| Message ID | or1smh5b6i.fsf@lxoliva.fsfla.org |
|---|---|
| State | New |
| Headers | show |
| Series | bootstrap-debug-lean + flags in producer vs compare | expand |
On 10/05/2017 07:15 PM, Alexandre Oliva wrote: > Unlike bootstrap-debug, bootstrap-debug-lean used to pass compare using > the traditional compare command, because it compiled both stage2 and > stage3 with options that used to generate identical output > (-fcompare-debug= in stage2 vs -fcompare-debug in stage3). > > Since we started adding relevant command-line flags to DW_AT_producer, > this is no longer the case, and stages 2 and 3 object files that differ > in nothing but the DW_AT_producer strings. > > > -fcompare-debug is short for -fcompare-debug=-gtoggle, so stage3 > compiles twice, once with the normal options, once with toggled -g, to > then compare the temporary final dumps. When enabled, both compilations > get from the driver an additional -frandom-seed flag (if none is given > explicitly). > > -fcompare-debug= is short for -fno-compare-debug, disabling the second > compilation. > > > The difference between the DW_AT_producer lines are the different > -fcompare-debug flags, and the presence of the -frandom-seed flag in the > stage3 compilation. > > It should be easy and sensible enough to filter the -fcompare-debug > flags out of the DW_AT_producer string. This option should never affect > the compilation output, it just determines whether or not to perform an > additional compilation that should produce the same executable output. > > However, doing that but that won't get us rid of the -frandom-seed > option. We could drop -frandom-seed from the DW_AT_producer output too, > but I don't think we should do that when the option is given by the > user, rather than implicitly introduced by -fcompare-debug. We could > introduce an option that causes the subsequent option to be omitted from > the DW_AT_producer string, and arrange for -fcompare-debug to issue that > option before the -frandom-seed option it issues. The problem with this > approach is that I can't decide whether it's an option prone to abuse, > or one that can have other legitimate uses. > > > Another approach to fix (or rather hide) this failure mode is to allow > the debug information to differ under bootstrap-debug-lean, by using the > same compare-debug script we use for bootstrap-debug. The first > patchlet below does just that. The second drops -fcompare-debug from > DW_AT_producer. A third (not written yet :-) might somehow deal with > the -frandom-seed added by -fcompare-debug, and either the first or the > others would be posted as a single, fully tested patch, once we decide > how we want to deal with -frandom-seed. > > > Thoughts? Thanks in advance, I'd support either or both. Your call. jeff
On Oct 30, 2017, Jeff Law <law@redhat.com> wrote:
> I'd support either or both. Your call.
Thanks. I think I'll go with both, then.
Ok to install as follows? (edited the comments and added a ChangeLog)
Use compare-debug for bootstrap-debug-lean to ignore != DW_AT_producer
Unlike bootstrap-debug, bootstrap-debug-lean used to pass compare using
the traditional compare command, because it compiled both stage2 and
stage3 with options that used to generate identical output
(-fcompare-debug= in stage2 vs -fcompare-debug in stage3).
Since we started adding relevant command-line flags to DW_AT_producer,
this is no longer the case, and stages 2 and 3 object files that differ
in nothing but the DW_AT_producer strings.
-fcompare-debug is short for -fcompare-debug=-gtoggle, so stage3
compiles twice, once with the normal options, once with toggled -g, to
then compare the temporary final dumps. When enabled, both compilations
get from the driver an additional -frandom-seed flag (if none is given
explicitly).
-fcompare-debug= is short for -fno-compare-debug, disabling the second
compilation.
The difference between the DW_AT_producer lines are the different
-fcompare-debug flags, and the presence of the -frandom-seed flag in the
stage3 compilation.
It is easy and sensible enough to filter the -fcompare-debug flags out
of the DW_AT_producer string. This option should never affect the
compilation output, it just determines whether or not to perform an
additional compilation that should produce the same executable output.
However, dropping -frandom-seed is not quite correct, in that it might
have other consequences on the compilation. So, it makes little sense
to make the effort to drop it when it's implicit; for those comparing
compiler output differences, it might even hint at what causes, and
could fix, difficult to explain differences, namely, explicitly
supplying -frandom-seed options.
They don't seem to matter for compiler bootstraps, though, at least
for now, so we can safely refrain from issuing -frandom-seed (or maybe
we already issue it where needed :-), and then, for
bootstrap-debug-lean, use the compare-debug script, that strips out
debug information before comparing the object files.
for config/ChangeLog
* bootstrap-debug-lean.mk (do-compare): Use the
contrib/compare-debug script.
for gcc/ChangeLog
* dwarf2out.c (gen_producer_string): Discard
OPT_fcompare_debug.
