Hi Aaron,
On Fri, 2026-10-30 at 01:16 -0400, Aaron Merey wrote:
> Store a Dwfl_Module's ebl field atomically in __libdwfl_module_getebl
> while holding the associated Dwfl load_lock.
>
> Change usage of the ebl field so that before using it's either been
> atomically read or else it's used after __libdwfl_module_getebl returns
> DWFL_E_NOERROR.
>
> In __libdwfl_getsym also initialize the backend before calling
> ebl_func_addr_mask and return early if it fails.
>
> Also fix a bug where ebl wasn't initialized before calling
> ebl_func_addr_mask.
>
> Signed-off-by: Aaron Merey <[email protected]>
> ---
> v2 changes: Initialize the backend before calling ebl_func_addr_mask.
In __libdwfl_getsym. This makes the code cleaner/simpler. Looks good.
Thanks,
Mark
> libdwfl/dwfl_module_getdwarf.c | 24 +++++++++++++++------
> libdwfl/dwfl_module_getsym.c | 24 ++++++++++++---------
> libdwfl/dwfl_module_register_names.c | 11 ++++------
> libdwfl/dwfl_module_return_value_location.c | 11 ++++------
> 4 files changed, 40 insertions(+), 30 deletions(-)
>
> diff --git a/libdwfl/dwfl_module_getdwarf.c b/libdwfl/dwfl_module_getdwarf.c
> index 77af5189..8420ba20 100644
> --- a/libdwfl/dwfl_module_getdwarf.c
> +++ b/libdwfl/dwfl_module_getdwarf.c
> @@ -1345,17 +1345,29 @@ Dwfl_Error
> internal_function
> __libdwfl_module_getebl (Dwfl_Module *mod)
> {
> + if (likely (atomic_load_acquire (&mod->ebl) != NULL))
> + return DWFL_E_NOERROR;
> +
> + Dwfl_Error ret = DWFL_E_NOERROR;
> + mutex_lock (mod->dwfl->load_lock);
> +
> if (mod->ebl == NULL)
> {
> __libdwfl_getelf (mod);
> - if (mod->elferr != DWFL_E_NOERROR)
> - return mod->elferr;
> + ret = mod->elferr;
>
> - mod->ebl = ebl_openbackend (mod->main.elf);
> - if (mod->ebl == NULL)
> - return DWFL_E_LIBEBL;
> + if (ret == DWFL_E_NOERROR)
> + {
> + Ebl *ebl = ebl_openbackend (mod->main.elf);
> + if (ebl == NULL)
> + ret = DWFL_E_LIBEBL;
> + else
> + atomic_store_release (&mod->ebl, ebl);
> + }
> }
> - return DWFL_E_NOERROR;
> +
> + mutex_unlock (mod->dwfl->load_lock);
> + return ret;
> }
>
> /* Try to start up libdw on DEBUGFILE. */
> diff --git a/libdwfl/dwfl_module_getsym.c b/libdwfl/dwfl_module_getsym.c
> index 2bb07fd8..3a364a76 100644
> --- a/libdwfl/dwfl_module_getsym.c
> +++ b/libdwfl/dwfl_module_getsym.c
> @@ -123,6 +123,13 @@ __libdwfl_getsym (Dwfl_Module *mod, int ndx, GElf_Sym
> *sym, GElf_Addr *addr,
> might know where the real value is (e.g. for function
> descriptors). */
>
> + Dwfl_Error error = __libdwfl_module_getebl (mod);
> + if (unlikely (error != DWFL_E_NOERROR))
> + {
> + __libdwfl_seterrno (error);
> + return NULL;
> + }
> +
> char *ident;
> GElf_Addr st_value = sym->st_value & ebl_func_addr_mask (mod->ebl);
> *resolved = false;
> @@ -132,18 +139,15 @@ __libdwfl_getsym (Dwfl_Module *mod, int ndx, GElf_Sym
> *sym, GElf_Addr *addr,
> && (ident = elf_getident (elf, NULL)) != NULL
> && ident[EI_OSABI] == ELFOSABI_LINUX)))
> {
> - if (likely (__libdwfl_module_getebl (mod) == DWFL_E_NOERROR))
> + if (elf != mod->main.elf)
> {
> - if (elf != mod->main.elf)
> - {
> - st_value = dwfl_adjusted_st_value (mod, elf, st_value);
> - st_value = dwfl_deadjust_st_value (mod, mod->main.elf, st_value);
> - }
> -
> - *resolved = ebl_resolve_sym_value (mod->ebl, &st_value);
> - if (! *resolved)
> - st_value = sym->st_value;
> + st_value = dwfl_adjusted_st_value (mod, elf, st_value);
> + st_value = dwfl_deadjust_st_value (mod, mod->main.elf, st_value);
> }
> +
> + *resolved = ebl_resolve_sym_value (mod->ebl, &st_value);
> + if (! *resolved)
> + st_value = sym->st_value;
> }
>
> if (shndxp != NULL)
> diff --git a/libdwfl/dwfl_module_register_names.c
> b/libdwfl/dwfl_module_register_names.c
> index 9ea09371..a8aa8a65 100644
> --- a/libdwfl/dwfl_module_register_names.c
> +++ b/libdwfl/dwfl_module_register_names.c
> @@ -43,14 +43,11 @@ dwfl_module_register_names (Dwfl_Module *mod,
> if (unlikely (mod == NULL))
> return -1;
>
> - if (unlikely (mod->ebl == NULL))
> + Dwfl_Error error = __libdwfl_module_getebl (mod);
> + if (unlikely (error != DWFL_E_NOERROR))
> {
> - Dwfl_Error error = __libdwfl_module_getebl (mod);
> - if (error != DWFL_E_NOERROR)
> - {
> - __libdwfl_seterrno (error);
> - return -1;
> - }
> + __libdwfl_seterrno (error);
> + return -1;
> }
>
> int nregs = ebl_register_info (mod->ebl, -1, NULL, 0,
> diff --git a/libdwfl/dwfl_module_return_value_location.c
> b/libdwfl/dwfl_module_return_value_location.c
> index ff6f56f8..8a3e63a9 100644
> --- a/libdwfl/dwfl_module_return_value_location.c
> +++ b/libdwfl/dwfl_module_return_value_location.c
> @@ -40,14 +40,11 @@ dwfl_module_return_value_location (Dwfl_Module *mod,
> Dwarf_Die *functypedie,
> if (mod == NULL)
> return -1;
>
> - if (mod->ebl == NULL)
> + Dwfl_Error error = __libdwfl_module_getebl (mod);
> + if (error != DWFL_E_NOERROR)
> {
> - Dwfl_Error error = __libdwfl_module_getebl (mod);
> - if (error != DWFL_E_NOERROR)
> - {
> - __libdwfl_seterrno (error);
> - return -1;
> - }
> + __libdwfl_seterrno (error);
> + return -1;
> }
>
> int nops = ebl_return_value_location (mod->ebl, functypedie, locops);
