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    SubjectRe: [PATCH] crypto: ccp - avoid uninitialized variable warning
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    On 07/31/2017 03:49 PM, Arnd Bergmann wrote:
    > The added support for version 5 CCPs introduced a false-positive
    > warning in the RSA implementation:
    >
    > drivers/crypto/ccp/ccp-ops.c: In function 'ccp_run_rsa_cmd':
    > drivers/crypto/ccp/ccp-ops.c:1856:3: error: 'sb_count' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    >
    > This changes the code in a way that should make it easier for
    > the compiler to track the state of the sb_count variable, and
    > avoid the warning.
    >
    > Fixes: 6ba46c7d4d7e ("crypto: ccp - Fix base RSA function for version 5 CCPs")
    > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
    > ---
    > drivers/crypto/ccp/ccp-ops.c | 3 ++-
    > 1 file changed, 2 insertions(+), 1 deletion(-)
    >
    > diff --git a/drivers/crypto/ccp/ccp-ops.c b/drivers/crypto/ccp/ccp-ops.c
    > index 40c062ad8726..a8bc207b099a 100644
    > --- a/drivers/crypto/ccp/ccp-ops.c
    > +++ b/drivers/crypto/ccp/ccp-ops.c
    > @@ -1758,6 +1758,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue *cmd_q, struct ccp_cmd *cmd)
    > o_len = 32 * ((rsa->key_size + 255) / 256);
    > i_len = o_len * 2;
    >
    > + sb_count = 0;
    > if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0)) {
    > /* sb_count is the number of storage block slots required
    > * for the modulus.
    > @@ -1852,7 +1853,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue *cmd_q, struct ccp_cmd *cmd)
    > ccp_dm_free(&exp);
    >
    > e_sb:
    > - if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0))
    > + if (sb_count)
    > cmd_q->ccp->vdata->perform->sbfree(cmd_q, op.sb_key, sb_count);
    >
    > return ret;
    >

    This is a fine solution. However, having lived with this annoyance for a
    while, and even hoping that a
    a later compiler fixes it, I would have preferred to either:

    1) Initialize the local variable at declaration time, or

    2) Use this patch, which the compiler could optimize as it sees fit, and
    maintains a clear distinction
    for the code path for older devices:

    diff --git a/drivers/crypto/ccp/ccp-ops.c b/drivers/crypto/ccp/ccp-ops.c
    index 40c062a..a3a884a 100644
    --- a/drivers/crypto/ccp/ccp-ops.c
    +++ b/drivers/crypto/ccp/ccp-ops.c
    @@ -1733,7 +1733,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
    *cmd_q, struct ccp_cmd *cmd)
    struct ccp_rsa_engine *rsa = &cmd->u.rsa;
    struct ccp_dm_workarea exp, src, dst;
    struct ccp_op op;
    - unsigned int sb_count, i_len, o_len;
    + unsigned int i_len, o_len;
    int ret;

    /* Check against the maximum allowable size, in bits */
    @@ -1762,7 +1762,7 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
    *cmd_q, struct ccp_cmd *cmd)
    /* sb_count is the number of storage block slots required
    * for the modulus.
    */
    - sb_count = o_len / CCP_SB_BYTES;
    + unsigned int sb_count = o_len / CCP_SB_BYTES;
    op.sb_key = cmd_q->ccp->vdata->perform->sballoc(cmd_q,
    sb_count);
    if (!op.sb_key)
    @@ -1853,7 +1853,10 @@ static int ccp_run_rsa_cmd(struct ccp_cmd_queue
    *cmd_q, struct ccp_cmd *cmd)

    e_sb:
    if (cmd_q->ccp->vdata->version < CCP_VERSION(5, 0))
    + {
    + unsigned int sb_count = o_len / CCP_SB_BYTES;
    cmd_q->ccp->vdata->perform->sbfree(cmd_q, op.sb_key,
    sb_count);
    + }

    return ret;
    }

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