Hi ALex, On 1/9/21 10:15 PM, Alejandro Colomar wrote: > A more detailed notice is on realloc(3p). > > ...... > > $ man 3p realloc \ > |sed -n \ > -e '/APPLICATION USAGE/,/^$/p' \ > -e '/FUTURE DIRECTIONS/,/^$/p'; > APPLICATION USAGE > The description of realloc() has been modified from pre‐ > vious versions of this standard to align with the > ISO/IEC 9899:1999 standard. Previous versions explicitly > permitted a call to realloc(p, 0) to free the space > pointed to by p and return a null pointer. While this be‐ > havior could be interpreted as permitted by this version > of the standard, the C language committee have indicated > that this interpretation is incorrect. Applications > should assume that if realloc() returns a null pointer, > the space pointed to by p has not been freed. Since this > could lead to double-frees, implementations should also > set errno if a null pointer actually indicates a failure, > and applications should only free the space if errno was > changed. > > FUTURE DIRECTIONS > This standard defers to the ISO C standard. While that > standard currently has language that might permit real‐ > loc(p, 0), where p is not a null pointer, to free p while > still returning a null pointer, the committee responsible > for that standard is considering clarifying the language > to explicitly prohibit that alternative. > > Bug: 211039 <https://bugzilla.kernel.org/show_bug.cgi?id=211039> > Reported-by: Johannes Pfister <johannes.pfister@xxxxxxxxxxx> > Cc: libc-alpha@xxxxxxxxxxxxxx > Signed-off-by: Alejandro Colomar <alx.manpages@xxxxxxxxx> Thanks. Patch applied. Cheers, Michael > --- > > Hi Johannes, Michael, > > Thanks for the report, Johannes! > Please review that your name is correct (I guessed it from the email). > > Michael, please review the wording. > > Thanks, > > Alex > > man3/malloc.3 | 18 +++++++++++++++++- > 1 file changed, 17 insertions(+), 1 deletion(-) > > diff --git a/man3/malloc.3 b/man3/malloc.3 > index d8b4da62f..467e2438a 100644 > --- a/man3/malloc.3 > +++ b/man3/malloc.3 > @@ -149,7 +149,8 @@ is equal to zero, > and > .I ptr > is not NULL, then the call is equivalent to > -.IR free(ptr) . > +.I free(ptr) > +(this behavior is nonportable; see NOTES). > Unless > .I ptr > is NULL, it must have been returned by an earlier call to > @@ -375,6 +376,21 @@ The > implementation is tunable via environment variables; see > .BR mallopt (3) > for details. > +.SS Nonportable behavior > +The behavior of > +.BR realloc () > +when > +.I size > +is equal to zero, > +and > +.I ptr > +is not NULL, > +is glibc specific; > +other implementations may return NULL, and set > +.IR errno . > +Portable POSIX programs should avoid it. > +See > +.BR realloc (3p). > .SH SEE ALSO > .\" http://g.oswego.edu/dl/html/malloc.html > .\" A Memory Allocator - by Doug Lea > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
