linux-stable/include/linux/rslib.h
Gustavo A. R. Silva 9dd8bb5f8c rslib.h: Replace zero-length array with flexible-array member
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
2020-04-18 15:44:56 -05:00

131 lines
3.7 KiB
C

// SPDX-License-Identifier: GPL-2.0
/*
* Generic Reed Solomon encoder / decoder library
*
* Copyright (C) 2004 Thomas Gleixner (tglx@linutronix.de)
*
* RS code lifted from reed solomon library written by Phil Karn
* Copyright 2002 Phil Karn, KA9Q
*/
#ifndef _RSLIB_H_
#define _RSLIB_H_
#include <linux/list.h>
#include <linux/types.h> /* for gfp_t */
#include <linux/gfp.h> /* for GFP_KERNEL */
/**
* struct rs_codec - rs codec data
*
* @mm: Bits per symbol
* @nn: Symbols per block (= (1<<mm)-1)
* @alpha_to: log lookup table
* @index_of: Antilog lookup table
* @genpoly: Generator polynomial
* @nroots: Number of generator roots = number of parity symbols
* @fcr: First consecutive root, index form
* @prim: Primitive element, index form
* @iprim: prim-th root of 1, index form
* @gfpoly: The primitive generator polynominal
* @gffunc: Function to generate the field, if non-canonical representation
* @users: Users of this structure
* @list: List entry for the rs codec list
*/
struct rs_codec {
int mm;
int nn;
uint16_t *alpha_to;
uint16_t *index_of;
uint16_t *genpoly;
int nroots;
int fcr;
int prim;
int iprim;
int gfpoly;
int (*gffunc)(int);
int users;
struct list_head list;
};
/**
* struct rs_control - rs control structure per instance
* @codec: The codec used for this instance
* @buffers: Internal scratch buffers used in calls to decode_rs()
*/
struct rs_control {
struct rs_codec *codec;
uint16_t buffers[];
};
/* General purpose RS codec, 8-bit data width, symbol width 1-15 bit */
#ifdef CONFIG_REED_SOLOMON_ENC8
int encode_rs8(struct rs_control *rs, uint8_t *data, int len, uint16_t *par,
uint16_t invmsk);
#endif
#ifdef CONFIG_REED_SOLOMON_DEC8
int decode_rs8(struct rs_control *rs, uint8_t *data, uint16_t *par, int len,
uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
uint16_t *corr);
#endif
/* General purpose RS codec, 16-bit data width, symbol width 1-15 bit */
#ifdef CONFIG_REED_SOLOMON_ENC16
int encode_rs16(struct rs_control *rs, uint16_t *data, int len, uint16_t *par,
uint16_t invmsk);
#endif
#ifdef CONFIG_REED_SOLOMON_DEC16
int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
uint16_t *corr);
#endif
struct rs_control *init_rs_gfp(int symsize, int gfpoly, int fcr, int prim,
int nroots, gfp_t gfp);
/**
* init_rs - Create a RS control struct and initialize it
* @symsize: the symbol size (number of bits)
* @gfpoly: the extended Galois field generator polynomial coefficients,
* with the 0th coefficient in the low order bit. The polynomial
* must be primitive;
* @fcr: the first consecutive root of the rs code generator polynomial
* in index form
* @prim: primitive element to generate polynomial roots
* @nroots: RS code generator polynomial degree (number of roots)
*
* Allocations use GFP_KERNEL.
*/
static inline struct rs_control *init_rs(int symsize, int gfpoly, int fcr,
int prim, int nroots)
{
return init_rs_gfp(symsize, gfpoly, fcr, prim, nroots, GFP_KERNEL);
}
struct rs_control *init_rs_non_canonical(int symsize, int (*func)(int),
int fcr, int prim, int nroots);
/* Release a rs control structure */
void free_rs(struct rs_control *rs);
/** modulo replacement for galois field arithmetics
*
* @rs: Pointer to the RS codec
* @x: the value to reduce
*
* where
* rs->mm = number of bits per symbol
* rs->nn = (2^rs->mm) - 1
*
* Simple arithmetic modulo would return a wrong result for values
* >= 3 * rs->nn
*/
static inline int rs_modnn(struct rs_codec *rs, int x)
{
while (x >= rs->nn) {
x -= rs->nn;
x = (x >> rs->mm) + (x & rs->nn);
}
return x;
}
#endif