We use the DWARF location information to match a variable with its
associated ELF section. 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 <xiyou.wangcong@xxxxxxxxx>
Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
---
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
