Le sam. 12 août 2023, 00:22, Glenn Washburn <developm...@efficientek.com> a écrit :
> The backtrace module is written assuming that the frame pointer is in %ebp. > By default, -Os optimization level is used, which enables the gcc option > -fomit-frame-pointer. This break the backtrace functionality. Enabling > this may cause an unnoticeable performance cost and virtually no size > increase. > Do you have numbers on core.img size on i386-pc? > > Signed-off-by: Glenn Washburn <developm...@efficientek.com> > --- > The backtrace command on x86_64 and probably i386 is broken due to the > above rationale. I've not verified, but presumably the backtrace that used > to be printed for an unhandled CPU exception is also broken. Do any distros > handle this? > > Considering that (to my knowledge) no one has complained about this in the > over 13 years that -Os has been used, has this code actually been useful? > Is it worth disabling -fomit-frame-pointer? Though, I don't see much > downside > right now in disabling it. Alternatively, we could disable/remove the > backtrace code. I think it would be nice to keep it and have it working. > > Nowadays, presumably QEMU makes the GDB stub rarely used as I imagine most > are developing in a virual machine. Also, the GDB stub does not work in > UEFI > so if anyone is using it on real hardware, they are doing so on pretty old > machines. The lack of a GDB stub does not seem to be a pain point because > no one has got it working on UEFI. > > This patch gets the backtrace command working on x86_64-efi in QEMU for me. > However, it hangs when run on my laptop. Not sure what's going on there. > > Also, I've noticed that recents builds have caused a big slow down in the > already slow LUKS unlock code on real hardware, but not noticeable in QEMU. > It seems to occur with and without this patch. I mention this if others > would be interested in testing this. > > Glenn > --- > configure.ac | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/configure.ac b/configure.ac > index 278e5a81f805..545cf69c272a 100644 > --- a/configure.ac > +++ b/configure.ac > @@ -1020,6 +1020,19 @@ if test x"$target_cpu" = xsparc64 ; then > TARGET_LDFLAGS="$TARGET_LDFLAGS $grub_cv_target_cc_mno_relax" > fi > > +# The backtrace module relies on frame pointers and the default > optimization > +# level, -Os, omits them. Make sure they are enabled. > +AC_CACHE_CHECK([whether -fno-omit-frame-pointer works], > [grub_cv_cc_fno_omit_frame_pointer], [ > + CFLAGS="$TARGET_CFLAGS -fno-omit-frame-pointer" > + AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[]], [[]])], > + [grub_cv_cc_fno_omit_frame_pointer=yes], > + [grub_cv_cc_fno_omit_frame_pointer=no]) > +]) > + > +if test "x$grub_cv_cc_fno_omit_frame_pointer" = xyes; then > + TARGET_CFLAGS="$TARGET_CFLAGS -fno-omit-frame-pointer" > +fi > + > # By default, GCC 4.4 generates .eh_frame sections containing unwind > # information in some cases where it previously did not. GRUB doesn't need > # these and they just use up vital space. Restore the old compiler > -- > 2.34.1 > >
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