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commitb8ec60e118upstream. .discard.retpoline_safe sections do not have the SHF_ALLOC flag. These sections referencing text sections' STT_SECTION symbols with PC-relative relocations like R_386_PC32 [0] is conceptually not suitable. Newer LLD will report warnings for REL relocations even for relocatable links [1]: ld.lld: warning: vmlinux.a(drivers/i2c/busses/i2c-i801.o):(.discard.retpoline_safe+0x120): has non-ABS relocation R_386_PC32 against symbol '' Switch to absolute relocations instead, which indicate link-time addresses. In a relocatable link, these addresses are also output section offsets, used by checks in tools/objtool/check.c. When linking vmlinux, these .discard.* sections will be discarded, therefore it is not a problem that R_X86_64_32 cannot represent a kernel address. Alternatively, we could set the SHF_ALLOC flag for .discard.* sections, but I think non-SHF_ALLOC for sections to be discarded makes more sense. Note: if we decide to never support REL architectures (e.g. arm, i386), we can utilize R_*_NONE relocations (.reloc ., BFD_RELOC_NONE, sym), making .discard.* sections zero-sized. That said, the section content waste is 4 bytes per entry, much smaller than sizeof(Elf{32,64}_Rel). [0] commit1c0c1faf56("objtool: Use relative pointers for annotations") [1] https://github.com/ClangBuiltLinux/linux/issues/1937 Signed-off-by: Fangrui Song <maskray@google.com> Signed-off-by: Ingo Molnar <mingo@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Link: https://lore.kernel.org/r/20230920001728.1439947-1-maskray@google.com Cc: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
174 lines
4.9 KiB
C
174 lines
4.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_OBJTOOL_H
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#define _LINUX_OBJTOOL_H
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#include <linux/objtool_types.h>
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#ifdef CONFIG_OBJTOOL
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#include <asm/asm.h>
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#ifndef __ASSEMBLY__
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#define UNWIND_HINT(type, sp_reg, sp_offset, signal) \
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"987: \n\t" \
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".pushsection .discard.unwind_hints\n\t" \
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/* struct unwind_hint */ \
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".long 987b - .\n\t" \
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".short " __stringify(sp_offset) "\n\t" \
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".byte " __stringify(sp_reg) "\n\t" \
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".byte " __stringify(type) "\n\t" \
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".byte " __stringify(signal) "\n\t" \
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".balign 4 \n\t" \
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".popsection\n\t"
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/*
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* This macro marks the given function's stack frame as "non-standard", which
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* tells objtool to ignore the function when doing stack metadata validation.
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* It should only be used in special cases where you're 100% sure it won't
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* affect the reliability of frame pointers and kernel stack traces.
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*
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* For more information, see tools/objtool/Documentation/objtool.txt.
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*/
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#define STACK_FRAME_NON_STANDARD(func) \
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static void __used __section(".discard.func_stack_frame_non_standard") \
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*__func_stack_frame_non_standard_##func = func
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/*
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* STACK_FRAME_NON_STANDARD_FP() is a frame-pointer-specific function ignore
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* for the case where a function is intentionally missing frame pointer setup,
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* but otherwise needs objtool/ORC coverage when frame pointers are disabled.
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*/
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#ifdef CONFIG_FRAME_POINTER
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#define STACK_FRAME_NON_STANDARD_FP(func) STACK_FRAME_NON_STANDARD(func)
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#else
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#define STACK_FRAME_NON_STANDARD_FP(func)
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#endif
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#define ANNOTATE_NOENDBR \
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"986: \n\t" \
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".pushsection .discard.noendbr\n\t" \
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".long 986b\n\t" \
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".popsection\n\t"
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#define ASM_REACHABLE \
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"998:\n\t" \
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".pushsection .discard.reachable\n\t" \
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".long 998b\n\t" \
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".popsection\n\t"
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#else /* __ASSEMBLY__ */
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/*
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* This macro indicates that the following intra-function call is valid.
