Re: [RFC PATCH v5 17/28] dyndbg: prevent build bugs via -DNO_DYNAMIC_DEBUG_TABLE

[Ard Biesheuvel]

On Tue, 11 May 2021 at 20:51, Jim Cromie <jim.cromie@xxxxxxxxx> wrote:
>
> The next patch adds DEFINE_DYNAMIC_DEBUG_TABLE(), which broke several
> subtrees, including efi, vdso, and some of arch/*/boot/compressed,
> with various relocation errors, iirc.
>
> Avoid those problems by adding a define to suppress the "transparent"
> DEFINE_DYNAMIC_DEBUG_TABLE() invocation.  I found the x86 problems
> myself, lkp@xxxxxxxxx found arm & sparc problems, and may yet find
> others.
>

Given that I was only cc'ed on this patch in isolation, would you mind
adding more clarification here? What is DEFINE_DYNAMIC_DEBUG_TABLE()
supposed to do, and why is it breaking standalone binaries?


> Reported-by: <lkp@xxxxxxxxx> # on [jimc:lkp-test/dyndbg-diet] recently
> Signed-off-by: Jim Cromie <jim.cromie@xxxxxxxxx>
> ---
>  arch/arm/boot/compressed/Makefile     | 2 ++
>  arch/sparc/vdso/Makefile              | 2 ++
>  arch/x86/boot/compressed/Makefile     | 1 +
>  arch/x86/entry/vdso/Makefile          | 3 +++
>  arch/x86/purgatory/Makefile           | 1 +
>  drivers/firmware/efi/libstub/Makefile | 3 ++-
>  6 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
> index fd94e27ba4fa..72f056a00ad4 100644
> --- a/arch/arm/boot/compressed/Makefile
> +++ b/arch/arm/boot/compressed/Makefile
> @@ -82,6 +82,8 @@ compress-$(CONFIG_KERNEL_LZMA) = lzma
>  compress-$(CONFIG_KERNEL_XZ)   = xzkern
>  compress-$(CONFIG_KERNEL_LZ4)  = lz4
>
> +KBUILD_CFLAGS += -DNO_DYNAMIC_DEBUG_TABLE
> +
>  libfdt_objs := fdt_rw.o fdt_ro.o fdt_wip.o fdt.o
>
>  ifeq ($(CONFIG_ARM_ATAG_DTB_COMPAT),y)
> diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
> index c5e1545bc5cf..960ed0fb6804 100644
> --- a/arch/sparc/vdso/Makefile
> +++ b/arch/sparc/vdso/Makefile
> @@ -30,6 +30,8 @@ obj-y += $(vdso_img_objs)
>  targets += $(vdso_img_cfiles)
>  targets += $(vdso_img_sodbg) $(vdso_img-y:%=vdso%.so)
>
> +KBUILD_CFLAGS += -DNO_DYNAMIC_DEBUG_TABLE
> +
>  CPPFLAGS_vdso.lds += -P -C
>
>  VDSO_LDFLAGS_vdso.lds = -m elf64_sparc -soname linux-vdso.so.1 --no-undefined \
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index e0bc3988c3fa..ada4eb960d95 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -31,6 +31,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \
>  KBUILD_CFLAGS := -m$(BITS) -O2
>  KBUILD_CFLAGS += -fno-strict-aliasing -fPIE
>  KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
> +KBUILD_CFLAGS += -DNO_DYNAMIC_DEBUG_TABLE
>  cflags-$(CONFIG_X86_32) := -march=i386
>  cflags-$(CONFIG_X86_64) := -mcmodel=small -mno-red-zone
>  KBUILD_CFLAGS += $(cflags-y)
> diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> index 05c4abc2fdfd..619878f2c427 100644
> --- a/arch/x86/entry/vdso/Makefile
> +++ b/arch/x86/entry/vdso/Makefile
> @@ -29,6 +29,9 @@ vobjs32-y := vdso32/note.o vdso32/system_call.o vdso32/sigreturn.o
>  vobjs32-y += vdso32/vclock_gettime.o
>  vobjs-$(CONFIG_X86_SGX)        += vsgx.o
>
> +# avoid a x86_64_RELATIVE error
> +KBUILD_CFLAGS += -DNO_DYNAMIC_DEBUG_TABLE
> +
>  # files to link into kernel
>  obj-y                          += vma.o extable.o
>  KASAN_SANITIZE_vma.o           := y
> diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> index 95ea17a9d20c..95ba7b18410f 100644
> --- a/arch/x86/purgatory/Makefile
> +++ b/arch/x86/purgatory/Makefile
> @@ -35,6 +35,7 @@ PURGATORY_CFLAGS_REMOVE := -mcmodel=kernel
>  PURGATORY_CFLAGS := -mcmodel=large -ffreestanding -fno-zero-initialized-in-bss -g0
>  PURGATORY_CFLAGS += $(DISABLE_STACKLEAK_PLUGIN) -DDISABLE_BRANCH_PROFILING
>  PURGATORY_CFLAGS += -fno-stack-protector
> +PURGATORY_CFLAGS += -DNO_DYNAMIC_DEBUG_TABLE
>
>  # Default KBUILD_CFLAGS can have -pg option set when FTRACE is enabled. That
>  # in turn leaves some undefined symbols like __fentry__ in purgatory and not
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index c23466e05e60..def8febefbd3 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -13,7 +13,8 @@ cflags-$(CONFIG_X86)          += -m$(BITS) -D__KERNEL__ \
>                                    -Wno-pointer-sign \
>                                    $(call cc-disable-warning, address-of-packed-member) \
>                                    $(call cc-disable-warning, gnu) \
> -                                  -fno-asynchronous-unwind-tables
> +                                  -fno-asynchronous-unwind-tables \
> +                                  -DNO_DYNAMIC_DEBUG_TABLE
>
>  # arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
>  # disable the stackleak plugin
> --
> 2.31.1
>