t)(x)), \ + abort()))))), \ + 0) + +#define __get_user(x, hptr) \ +((x) = \ + __builtin_choose_expr(sizeof(*(hptr)) == 1, *(hptr), \ + __builtin_choose_expr(sizeof(*(hptr)) == 2, \ + (typeof(*(hptr)))tswap16(unaligned_r16(hptr)), \ + __builtin_choose_expr(sizeof(*(hptr)) == 4, \ + (typeof(*(hptr)))tswap32(unaligned_r32(hptr)), \ + __builtin_choose_expr(sizeof(*(hptr)) == 8, \ + (typeof(*(hptr)))tswap64(unaligned_r64(hptr)), \ + abort())))), \ + 0) /* put_user()/get_user() take a guest address and check access */ /* These are usually used to access an atomic data type, such as an int, -- 1.7.11.7