[LLVMbugs] [Bug 24168] New: #including files from /sys on Linux adds extra null characters

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=24168

            Bug ID: 24168
           Summary: #including files from /sys on Linux adds extra null
                    characters
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: ncraun at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Hello,

I recently encountered a bug where #including files from /sys on Linux will
read extra null characters that are not originally in that file.

The bug can be reproduced by #including any file from /sys, for example:

bug.c:
    #include "/sys/devices/system/cpu/cpu0/cache/index0/coherency_line_size"

This makes clang generate about several thousand warnings about null
characters:

/sys/devices/system/cpu/cpu0/cache/index0/coherency_line_size:2:1968: warning: 
      null character ignored [-Wnull-character

However, if you run something like cat
/sys/devices/system/cpu/cpu0/cache/index0/coherency_line_size you see that the
file does not have all these extra null characters. On my machine cat cat
/sys/devices/system/cpu/cpu0/cache/index0/coherency_line_size just prints out
"64".

So somehow the preprocessor is reading many more null characters than are
actually in the file. Now of course there's probably no practical reason to
#include files from /sys, but still it should read the file in correctly
without appending extra null bytes.

I think the preprocessor is not correctly reading the file from the sysfs
virtual file system on /sys.

I am running clang version 3.5.0 on Linux kernel 4.0.6.

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