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* Any non-annotated intra-function call will cause objtool to issue a warning.
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*/
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#define ANNOTATE_INTRA_FUNCTION_CALL \
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999: \
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.pushsection .discard.intra_function_calls; \
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.long 999b; \
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.popsection;
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/*
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* In asm, there are two kinds of code: normal C-type callable functions and
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* the rest. The normal callable functions can be called by other code, and
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* don't do anything unusual with the stack. Such normal callable functions
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* are annotated with the ENTRY/ENDPROC macros. Most asm code falls in this
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* category. In this case, no special debugging annotations are needed because
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* objtool can automatically generate the ORC data for the ORC unwinder to read
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* at runtime.
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*
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* Anything which doesn't fall into the above category, such as syscall and
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* interrupt handlers, tends to not be called directly by other functions, and
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* often does unusual non-C-function-type things with the stack pointer. Such
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* code needs to be annotated such that objtool can understand it. The
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* following CFI hint macros are for this type of code.
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*
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* These macros provide hints to objtool about the state of the stack at each
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* instruction. Objtool starts from the hints and follows the code flow,
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* making automatic CFI adjustments when it sees pushes and pops, filling out
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* the debuginfo as necessary. It will also warn if it sees any
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* inconsistencies.
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*/
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.macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 signal=0
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.Lhere_\@:
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.pushsection .discard.unwind_hints
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/* struct unwind_hint */
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.long .Lhere_\@ - .
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.short \sp_offset
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.byte \sp_reg
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.byte \type
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.byte \signal
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.balign 4
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.popsection
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.endm
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.macro STACK_FRAME_NON_STANDARD func:req
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.pushsection .discard.func_stack_frame_non_standard, "aw"
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.long \func - .
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.popsection
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.endm
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.macro STACK_FRAME_NON_STANDARD_FP func:req
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#ifdef CONFIG_FRAME_POINTER
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STACK_FRAME_NON_STANDARD \func
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#endif
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.endm
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.macro ANNOTATE_NOENDBR
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.Lhere_\@:
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.pushsection .discard.noendbr
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.long .Lhere_\@
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.popsection
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.endm
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/*
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* Use objtool to validate the entry requirement that all code paths do
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* VALIDATE_UNRET_END before RET.
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*
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* NOTE: The macro must be used at the beginning of a global symbol, otherwise
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* it will be ignored.
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*/
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.macro VALIDATE_UNRET_BEGIN
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#if defined(CONFIG_NOINSTR_VALIDATION) && \
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(defined(CONFIG_CPU_UNRET_ENTRY) || defined(CONFIG_CPU_SRSO))
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.Lhere_\@:
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.pushsection .discard.validate_unret
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.long .Lhere_\@ - .
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.popsection
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#endif
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.endm
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.macro REACHABLE
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.Lhere_\@:
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.pushsection .discard.reachable
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.long .Lhere_\@
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.popsection
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.endm
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#endif /* __ASSEMBLY__ */
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#else /* !CONFIG_OBJTOOL */
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#ifndef __ASSEMBLY__
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#define UNWIND_HINT(type, sp_reg, sp_offset, signal) "\n\t"
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#define STACK_FRAME_NON_STANDARD(func)
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#define STACK_FRAME_NON_STANDARD_FP(func)
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#define ANNOTATE_NOENDBR
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#define ASM_REACHABLE
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#else
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#define ANNOTATE_INTRA_FUNCTION_CALL
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.macro UNWIND_HINT type:req sp_reg=0 sp_offset=0 signal=0
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.endm
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.macro STACK_FRAME_NON_STANDARD func:req
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.endm
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.macro ANNOTATE_NOENDBR
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.endm
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.macro REACHABLE
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.endm
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#endif
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#endif /* CONFIG_OBJTOOL */
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#endif /* _LINUX_OBJTOOL_H */
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