read(2) into some addresses doesn't return data on RPi

[Peter Jeremy]

On 2015-Jan-10 17:04:12 +1100, Peter Jeremy <peter at rulingia.com> wrote:
>Running the attached program on /dev/mmcsd0s1 gave me the following results:

Which got stripped (hence the signature failure).

-- 
Peter Jeremy
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#include <fcntl.h>
#include <unistd.h>
#include <err.h>
#include <stdio.h>
#include <stdlib.h>

#define RLEN 512

static void check(int fd, int num, char *buf);
static void initbuf(char *buf);
static void checkbuf(char *buf, int num);

int main(int argc, char **argv) {
	char buf[65536];
	int fd, off;

	fd = open(argv[1], O_RDONLY);
	if (fd < 0)
		err(1, "open %s failed", argv[1]);

	for (off = 2*RLEN; off < sizeof(buf) - 2*RLEN; off += 8)
		check(fd, 1, buf + off);
}

static void check(int fd, int num, char *buf) {
	initbuf(buf);
	if (read(fd, buf, RLEN) != RLEN)
		err(1, "read%d failed", num);
	checkbuf(buf, num);
}

static void initbuf(char *buf) {
	int i;
	for (i = -RLEN; i < RLEN*2; i += sizeof(0ULL)) {
		*(unsigned long long *)(buf + i) = 0xfeedbabedeadbeefULL;
	}
}

#define FAIL (RLEN / sizeof(0ULL))

static void checkbuf(char *buf, int num) {
	int i, j;

	for (i = -RLEN, j = 0; i < 0; i += sizeof(0ULL)) {
		if (*(unsigned long long *)(buf + i) != 0xfeedbabedeadbeefULL)
			j++;
	}
	printf("read%d(%p) pre:%s", num, buf,
	       (j == 0) ? "OK" : (j == FAIL) ? "FAIL" : "PFAIL");
	fprintf(stderr, "read%d(%p) pre:%s", num, buf,
	       (j == 0) ? "OK" : (j == FAIL) ? "FAIL" : "PFAIL");

	for (i = 0, j = 0; i < RLEN; i += sizeof(0ULL)) {
		if (*(unsigned long long *)(buf + i) == 0xfeedbabedeadbeefULL)
			j++;
	}
	printf(" buf:%s", (j == 0) ? "OK" : (j == FAIL) ? "FAIL" : "PFAIL");
	fprintf(stderr, " buf:%s",
		(j == 0) ? "OK" : (j == FAIL) ? "FAIL" : "PFAIL");

	for (i = RLEN, j = 0; i < RLEN*2; i += sizeof(0ULL)) {
		if (*(unsigned long long *)(buf + i) != 0xfeedbabedeadbeefULL)
			j++;
	}
	printf(" post:%s\n", (j == 0) ? "OK" : (j == FAIL) ? "FAIL" : "PFAIL");
	fprintf(stderr, " post:%s\n",
		(j == 0) ? "OK" : (j == FAIL) ? "FAIL" : "PFAIL");
	fflush(stdout);
	fsync(1);
	fflush(stderr);
	fsync(2);
}
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