Date: Fri, 21 Feb 2020 14:07:05 -0800 From: Conrad Meyer <cem@freebsd.org> To: Li-Wen Hsu <lwhsu@freebsd.org> Cc: Antoine Brodin <antoine@freebsd.org>, Hiroki Sato <hrs@freebsd.org>, src-committers <src-committers@freebsd.org>, svn-src-all <svn-src-all@freebsd.org>, svn-src-head <svn-src-head@freebsd.org> Subject: Re: svn commit: r358152 - head/bin/sh Message-ID: <CAG6CVpXfjoGmCME0ph87YpfDc=VYQVLpoQ4NpvvajxOb9xSh0A@mail.gmail.com> In-Reply-To: <CAKBkRUzv%2BkB5W-VBacSp4k6YqWyDyCEKZr1W5vEtajojnAMs9A@mail.gmail.com> References: <202002200301.01K31RTk043426@repo.freebsd.org> <CAALwa8kNAb0ME7v6gqdUPCcc%2BnZ9si0VYk0AveEndmTQfxsQ2g@mail.gmail.com> <CAKBkRUzv%2BkB5W-VBacSp4k6YqWyDyCEKZr1W5vEtajojnAMs9A@mail.gmail.com>
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Given the report and looking at the change, I suspect the problem is
the promotion of '-residue' from size_t (unsigned 32-bit on i386) to
off_t (signed 64-bit). Something like '-(off_t)residue' or even
'off_t residue;' should fix it.
Repro:
static void
myoff(off_t foo)
{
printf("%jd\n", (intmax_t)foo);
}
void
main(int argc, char **argv)
{
uint32_t sz = 1023;
myoff(-sz);
}
Prints: "4294966273" (not: "-1023"). Either proposed fix above
produces the expected -1023.
Best,
Conrad
On Fri, Feb 21, 2020 at 1:53 PM Li-Wen Hsu <lwhsu@freebsd.org> wrote:
>
> On Sat, Feb 22, 2020 at 4:58 AM Antoine Brodin <antoine@freebsd.org> wrote:
> >
> > On Thu, Feb 20, 2020 at 4:01 AM Hiroki Sato <hrs@freebsd.org> wrote:
> > >
> > > Author: hrs
> > > Date: Thu Feb 20 03:01:27 2020
> > > New Revision: 358152
> > > URL: https://svnweb.freebsd.org/changeset/base/358152
> > >
> > > Log:
> > > Improve performance of "read" built-in command when using a seekable
> > > fd.
> > >
> > > The read built-in command calls read(2) with a 1-byte buffer because
> > > newline characters need to be detected even on a byte stream which
> > > comes from a non-seekable file descriptor. Because of this, the
> > > following script calls >6,000 read(2) to show a 6KiB file:
> > >
> > > while read IN; do echo "$IN"; done < /COPYRIGHT
> > >
> > > When the input byte stream is seekable, it is possible to read a data
> > > block and then reposition the file pointer to where a newline
> > > character found. This change adds a small buffer to do this and
> > > reduces the number of read(2) calls.
> > >
> > > Theoretically, multiple built-in commands reading the same seekable
> > > byte stream in a single pipe chain can share the buffer. However,
> > > this change just makes a single invocation of the read built-in
> > > allocate a buffer and deallocate it every time for simplicity.
> > > Although this causes read(2) to read the same regions multiple times,
> > > the performance penalty should be small compared to the reduction of
> > > read(2) calls.
> > >
> > > Reviewed by: jilles
> > > MFC after: 1 week
> > > Differential Revision: https://reviews.freebsd.org/D23747
> >
> > This seems to be broken on at least i386.
> > Please either fix or revert.
> >
> > Antoine (with hat: portmgr)
>
> Could you provide more detail? I'm worried because I didn't see
> related regression from the recent test results. We may need to add
> more test against the breakage you mentioned.
>
> Thanks,
> Li-Wen
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