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From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Date: Thu, 4 Mar 2021 11:41:40 -0300
Message-ID: <CAMXh4bW=kh5K3=fD1HqbXfRC8r4tmSjsCh6xGtV74CWLdSsA_w@mail.gmail.com>
Subject: Re: Directory structure of glibc and header files installed on Linux
To: Peng Yu <pengyu.ut@gmail.com>
Cc: Florian Weimer <fweimer@redhat.com>,
 Peng Yu via Libc-help <libc-help@sourceware.org>
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On Thu, Mar 4, 2021 at 11:20 AM Peng Yu via Libc-help
<libc-help@sourceware.org> wrote:
>
> I can see what files are in the ubuntu package libc6-dev. But that
> does not help with where they come from and what the structure of the
> glibc is. An explanation of the source tree would be helpful.
>
> On 3/4/21, Florian Weimer <fweimer@redhat.com> wrote:
> > * Peng Yu via Libc-help:
> >
> >> I'd like to know the complete list header files installed on Linux.
> >
> > The easiest way is to run build-many-glibcs.py and look at the install
> > trees.  The answer varies from architecture to architecture.

The installed headers are defined by the rule 'headers' in the Makefile:

$ grep -w '\<headers\>.*:=' `find . -iname Makefile`
./dirent/Makefile:headers               := dirent.h bits/dirent.h
bits/dirent_ext.h
./pwd/Makefile:headers := pwd.h
./math/Makefile:headers         := math.h bits/mathcalls.h \
./resource/Makefile:headers       := sys/resource.h bits/resource.h
sys/vlimit.h        \
[...]

However each system can add extra installed headers with the
'sysdep_headers' rule:
 grep -w '\<sysdep_headers\>' `find . -iname Makefile`
./sysdeps/aarch64/Makefile:sysdep_headers += sys/ifunc.h
./sysdeps/x86/Makefile:sysdep_headers += sys/platform/x86.h
./sysdeps/powerpc/Makefile:sysdep_headers += sys/platform/ppc.h
./sysdeps/mach/hurd/Makefile:sysdep_headers += nfs/nfs.h
[...]

And each architecture can still override the header using the sysdeps folders.
For instance, the sysdeps/unix/sysv/linux/Makefile add the
bits/struct_stat.h, and
some architectures override it:

$ find . -iname struct_stat.h
./sysdeps/unix/sysv/linux/generic/bits/struct_stat.h
./sysdeps/unix/sysv/linux/sparc/bits/struct_stat.h
./sysdeps/unix/sysv/linux/alpha/bits/struct_stat.h
./sysdeps/unix/sysv/linux/s390/bits/struct_stat.h
./sysdeps/unix/sysv/linux/microblaze/bits/struct_stat.h
./sysdeps/unix/sysv/linux/x86/bits/struct_stat.h
./sysdeps/unix/sysv/linux/powerpc/bits/struct_stat.h
./sysdeps/unix/sysv/linux/ia64/bits/struct_stat.h
./sysdeps/unix/sysv/linux/m68k/bits/struct_stat.h
./sysdeps/unix/sysv/linux/bits/struct_stat.h
./sysdeps/unix/sysv/linux/mips/bits/struct_stat.h

That's why the simplest solution is as Florian has put it to build a
glibc to the target you want to
inspect and check the installed headers.