---
config/bootstrap-debug-lean.mk | 1 +
gcc/dwarf2out.c | 1 +
2 files changed, 2 insertions(+)
diff --git a/config/bootstrap-debug-lean.mk b/config/bootstrap-debug-lean.mk
index e215280b09f3..5f2db80687fa 100644
--- a/config/bootstrap-debug-lean.mk
+++ b/config/bootstrap-debug-lean.mk
@@ -9,3 +9,4 @@
STAGE2_CFLAGS += -fcompare-debug=
STAGE3_CFLAGS += -fcompare-debug
+do-compare = $(SHELL) $(srcdir)/contrib/compare-debug $$f1 $$f2
diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index b8f4e4888f1b..01d90808fd3b 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -23403,6 +23403,7 @@ gen_producer_string (void)
case OPT_fltrans_output_list_:
case OPT_fresolution_:
case OPT_fdebug_prefix_map_:
+ case OPT_fcompare_debug:
/* Ignore these. */
continue;
default:
On Sat, Nov 11, 2017 at 1:15 AM, Alexandre Oliva <aoliva@redhat.com> wrote: > On Oct 30, 2017, Jeff Law <law@redhat.com> wrote: > >> I'd support either or both. Your call. > > Thanks. I think I'll go with both, then. > > Ok to install as follows? (edited the comments and added a ChangeLog) Ok. > > Use compare-debug for bootstrap-debug-lean to ignore != DW_AT_producer > > Unlike bootstrap-debug, bootstrap-debug-lean used to pass compare using > the traditional compare command, because it compiled both stage2 and > stage3 with options that used to generate identical output > (-fcompare-debug= in stage2 vs -fcompare-debug in stage3). > > Since we started adding relevant command-line flags to DW_AT_producer, > this is no longer the case, and stages 2 and 3 object files that differ > in nothing but the DW_AT_producer strings. > > > -fcompare-debug is short for -fcompare-debug=-gtoggle, so stage3 > compiles twice, once with the normal options, once with toggled -g, to > then compare the temporary final dumps. When enabled, both compilations > get from the driver an additional -frandom-seed flag (if none is given > explicitly). > > -fcompare-debug= is short for -fno-compare-debug, disabling the second > compilation. > > > The difference between the DW_AT_producer lines are the different > -fcompare-debug flags, and the presence of the -frandom-seed flag in the > stage3 compilation. > > It is easy and sensible enough to filter the -fcompare-debug flags out > of the DW_AT_producer string. This option should never affect the > compilation output, it just determines whether or not to perform an > additional compilation that should produce the same executable output. > > However, dropping -frandom-seed is not quite correct, in that it might > have other consequences on the compilation. So, it makes little sense > to make the effort to drop it when it's implicit; for those comparing > compiler output differences, it might even hint at what causes, and > could fix, difficult to explain differences, namely, explicitly > supplying -frandom-seed options. > > They don't seem to matter for compiler bootstraps, though, at least > for now, so we can safely refrain from issuing -frandom-seed (or maybe > we already issue it where needed :-), and then, for > bootstrap-debug-lean, use the compare-debug script, that strips out > debug information before comparing the object files. > > > for config/ChangeLog > > * bootstrap-debug-lean.mk (do-compare): Use the > contrib/compare-debug script. > > for gcc/ChangeLog > > * dwarf2out.c (gen_producer_string): Discard > OPT_fcompare_debug. > > --- > config/bootstrap-debug-lean.mk | 1 + > gcc/dwarf2out.c | 1 + > 2 files changed, 2 insertions(+) > > diff --git a/config/bootstrap-debug-lean.mk b/config/bootstrap-debug-lean.mk > index e215280b09f3..5f2db80687fa 100644 > --- a/config/bootstrap-debug-lean.mk > +++ b/config/bootstrap-debug-lean.mk > @@ -9,3 +9,4 @@ > > STAGE2_CFLAGS += -fcompare-debug= > STAGE3_CFLAGS += -fcompare-debug > +do-compare = $(SHELL) $(srcdir)/contrib/compare-debug $$f1 $$f2 > diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c > index b8f4e4888f1b..01d90808fd3b 100644 > --- a/gcc/dwarf2out.c > +++ b/gcc/dwarf2out.c > @@ -23403,6 +23403,7 @@ gen_producer_string (void) > case OPT_fltrans_output_list_: > case OPT_fresolution_: > case OPT_fdebug_prefix_map_: > + case OPT_fcompare_debug: > /* Ignore these. */ > continue; > default: > > > -- > Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/ > You must be the change you wish to see in the world. -- Gandhi > Be Free! -- http://FSFLA.org/ FSF Latin America board member > Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer
diff --git a/config/bootstrap-debug-lean.mk b/config/bootstrap-debug-lean.mk index e215280..5f2db80 100644 --- a/config/bootstrap-debug-lean.mk +++ b/config/bootstrap-debug-lean.mk @@ -9,3 +9,4 @@ STAGE2_CFLAGS += -fcompare-debug= STAGE3_CFLAGS += -fcompare-debug +do-compare = $(SHELL) $(srcdir)/contrib/compare-debug $$f1 $$f2 diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c index ed7a85a..f077b35 100644 --- a/gcc/dwarf2out.c +++ b/gcc/dwarf2out.c @@ -23846,6 +23846,7 @@ gen_producer_string (void) case OPT_fltrans_output_list_: case OPT_fresolution_: case OPT_fdebug_prefix_map_: + case OPT_fcompare_debug: /* Ignore these. */ continue; default: