2018-03-28 14:01:52

by Arnd Bergmann

Subject: [PATCH] nvme: use upper_32_bits() instead of bit shift

On 32-bit architectures, we cannot shift a size_t by 32 bits to the right
without a compiler warning:

drivers/nvme/host/core.c: In function 'nvme_get_log_ext':
drivers/nvme/host/core.c:2237:43: error: right shift count >= width of type [-Werror=shift-count-overflow]
c.get_log_page.lpou = cpu_to_le32(offset >> 32ULL);
^~
include/uapi/linux/byteorder/little_endian.h:33:51: note: in definition of macro '__cpu_to_le32'
#define __cpu_to_le32(x) ((__force __le32)(__u32)(x))
^
drivers/nvme/host/core.c:2237:24: note: in expansion of macro 'cpu_to_le32'
c.get_log_page.lpou = cpu_to_le32(offset >> 32ULL);

The code is correct, but using the upper_32_bits() and lower_32_bits()
macros that were introduced for this operation makes it easier to read
and avoids the warning.

Fixes: 70da6094a646 ("nvme: implement log page low/high offset and dwords")
Signed-off-by: Arnd Bergmann <[email protected]>
---
drivers/nvme/host/core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 4e4136bfc37f..0a81704b763f 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -2233,8 +2233,8 @@ int nvme_get_log_ext(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
c.get_log_page.lid = log_page;
c.get_log_page.numdl = cpu_to_le16(dwlen & ((1 << 16) - 1));
c.get_log_page.numdu = cpu_to_le16(dwlen >> 16);
- c.get_log_page.lpol = cpu_to_le32(offset & ((1ULL << 32) - 1));
- c.get_log_page.lpou = cpu_to_le32(offset >> 32ULL);
+ c.get_log_page.lpol = cpu_to_le32(lower_32_bits(offset));
+ c.get_log_page.lpou = cpu_to_le32(upper_32_bits(offset));

return nvme_submit_sync_cmd(ctrl->admin_q, &c, log, size);
}
--
2.9.0

2018-03-28 14:07:26

by Johannes Thumshirn

Subject: Re: [PATCH] nvme: use upper_32_bits() instead of bit shift

Looks good,
Reviewed-by: Johannes Thumshirn <[email protected]>
--
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2018-03-28 14:20:22

by Keith Busch

Subject: Re: [PATCH] nvme: use upper_32_bits() instead of bit shift

On Wed, Mar 28, 2018 at 03:57:47PM +0200, Arnd Bergmann wrote:
> @@ -2233,8 +2233,8 @@ int nvme_get_log_ext(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
> c.get_log_page.lid = log_page;
> c.get_log_page.numdl = cpu_to_le16(dwlen & ((1 << 16) - 1));
> c.get_log_page.numdu = cpu_to_le16(dwlen >> 16);
> - c.get_log_page.lpol = cpu_to_le32(offset & ((1ULL << 32) - 1));
> - c.get_log_page.lpou = cpu_to_le32(offset >> 32ULL);
> + c.get_log_page.lpol = cpu_to_le32(lower_32_bits(offset));
> + c.get_log_page.lpou = cpu_to_le32(upper_32_bits(offset));
>
> return nvme_submit_sync_cmd(ctrl->admin_q, &c, log, size);
> }

Right, Matias posted the same fix here:

http://lists.infradead.org/pipermail/linux-nvme/2018-March/016474.html

In addition to the type safe shifting, a 64-bit type was used to match
the spec.