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[PATCH v2 03/20] Allow glibc to be compiled without EXEC_PAGESIZE

From: Sergey Bugaev
Subject: [PATCH v2 03/20] Allow glibc to be compiled without EXEC_PAGESIZE
Date: Sat, 23 Mar 2024 20:32:44 +0300

We would like to avoid statically defining any specific page size on
aarch64-gnu, and instead make sure that everything uses the dynamic
page size, available via vm_page_size and GLRO(dl_pagesize).

There are currently a few places in glibc that require EXEC_PAGESIZE
to be defined. Per Roland's suggestion [0], drop the static
GLRO(dl_pagesize) initializers (for now, only if EXEC_PAGESIZE is not
defined), and don't require EXEC_PAGESIZE definition for libio to
enable mmap usage.

[0]: https://mail.gnu.org/archive/html/bug-hurd/2011-10/msg00035.html

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>

Same patch as last time. At least in the Hurd port, GLRO(dl_pagesize)
is one of the very things to get initialized, so this shouldn't cause
any initialization order issues. But, if it's really undesirable for
EXEC_PAGESIZE to be dropped, we could of course also define
EXEC_PAGESIZE to some large value (16K?) on aarch64-gnu, provided that
nothing actually tries to use it for anything.

PAGE_SIZE is 4k in the current AArch64 GNU Mach, for what it's worth,
but this is intended to eventually be build-time configurable.

 elf/dl-support.c | 6 +++++-
 elf/rtld.c       | 2 ++
 libio/libioP.h   | 2 +-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/elf/dl-support.c b/elf/dl-support.c
index 451932dd..cb0bbd21 100644
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -135,7 +135,11 @@ void *_dl_random;
 #include <dl-procruntime.c>
 #include <dl-procinfo.c>
-size_t _dl_pagesize = EXEC_PAGESIZE;
+size_t _dl_pagesize
 size_t _dl_minsigstacksize = CONSTANT_MINSIGSTKSZ;
diff --git a/elf/rtld.c b/elf/rtld.c
index ac4bb236..18d73f19 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -358,7 +358,9 @@ struct rtld_global_ro _rtld_global_ro attribute_relro =
     ._dl_debug_fd = STDERR_FILENO,
     ._dl_lazy = 1,
     ._dl_fpu_control = _FPU_DEFAULT,
     ._dl_pagesize = EXEC_PAGESIZE,
     ._dl_inhibit_cache = 0,
     ._dl_profile_output = "/var/tmp",
diff --git a/libio/libioP.h b/libio/libioP.h
index 1af287b1..1a7f547e 100644
--- a/libio/libioP.h
+++ b/libio/libioP.h
@@ -852,7 +852,7 @@ extern off64_t _IO_seekpos_unlocked (FILE *, off64_t, int)
 # endif
-# if !defined(MAP_ANONYMOUS) || !defined(EXEC_PAGESIZE)
+# if !defined(MAP_ANONYMOUS)
 #  undef _G_HAVE_MMAP
 #  define _G_HAVE_MMAP 0
 # endif

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