Steffen Nurpmeso wrote in <20180823231413.QeahD%steffen at sdaoden.eu>:
|ron at ronnatalie.com wrote in <151301d43b2f$07881ed0$16985c70$@ronnatalie.\
|com>:
...
||This union was right in the middle of the buf struct:
...
||
|| union {
|| caddr_t b_addr; /* low order core address */
|| int *b_words; /* words for clearing */
|| struct filsys *b_filsys; /* superblocks */
|| struct dinode *b_dino; /* ilist */
|| daddr_t *b_daddr; /* indirect block */
||} b_un;
||There were a number of other places that did the same thing. It's
||OFFICIALLY now in undefined behavior by the standard (though of course \
||that
||didn't exist in the BSD days) ,
||to store in one element of the union and retrieve it via another. \
|| This is
||one of the reasons why.
|
|Luckily "type punning" is possible. Ach, what do i know;
|nonetheless, i think it is a terrible direction that C goes to,
|now you often need memcpy() to local storage instead of a simple
|assignment (with a cast) in order to avoid undefined behaviour
|that allows compilers to do bad things. On a NetBSD list there
|was a link to such a story not too long ago, the resulting
|C standard compliant code was ridiculous, the last string of fun
|has been screwed out of C. Unfortunately i have not saved the
|message, but Christos Zoulas has been the author.
I have found the link in the history of my browser, the story was
http://pzemtsov.github.io/2016/11/06/bug-story-alignment-on-x86.html
--steffen
|
|Der Kragenbaer, The moon bear,
|der holt sich munter he cheerfully and one by one
|einen nach dem anderen runter wa.ks himself off
|(By Robert Gernhardt)