Re: [PATCH] contrib/elf2dmp: prevent uninitialized warning

[Viktor Prutyanov <viktor.prutyanov@phystech.edu>]

On Fri, 7 Feb 2020 12:16:01 +0800
<kuhn.chenqun@huawei.com> wrote:

> From: Chen Qun <kuhn.chenqun@huawei.com>
> 
> Fix compilation warnings:
> contrib/elf2dmp/main.c:66:17: warning: ‘KdpDataBlockEncoded’ may be
> used uninitialized in this function [-Wmaybe-uninitialized]
>          block = __builtin_bswap64(block ^ kdbe) ^ kwa;
>                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> contrib/elf2dmp/main.c:78:24: note: ‘KdpDataBlockEncoded’ was
> declared here uint64_t kwn, kwa, KdpDataBlockEncoded;
>                         ^~~~~~~~~~~~~~~~~~~
> 
> Reported-by: Euler Robot <euler.robot@huawei.com>
> Signed-off-by: Chen Qun <kuhn.chenqun@huawei.com>
> ---
>  contrib/elf2dmp/main.c | 25 ++++++++++++-------------
>  1 file changed, 12 insertions(+), 13 deletions(-)
> 
> diff --git a/contrib/elf2dmp/main.c b/contrib/elf2dmp/main.c
> index 9a2dbc2902..203b9e6d04 100644
> --- a/contrib/elf2dmp/main.c
> +++ b/contrib/elf2dmp/main.c
> @@ -76,6 +76,7 @@ static KDDEBUGGER_DATA64 *get_kdbg(uint64_t
> KernBase, struct pdb_reader *pdb, DBGKD_DEBUG_DATA_HEADER64 kdbg_hdr;
>      bool decode = false;
>      uint64_t kwn, kwa, KdpDataBlockEncoded;
> +    uint64_t KiWaitNever, KiWaitAlways;
>  
>      if (va_space_rw(vs,
>                  KdDebuggerDataBlock + offsetof(KDDEBUGGER_DATA64,
> Header), @@ -84,21 +85,19 @@ static KDDEBUGGER_DATA64
> *get_kdbg(uint64_t KernBase, struct pdb_reader *pdb, return NULL;
>      }
>  
> -    if (memcmp(&kdbg_hdr.OwnerTag, OwnerTag, sizeof(OwnerTag))) {
> -        uint64_t KiWaitNever, KiWaitAlways;
> -
> -        decode = true;
> +    if (!SYM_RESOLVE(KernBase, pdb, KiWaitNever) ||
> +            !SYM_RESOLVE(KernBase, pdb, KiWaitAlways) ||
> +            !SYM_RESOLVE(KernBase, pdb, KdpDataBlockEncoded)) {
> +        return NULL;
> +    }
>  
> -        if (!SYM_RESOLVE(KernBase, pdb, KiWaitNever) ||
> -                !SYM_RESOLVE(KernBase, pdb, KiWaitAlways) ||
> -                !SYM_RESOLVE(KernBase, pdb, KdpDataBlockEncoded)) {
> -            return NULL;
> -        }
> +    if (va_space_rw(vs, KiWaitNever, &kwn, sizeof(kwn), 0) ||
> +            va_space_rw(vs, KiWaitAlways, &kwa, sizeof(kwa), 0)) {
> +        return NULL;
> +    }
>  
> -        if (va_space_rw(vs, KiWaitNever, &kwn, sizeof(kwn), 0) ||
> -                va_space_rw(vs, KiWaitAlways, &kwa, sizeof(kwa), 0))
> {
> -            return NULL;
> -        }
> +    if (memcmp(&kdbg_hdr.OwnerTag, OwnerTag, sizeof(OwnerTag))) {
> +        decode = true;
>  
>          printf("[KiWaitNever] = 0x%016"PRIx64"\n", kwn);
>          printf("[KiWaitAlways] = 0x%016"PRIx64"\n", kwa);

Hi!

I suppose the problem is in your compiler, because kdbg_decode() is
only used when KdpDataBlockEncoded is already initialized by
SYM_RESOLVE(). 

-- 
Viktor Prutyanov