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In the case of per-CPU variables their > ELF section address range starts at 0, so any 0 address variables will > appear to belong in that ELF section. However, for "discard" sections > DWARF encodes the associated variables with address location 0 so > we need to double-check that address 0 variables really are in the > associated section by checking the ELF symbol table. > > This resolves an issue exposed by CONFIG_DEBUG_FORCE_WEAK_PER_CPU=y > kernel builds where __pcpu_* dummary variables in a .discard section > get misclassified as belonging in the per-CPU variable section since > they specify location address 0. > > Reported-by: Cong Wang > Signed-off-by: Alan Maguire Reviewed-by: Stephen Brennan > --- > btf_encoder.c | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/btf_encoder.c b/btf_encoder.c > index 3754884..04f547c 100644 > --- a/btf_encoder.c > +++ b/btf_encoder.c > @@ -2189,6 +2189,26 @@ static bool filter_variable_name(const char *name) > return false; > } > > +bool variable_in_sec(struct btf_encoder *encoder, const char *name, size_t shndx) > +{ > + uint32_t sym_sec_idx; > + uint32_t core_id; > + GElf_Sym sym; > + > + elf_symtab__for_each_symbol_index(encoder->symtab, core_id, sym, sym_sec_idx) { > + const char *sym_name; > + > + if (sym_sec_idx != shndx || elf_sym__type(&sym) != STT_OBJECT) > + continue; > + sym_name = elf_sym__name(&sym, encoder->symtab); > + if (!sym_name) > + continue; > + if (strcmp(name, sym_name) == 0) > + return true; > + } > + return false; > +} > + > static int btf_encoder__encode_cu_variables(struct btf_encoder *encoder) > { > struct cu *cu = encoder->cu; > @@ -2258,6 +2278,13 @@ static int btf_encoder__encode_cu_variables(struct btf_encoder *encoder) > if (filter_variable_name(name)) > continue; > > + /* A 0 address may be in a "discard" section; DWARF provides > + * location information with address 0 for such variables. > + * Ensure the variable really is in this section by checking > + * the ELF symtab. > + */ > + if (addr == 0 && !variable_in_sec(encoder, name, shndx)) > + continue; > /* Check for invalid BTF names */ > if (!btf_name_valid(name)) { > dump_invalid_symbol("Found invalid variable name when encoding btf", > -- > 2.31.1