llvm-strings excessive memory use when used in a pipe

[emaste]

As reported in FreeBSD bugzilla, after FreeBSD switched from ELF Tool Chain's binary utilities to using LLVM's by default:

It seems the LLVM’s version isn’t able to mmap while
used in a pipe, so it copy ALL the file into memory.

Example:
$ dd if=/dev/urandom of=/tmp/test.file bs=1M count=1024
$ cat /tmp/test.file | strings > /dev/null &

Now with elftoolchain’s strings:
$ ps -o pid,command,vsz,rss | grep strings
53243 strings          12992  2556

And with LLVM’strings:
$ ps -o pid,command,vsz,rss | grep strings
41791 strings          5027836 3413864

And with our use-case, we are using strings on GB files
(like core dump), and it is now consumming all our memory.

[llvmbot]

@llvm/issue-subscribers-tools-llvm-strings

Author: Ed Maste (emaste)

As [reported in FreeBSD bugzilla](https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=286605), after FreeBSD switched from ELF Tool Chain's binary utilities to using LLVM's by default:

It seems the LLVM’s version isn’t able to mmap while
used in a pipe, so it copy ALL the file into memory.

Example:
$ dd if=/dev/urandom of=/tmp/test.file bs=1M count=1024
$ cat /tmp/test.file | strings > /dev/null &

Now with elftoolchain’s strings:
$ ps -o pid,command,vsz,rss | grep strings
53243 strings          12992  2556

And with LLVM’strings:
$ ps -o pid,command,vsz,rss | grep strings
41791 strings          5027836 3413864

And with our use-case, we are using strings on GB files
(like core dump), and it is now consumming all our memory.

[aokblast]

Hello ed, I think #162013 should workaround this issue. You still cannot use cat + pipe. However, you can use ./prog < test.file. The reason is that cat + pipe is actually a FIFO fd. Instead, < works as a regular file.
I have test by your example and works well.