[klibc] [klibc:master] Work around ELF loader bugs when executables have only BSS

[klibc-bot for Ben Hutchings]

Commit-ID:  05eee5acb41c12ceb6e5e51ccfb2442271128679
Gitweb:     http://git.kernel.org/?p=libs/klibc/klibc.git;a=commit;h=05eee5acb41c12ceb6e5e51ccfb2442271128679
Author:     Ben Hutchings <ben at decadent.org.uk>
AuthorDate: Sat, 6 Aug 2022 01:20:11 +0200
Committer:  Ben Hutchings <ben at decadent.org.uk>
CommitDate: Sat, 6 Aug 2022 01:30:28 +0200

[klibc] Work around ELF loader bugs when executables have only BSS

Some of klibc's test programs have BSS but no static data when built
to use the shared library.  This is apparently very unusual, and
existing ELF loaders don't always handle it correctly.

I previously found that QEMU's ELF loader rejected such executables,
though this was eventually fixed.

Now a change in binutils for arm64 has revealed a bug in the kernel
ELF loader, that's causing it to reject those same executables.  While
this might get fixed in one way or another, I think it's a sign that
this case is just not tested and it would be best to avoid it.

Therefore:

- Rename interp.S to shared-stub.S
- Add a single byte of static data to it

Signed-off-by: Ben Hutchings <ben at decadent.org.uk>

---
 klibc.spec.in                         |  4 ++--
 scripts/Kbuild.klibc                  |  2 +-
 usr/klibc/.gitignore                  |  2 +-
 usr/klibc/Kbuild                      | 14 +++++++-------
 usr/klibc/{interp.S => shared-stub.S} |  9 +++++++++
 5 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/klibc.spec.in b/klibc.spec.in
index 7d78b9ab..db10363e 100644
--- a/klibc.spec.in
+++ b/klibc.spec.in
@@ -90,7 +90,7 @@ install -m 444 usr/kinit/README %{buildroot}%{bindocdir}/README.kinit
 rm -rf $RPM_BUILD_ROOT
 
 #
-# Note: libc.so and interp.o are technically -devel files, but
+# Note: libc.so and shared-stub.o are technically -devel files, but
 # put them in this package until we can make really, really sure
 # the dependency system can avoid confusion.  (In fact, it would be
 # good to eventually get them out of here, so that multiple runtimes
@@ -100,7 +100,7 @@ rm -rf $RPM_BUILD_ROOT
 %defattr(-,root,root,-)
 /lib/klibc-*.so
 %{klibcdir}/lib/*.so
-%{klibcdir}/lib/interp.o
+%{klibcdir}/lib/shared-stub.o
 
 %files devel
 %defattr(-,root,root,-)
diff --git a/scripts/Kbuild.klibc b/scripts/Kbuild.klibc
index 64da31ac..accf7f1b 100644
--- a/scripts/Kbuild.klibc
+++ b/scripts/Kbuild.klibc
@@ -82,7 +82,7 @@ KLIBCCFLAGS       :=
 
 # Defaults for arch to override
 KLIBCARCHINCFLAGS =
-KLIBCCRTSHARED    := $(KLIBCOBJ)/interp.o
+KLIBCCRTSHARED    := $(KLIBCOBJ)/shared-stub.o
 
 LD_IS_LLD         := $(shell $(LD) --version 2>&1 | grep LLD)
 LD_IMAGE_BASE_OPT := $(if $(LD_IS_LLD),--image-base,-Ttext-segment)
diff --git a/usr/klibc/.gitignore b/usr/klibc/.gitignore
index f24c971e..5f4a9af7 100644
--- a/usr/klibc/.gitignore
+++ b/usr/klibc/.gitignore
@@ -1,5 +1,5 @@
 errlist.c
-.interp.o.d
+.shared-stub.o.d
 klibc*.so
 klib.list
 .klib.list.cmd
diff --git a/usr/klibc/Kbuild b/usr/klibc/Kbuild
index 5933f89a..973b0c81 100644
--- a/usr/klibc/Kbuild
+++ b/usr/klibc/Kbuild
@@ -99,17 +99,17 @@ LIBC     := libc.a
 SOLIB    := libc.so
 SOHASH   := klibc.so
 CRT0     := arch/$(KLIBCARCHDIR)/crt0.o
-INTERP_O := interp.o
+SHARED_STUB := shared-stub.o
 
 always   := $(LIBC)
 ifdef KLIBCSHAREDFLAGS
-always   += $(SOLIB) $(SOHASH) $(INTERP_O)
+always   += $(SOLIB) $(SOHASH) $(SHARED_STUB)
 endif
 LIBC     := $(call objectify,$(LIBC))
 SOLIB    := $(call objectify,$(SOLIB))
 SOHASH   := $(call objectify,$(SOHASH))
 CRT0     := $(call objectify,$(CRT0))
-INTERP_O := $(call objectify,$(INTERP_O))
+SHARED_STUB := $(call objectify,$(SHARED_STUB))
 
 SOLIBHASH = $(shell cat $(SOLIB).hash)
 
@@ -179,8 +179,8 @@ $(SOHASH): $(SOLIB) $(SOLIB).hash
 
 
 #####
-# build interp.o
-targets += interp.o
+# build shared-stub.o
+targets += shared-stub.o
 
 quiet_cmd_interp = BUILD   $@
       cmd_interp = $(KLIBCCC) $(klibccflags) -D__ASSEMBLY__     \
@@ -188,7 +188,7 @@ quiet_cmd_interp = BUILD   $@
 			     -DSOHASH=\"$(SOLIBHASH)\" \
 			     -c -o $@ $<
 
-$(INTERP_O): $(obj)/interp.S $(SOLIB).hash
+$(SHARED_STUB): $(obj)/shared-stub.S $(SOLIB).hash
 	$(call if_changed,interp)
 
 #####
@@ -199,7 +199,7 @@ install-rule:
 	  $(shell $(install-data) $(f) \
 	          $(INSTALLROOT)$(INSTALLDIR)/$(KLIBCCROSS)lib))
 ifdef KLIBCSHAREDFLAGS
-	$(Q)$(foreach f, $(SOLIB) $(INTERP_O), \
+	$(Q)$(foreach f, $(SOLIB) $(SHARED_STUB), \
 	  $(shell $(install-data) $(f) \
 	          $(INSTALLROOT)$(INSTALLDIR)/$(KLIBCCROSS)lib))
 	$(Q)$(install-lib) $(obj)/klibc-$(SOLIBHASH).so \
diff --git a/usr/klibc/interp.S b/usr/klibc/shared-stub.S
similarity index 59%
rename from usr/klibc/interp.S
rename to usr/klibc/shared-stub.S
index 4b15cfbd..15c0f02a 100644
--- a/usr/klibc/interp.S
+++ b/usr/klibc/shared-stub.S
@@ -11,3 +11,12 @@
         .ascii SOHASH
         .ascii ".so"
         .byte 0
+
+#
+# Ensure that every executable includes some static data, as
+# ELF loaders tend to assume this - see
+# <https://bugs.debian.org/919921>, <https://bugs.debian.org/1016718>.
+#
+
+	.section ".data"
+	.byte 0