For very large ELF objects (with many sections), we could
get special value SHN_XINDEX (65535) for symbol's st_shndx.
This patch is adding code to detect the optional extended
section index table and use it to resolve symbol's section
index id needed.
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
btf_encoder.c | 18 ++++++++++++++++++
elf_symtab.c | 31 ++++++++++++++++++++++++++++++-
elf_symtab.h | 1 +
3 files changed, 49 insertions(+), 1 deletion(-)
diff --git a/btf_encoder.c b/btf_encoder.c
index 5557c9efd365..2ab6815dc2b3 100644
--- a/btf_encoder.c
+++ b/btf_encoder.c
@@ -609,6 +609,24 @@ static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
/* search within symtab for percpu variables */
elf_symtab__for_each_symbol(btfe->symtab, core_id, sym) {
+ struct elf_symtab *symtab = btfe->symtab;
+
+ /*
+ * Symbol's st_shndx needs to be translated with the
+ * extended section index table.
+ */
+ if (sym.st_shndx == SHN_XINDEX) {
+ Elf32_Word xndx;
+
+ if (!symtab->syms_shndx) {
+ fprintf(stderr, "SHN_XINDEX found, but no symtab shndx section.\n");
+ return -1;
+ }
+
+ if (gelf_getsymshndx(symtab->syms, symtab->syms_shndx, core_id, &sym, &xndx))
+ sym.st_shndx = xndx;
+ }
+
if (collect_percpu_vars && collect_percpu_var(btfe, &sym))
return -1;
if (collect_function(btfe, &sym))
diff --git a/elf_symtab.c b/elf_symtab.c
index 741990ea3ed9..c1def0189652 100644
--- a/elf_symtab.c
+++ b/elf_symtab.c
@@ -17,11 +17,13 @@
struct elf_symtab *elf_symtab__new(const char *name, Elf *elf, GElf_Ehdr *ehdr)
{
+ size_t index;
+
if (name == NULL)
name = ".symtab";
GElf_Shdr shdr;
- Elf_Scn *sec = elf_section_by_name(elf, ehdr, &shdr, name, NULL);
+ Elf_Scn *sec = elf_section_by_name(elf, ehdr, &shdr, name, &index);
if (sec == NULL)
return NULL;
@@ -29,6 +31,8 @@ struct elf_symtab *elf_symtab__new(const char *name, Elf *elf, GElf_Ehdr *ehdr)
if (gelf_getshdr(sec, &shdr) == NULL)
return NULL;
+ int xindex = elf_scnshndx(sec);
+
struct elf_symtab *symtab = malloc(sizeof(*symtab));
if (symtab == NULL)
return NULL;
@@ -49,6 +53,31 @@ struct elf_symtab *elf_symtab__new(const char *name, Elf *elf, GElf_Ehdr *ehdr)
if (symtab->symstrs == NULL)
goto out_free_name;
+ /*
+ * The .symtab section has optional extended section index
+ * table, load its data so it can be used to resolve symbol's
+ * section index.
+ **/
+ if (xindex > 0) {
+ GElf_Shdr shdr_shndx;
+ Elf_Scn *sec_shndx;
+
+ sec_shndx = elf_getscn(elf, xindex);
+ if (sec_shndx == NULL)
+ goto out_free_name;
+
+ if (gelf_getshdr(sec_shndx, &shdr_shndx) == NULL)
+ goto out_free_name;
+
+ /* Extra check to verify it belongs to the .symtab */
+ if (index != shdr_shndx.sh_link)
+ goto out_free_name;
+
+ symtab->syms_shndx = elf_getdata(elf_getscn(elf, xindex), NULL);
+ if (symtab->syms_shndx == NULL)
+ goto out_free_name;
+ }
+
symtab->nr_syms = shdr.sh_size / shdr.sh_entsize;
return symtab;
diff --git a/elf_symtab.h b/elf_symtab.h
index 359add69c8ab..f9277a48ed4c 100644
--- a/elf_symtab.h
+++ b/elf_symtab.h
@@ -16,6 +16,7 @@ struct elf_symtab {
uint32_t nr_syms;
Elf_Data *syms;
Elf_Data *symstrs;
+ Elf_Data *syms_shndx;
char *name;
};
--
2.27.0
