[musl] Invalid page size reference in __dls2

[Markus Wichmann <nullplan@gmx.net>]

Hi all,

__dls2 calls kernel_mapped_dso(), and that one uses the PAGE_SIZE macro.
Whenever <bits/limits.h> does not define PAGESIZE, PAGE_SIZE is defined
as libc.page_size. That variable is only initialized at the start of
__dls3, so the DSO descriptor for libc ends up being wrong.

Since the libc object has static storage duration, page_size is
initialized with zero. So at least nothing undefined happens. The impact
is, it will calculate the relro pointers as being zero, so no relro will
happen, and it will calculate maximum and minimum addresses as being
zero, therefore setting map to base and map_len to zero. This will cause
dladdr() not to find the libc. Yeah, not the biggest of impacts.

This, again, affects all architectures that don't define PAGESIZE, so at
this time those are

aarch64
arm
m68k
microblaze
mips
mips64
mipsn32
powerpc
powerpc64
riscv64

I don't know whether references to libc are even valid in __dls2, but it
is defined as "hidden", so that ought to be good enough. In that case it
may be enough to just move the initialization. Otherwise it may be
necessary to add page size as parameter to kernel_mapped_dso(). Then
__dls2 can look it up in the aux vector at its leisure.

Ciao,
Markus