On Thu, Jul 27, 2023 at 10:11 AM Richard Henderson <
richard.hender...@linaro.org> wrote:
> Do not hard-code guest_base at 32GB.
> Do not override mmap_next_start for reserved_va.
>
> Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
> ---
>
> Hi Warner,
>
> With the blitz-trial branch you provided, the host libc allocates
> thread-local storage within the [32GB, 36GB) region that you currently
> assume is free.
>
> The armv7-hello program happens to map on top of this thread-local
> storage, and then we crash later accessing some host TLS variable.
>
> While the linux-user probe_guest_base is significantly more complex,
> we are also trying to handle 32-bit hosts. I think freebsd is always
> assuming 64-bit hosts, which makes this simpler.
>
Double mapping makes sense for problems to arise. I'd not have thought
this would be the problem, but it does eliminate a bunch of code that I'd
thought suspect (made worse by my trying to 'fix' old kludges with new
kludges of my own).
Yes. FreeBSD's bsd-user binary will only run on 64-bit hosts. The project
has started phasing out support for 32-bit hosts, and the role of bsd-user
(package builder tool) is such that 32-bit hosts don't make sense.
I've tested this out, and it works for me. Any chance we can get this into
8.1 as a bug fix for the last minute breakage of bsd-user (without this and
another patch, the static hello world that used to work broke). I can send
that second patch out for review. I can queue this fix in the mean time for
whenever the tree opens up.
Reviewed by: Warner Losh <i...@bsdimp.com>
>
> r~
> ---
> bsd-user/main.c | 37 +++++++++++++++++++------------------
> 1 file changed, 19 insertions(+), 18 deletions(-)
>
> diff --git a/bsd-user/main.c b/bsd-user/main.c
> index f500ec292b..9760aad9f6 100644
> --- a/bsd-user/main.c
> +++ b/bsd-user/main.c
> @@ -50,20 +50,8 @@
>
> int do_strace;
>
> -/*
> - * Going hand in hand with the va space needed (see below), we need
> - * to find a host address to map the guest to. Assume that qemu
> - * itself doesn't need memory above 32GB (or that we don't collide
> - * with anything interesting). This is selected rather arbitrarily,
> - * but seems to produce good results in tests to date.
> - */
> -# if HOST_LONG_BITS >= 64
> -uintptr_t guest_base = 0x800000000ul; /* at 32GB */
> -bool have_guest_base = true;
> -#else
> -uintptr_t guest_base; /* TODO: use sysctl to find big enough hole */
> +uintptr_t guest_base;
> bool have_guest_base;
> -#endif
> static bool opt_one_insn_per_tb;
> static const char *cpu_model;
> static const char *cpu_type;
> @@ -522,10 +510,6 @@ int main(int argc, char **argv)
> target_environ = envlist_to_environ(envlist, NULL);
> envlist_free(envlist);
>
> - if (reserved_va) {
> - mmap_next_start = reserved_va + 1;
> - }
> -
> {
> Error *err = NULL;
> if (seed_optarg != NULL) {
> @@ -543,7 +527,24 @@ int main(int argc, char **argv)
> * Now that page sizes are configured we can do
> * proper page alignment for guest_base.
> */
> - guest_base = HOST_PAGE_ALIGN(guest_base);
> + if (have_guest_base) {
> + if (guest_base & ~qemu_host_page_mask) {
> + error_report("Selected guest base not host page aligned");
> + exit(1);
> + }
> + } else if (reserved_va) {
> + void *p = mmap(NULL, reserved_va + 1, PROT_NONE, MAP_GUARD, -1,
> 0);
> + if (p == MAP_FAILED) {
> + const char *err = strerror(errno);
> + char *sz = size_to_str(reserved_va + 1);
> +
> + error_report("Cannot allocate %s bytes for guest address
> space: %s",
> + sz, err);
> + exit(1);
> + }
> + guest_base = (uintptr_t)p;
> + have_guest_base = true;
> + }
>
> if (loader_exec(filename, argv + optind, target_environ, regs, info,
> &bprm) != 0) {
> --
> 2.41.0
>
>
