RE: [PATCH] mmc-utils: mmc_cmds: fix type-punned warning on &ext_csd[] casting

[Avri Altman <Avri.Altman@xxxxxxx>]

> > When building with -Werror=strict-aliasing error is thrown:
> >
> > mmc_cmds.c: In function 'do_ffu':
> > mmc_cmds.c:2972:2: error: dereferencing type-punned pointer will break
> > strict- aliasing rules [-Werror=strict-aliasing]
> >   sect_done = htole32(*((__u32
> > *)&ext_csd[EXT_CSD_NUM_OF_FW_SEC_PROG_0]));
> >   ^
> > cc1: all warnings being treated as errors
> >
> > Let's fix type-punned breaking strict-aliasing by memcpy() the variable.
> If any, I would just revert commit a1b594ca735e.
> 
> Thanks,
> Avri
Or, how about this untested option.

Thanks,
Avri


index ae7b876..10f7532 100644
--- a/mmc_cmds.c
+++ b/mmc_cmds.c
@@ -58,6 +58,11 @@
 #define WPTYPE_PWRON 2
 #define WPTYPE_PERM 3

+static inline __u32 strict_htole32(__u8 *arr)
+{
+       return arr[0] | arr[1] << 8 | arr[2] << 16 | arr[3] << 24;
+}
+
 int read_extcsd(int fd, __u8 *ext_csd)
 {
        int ret = 0;
@@ -2807,7 +2812,7 @@ static void set_ffu_single_cmd(struct mmc_ioc_multi_cmd *multi_cmd,
                               __u8 *ext_csd, unsigned int bytes, __u8 *buf,
                               off_t offset)
 {
-       __u32 arg = htole32(*((__u32 *)&ext_csd[EXT_CSD_FFU_ARG_0]));
+       __u32 arg = safe_htole32(&ext_csd[EXT_CSD_FFU_ARG_0]);

        /* send block count */
        set_single_cmd(&multi_cmd->cmds[1], MMC_SET_BLOCK_COUNT, 0, 0,
@@ -2827,7 +2832,7 @@ static void set_ffu_single_cmd(struct mmc_ioc_multi_cmd *multi_cmd,
 int do_ffu(int nargs, char **argv)
 {
        int dev_fd, img_fd;
-       int sect_done = 0, retry = 3, ret = -EINVAL;
+       int retry = 3, ret = -EINVAL;
        unsigned int sect_size;
        __u8 ext_csd[512];
        __u8 *buf = NULL;
@@ -2835,6 +2840,7 @@ int do_ffu(int nargs, char **argv)
        char *device;
        struct mmc_ioc_multi_cmd *multi_cmd = NULL;
        unsigned int default_chunk = MMC_IOC_MAX_BYTES;
+       __u32 sect_done = 0;

        assert (nargs == 3 || nargs == 4);

@@ -2968,7 +2974,7 @@ do_retry:
        }

        /* Test if we need to restart the download */
-       sect_done = htole32(*((__u32 *)&ext_csd[EXT_CSD_NUM_OF_FW_SEC_PROG_0]));
+       sect_done = strict_htole32(&ext_csd[EXT_CSD_NUM_OF_FW_SEC_PROG_0]);
        /* By spec, host should re-start download from the first sector if sect_done is 0 */
        if (sect_done == 0) {
                if (retry--) {