how to fool gcc?

[Harish Mohanan]

try compiling without optimisation i.e. without the -O flag to gcc.

Harish

Dag-Erling Smørgrav wrote:

>I'm having trouble with some uncommitted OpenPAM patches that I'd like
>to get into the tree.  The problem actually doesn't occur with a
>normal build, but it prevents me from building a debugging version of
>libpam.
>
>Part of the patch declares openpam_log(3) as printf-like so gcc can
>check format strings etc.  However, openpam_log(3) is also used in
>debugging macros such as this:
>
>#define RETURNS(s) do { \
>        if ((s) == NULL) \
>                openpam_log(PAM_LOG_DEBUG, "returning NULL"); \
>        else \
>                openpam_log(PAM_LOG_DEBUG, "returning '%s'", (s)); \
>        return (s); \
>} while (0)
>
>The problem is that when it encounters RETURNS(NULL), gcc complains
>that I'm passing a NULL argument to printf(3), even though it should
>be obvious that I'm not:
>
>cc -O -pipe -march=pentium2 -I/usr/src/lib/libpam/libpam -I/home/des/projects/openpam/include -DLIB_MAJ=2 -g -DDEBUG -Wsystem-headers -Werror -Wall -Wno-format-y2k -W -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wreturn-type -Wcast-qual -Wwrite-strings -Wswitch -Wshadow -Wcast-align -Wbad-function-cast -Wchar-subscripts -Winline -Wnested-externs -Wredundant-decls -c /home/des/projects/openpam/lib/openpam_get_option.c
>/home/des/projects/openpam/lib/openpam_get_option.c: In function `openpam_get_option':
>/home/des/projects/openpam/lib/openpam_get_option.c:62: warning: reading through null pointer (arg 4)
>/home/des/projects/openpam/lib/openpam_get_option.c:73: warning: reading through null pointer (arg 4)
>*** Error code 1
>
>Stop in /usr/src/lib/libpam/libpam.
>
>I've tried various twists to fool gcc, such as casting (s) to (const
>char *) and adding 0 to it hoping that the addition would defeat its
>NULL pointer check.  Nothing I've tried works, though, and I would
>really hate to have to lower the WANRS level just for this.
>
>Any suggestions?
>
>DES
>  
>