The 05/04/2020 20:02, Joseph Myers wrote:
> On Mon, 4 May 2020, Szabolcs Nagy wrote:
> > i think __getauxval needs to be declared where it is used.
>
> Yes.
>
> > and libgcc should do a link test in configure becasuse a
> > libc may provide sys/auxv.h but not have __getauxval e.g.
> > musl libc does not export __getauxval, only getauxval.
>
> libgcc can't do link tests, since it's built before libc. It can use the
> glibc version number ($glibc_version_major and $glibc_version_minor)
> already computed in libgcc/configure.ac, which uses --with-glibc-version
> or target headers if available and otherwise defaults to 0.0.
>
> A design principle is that glibc built with libgcc configured without
> glibc headers but with --with-glibc-version should produce an identical
> stripped binary to the glibc resulting from a longer alternating sequence
> of GCC and glibc builds. So it is not correct for any libgcc
> functionality that would end up being linked into glibc binaries to depend
> on glibc headers or libraries being available when libgcc is configured.
>
> Thus, this libgcc code should not actually be conditional on
> !inhibit_libc, without a fallback when configured using
> --with-glibc-version to specify a glibc version with __getauxval, because
> that would mean the modern process for bootstrapping a cross glibc build
> produces a glibc binary that quietly differs from one produced by a longer
> alternating sequence of builds (missing this constructor).
i.e. libgcc needs to replicate definitions from sys/auxv.h?
like
_Bool flag = 0;
#if GLIBC_VERSION_OK
# define AT_HWCAP ...
# define HWCAP_ATOMICS ...
unsigned long __getauxval (unsigned long);
__attribute__ ((constructor)) static void
init ()
{
flag = (__getauxval(AT_HWCAP) & HWCAP_ATOMICS) != 0;
}
#endif
