Re: objtool segfault with ORC unwinder enabled

[Josh Poimboeuf <jpoimboe@redhat.com>]

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On Thu, Jan 11, 2018 at 09:00:33PM +0100, Markus wrote:
> On Thursday, 11 January 2018 20:38:10 CET Josh Poimboeuf wrote:
> > On Thu, Jan 11, 2018 at 07:52:00PM +0100, Markus wrote:
> > > On Thursday, 11 January 2018 19:20:57 CET Josh Poimboeuf wrote:
> > > > On Thu, Jan 11, 2018 at 07:11:03PM +0100, Markus wrote:
> > > > > On Thursday, 11 January 2018 05:25:51 CET Josh Poimboeuf wrote:
> > > > > > On Wed, Jan 10, 2018 at 10:13:00PM -0600, Josh Poimboeuf wrote:
> > > > > > > On Wed, Jan 10, 2018 at 06:14:56PM +0100, Markus wrote:
> > > > > > > > On Thursday, 4 January 2018 19:25:12 CET Markus wrote:
> > > > > > > > > On Thursday, 4 January 2018 18:32:03 CET Josh Poimboeuf wrote:
> > > > > > > > > > On Thu, Jan 04, 2018 at 05:56:30PM +0100, Markus wrote:
> > > > > > > > > > > On Thursday, 4 January 2018 16:46:13 CET Josh Poimboeuf 
> wrote:
> > > > > > > > > > > > I don't see anything unusual there.  Are there any
> > > > > > > > > > > > Gentoo
> > > > > > > > > > > > patches
> > > > > > > > > > > > against either the kernel or GCC which would strip
> > > > > > > > > > > > unused
> > > > > > > > > > > > symbols?
> > > > > > > > > > > 
> > > > > > > > > > > The kernel is the vanilla kernel. (4.14.11 and also
> > > > > > > > > > > 4.15-rc6)
> > > > > > > > > > > Its not a gentoo specific gcc patch. (Then every gentoo
> > > > > > > > > > > user
> > > > > > > > > > > would
> > > > > > > > > > > be
> > > > > > > > > > > affected?)
> > > > > > > > > > > 
> > > > > > > > > > > But I enabled ld.gold as default linker like 5 years ago.
> > > > > > > > > > > Never
> > > > > > > > > > > had a
> > > > > > > > > > > problem with this.
> > > > > > > > > > > 
> > > > > > > > > > > Is ld.gold supposed to fail here?
> > > > > > > > > > > 
> > > > > > > > > > > I switched back to ld.bfd and it seems to work.
> > > > > > > > > > 
> > > > > > > > > > Ah, that explains it.  With CONFIG_MODVERSIONS, the linker
> > > > > > > > > > does
> > > > > > > > > > some
> > > > > > > > > > work after gcc, but before objtool.  Can you try this patch?
> > > > > > > > > > (Note
> > > > > > > > > > this
> > > > > > > > > > isn't the final patch, as this breaks the
> > > > > > > > > > CONFIG_MODVERSIONS=n
> > > > > > > > > > case.)
> > > > > > > > 
> > > > > > > > Any more final patch I should test?
> > > > > > > 
> > > > > > > Sorry, this fell off my radar.  I'll try to get a final patch
> > > > > > > soon.
> > > > > > > (But feel free to keep bugging me if I don't!)
> > > > > > 
> > > > > > Ok, this should be the final patch (no description yet though). 
> > > > > > Want to
> > > > > > test it?
> > > > > 
> > > > > Tried to apply to 4.14.13 and 4.15-rc7. Neither applied cleanly.
> > > > > Manually editing just breaks the build with many "open: No such file
> > > > > or
> > > > > directory".
> > > > > 
> > > > > Dont know what went wrong. Can you maybe append patch as file?
> > > > 
> > > > Sure, patch is attached, based on 4.15-rc7.
> > > 
> > > Applies cleanly to 4.15-rc7. But still:
> > >   HOSTCC  scripts/asn1_compiler
> > >   HOSTCC  scripts/extract-cert
> > >   CC      init/main.o
> > > 
> > > open: No such file or directory
> > > make[1]: *** [scripts/Makefile.build:317: init/main.o] Error 1
> > > make: *** [Makefile:1015: init] Error 2
> > > 
> > > 
> > > Reverting that patch makes it build again.
> > 
> > Weird.  Here's a version which should hopefully give a better error
> > message.
> 
>   CC      init/main.o
> objtool: can't open file /.tmp_
> open: No such file or directory

Got it figured out.  I used the wrong assignment variables in the
makefile (':=' instead of '=') and I didn't see the error because I was
accidentally testing with objtool disabled.  Oops.

New patch attached.

-- 
Josh

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diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index cb8997ed0149..bc277d7c081d 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -265,12 +265,18 @@ else
 objtool_args += $(call cc-ifversion, -lt, 0405, --no-unreachable)
 endif
 
+ifdef CONFIG_MODVERSIONS
+objtool_o = $(@D)/.tmp_$(@F)
+else
+objtool_o = $(@)
+endif
+
 # 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory
 # 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file
 # 'OBJECT_FILES_NON_STANDARD_foo.o := 'n': override directory skip for a file
 cmd_objtool = $(if $(patsubst y%,, \
 	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
-	$(__objtool_obj) $(objtool_args) "$(@)";)
+	$(__objtool_obj) $(objtool_args) "$(objtool_o)";)
 objtool_obj = $(if $(patsubst y%,, \
 	$(OBJECT_FILES_NON_STANDARD_$(basetarget).o)$(OBJECT_FILES_NON_STANDARD)n), \
 	$(__objtool_obj))
@@ -286,16 +292,16 @@ objtool_dep = $(objtool_obj)					\
 define rule_cc_o_c
 	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \
 	$(call cmd_and_fixdep,cc_o_c)					  \
+	$(call echo-cmd,objtool) $(cmd_objtool)				  \
 	$(cmd_modversions_c)						  \
 	$(cmd_checkdoc)							  \
-	$(call echo-cmd,objtool) $(cmd_objtool)				  \
 	$(call echo-cmd,record_mcount) $(cmd_record_mcount)
 endef
 
 define rule_as_o_S
 	$(call cmd_and_fixdep,as_o_S)					  \
-	$(cmd_modversions_S)						  \
-	$(call echo-cmd,objtool) $(cmd_objtool)
+	$(call echo-cmd,objtool) $(cmd_objtool)				  \
+	$(cmd_modversions_S)
 endef
 
 # List module undefined symbols (or empty line if not enabled)
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 24460155c82c..cc56e7ac8122 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -358,6 +358,7 @@ struct elf *elf_open(const char *name, int flags)
 
 	elf->fd = open(name, flags);
 	if (elf->fd == -1) {
+		fprintf(stderr, "objtool: can't open file %s\n", name);
 		perror("open");
 		goto err;
 	}