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[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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