[PATCH] Unify Solaris procfs and largefile handling
Simon Marchi
simark@simark.ca
Tue Jul 28 13:47:19 GMT 2020
On 2020-06-30 11:15 a.m., Rainer Orth wrote:
> GDB currently doesn't build on 32-bit Solaris:
>
> * On Solaris 11.4/x86:
>
> In file included from /usr/include/sys/procfs.h:26,
> from /vol/src/gnu/gdb/hg/master/dist/gdb/i386-sol2-nat.c:24:
> /usr/include/sys/old_procfs.h:31:2: error: #error "Cannot use procfs in the large file compilation environment"
> #error "Cannot use procfs in the large file compilation environment"
> ^~~~~
>
> * On Solaris 11.3/x86 there are several more instances of this.
>
> The interaction between procfs and large-file support historically has
> been a royal mess on Solaris:
>
> * There are two versions of the procfs interface:
>
> ** The old ioctl-based /proc, deprecated and not used any longer in
> either gdb or binutils.
>
> ** The `new' (introduced in Solaris 2.6, 1997) structured /proc.
>
> * There are two headers one can possibly include:
>
> ** <procfs.h> which only provides the structured /proc, definining
> _STRUCTURED_PROC=1 and then including ...
>
> ** <sys/procfs.h> which defaults to _STRUCTURED_PROC=0, the ioctl-based
> /proc, but provides structured /proc if _STRUCTURED_PROC == 1.
>
> * procfs and the large-file environment didn't go well together:
>
> ** Until Solaris 11.3, <sys/procfs.h> would always #error in 32-bit
> compilations when the large-file environment was active
> (_FILE_OFFSET_BITS == 64).
>
> ** In both Solaris 11.4 and Illumos, this restriction was lifted for
> structured /proc.
>
> So one has to be careful always to define _STRUCTURED_PROC=1 when
> testing for or using <sys/procfs.h> on Solaris. As the errors above
> show, this isn't always the case in binutils-gdb right now.
>
> Also one may need to disable large-file support for 32-bit compilations
> on Solaris. config/largefile.m4 meant to do this by wrapping the
> AC_SYS_LARGEFILE autoconf macro with appropriate checks, yielding
> ACX_LARGEFILE. Unfortunately the macro doesn't always succeed because
> it neglects the _STRUCTURED_PROC part.
>
> To make things even worse, since GCC 9 g++ predefines
> _FILE_OFFSET_BITS=64 on Solaris. So even if largefile.m4 deciced not to
> enable large-file support, this has no effect, breaking the gdb build.
>
> This patch addresses all this as follows:
>
> * All tests for the <sys/procfs.h> header are made with
> _STRUCTURED_PROC=1, the definition going into the various config.h
> files instead of having to make them (and sometimes failing) in the
> affected sources.
>
> * To cope with the g++ predefine of _FILE_OFFSET_BITS=64,
> -U_FILE_OFFSET_BITS is added to various *_CPPFLAGS variables. It had
> been far easier to have just
>
> #undef _FILE_OFFSET_BITS
>
> in config.h, but unfortunately such a construct in config.in is
> commented by config.status irrespective of indentation and whitespace
> if large-file support is disabled. I found no way around this and
> putting the #undef in several global headers for bfd, binutils, ld,
> and gdb seemed way more invasive.
>
> * Last, the applicability check in largefile.m4 was modified only to
> disable largefile support if really needed. To do so, it checks if
> <sys/procfs.h> compiles with _FILE_OFFSET_BITS=64 defined. If it
> doesn't, the disabling only happens if gdb exists in-tree and isn't
> disabled, otherwise (building binutils from a tarball), there's no
> conflict.
>
> What initially confused me was the check for $plugins here, which
> originally caused the disabling not to take place. Since AC_PLUGINGS
> does enable plugin support if <dlfcn.h> exists (which it does on
> Solaris), the disabling never happened.
>
> I could find no explanation why the linker plugin needs large-file
> support but thought it would be enough if gld and GCC's lto-plugin
> agreed on the _FILE_OFFSET_BITS value. Unfortunately, that's not
> enough: lto-plugin uses the simple-object interface from libiberty,
> which includes off_t arguments. So to fully disable large-file
> support would mean also disabling it in libiberty and its users: gcc
> and libstdc++-v3. This seems highly undesirable, so I decided to
> disable the linker plugin instead if large-file support won't work.
>
> The patch allows binutils+gdb to build on i386-pc-solaris2.11 (both
> Solaris 11.3 and 11.4, using GCC 9.3.0 which is the worst case due to
> predefined _FILE_OFFSET_BITS=64). Also regtested on
> amd64-pc-solaris2.11 (again on Solaris 11.3 and 11.4),
> x86_64-pc-linux-gnu and i686-pc-linux-gnu.
>
> Ok for master? While it would be nice to have this in the binutils 2.35
> and gdb 10 releases, I'd fully understand if the patch were considered
> too risky so close to the branch dates.
>
> Rainer
I understood some (not all of this).
Regarding the "old" and "new" procfs interfaces, can't you just always include
procfs.h and never sys/procfs.h? Using sys/procfs.h seems like it would only
be useful for pre-1997 Solaris, which doesn't seem useful. And then you could
have large file support always on?
Simon
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