[Bug general/21008] New: Incompatible with MUSL libc: error.h and error() not provided

[luizluca at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=21008

            Bug ID: 21008
           Summary: Incompatible with MUSL libc: error.h and error() not
                    provided
           Product: elfutils
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: general
          Assignee: unassigned at sourceware dot org
          Reporter: luizluca at gmail dot com
                CC: elfutils-devel at sourceware dot org
  Target Milestone: ---

Hello,

>From original bug 21002:

- The idea of using system.h to define error () seems fine. But the current
replacement doesn't seem complete. error () also flushes stdout first. Which we
don't really seem to use, so might not be essential. But it also calls exit
(status) if status != 0. Which is essential to how error is used in elfutils.
Also error () updates error_message_count which is used in a couple of cases to
know what exit code a program should use (if error itself didn't exit).

The proposed solution would be to:

1) move error.h inclusion into system.h and conditionally include either
error.h or err.h
2) build a good replacement for error()

The only problem is #2. 

This thread is about this problem:
http://marc.info/?l=musl&m=140404527111778&w=2

The solution that was already present in OpenWRT/LEDE was simply to use:

#define error(status, errno, ...) err(status, __VA_ARGS__)

Which is not enough as error replacement. It always exits even when status is
0, it does not flush stdout and it does not increase the (absent)
error_message_count.

I didn't noticed the missing error_message_count as a problem because, for
OpenWRT/LEDE, only elfutils libs where compiled (and they don't use
error_message_count). So, for my use case, this might be enough:

#define error(status, errno, ...) \
   fflush(stdout); \
   warn(__VA_ARGS__); \ // == err(status,...) without exit
   if (errno) exit(errno);

There is a minor problem of ignoring errno, which might be considered an
"optional feature".

For a full built, the problem is error_message_count. It is a global variable
and it must be initialized. Probably the best solution would be to create a
simplified error.h/error.c, which exports error and error_message_count and
gets optionally build and linked (autoconf) into the generated files when
error.h is absent.

Some existing approaches so far:

https://github.com/GregorR/musl-cross/blob/master/patches/elfutils-no_error.patch
(original inspiration)
https://patchwork.openembedded.org/patch/111665/

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