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3381df0954
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 <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200521185707.GA3661@embeddedor
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
69 lines
1.6 KiB
C
69 lines
1.6 KiB
C
/*
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* linux/arch/m68k/tools/amiga/dmesg.c -- Retrieve the kernel messages stored
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* in Chip RAM with the kernel command
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* line option `debug=mem'.
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*
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* © Copyright 1996 by Geert Uytterhoeven <geert@linux-m68k.org>
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*
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*
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* Usage:
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*
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* dmesg
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* dmesg <CHIPMEM_END>
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*
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*
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* This file is subject to the terms and conditions of the GNU General Public
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* License. See the file COPYING in the main directory of the Linux
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* distribution for more details.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <unistd.h>
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#define CHIPMEM_START 0x00000000
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#define CHIPMEM_END 0x00200000 /* overridden by argv[1] */
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#define SAVEKMSG_MAGIC1 0x53415645 /* 'SAVE' */
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#define SAVEKMSG_MAGIC2 0x4B4D5347 /* 'KMSG' */
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struct savekmsg {
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u_long magic1; /* SAVEKMSG_MAGIC1 */
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u_long magic2; /* SAVEKMSG_MAGIC2 */
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u_long magicptr; /* address of magic1 */
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u_long size;
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char data[];
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};
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int main(int argc, char *argv[])
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{
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u_long start = CHIPMEM_START, end = CHIPMEM_END, p;
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int found = 0;
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struct savekmsg *m = NULL;
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if (argc >= 2)
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end = strtoul(argv[1], NULL, 0);
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printf("Searching for SAVEKMSG magic...\n");
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for (p = start; p <= end-sizeof(struct savekmsg); p += 4) {
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m = (struct savekmsg *)p;
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if ((m->magic1 == SAVEKMSG_MAGIC1) && (m->magic2 == SAVEKMSG_MAGIC2) &&
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(m->magicptr == p)) {
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found = 1;
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break;
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}
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}
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if (!found)
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printf("Not found\n");
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else {
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printf("Found %ld bytes at 0x%08lx\n", m->size, (u_long)&m->data);
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puts(">>>>>>>>>>>>>>>>>>>>");
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fflush(stdout);
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write(1, &m->data, m->size);
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fflush(stdout);
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puts("<<<<<<<<<<<<<<<<<<<<");
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}
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return(0);
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}
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