Re: [TUHS] C++ / Kernel

Steffen Nurpmeso wrote in <20180823231413.QeahD%steffen(a)sdaoden.eu>: |ron(a)ronnatalie.com wrote in <151301d43b2f$07881ed0$16985c70$(a)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)