Hello Alex, On 8/25/20 3:05 PM, Alejandro Colomar wrote: > Hi Michael, > > On 8/25/20 2:35 PM, Michael Kerrisk (man-pages) wrote: >> Patch applied, but I had to fix up the title line, which got taken >> from the mail subject line. Probably best to send subsequent patches >> as new mails, rather than as replies to this thread. > > This time I replied to the thread (so that the conversation can be > followed in the archive), but changed the subject. I hope that works. > > (I sent this email only to you by accident; I'm sending it again with > the CCs). > > Patch (3) as numbered in the previous replies: > > -------------------------------------------------------------------- >>From 1cb973629d94a048c5dcbe13fef76173f99dc3de Mon Sep 17 00:00:00 2001 > From: Alejandro Colomar <colomar.6.4.3@xxxxxxxxx> > Date: Tue, 25 Aug 2020 14:52:03 +0200 > Subject: [PATCH] cmsg.3, getaddrinfo_a.3 getgrouplist.3: Use sizeof > consistently > > Use ``sizeof`` consistently through all the examples in the following > way: > > - When the result of ``sizeof`` is multiplied (or otherwise modified), > write ``sizeof`` in the first place. > > Rationale: > > ``(sizeof(x) * INT_MAX * 2)`` doesn't overflow. > > ``(INT_MAX * 2 * sizeof(x))`` overflows, giving incorrect > results. > > As a side effect, the parentheses of ``sizeof`` are not next to > the parentheses of the whole expression, and it is visually > easier to read. > > Detailed rationale: > > In C, successive multiplications are evaluated left to right (*), and > therefore here is what happens (assuming x86_64): > > ``(sizeof(x) * INT_MAX * 2)``: > > 1) sizeof(x) * INT_MAX (the type is the largest of both, which is > size_t (unsigned long; uint64_t)). > 2) ANS * 2 (the type is again the largest: size_t) > > ``(INT_MAX * 2 * sizeof(x))``: > > 1) INT_MAX * 2 (the type is the largest of both, which is > int as both are int (int; int32_t), so the > result is already truncated as it doesn't fit > an int; at this point, the intermediate result > will be 2^32 - 2 (``INT_MAX - 1``) (if I did > the math right)). > 2) ANS * 2 (the type is again the largest of both: size_t; > however, ANS was already incorrect, so the > result will be an incorrect size_t value) > > (*): https://en.cppreference.com/w/c/language/operator_precedence > > Signed-off-by: Alejandro Colomar <colomar.6.4.3@xxxxxxxxx> Thanks! Patch applied. Cheers, Michael > --- > man3/cmsg.3 | 2 +- > man3/getaddrinfo_a.3 | 2 +- > man3/getgrouplist.3 | 2 +- > 3 files changed, 3 insertions(+), 3 deletions(-) > > diff --git a/man3/cmsg.3 b/man3/cmsg.3 > index 2f9910093..99ee950f9 100644 > --- a/man3/cmsg.3 > +++ b/man3/cmsg.3 > @@ -242,7 +242,7 @@ cmsg = CMSG_FIRSTHDR(&msg); > cmsg\->cmsg_level = SOL_SOCKET; > cmsg\->cmsg_type = SCM_RIGHTS; > cmsg\->cmsg_len = CMSG_LEN(sizeof(int) * NUM_FD); > -memcpy(CMSG_DATA(cmsg), myfds, NUM_FD * sizeof(int)); > +memcpy(CMSG_DATA(cmsg), myfds, sizeof(int) * NUM_FD); > .EE > .in > .SH SEE ALSO > diff --git a/man3/getaddrinfo_a.3 b/man3/getaddrinfo_a.3 > index af8f88937..cd4cad0dc 100644 > --- a/man3/getaddrinfo_a.3 > +++ b/man3/getaddrinfo_a.3 > @@ -473,7 +473,7 @@ add_requests(void) > > while ((host = strtok(NULL, " "))) { > nreqs++; > - reqs = realloc(reqs, nreqs * sizeof(reqs[0])); > + reqs = realloc(reqs, sizeof(reqs[0]) * nreqs); > > reqs[nreqs \- 1] = calloc(1, sizeof(*reqs[0])); > reqs[nreqs \- 1]\->ar_name = strdup(host); > diff --git a/man3/getgrouplist.3 b/man3/getgrouplist.3 > index aea52d999..372f2613f 100644 > --- a/man3/getgrouplist.3 > +++ b/man3/getgrouplist.3 > @@ -164,7 +164,7 @@ main(int argc, char *argv[]) > > ngroups = atoi(argv[2]); > > - groups = malloc(ngroups * sizeof(gid_t)); > + groups = malloc(sizeof(gid_t) * ngroups); > if (groups == NULL) { > perror("malloc"); > exit(EXIT_FAILURE); > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
