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SubjectRe: [PATCH] x86: clean up vdso-layout.lds.S
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Petr Tesarik píše v Po 01. 06. 2009 v 16:05 +0200:
> The handling of various sections in the VDSO linker script
> looks pretty haphazard. This patch cleans it up in this
> regards:
>
> - re-order sections to more closely match the result of
> a normal shared link
> - discard sections which are not useful to user-space
> - issue a linker error if a section is encountered which
> is known not to work
> - check that the .got section is empty, except for the
> three entries defined by the ABI
>
> Signed-off-by: Petr Tesarik <ptesarik@suse.cz>

Any comments on this? It doesn't change anything. It only makes it
harder to break vDSOs by accident (such as the latest buglet with TSC
synchronization).

Petr Tesarik

> ---
> Makefile | 5 ++--
> vdso-layout.lds.S | 57 +++++++++++++++++++++++++++++++++++++++++++++---------
> 2 files changed, 51 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/vdso/Makefile b/arch/x86/vdso/Makefile
> index 16a9020..8c7f06a 100644
> --- a/arch/x86/vdso/Makefile
> +++ b/arch/x86/vdso/Makefile
> @@ -23,7 +23,8 @@ $(obj)/vdso.o: $(obj)/vdso.so
>
> targets += vdso.so vdso.so.dbg vdso.lds $(vobjs-y)
>
> -export CPPFLAGS_vdso.lds += -P -C
> +vdso-cppflags = -P -C
> +export CPPFLAGS_vdso.lds += -m64 $(vdso-cppflags)
>
> VDSO_LDFLAGS_vdso.lds = -m elf_x86_64 -Wl,-soname=linux-vdso.so.1 \
> -Wl,-z,max-page-size=4096 -Wl,-z,common-page-size=4096
> @@ -68,7 +69,7 @@ vdso32.so-$(VDSO32-y) += sysenter
>
> vdso32-images = $(vdso32.so-y:%=vdso32-%.so)
>
> -CPPFLAGS_vdso32.lds = $(CPPFLAGS_vdso.lds)
> +CPPFLAGS_vdso32.lds = -m32 $(vdso-cppflags)
> VDSO_LDFLAGS_vdso32.lds = -m elf_i386 -Wl,-soname=linux-gate.so.1
>
> # This makes sure the $(obj) subdirectory exists even though vdso32/
> diff --git a/arch/x86/vdso/vdso-layout.lds.S b/arch/x86/vdso/vdso-layout.lds.S
> index 634a2cf..1f4b215 100644
> --- a/arch/x86/vdso/vdso-layout.lds.S
> +++ b/arch/x86/vdso/vdso-layout.lds.S
> @@ -22,16 +22,15 @@ SECTIONS
> .eh_frame : { KEEP (*(.eh_frame)) } :text
>
> .dynamic : { *(.dynamic) } :text :dynamic
> + .got : { *(.got.plt) *(.got) } :text
>
> - .rodata : { *(.rodata*) } :text
> + .rodata : {
> + *(.rodata .rodata.* .gnu.linkonce.r.*)
> + }
> .data : {
> - *(.data*)
> - *(.sdata*)
> - *(.got.plt) *(.got)
> - *(.gnu.linkonce.d.*)
> - *(.bss*)
> - *(.dynbss*)
> - *(.gnu.linkonce.b.*)
> + *(.data .data.* .gnu.linkonce.d.*)
> + *(.bss .bss.* .gnu.linkonce.b.*)
> + *(COMMON)
> }
>
> .altinstructions : { *(.altinstructions) }
> @@ -43,9 +42,49 @@ SECTIONS
> */
> . = ALIGN(0x100);
>
> - .text : { *(.text*) } :text =0x90909090
> + .text : {
> + *(.text .text.* .gnu.linkonce.t.*)
> + } :text =0x90909090
> +
> + /* We would need a more sophisticated dynamic linker for the
> + * vDSO to make the following sections work. Put them into
> + * a special section and raise a link-time error if they get
> + * used.
> + */
> + .broken : {
> + /* Code in the Procedure Linkage Table will segfault */
> + *(.plt)
> +
> + /* Relocation will not be done, so any pointers will
> + * still point to the prelinked address, which is wrong
> + */
> + *(.data.rel.ro*)
> + *(.gnu.linkonce.d.rel.ro.*)
> +
> + /* Initialization/termination won't work this way */
> + *(.init) *(.fini)
> + *(.preinit_array) *(.init_array*)
> + *(.fini_array*)
> +
> + /* Thread-local data cannot be defined like this */
> + *(.tdata .tdata.* .gnu.linkonce.td.*)
> + *(.tbss .tbss.* .gnu.linkonce.tb.*)
> + *(.tcommon)
> + }
> +
> + /* These sections are not useful */
> + /DISCARD/ : {
> + *(.gnu.warning.*)
> + *(.note.GNU-stack)
> + }
> }
>
> +ASSERT(!SIZEOF(.broken), "VDSO contains sections that don't work properly");
> +
> +/* Check that GOT has only the three entries defined by the ABI */
> +ASSERT(SIZEOF(.got) == 3*__SIZEOF_POINTER__,
> + "Found extra GOT entries. Check your use of external vars.");
> +
> /*
> * Very old versions of ld do not recognize this name token; use the constant.
> */
>
>
> --
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