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Date: Tue, 14 Jul 2020 10:44:49 -0500
From: "Gustavo A. R. Silva" <gustavoars@...nel.org>
To: Arnd Bergmann <arnd@...db.de>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org,
"Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: [PATCH][next] hpilo: Replace one-element array with flexible-array
member
There is a regular need in the kernel to provide a way to declare
having a dynamically sized set of trailing elements in a structure.
Kernel code should always use “flexible array members”[1] for these
cases. The older style of one-element or zero-length arrays should
no longer be used[2].
For this particular case, it is important to notice that the cachelines
change from 7 to 6 after the flexible-array conversion:
$ pahole -C 'fifo' drivers/misc/hpilo.o
struct fifo {
u64 nrents; /* 0 8 */
u64 imask; /* 8 8 */
u64 merge; /* 16 8 */
u64 reset; /* 24 8 */
u8 pad_0[96]; /* 32 96 */
/* --- cacheline 2 boundary (128 bytes) --- */
u64 head; /* 128 8 */
u8 pad_1[120]; /* 136 120 */
/* --- cacheline 4 boundary (256 bytes) --- */
u64 tail; /* 256 8 */
u8 pad_2[120]; /* 264 120 */
/* --- cacheline 6 boundary (384 bytes) --- */
u64 fifobar[1]; /* 384 8 */
/* size: 392, cachelines: 7, members: 10 */
/* last cacheline: 8 bytes */
};
$ pahole -C 'fifo' drivers/misc/hpilo.o
struct fifo {
u64 nrents; /* 0 8 */
u64 imask; /* 8 8 */
u64 merge; /* 16 8 */
u64 reset; /* 24 8 */
u8 pad_0[96]; /* 32 96 */
/* --- cacheline 2 boundary (128 bytes) --- */
u64 head; /* 128 8 */
u8 pad_1[120]; /* 136 120 */
/* --- cacheline 4 boundary (256 bytes) --- */
u64 tail; /* 256 8 */
u8 pad_2[120]; /* 264 120 */
/* --- cacheline 6 boundary (384 bytes) --- */
u64 fifobar[]; /* 384 0 */
/* size: 384, cachelines: 6, members: 10 */
};
Lastly, remove unnecessary parentheses in fifo_sz() and fix the following
checkpatch.pl warning for the whole fifo structure:
WARNING: please, no spaces at the start of a line
[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://github.com/KSPP/linux/issues/79
Tested-by: kernel test robot <lkp@...el.com>
Link: https://github.com/GustavoARSilva/linux-hardening/blob/master/cii/kernel-ci/hpilo-20200714.md
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
drivers/misc/hpilo.c | 2 +-
drivers/misc/hpilo.h | 22 +++++++++++-----------
2 files changed, 12 insertions(+), 12 deletions(-)
diff --git a/drivers/misc/hpilo.c b/drivers/misc/hpilo.c
index 927309b86bab..10c975662f8b 100644
--- a/drivers/misc/hpilo.c
+++ b/drivers/misc/hpilo.c
@@ -207,7 +207,7 @@ static void ctrl_setup(struct ccb *ccb, int nr_desc, int l2desc_sz)
static inline int fifo_sz(int nr_entry)
{
/* size of a fifo is determined by the number of entries it contains */
- return (nr_entry * sizeof(u64)) + FIFOHANDLESIZE;
+ return nr_entry * sizeof(u64) + FIFOHANDLESIZE;
}
static void fifo_setup(void *base_addr, int nr_entry)
diff --git a/drivers/misc/hpilo.h b/drivers/misc/hpilo.h
index 1aa433a7f66c..f69ff645cac9 100644
--- a/drivers/misc/hpilo.h
+++ b/drivers/misc/hpilo.h
@@ -160,23 +160,23 @@ struct ccb_data {
#define ILO_START_ALIGN 4096
#define ILO_CACHE_SZ 128
struct fifo {
- u64 nrents; /* user requested number of fifo entries */
- u64 imask; /* mask to extract valid fifo index */
- u64 merge; /* O/C bits to merge in during enqueue operation */
- u64 reset; /* set to non-zero when the target device resets */
- u8 pad_0[ILO_CACHE_SZ - (sizeof(u64) * 4)];
+ u64 nrents; /* user requested number of fifo entries */
+ u64 imask; /* mask to extract valid fifo index */
+ u64 merge; /* O/C bits to merge in during enqueue operation */
+ u64 reset; /* set to non-zero when the target device resets */
+ u8 pad_0[ILO_CACHE_SZ - (sizeof(u64) * 4)];
- u64 head;
- u8 pad_1[ILO_CACHE_SZ - (sizeof(u64))];
+ u64 head;
+ u8 pad_1[ILO_CACHE_SZ - (sizeof(u64))];
- u64 tail;
- u8 pad_2[ILO_CACHE_SZ - (sizeof(u64))];
+ u64 tail;
+ u8 pad_2[ILO_CACHE_SZ - (sizeof(u64))];
- u64 fifobar[1];
+ u64 fifobar[];
};
/* convert between struct fifo, and the fifobar, which is saved in the ccb */
-#define FIFOHANDLESIZE (sizeof(struct fifo) - sizeof(u64))
+#define FIFOHANDLESIZE (sizeof(struct fifo))
#define FIFOBARTOHANDLE(_fifo) \
((struct fifo *)(((char *)(_fifo)) - FIFOHANDLESIZE))
--
2.27.0
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