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| author | Ard Biesheuvel <ardb@kernel.org> | 2024-04-15 19:20:43 +0300 |
|---|---|---|
| committer | Masahiro Yamada <masahiroy@kernel.org> | 2024-05-02 13:48:26 +0300 |
| commit | 951bcae6c5a0bfaa55b27c5f16178204988f0379 (patch) | |
| tree | bc40f7a42a32785eba057dd7128580e7c5a1c851 /include/asm-generic | |
| parent | c3f7bed8fa141c02d715f856ba1a6a757b8c8db9 (diff) | |
| download | linux-951bcae6c5a0bfaa55b27c5f16178204988f0379.tar.xz | |
kallsyms: Avoid weak references for kallsyms symbols
kallsyms is a directory of all the symbols in the vmlinux binary, and so
creating it is somewhat of a chicken-and-egg problem, as its non-zero
size affects the layout of the binary, and therefore the values of the
symbols.
For this reason, the kernel is linked more than once, and the first pass
does not include any kallsyms data at all. For the linker to accept
this, the symbol declarations describing the kallsyms metadata are
emitted as having weak linkage, so they can remain unsatisfied. During
the subsequent passes, the weak references are satisfied by the kallsyms
metadata that was constructed based on information gathered from the
preceding passes.
Weak references lead to somewhat worse codegen, because taking their
address may need to produce NULL (if the reference was unsatisfied), and
this is not usually supported by RIP or PC relative symbol references.
Given that these references are ultimately always satisfied in the final
link, let's drop the weak annotation, and instead, provide fallback
definitions in the linker script that are only emitted if an unsatisfied
reference exists.
While at it, drop the FRV specific annotation that these symbols reside
in .rodata - FRV is long gone.
Tested-by: Nick Desaulniers <ndesaulniers@google.com> # Boot
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lkml.kernel.org/r/20230504174320.3930345-1-ardb%40kernel.org
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Diffstat (limited to 'include/asm-generic')
| -rw-r--r-- | include/asm-generic/vmlinux.lds.h | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index f7749d0f2562..e8449be62058 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -449,10 +449,29 @@ #endif /* + * Some symbol definitions will not exist yet during the first pass of the + * link, but are guaranteed to exist in the final link. Provide preliminary + * definitions that will be superseded in the final link to avoid having to + * rely on weak external linkage, which requires a GOT when used in position + * independent code. + */ +#define PRELIMINARY_SYMBOL_DEFINITIONS \ + PROVIDE(kallsyms_addresses = .); \ + PROVIDE(kallsyms_offsets = .); \ + PROVIDE(kallsyms_names = .); \ + PROVIDE(kallsyms_num_syms = .); \ + PROVIDE(kallsyms_relative_base = .); \ + PROVIDE(kallsyms_token_table = .); \ + PROVIDE(kallsyms_token_index = .); \ + PROVIDE(kallsyms_markers = .); \ + PROVIDE(kallsyms_seqs_of_names = .); + +/* * Read only Data */ #define RO_DATA(align) \ . = ALIGN((align)); \ + PRELIMINARY_SYMBOL_DEFINITIONS \ .rodata : AT(ADDR(.rodata) - LOAD_OFFSET) { \ __start_rodata = .; \ *(.rodata) *(.rodata.*) \ |