* [PATCH v3 0/2] efi/arm64: add vmlinux link to PE/COFF debug table @ 2017-01-26 19:24 Ard Biesheuvel 2017-01-26 19:24 ` [PATCH v3 1/2] efi: libstub: Preserve .debug sections after absolute relocation check Ard Biesheuvel [not found] ` <1485458686-32544-1-git-send-email-ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> 0 siblings, 2 replies; 3+ messages in thread From: Ard Biesheuvel @ 2017-01-26 19:24 UTC (permalink / raw) To: linux-efi, linux-arm-kernel, matt, mark.rutland, will.deacon, catalin.marinas Cc: leif.lindholm, Ard Biesheuvel Much like GNU debug links, PE/COFF binaries can carry the path on the build host to the binary containing the debugging symbols. Since the kernel binary is loaded by UEFI at an a priori unknown offset in the 1:1 mapping of physical memory, having this information is useful for the debugger automation to find the file and the offset, and load the symbols automatically. So if we have debugging symbols to begin with (CONFIG_DEBUG_INFO=y), add the absolute path to vmlinux to the PE/COFF debug table. v3: move the EFI debug table itself into the EFI header, which removes the need for externally visible symbols or changes to the linker script (#2) update commit log to explain that the debug support table is defined in the UEFI spec, and is thus not EDK2/PI specific v2: rebase onto v4.10-rc use strip rather than objcopy for first pass (#1) move debug table inside #ifdef CONFIG_EFI region in head.S (#2) Note that these patches can be merged independently, although they are both required to get the functionality. Ard Biesheuvel (2): efi: libstub: Preserve .debug sections after absolute relocation check efi: arm64: Add vmlinux debug link to the Image binary arch/arm64/kernel/Makefile | 4 ++ arch/arm64/kernel/head.S | 46 +++++++++++++++++++- drivers/firmware/efi/libstub/Makefile | 24 ++++++---- 3 files changed, 65 insertions(+), 9 deletions(-) -- 2.7.4 ^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH v3 1/2] efi: libstub: Preserve .debug sections after absolute relocation check 2017-01-26 19:24 [PATCH v3 0/2] efi/arm64: add vmlinux link to PE/COFF debug table Ard Biesheuvel @ 2017-01-26 19:24 ` Ard Biesheuvel [not found] ` <1485458686-32544-1-git-send-email-ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> 1 sibling, 0 replies; 3+ messages in thread From: Ard Biesheuvel @ 2017-01-26 19:24 UTC (permalink / raw) To: linux-efi, linux-arm-kernel, matt, mark.rutland, will.deacon, catalin.marinas Cc: leif.lindholm, Ard Biesheuvel The build commands for the ARM and arm64 EFI stubs strip the .debug sections and other sections that may legally contain absolute relocations, in order to inspect the remaining sections for the presence of such relocations. This leaves us without debugging symbols in the stub for no good reason, considering that these sections are omitted from the kernel binary anyway, and that these relocations are thus only consumed by users of the ELF binary, such as debuggers. So move to 'strip' for performing the relocation check, and if it succeeds, invoke objcopy as before, but leaving the .debug sections in place. Note that these sections may refer to ksymtab/kcrctab contents, so leave those in place as well. Cc: Matt Fleming <matt@codeblueprint.co.uk> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> --- drivers/firmware/efi/libstub/Makefile | 24 +++++++++++++------- 1 file changed, 16 insertions(+), 8 deletions(-) diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile index d564d25df8ab..33e0e2f1a730 100644 --- a/drivers/firmware/efi/libstub/Makefile +++ b/drivers/firmware/efi/libstub/Makefile @@ -11,7 +11,7 @@ cflags-$(CONFIG_X86) += -m$(BITS) -D__KERNEL__ -O2 \ -mno-mmx -mno-sse cflags-$(CONFIG_ARM64) := $(subst -pg,,$(KBUILD_CFLAGS)) -cflags-$(CONFIG_ARM) := $(subst -pg,,$(KBUILD_CFLAGS)) -g0 \ +cflags-$(CONFIG_ARM) := $(subst -pg,,$(KBUILD_CFLAGS)) \ -fno-builtin -fpic -mno-single-pic-base cflags-$(CONFIG_EFI_ARMSTUB) += -I$(srctree)/scripts/dtc/libfdt @@ -60,7 +60,7 @@ CFLAGS_arm64-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET) extra-$(CONFIG_EFI_ARMSTUB) := $(lib-y) lib-$(CONFIG_EFI_ARMSTUB) := $(patsubst %.o,%.stub.o,$(lib-y)) -STUBCOPY_FLAGS-y := -R .debug* -R *ksymtab* -R *kcrctab* +STUBCOPY_RM-y := -R *ksymtab* -R *kcrctab* STUBCOPY_FLAGS-$(CONFIG_ARM64) += --prefix-alloc-sections=.init \ --prefix-symbols=__efistub_ STUBCOPY_RELOC-$(CONFIG_ARM64) := R_AARCH64_ABS @@ -68,17 +68,25 @@ STUBCOPY_RELOC-$(CONFIG_ARM64) := R_AARCH64_ABS $(obj)/%.stub.o: $(obj)/%.o FORCE $(call if_changed,stubcopy) +# +# Strip debug sections and some other sections that may legally contain +# absolute relocations, so that we can inspect the remaining sections for +# such relocations. If none are found, regenerate the output object, but +# this time, use objcopy and leave all sections in place. +# quiet_cmd_stubcopy = STUBCPY $@ - cmd_stubcopy = if $(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@; then \ - $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y) \ - && (echo >&2 "$@: absolute symbol references not allowed in the EFI stub"; \ - rm -f $@; /bin/false); else /bin/false; fi + cmd_stubcopy = if $(STRIP) --strip-debug $(STUBCOPY_RM-y) -o $@ $<; \ + then if $(OBJDUMP) -r $@ | grep $(STUBCOPY_RELOC-y); \ + then (echo >&2 "$@: absolute symbol references not allowed in the EFI stub"; \ + rm -f $@; /bin/false); \ + else $(OBJCOPY) $(STUBCOPY_FLAGS-y) $< $@; fi \ + else /bin/false; fi # # ARM discards the .data section because it disallows r/w data in the # decompressor. So move our .data to .data.efistub, which is preserved # explicitly by the decompressor linker script. # -STUBCOPY_FLAGS-$(CONFIG_ARM) += --rename-section .data=.data.efistub \ - -R ___ksymtab+sort -R ___kcrctab+sort +STUBCOPY_FLAGS-$(CONFIG_ARM) += --rename-section .data=.data.efistub +STUBCOPY_RM-$(CONFIG_ARM) += -R ___ksymtab+sort -R ___kcrctab+sort STUBCOPY_RELOC-$(CONFIG_ARM) := R_ARM_ABS -- 2.7.4 ^ permalink raw reply related [flat|nested] 3+ messages in thread
[parent not found: <1485458686-32544-1-git-send-email-ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]
* [PATCH v3 2/2] efi: arm64: Add vmlinux debug link to the Image binary [not found] ` <1485458686-32544-1-git-send-email-ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> @ 2017-01-26 19:24 ` Ard Biesheuvel 0 siblings, 0 replies; 3+ messages in thread From: Ard Biesheuvel @ 2017-01-26 19:24 UTC (permalink / raw) To: linux-efi-u79uwXL29TY76Z2rM5mHXA, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r, matt-mF/unelCI9GS6iBeEJttW/XRex20P6io, mark.rutland-5wv7dgnIgG8, will.deacon-5wv7dgnIgG8, catalin.marinas-5wv7dgnIgG8 Cc: leif.lindholm-QSEj5FYQhm4dnm+yROfE0A, Ard Biesheuvel When building with debugging symbols, take the absolute path to the vmlinux binary and add it to the special PE/COFF debug table entry. This allows a debug EFI build to find the vmlinux binary, which is very helpful in debugging, given that the offset where the Image is first loaded by EFI is highly unpredictable. On implementations of UEFI that choose to implement it, this information is exposed via the EFI debug support table, which is a UEFI configuration table that is accessible both by the firmware at boot time and by the OS at runtime, and lists all PE/COFF images