Hi,
On 28/01/14 16:43, Christian Kruse wrote:
> ereport(FATAL,
> (errmsg("could not map anonymous shared memory:
> %m"),
> (errno == ENOMEM) ?
> errhint("This error usually means that
> PostgreSQL's request "
> "for a shared memory segment
> exceeded available memory "
> "or swap space. To reduce the
> request size (currently "
> "%zu bytes), reduce
> PostgreSQL's shared memory usage, "
> "perhaps by reducing
> shared_buffers or "
> "max_connections.",
> *size) : 0));
>
> did not emit a errhint when using clang, although errno == ENOMEM was
> true. The same code works with gcc.According to http://llvm.org/bugs/show_bug.cgi?id=18644#c5 this is not a compiler bug but a difference between gcc and clang. Clang seems to use a left-to-right order of evaluation while gcc uses a right-to-left order of evaluation. So if errmsg changes errno this would lead to errno == ENOMEM evaluated to false. I added a watch point on errno and it turns out that exactly this happens: in src/common/psprintf.c line 114 nprinted = vsnprintf(buf, len, fmt, args); errno gets set to 0. This means that we will miss errhint/errdetail if we use errno in a ternary operator and clang. Should we work on this issue? Best regards, -- Christian Kruse http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
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