| Message ID | 1347895732-22212-2-git-send-email-rth@twiddle.net |
|---|---|
| State | New |
| Headers | show |
On 17 September 2012 16:28, Richard Henderson <rth@twiddle.net> wrote: > Not sure whether this is a gcc bug, but on sparc we wind up > trying to use std to an unaligned address. The patch does > work around the problem. Hmm. I guess this is guest and host having differing alignment requirements for 64 bit types? What case does it fail on? -- PMM
On 09/17/2012 08:35 AM, Peter Maydell wrote: > On 17 September 2012 16:28, Richard Henderson <rth@twiddle.net> wrote: >> Not sure whether this is a gcc bug, but on sparc we wind up >> trying to use std to an unaligned address. The patch does >> work around the problem. > > Hmm. I guess this is guest and host having differing alignment > requirements for 64 bit types? What case does it fail on? I'll have to re-check. I'm pretty sure this was sparc32 hosting arm-linux-user. r~
On 17 September 2012 16:28, Richard Henderson <rth@twiddle.net> wrote: > Not sure whether this is a gcc bug, but on sparc we wind up > trying to use std to an unaligned address. The patch does > work around the problem. > > Signed-off-by: Richard Henderson <rth@twiddle.net> As far as the code is concerned: Reviewed-by: Peter Maydell <peter.maydell@linaro.org> but please rewrite the commit message to be more sure of itself :-) Specifically, this is required because the guest's alignment requirements may be laxer than those of the host, so we can't take a hptr for a 16/32/64 bit type (which only has the alignment restrictions of the guest) and do a gcc pointer dereference on it (which may assume the alignment restrictions of the host). Does anybody know the semantics of the kernel's copy_from_user()? Does it fail on misaligned userspace structs or does it allow them? -- PMM
diff --git a/linux-user/qemu.h b/linux-user/qemu.h index 69b27d7..fc4cc00 100644 --- a/linux-user/qemu.h +++ b/linux-user/qemu.h @@ -289,46 +289,29 @@ static inline int access_ok(int type, abi_ulong addr, abi_ulong size) * struct has been locked - usually with lock_user_struct(). */ #define __put_user(x, hptr)\ -({\ +({ __typeof(*hptr) pu_ = (x);\ switch(sizeof(*hptr)) {\ - case 1:\ - *(uint8_t *)(hptr) = (uint8_t)(typeof(*hptr))(x);\ - break;\ - case 2:\ - *(uint16_t *)(hptr) = tswap16((uint16_t)(typeof(*hptr))(x));\ - break;\ - case 4:\ - *(uint32_t *)(hptr) = tswap32((uint32_t)(typeof(*hptr))(x));\ - break;\ - case 8:\ - *(uint64_t *)(hptr) = tswap64((typeof(*hptr))(x));\ - break;\ - default:\ - abort();\ + 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:\ - x = (typeof(*hptr))*(uint8_t *)(hptr);\ - break;\ - case 2:\ - x = (typeof(*hptr))tswap16(*(uint16_t *)(hptr));\ - break;\ - case 4:\ - x = (typeof(*hptr))tswap32(*(uint32_t *)(hptr));\ - break;\ - case 8:\ - x = (typeof(*hptr))tswap64(*(uint64_t *)(hptr));\ - break;\ - default:\ - /* avoid warning */\ - x = 0;\ - abort();\ + 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;\ })
Not sure whether this is a gcc bug, but on sparc we wind up trying to use std to an unaligned address. The patch does work around the problem. Signed-off-by: Richard Henderson <rth@twiddle.net> --- linux-user/qemu.h | 47 +++++++++++++++-------------------------------- 1 file changed, 15 insertions(+), 32 deletions(-)