linux-kernel - [PATCH 2/2] powerpc/vdso32: link vdso64 with linker

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Message-Id: <20200901222523.1941988-3-ndesaulniers@google.com>
Date:   Tue,  1 Sep 2020 15:25:23 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Kees Cook <keescook@...omium.org>,
        Fangrui Song <maskray@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH 2/2] powerpc/vdso32: link vdso64 with linker

Rather than invoke the compiler as the driver, use the linker. That way
we can check --orphan-handling=warn support correctly, as cc-ldoption
was removed in
commit 055efab3120b ("kbuild: drop support for cc-ldoption").

Requires dropping the .got section.  I couldn't find how it was used in
the vdso32.

Fixes: commit f2af201002a8 ("powerpc/build: vdso linker warning for orphan sections")
Link: https://lore.kernel.org/lkml/CAKwvOdnn3wxYdJomvnveyD_njwRku3fABWT_bS92duihhywLJQ@mail.gmail.com/
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
Not sure removing .got is a good idea or not.  Otherwise I observe the
following link error:
powerpc-linux-gnu-ld: warning: orphan section `.got' from `arch/powerpc/kernel/vdso32/sigtramp.o' being placed in section `.got'
powerpc-linux-gnu-ld: _GLOBAL_OFFSET_TABLE_ not defined in linker created .got
powerpc-linux-gnu-ld: final link failed: bad value

sigtramp.c doesn't mention anything from the GOT AFAICT, and doesn't
look like it contains relocations that do, so I'm not sure where
references to _GLOBAL_OFFSET_TABLE_ are coming from.

 arch/powerpc/kernel/vdso32/Makefile     | 7 +++++--
 arch/powerpc/kernel/vdso32/vdso32.lds.S | 3 ++-
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/vdso32/Makefile b/arch/powerpc/kernel/vdso32/Makefile
index 87ab1152d5ce..611a5951945a 100644
--- a/arch/powerpc/kernel/vdso32/Makefile
+++ b/arch/powerpc/kernel/vdso32/Makefile
@@ -27,6 +27,9 @@ UBSAN_SANITIZE := n
 ccflags-y := -shared -fno-common -fno-builtin -nostdlib \
 	-Wl,-soname=linux-vdso32.so.1 -Wl,--hash-style=both
 asflags-y := -D__VDSO32__ -s
+ldflags-y := -shared -soname linux-vdso32.so.1 \
+	$(call ld-option, --eh-frame-hdr) \
+	$(call ld-option, --orphan-handling=warn) -T
 
 obj-y += vdso32_wrapper.o
 extra-y += vdso32.lds
@@ -49,8 +52,8 @@ $(obj-vdso32): %.o: %.S FORCE
 	$(call if_changed_dep,vdso32as)
 
 # actual build commands
-quiet_cmd_vdso32ld = VDSO32L $@
-      cmd_vdso32ld = $(VDSOCC) $(c_flags) $(CC32FLAGS) -o $@ $(call cc-ldoption, -Wl$(comma)--orphan-handling=warn) -Wl,-T$(filter %.lds,$^) $(filter %.o,$^)
+quiet_cmd_vdso32ld = LD      $@
+      cmd_vdso32ld = $(cmd_ld)
 quiet_cmd_vdso32as = VDSO32A $@
       cmd_vdso32as = $(VDSOCC) $(a_flags) $(CC32FLAGS) -c -o $@ $<
 
diff --git a/arch/powerpc/kernel/vdso32/vdso32.lds.S b/arch/powerpc/kernel/vdso32/vdso32.lds.S
index 4c985467a668..0ccdebad18b8 100644
--- a/arch/powerpc/kernel/vdso32/vdso32.lds.S
+++ b/arch/powerpc/kernel/vdso32/vdso32.lds.S
@@ -61,7 +61,6 @@ SECTIONS
 	.fixup		: { *(.fixup) }
 
 	.dynamic	: { *(.dynamic) }		:text	:dynamic
-	.got		: { *(.got) }			:text
 	.plt		: { *(.plt) }
 
 	_end = .;
@@ -108,7 +107,9 @@ SECTIONS
 	.debug_varnames  0 : { *(.debug_varnames) }
 
 	/DISCARD/	: {
+		*(.got)
 		*(.note.GNU-stack)
+		*(.branch_lt)
 		*(.data .data.* .gnu.linkonce.d.* .sdata*)
 		*(.bss .sbss .dynbss .dynsbss)
 		*(.glink .iplt .plt .rela*)
-- 
2.28.0.402.g5ffc5be6b7-goog