loaded by the system. The format of the NB10 Codeview entry is based on the definition used by EDK2, which is not entirely unreasonable given that our implementation of the PE/COFF header targets UEFI specifically, and is not for general consumption of PE/COFF compatible systems. Cc: Matt Fleming <matt-mF/unelCI9GS6iBeEJttW/XRex20P6io@public.gmane.org> Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> --- arch/arm64/kernel/Makefile | 4 ++ arch/arm64/kernel/head.S | 46 +++++++++++++++++++- 2 files changed, 49 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile index 7d66bbaafc0c..6dbc0e5527f5 100644 --- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -55,3 +55,7 @@ obj-y += $(arm64-obj-y) vdso/ probes/ obj-m += $(arm64-obj-m) head-y := head.o extra-y += $(head-y) vmlinux.lds + +ifeq ($(CONFIG_EFI)$(CONFIG_DEBUG_INFO),yy) +AFLAGS_head.o += -DVMLINUX_PATH="\"$(shell readlink -f $(objtree)/vmlinux)\"" +endif diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 4b1abac3485a..3942d2af3f67 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -149,7 +149,7 @@ extra_header_fields: .quad 0 // SizeOfHeapReserve .quad 0 // SizeOfHeapCommit .long 0 // LoaderFlags - .long 0x6 // NumberOfRvaAndSizes + .long (section_table - .) / 8 // NumberOfRvaAndSizes .quad 0 // ExportTable .quad 0 // ImportTable @@ -158,6 +158,11 @@ extra_header_fields: .quad 0 // CertificationTable .quad 0 // BaseRelocationTable +#ifdef CONFIG_DEBUG_INFO + .long efi_debug_table - _head // DebugTable + .long efi_debug_table_size +#endif + // Section table section_table: @@ -195,6 +200,45 @@ section_table: .short 0 // NumberOfLineNumbers (0 for executables) .long 0xe0500020 // Characteristics (section flags) +#ifdef CONFIG_DEBUG_INFO + /* + * The debug table is referenced via its Relative Virtual Address (RVA), + * which is only defined for those parts of the image that are covered + * by a section declaration. Since this header is not covered by any + * section, the debug table must be emitted elsewhere. So stick it in + * the .init.rodata section instead. + * + * Note that the EFI debug entry itself may legally have a zero RVA, + * which means we can simply put it right after the section headers. + */ + __INITRODATA + .align 2 +efi_debug_table: + // EFI_IMAGE_DEBUG_DIRECTORY_ENTRY + .long 0 // Characteristics + .long 0 // TimeDateStamp + .short 0 // MajorVersion + .short 0 // MinorVersion + .long 2 // Type == EFI_IMAGE_DEBUG_TYPE_CODEVIEW + .long efi_debug_entry_size // SizeOfData + .long 0 // RVA + .long efi_debug_entry - _head // FileOffset + + .set efi_debug_table_size, . - efi_debug_table + .previous + +efi_debug_entry: + // EFI_IMAGE_DEBUG_CODEVIEW_NB10_ENTRY + .long 0x3031424E // Signature + .long 0 // Unknown + .long 0 // Unknown2 + .long 0 // Unknown3 + + .asciz VMLINUX_PATH + + .set efi_debug_entry_size, . - efi_debug_entry +#endif + /* * EFI will load .text onwards at the 4k section alignment * described in the PE/COFF header. To ensure that instruction -- 2.7.4 ^ permalink raw reply related [flat|nested] 3+ messages in thread
end of thread, other threads:[~2017-01-26 19:24 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2017-01-26 19:24 [PATCH v3 0/2] efi/arm64: add vmlinux link to PE/COFF debug table Ard Biesheuvel 2017-01-26 19:24 ` [PATCH v3 1/2] efi: libstub: Preserve .debug sections after absolute relocation check Ard Biesheuvel [not found] ` <1485458686-32544-1-git-send-email-ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> 2017-01-26 19:24 ` [PATCH v3 2/2] efi: arm64: Add vmlinux debug link to the Image binary Ard Biesheuvel
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