Horton

Re: Allowing printf("%m") only where it actually works

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Thomas Munro <thomas.munro@enterprisedb.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2018-05-27T01:00:33Z
Lists: pgsql-hackers 
I wrote:
> ... It doesn't take much to make one nontrivial either.  If
> memory serves, malloc() can trash errno on some platforms such as macOS,
> so even just a palloc creates a hazard of a hard-to-reproduce problem.

After digging around in the archives, the closest thing that we seem to
know for certain is that some versions of free() can trash errno, cf

https://www.postgresql.org/message-id/flat/E1UcmpR-0004nn-2i%40wrigleys.postgresql.org

as a result of possibly calling madvise() which might or might not
succeed.  But in the light of that knowledge, how much do you want
to bet that malloc() can't change errno?  And there's the possibility
that a called function does both a palloc and a pfree ...

			regards, tom lane

Commits

  1. In pg_log_generic(), be more paranoid about preserving errno.

  2. Make src/common/exec.c's error logging less ugly.

  3. Select appropriate PG_PRINTF_ATTRIBUTE for recent NetBSD.

  4. Fix detection of the result type of strerror_r().

  5. Try another way to detect the result type of strerror_r().

  6. Clean up *printf macros to avoid conflict with format archetypes.

  7. Fix link failures due to snprintf/strerror changes.

  8. Implement %m in src/port/snprintf.c, and teach elog.c to rely on that.

  9. Always use our own versions of *printf().

  10. Incorporate strerror_r() into src/port/snprintf.c, too.

  11. Convert elog.c's useful_strerror() into a globally-used strerror wrapper.

  12. Revert "Distinguish printf-like functions that support %m from those that don't."

  13. Produce compiler errors if errno is referenced inside elog/ereport calls.

  14. Distinguish printf-like functions that support %m from those that don't.

  15. Fix unportable usage of printf("%m").

  16. Be more robust when strerror() doesn't give a useful result.