Re: [PATCH 1/5] scripts: Add mkstrerror.sh

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On 09/18/2013 06:38 AM, David Howells wrote:
danielfsantos@xxxxxxx wrote:

This is a simple bash script that parses our errno*.h files and formats
them into the error_strings.h header that our strerror and strerror_name
functions will use later.
I presume you haven't tried building with a "make O=foo" build directory?  I
see:

       /bin/sh: /data/fs/linux-2.6-fscache/include/generated/error_strings.h: No such file or directory

when I try it.

No, indeed I haven't, thanks. I'm going to need help figuring out the correct way to put this in the build because the current definitely isn't correct. From what I could tell from digging into the build last night (which I've never carefully analyzed), this should be added somewhere in one of the scripts/Makefile*s and not in the root makefile (as I have done), or maybe even in lib/Makefile.


  (2) Storing the leading 'E' for each symbol is redundant as you can add that
      later so you might want to discard it.

This is a good thought, that's 150-ish bytes, but it will introduce some new challenges. Currently, strerror() functions exactly like "man 3p strerror", except that it returns a pointer to a const string like the POSIX specification should have done. :) So I directly return a pointer to the string within the .rodata section of the object file (same for strerror_name). Omitting the 'E' would require I work up another solution requiring a return buffer or some such, thus increasing complexity and possibly loosing that savings to code.

However, if we wanted to squeze that much more out of it, then we could 7-th bit terminate the strings and save another 150-ish bytes on null terminators or go even further and use some encoding scheme (maybe 32 bits per character)? At 2k for both the error names and the code, I figured it was already pretty low, but if there are some existing libraries in the kernel we could use to do this and not further bloat the text size for decompression then I wouldn't be opposed, so long as it makes sense. And since we're dealing with error conditions which don't happen often, speed shouldn't be a concern.

Thanks!
Daniel

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