diff mbox series

[v2] Enable DT_RELR in glibc shared libraries and PIEs automatically

Message ID 20220516131714.37463-1-hjl.tools@gmail.com
State Committed
Commit 2d5ec6692f5746ccb11db60976a6481ef8e9d74f
Headers
Series [v2] Enable DT_RELR in glibc shared libraries and PIEs automatically |

Checks

Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent
dj/TryBot-32bit success Build for i686

Commit Message

H.J. Lu May 16, 2022, 1:17 p.m. UTC 
  Enable DT_RELR in glibc shared libraries and position independent
executables (PIE) automatically if linker supports -z pack-relative-relocs.
---
 Makeconfig   | 12 ++++++++++++
 Makerules    |  2 ++
 elf/Makefile |  5 ++++-
 3 files changed, 18 insertions(+), 1 deletion(-)

Comments

Florian Weimer May 16, 2022, 1:44 p.m. UTC | #1 
* H. J. Lu via Libc-alpha:

> Enable DT_RELR in glibc shared libraries and position independent
> executables (PIE) automatically if linker supports -z
> pack-relative-relocs.

Thanks for updating the commit subject.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

Florian
Fangrui Song May 20, 2022, 10:50 p.m. UTC | #2 
On 2022-05-16, Florian Weimer via Libc-alpha wrote:
>* H. J. Lu via Libc-alpha:
>
>> Enable DT_RELR in glibc shared libraries and position independent
>> executables (PIE) automatically if linker supports -z
>> pack-relative-relocs.
>
>Thanks for updating the commit subject.
>
>Reviewed-by: Florian Weimer <fweimer@redhat.com>
>
>Florian
>

Thanks for the patch.

Question: does gdb need DT_RELR support to debug such a shared object?
`gdb elf/ld.so` will report

   BFD: path/to/elf/ld.so: unknown type [0x13] section `.relr.dyn'

but I do not know whether any functionality is affected in the absence
of SHT_RELR support.
H.J. Lu May 21, 2022, 1:51 a.m. UTC | #3 
On Fri, May 20, 2022 at 3:50 PM Fangrui Song via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On 2022-05-16, Florian Weimer via Libc-alpha wrote:
> >* H. J. Lu via Libc-alpha:
> >
> >> Enable DT_RELR in glibc shared libraries and position independent
> >> executables (PIE) automatically if linker supports -z
> >> pack-relative-relocs.
> >
> >Thanks for updating the commit subject.
> >
> >Reviewed-by: Florian Weimer <fweimer@redhat.com>
> >
> >Florian
> >
>
> Thanks for the patch.
>
> Question: does gdb need DT_RELR support to debug such a shared object?
> `gdb elf/ld.so` will report
>
>    BFD: path/to/elf/ld.so: unknown type [0x13] section `.relr.dyn'
>
> but I do not know whether any functionality is affected in the absence
> of SHT_RELR support.

You need GDB 12 or 11.2 for  DT_RELR.
diff mbox series

Patch

diff --git a/Makeconfig b/Makeconfig
index 760f14e92f..c87d644044 100644
--- a/Makeconfig
+++ b/Makeconfig
@@ -362,6 +362,15 @@  relro-LDFLAGS = -Wl,-z,relro
 LDFLAGS.so += $(relro-LDFLAGS)
 LDFLAGS-rtld += $(relro-LDFLAGS)
 
+# Linker options to enable and disable DT_RELR.
+ifeq ($(have-dt-relr),yes)
+dt-relr-ldflag = -Wl,-z,pack-relative-relocs
+no-dt-relr-ldflag = -Wl,-z,nopack-relative-relocs
+else
+dt-relr-ldflag =
+no-dt-relr-ldflag =
+endif
+
 ifeq (no,$(build-pie-default))
 pie-default = $(no-pie-ccflag)
 else # build-pie-default
@@ -370,6 +379,7 @@  pic-default = -DPIC
 pie-default = $(pie-ccflag)
 
