svn commit: r285644 - head/contrib/sqlite3

Dimitry Andric dim at FreeBSD.org
Sat Jul 18 22:46:47 UTC 2015


On 18 Jul 2015, at 00:53, Pedro Giffuni <pfg at freebsd.org> wrote:
> 
> On 07/17/15 17:26, Peter Jeremy wrote:
>> On 2015-Jul-16 22:07:14 +0000, "Pedro F. Giffuni" <pfg at FreeBSD.org> wrote:
>>> Log:
>> ...
>>>  sqlite: clean a couple of invocations of memcpy(3)
>>>    Found almost accidentally by our native gcc when enhanced with
>>>  FORTIFY_SOURCE.
>> ...
>>> -  memcpy((void *)&aHdr[1], (void *)&pWal->hdr, sizeof(WalIndexHdr));
>>> +  memcpy((void *)&aHdr[1], (const void *)&pWal->hdr, sizeof(WalIndexHdr));
>>>   walShmBarrier(pWal);
>>> -  memcpy((void *)&aHdr[0], (void *)&pWal->hdr, sizeof(WalIndexHdr));
>>> +  memcpy((void *)&aHdr[0], (const void *)&pWal->hdr, sizeof(WalIndexHdr));
>> If the compiler complained about that, the compiler is broken.
> 
> The change was rather collateral (read cosmetical) to the real warning
> which remains unfixed.
> 
> The compiler warning is this:
> ...
> ===> lib/libsqlite3 (obj,depend,all,install)
> cc1: warnings being treated as errors
> /scratch/tmp/pfg/head/lib/libsqlite3/../../contrib/sqlite3/sqlite3.c: In function 'walIndexWriteHdr':
> /scratch/tmp/pfg/head/lib/libsqlite3/../../contrib/sqlite3/sqlite3.c:49490: warning: passing argument 1 of 'memcpy' discards qualifiers from pointer target type
> /scratch/tmp/pfg/head/lib/libsqlite3/../../contrib/sqlite3/sqlite3.c:49492: warning: passing argument 1 of 'memcpy' discards qualifiers from pointer target type
> --- sqlite3.So ---
> *** [sqlite3.So] Error code 1
> ...
> 
> make[6]: stopped in /scratch/tmp/pfg/head/lib/libsqlite3
> 
> It only happens when using the experimental FORTIFY_SOURCE support [1],
> and it only happens with gcc (the base one is the only tested).
> 
> Yes, I am suspecting a compiler bug but gcc has been really useful to find
> bugs in fortify_source.

Actually, it is right to warn about this, as the casts drop a volatile
specifier:

 49482  static void walIndexWriteHdr(Wal *pWal){
 49483    volatile WalIndexHdr *aHdr = walIndexHdr(pWal);
...
 49490    memcpy((void *)&aHdr[1], (void *)&pWal->hdr, sizeof(WalIndexHdr));
 49491    walShmBarrier(pWal);
 49492    memcpy((void *)&aHdr[0], (void *)&pWal->hdr, sizeof(WalIndexHdr));

If you compile this with clang, and a high enough WARNS level, it tells
you where the problem is:

contrib/sqlite3/sqlite3.c:49490:18: error: cast from 'volatile struct WalIndexHdr *' to 'void *' drops volatile qualifier [-Werror,-Wcast-qual]
  memcpy((void *)&aHdr[1], (void *)&pWal->hdr, sizeof(WalIndexHdr));
                 ^
contrib/sqlite3/sqlite3.c:49492:18: error: cast from 'volatile struct WalIndexHdr *' to 'void *' drops volatile qualifier [-Werror,-Wcast-qual]
  memcpy((void *)&aHdr[0], (void *)&pWal->hdr, sizeof(WalIndexHdr));
                 ^

Similar with newer versions of gcc:

contrib/sqlite3/sqlite3.c:49490:10: error: cast discards 'volatile' qualifier from pointer target type [-Werror=cast-qual]
   memcpy((void *)&aHdr[1], (void *)&pWal->hdr, sizeof(WalIndexHdr));
          ^
contrib/sqlite3/sqlite3.c:49492:10: error: cast discards 'volatile' qualifier from pointer target type [-Werror=cast-qual]
   memcpy((void *)&aHdr[0], (void *)&pWal->hdr, sizeof(WalIndexHdr));
          ^

Removing all the casts does not help, with base gcc it still gives:

contrib/sqlite3/sqlite3.c:49490: warning: passing argument 1 of 'memcpy' discards qualifiers from pointer target type
contrib/sqlite3/sqlite3.c:49492: warning: passing argument 1 of 'memcpy' discards qualifiers from pointer target type

and with clang:

contrib/sqlite3/sqlite3.c:49490:10: error: passing 'volatile WalIndexHdr *' (aka 'volatile struct WalIndexHdr *') to parameter of type 'void *' discards qualifiers
      [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
  memcpy(&aHdr[1], &pWal->hdr, sizeof(WalIndexHdr));
         ^~~~~~~~
/usr/include/string.h:62:31: note: passing argument to parameter here
void    *memcpy(void * __restrict, const void * __restrict, size_t);
                                 ^
contrib/sqlite3/sqlite3.c:49492:10: error: passing 'volatile WalIndexHdr *' (aka 'volatile struct WalIndexHdr *') to parameter of type 'void *' discards qualifiers
      [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
  memcpy(&aHdr[0], &pWal->hdr, sizeof(WalIndexHdr));
         ^~~~~~~~
/usr/include/string.h:62:31: note: passing argument to parameter here
void    *memcpy(void * __restrict, const void * __restrict, size_t);
                                 ^

>>  'const'
>> is a promise to the caller that the given parameter will not be modified
>> by the callee.  There's no requirement that the passed argument be const.
>> As bde commented, the casts are all spurious.
> 
> And since this is contrib'ed code I am not going through the
> code churn but upstream has been notified.

I don't think it is likely that upstream will go through the trouble of
removing -Wcast-qual warnings.  There are 152 of them in sqlite3.c. :-)

-Dimitry

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