Thread: spurious use of %m format in pg_upgrade
pg_upgrade's pg_scandir_internal() makes use of the non-standard %m format: pg_log(PG_FATAL, "could not open directory \"%s\": %m\n", dirname); Is this an oversight, or is there an undocumented assumption that this code will only be used on platforms where %m works? (Which platforms don't have scandir() anyway?)
Peter Eisentraut <peter_e@gmx.net> writes: > pg_upgrade's pg_scandir_internal() makes use of the non-standard %m > format: > > pg_log(PG_FATAL, "could not open directory \"%s\": %m\n", dirname); > > Is this an oversight, or is there an undocumented assumption that this > code will only be used on platforms where %m works? Surely an oversight; everywhere else in frontend code, we take care to use strerror instead. Is there a way to persuade gcc to complain about such extensions when used in contexts where we don't know they work? > (Which platforms don't have scandir() anyway?) Hmmm ... my neolithic HPUX box has it, but OTOH the Open Group specs seem to have added it only in Issue 7 (2008), so I'd not want to bet money that any random Unix has got it. regards, tom lane
On tor, 2011-07-07 at 00:22 -0400, Tom Lane wrote: > Is there a way to persuade gcc to complain about such extensions when > used in contexts where we don't know they work? I don't think so. First of all, the comment in pg_config_manual.h says that we *want* the compiler to recognize %m as valid, and we apply the same attribute globally. And secondly, the difference between the gnu_printf attribute and the plain printf attribute is that the latter checks for what the target's C library accepts, which is equivalent to gnu_printf if you're on glibc, at least. According to the gcc source code, the target is supposed to override the conversion specifier list accordingly, but it looks like, for example, FreeBSD doesn't do that, which could be considered a bug there. The only override in the gcc source code itself is MinGW, which is where the whole trouble in pg_config_manual.h stems from in the first place. (Look for TARGET_OVERRIDES_FORMAT_ATTRIBUTES in the gcc source if you want to investigate.) There does not, unfortunately, appear to be an attribute that says to check conversion specifiers according to some standard (even though the internal structures of gcc appear to support that, but they'd currently have %m in the wrong category there anyway).
Peter Eisentraut wrote: > pg_upgrade's pg_scandir_internal() makes use of the non-standard %m > format: > > pg_log(PG_FATAL, "could not open directory \"%s\": %m\n", dirname); > > Is this an oversight, or is there an undocumented assumption that this > code will only be used on platforms where %m works? > > (Which platforms don't have scandir() anyway?) Yes, surely an oversight, and I see it has been removed --- good. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. +