On Thu, Jan 21, 2021 at 12:25 PM Jiri Olsa <[email protected]> wrote:
>
> 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.
>
> Adding elf_symtab__for_each_symbol_index macro that returns
> symbol's section index and usign it in collect_symbols function.
>
> Signed-off-by: Jiri Olsa <[email protected]>
> ---
You missed fixing up collect_function() as well, which is using
elf_sym__section(), which doesn't know about extended numbering.
> btf_encoder.c | 36 ++++++++++++++++++++++++++++++++----
> elf_symtab.c | 39 ++++++++++++++++++++++++++++++++++++++-
> elf_symtab.h | 2 ++
> 3 files changed, 72 insertions(+), 5 deletions(-)
>
> diff --git a/btf_encoder.c b/btf_encoder.c
> index 5557c9efd365..6e6f22c438ce 100644
> --- a/btf_encoder.c
> +++ b/btf_encoder.c
> @@ -585,12 +585,13 @@ static int collect_percpu_var(struct btf_elf *btfe,
> GElf_Sym *sym)
> return 0;
> }
>
> -static void collect_symbol(GElf_Sym *sym, struct funcs_layout *fl)
> +static void collect_symbol(GElf_Sym *sym, struct funcs_layout *fl,
> + Elf32_Word sym_sec_idx)
> {
> if (!fl->mcount_start &&
> !strcmp("__start_mcount_loc", elf_sym__name(sym, btfe->symtab))) {
> fl->mcount_start = sym->st_value;
> - fl->mcount_sec_idx = sym->st_shndx;
> + fl->mcount_sec_idx = sym_sec_idx;
> }
>
> if (!fl->mcount_stop &&
> @@ -598,9 +599,36 @@ static void collect_symbol(GElf_Sym *sym, struct
> funcs_layout *fl)
> fl->mcount_stop = sym->st_value;
> }
>
> +static bool elf_sym__get(Elf_Data *syms, Elf_Data *syms_sec_idx_table,
> + int id, GElf_Sym *sym, Elf32_Word *sym_sec_idx)
> +{
> + if (!gelf_getsym(syms, id, sym))
> + return false;
> +
> + *sym_sec_idx = sym->st_shndx;
> +
> + if (sym->st_shndx == SHN_XINDEX) {
> + if (!syms_sec_idx_table)
> + return false;
> + if (!gelf_getsymshndx(syms, syms_sec_idx_table,
> + id, sym, sym_sec_idx))
gelf_getsymshndx() is supposed to work even for cases that don't use
extended numbering, so this should work, right?
if (!gelf_getsymshndx(syms, syms_sec_idx_table, id, sym, sym_sec_idx))
return false;
if (sym->st_shndx == SHN_XINDEX)
*sym_sec_idx = sym->st_shndx;
return true;
?
> + return false;
> + }
> +
> + return true;
> +}
> +
> +#define elf_symtab__for_each_symbol_index(symtab, id, sym, sym_sec_idx)
> \
> + for (id = 0, elf_sym__get(symtab->syms, symtab->syms_sec_idx_table,
> \
> + id, &sym, &sym_sec_idx);
> \
> + id < symtab->nr_syms;
> \
> + id++, elf_sym__get(symtab->syms, symtab->syms_sec_idx_table,
> \
> + id, &sym, &sym_sec_idx))
what do we want to do if elf_sym__get() returns error (false)? We can
either stop or ignore that symbol, right? But currently you are
returning invalid symbol data.
so either
for (id = 0; id < symtab->nr_syms && elf_sym__get(symtab->syms,
symtab->syms_sec_idx_table, d, &sym, &sym_sec_idx); id++)
or
for (id = 0; id < symtab->nr_syms; id++)
if (elf_sym__get(symtab->syms, symtab->syms_sec_idx_table, d, &sym,
&sym_sec_idx))
But the current variant looks broken. Oh, and
elf_symtab__for_each_symbol() is similarly broken, can you please fix
that as well?
And this new macro should probably be in elf_symtab.h, along the
elf_symtab__for_each_symbol.
> +
> static int collect_symbols(struct btf_elf *btfe, bool collect_percpu_vars)
> {
> struct funcs_layout fl = { };
> + Elf32_Word sym_sec_idx;
> uint32_t core_id;
> GElf_Sym sym;
>
[...]
