Em Thu, May 02, 2019 at 09:55:26AM -0700, Vineet Gupta escreveu: > On 4/30/19 8:12 PM, Rich Felker wrote: > >>> What are you trying to achieve? I was just CC'd and I'm missing the > >>> context. > >> > >> Sorry I added you as a subject matter expert but didn't provide enough > >> context. > >> > >> The original issue [1] was perf failing to build on ARC due to perf tools > >> needing > >> a copy of unistd.h but this thread [2] was a small side issue of > >> auto-detecting > >> libc variaint in perf tools where despite uClibc tools, glibc is declared > >> to be > >> detected, due to uClibc's historical hack of defining __GLIBC__. So > >> __GLIBC__ is > >> not sufficient (and probably not the right interface to begin wtih) to > >> ensure glibc. > >> > >> [1] > >> http://lists.infradead.org/pipermail/linux-snps-arc/2019-April/005676.html > >> [2] > >> http://lists.infradead.org/pipermail/linux-snps-arc/2019-April/005684.html > > > > I think you misunderstood -- > > :-) > > > I'm asking what you're trying to achieve > > by detecting whether the libc is glibc, rather than whether it has > > some particular interface you want to conditionally use. This is a > > major smell and is usually something wrong that shouldn't be done. > > Good question indeed. Back in 2015 I initially ran into some quirks due to > subtle > libc differences. At the time perf has a fwd ref for strlcpy which exactly > matched glibc but not uClibc. see commit a83d869f300bf91 "(perf tools: Elide > strlcpy warning with uclibc)" or 0215d59b154 "(tools lib: Reinstate strlcpy() > header guard with __UCLIBC__)" > > But this still used the libc defined symbol __UCLIBC__ or __GLIBC__ > > Your question however pertains to perf glibc feature check where perf > generates an > alternate symbol HAVE_GLIBC_SUPPORT. > > This is dubious as first of all it detects glibc even for uClibc builds.
> Even of we were to improve it, there seems to be no users of this symbol. > > $git grep HAVE_GLIBC_SUPPORT > perf/Makefile.config: CFLAGS += -DHAVE_GLIBC_SUPPORT > perf/builtin-version.c: STATUS(HAVE_GLIBC_SUPPORT, glibc) > > So I'd propose to remove it ! This is some remnant of the past, I'll check further but will end up just ditching it altogether as you suggest :-) [acme@quaco perf]$ find tools/ -type f | xargs grep HAVE_GLIBC_SUPPORT tools/perf/builtin-version.c: STATUS(HAVE_GLIBC_SUPPORT, glibc); tools/perf/Makefile.config: CFLAGS += -DHAVE_GLIBC_SUPPORT [acme@quaco perf]$ Its just this case that ends up using that feature detection program, [acme@quaco perf]$ vim tools/perf/Makefile.config [acme@quaco perf]$ find tools/ -type f | xargs grep feature-glibc tools/perf/Makefile.config: ifeq ($(feature-glibc), 1) tools/perf/Makefile.config:ifeq ($(feature-glibc), 1) [acme@quaco perf]$ BTW the function on it doesn't mean anything, what matters is if the program builds or not :-) - Arnaldo _______________________________________________ linux-snps-arc mailing list linux-snps-arc@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-snps-arc