 ifeq (yes,$(enable-static-pie))
+static-pie-dt-relr-ldflag = $(dt-relr-ldflag)
 ifeq (yes,$(have-static-pie))
 static-pie-ldflag = -static-pie
 else
@@ -404,6 +414,7 @@  link-extra-libs-tests = $(libsupport)
 # Command for linking PIE programs with the C library.
 ifndef +link-pie
 +link-pie-before-inputs = $(if $($(@F)-no-pie),$(no-pie-ldflag),-pie) \
+	     $(if $($(@F)-no-dt-relr),$(no-dt-relr-ldflag),$(dt-relr-ldflag)) \
 	     -Wl,-O1 -nostdlib -nostartfiles \
 	     $(sysdep-LDFLAGS) $(LDFLAGS) $(LDFLAGS-$(@F)) \
 	     $(relro-LDFLAGS) $(hashstyle-LDFLAGS) \
@@ -436,6 +447,7 @@  endif
 ifndef +link-static
 +link-static-before-inputs = -nostdlib -nostartfiles -static \
 	      $(if $($(@F)-no-pie),$(no-pie-ldflag),$(static-pie-ldflag)) \
+	      $(if $($(@F)-no-dt-relr),$(no-dt-relr-ldflag),$(static-pie-dt-relr-ldflag)) \
 	      $(sysdep-LDFLAGS) $(LDFLAGS) $(LDFLAGS-$(@F))  \
 	      $(firstword $(CRT-$(@F)) $(csu-objpfx)$(real-static-start-installed-name)) \
 	      $(+preinit) $(+prectorT)
diff --git a/Makerules b/Makerules
index 354528b8c7..dfe89e9e39 100644
--- a/Makerules
+++ b/Makerules
@@ -536,6 +536,7 @@  lib%.so: lib%_pic.a $(+preinit) $(+postinit) $(link-libc-deps)
 define build-shlib-helper
 $(LINK.o) -shared -static-libgcc -Wl,-O1 $(sysdep-LDFLAGS) \
 	  $(if $($(@F)-no-z-defs)$(no-z-defs),,-Wl,-z,defs) $(rtld-LDFLAGS) \
+	  $(if $($(@F)-no-dt-relr),$(no-dt-relr-ldflag),$(dt-relr-ldflag)) \
 	  $(extra-B-$(@F:lib%.so=%).so) -B$(csu-objpfx) \
 	  $(extra-B-$(@F:lib%.so=%).so) $(load-map-file) \
 	  -Wl,-soname=lib$(libprefix)$(@F:lib%.so=%).so$($(@F)-version) \
@@ -588,6 +589,7 @@  endef
 define build-module-helper
 $(LINK.o) -shared -static-libgcc $(sysdep-LDFLAGS) $(rtld-LDFLAGS) \
 	  $(if $($(@F)-no-z-defs)$(no-z-defs),,-Wl,-z,defs) \
+	  $(if $($(@F)-no-dt-relr),$(no-dt-relr-ldflag),$(dt-relr-ldflag)) \
 	  -B$(csu-objpfx) $(load-map-file) \
 	  $(LDFLAGS.so) $(LDFLAGS-$(@F:%.so=%).so) \
 	  $(link-test-modules-rpath-link) \
diff --git a/elf/Makefile b/elf/Makefile
index fc9860edee..fa98e188df 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -1335,6 +1335,7 @@  $(objpfx)ld.so: $(objpfx)librtld.os $(ld-map)
 # if the sanity check below fails.
 	$(LINK.o) -nostdlib -nostartfiles -shared -o $@.new		\
 		  $(LDFLAGS-rtld) -Wl,-z,defs $(z-now-$(bind-now))	\
+		  $(dt-relr-ldflag) \
 		  $(filter-out $(map-file),$^) $(load-map-file)		\
 		  -Wl,-soname=$(rtld-installed-name)
 	$(call after-link,$@.new)
@@ -1659,6 +1660,7 @@  $(objpfx)nodlopen2.out: $(objpfx)nodlopenmod2.so
 
 $(objpfx)filtmod1.so: $(objpfx)filtmod1.os $(objpfx)filtmod2.so
 	$(LINK.o) -shared -o $@ -B$(csu-objpfx) $(LDFLAGS.so) \
+		  $(dt-relr-ldflag) \
 		  -L$(subst :, -L,$(rpath-link)) \
 		  -Wl,-rpath-link=$(rpath-link) \
 		  $< -Wl,-F,$(objpfx)filtmod2.so
@@ -2462,7 +2464,7 @@  $(objpfx)tst-big-note: $(objpfx)tst-big-note-lib.so
 # artificial, large note in tst-big-note-lib.o and invalidate the
 # test.
 $(objpfx)tst-big-note-lib.so: $(objpfx)tst-big-note-lib.o
-	$(LINK.o) -shared -o $@ $(LDFLAGS.so) $<
+	$(LINK.o) -shared -o $@ $(LDFLAGS.so) $(dt-relr-ldflag) $<
 
 $(objpfx)tst-unwind-ctor: $(objpfx)tst-unwind-ctor-lib.so
 
@@ -2771,6 +2773,7 @@  $(objpfx)tst-ro-dynamic: $(objpfx)tst-ro-dynamic-mod.so
 $(objpfx)tst-ro-dynamic-mod.so: $(objpfx)tst-ro-dynamic-mod.os \
   tst-ro-dynamic-mod.map
 	$(LINK.o) -nostdlib -nostartfiles -shared -o $@ \
+		$(dt-relr-ldflag) \
 		-Wl,--script=tst-ro-dynamic-mod.map \
 		$(objpfx)tst-ro-dynamic-mod.os