From: Heather McIntyre <hsm2@rice.edu>
To: Mark Wielaard <mark@klomp.org>
Cc: elfutils-devel@sourceware.org
Subject: Re: [PATCH 02/16] libelf: Make elf_version thread-safe
Date: Tue, 17 Oct 2023 14:05:58 -0500 [thread overview]
Message-ID: <CAK-+vz1uTVsmH93vfzwyDOYfPKDOHbq_kQqxrpfsv-JWfrfCdg@mail.gmail.com> (raw)
In-Reply-To: <99c0df19c4fe86f9142597b62fedac1bc1b85e75.camel@klomp.org>
[-- Attachment #1: Type: text/plain, Size: 2669 bytes --]
John and I discussed that atomic_compare_exchange_strong could have been
used here. I see that this has been pushed to the main branch, but I can
make the change to the atomic operation if you think that is a better
option.
Best,
Heather
On Tue, Oct 10, 2023 at 9:00 AM Mark Wielaard <mark@klomp.org> wrote:
> Hi Heather,
>
> On Tue, 2023-10-10 at 15:42 +0200, Mark Wielaard wrote:
> > From: Heather McIntyre <hsm2@rice.edu>
> >
> > * elf_version.c (version_once): Define once.
> > (initialize_version): New static function.
> > (elf_version): Use initialize_version version_once.
> >
> > Signed-off-by: Heather S. McIntyre <hsm2@rice.edu>
> > Signed-off-by: Mark Wielaard <mark@klomp.org>
> > ---
> > libelf/elf_version.c | 11 ++++++++++-
> > 1 file changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/libelf/elf_version.c b/libelf/elf_version.c
> > index 6ec534ab..8296bb65 100644
> > --- a/libelf/elf_version.c
> > +++ b/libelf/elf_version.c
> > @@ -32,12 +32,21 @@
> > #endif
> >
> > #include <libelfP.h>
> > +#include <pthread.h>
> >
> > +/* Multiple threads may initialize __libelf_version.
> > + pthread_once() ensures that __libelf_version is initialized only
> once. */
> > +once_define(static, version_once);
> >
> > /* Currently selected version. Should be EV_CURRENT.
> > Will be EV_NONE if elf_version () has not been called yet. */
> > unsigned int __libelf_version = EV_NONE;
> >
> > +static void initialize_version(void)
> > +{
> > + __libelf_version = EV_CURRENT;
> > +}
> > +
> > unsigned int
> > elf_version (unsigned int version)
> > {
> > @@ -49,7 +58,7 @@ elf_version (unsigned int version)
> > /* Phew, we know this version. */
> >
> > /* Signal that the version is now initialized. */
> > - __libelf_version = EV_CURRENT;
> > + once(version_once, initialize_version);
> >
> > /* And return the last (or initial) version. */
> > return EV_CURRENT;
>
> This is an odd function. The intention clearly was to support more "ELF
> versions" at some point. But (luckily) that never happened and I doubt
> there will ever be a different (incompatible) ELF version that we'll
> have to support. So in the end this will always be EV_CURRENT == 1. But
> the function has to be called to make the rest of the library work.
>
> I think this works and is fine. There will most likely never be real
> contention calling elf_version because normally a program just calls it
> once at the start.
>
> But have you thought about using some atomic operation here instead?
>
> Cheers,
>
> Mark
>
next prev parent reply other threads:[~2023-10-17 19:06 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-08 17:07 [PATCH] Fix thread-safety for elfutils Heather McIntyre
2023-08-21 22:08 ` John Mellor-Crummey
2023-08-25 14:10 ` Mark Wielaard
2023-10-10 13:40 ` Mark Wielaard
2023-10-10 13:42 ` [PATCH 01/16] lib: Add new once_define and once macros to eu-config.h Mark Wielaard
2023-10-10 13:42 ` [PATCH 02/16] libelf: Make elf_version thread-safe Mark Wielaard
2023-10-10 14:00 ` Mark Wielaard
2023-10-17 19:05 ` Heather McIntyre [this message]
2023-10-19 21:00 ` Mark Wielaard
2023-10-10 13:42 ` [PATCH 03/16] libelf: Fix deadlock in __libelf_readall Mark Wielaard
2023-10-10 15:06 ` Mark Wielaard
2023-10-17 19:11 ` Heather McIntyre
2023-11-09 13:26 ` Mark Wielaard
2023-10-10 13:42 ` [PATCH 04/16] libelf: Fix deadlock in elf_cntl Mark Wielaard
2023-10-10 15:23 ` Mark Wielaard
2023-10-17 19:14 ` Heather McIntyre
2023-10-10 13:42 ` [PATCH 05/16] libelf: Fix elf_end deadlock Mark Wielaard
2023-10-10 15:28 ` Mark Wielaard
2023-10-10 13:42 ` [PATCH 06/16] libelf: Make elf32_getchdr and elf64_getchdr thread-safe Mark Wielaard
2023-10-10 16:28 ` Mark Wielaard
2023-10-10 13:42 ` [PATCH 07/16] lib: Add eu_tsearch and eu_tfind Mark Wielaard
2023-10-10 16:51 ` Mark Wielaard
2023-10-17 20:52 ` Heather McIntyre
2023-10-10 13:42 ` [PATCH 08/16] libcpu: Change calls for tsearch/tfind to eu_tsearch/eu_tfind Mark Wielaard
2023-10-10 21:10 ` Mark Wielaard
2023-10-10 13:42 ` [PATCH 09/16] src: Use eu-search in nm and findtextrel Mark Wielaard
2023-10-10 21:25 ` Mark Wielaard
2023-10-17 19:20 ` Heather McIntyre
2023-10-10 13:42 ` [PATCH 10/16] libdw: make dwarf_getalt thread-safe Mark Wielaard
2023-10-10 22:02 ` Mark Wielaard
2023-10-17 19:25 ` Heather McIntyre
2023-10-10 13:42 ` [PATCH 11/16] libdw: Add locking around __libdw_dieabbrev for dwarf_hasattr Mark Wielaard
2023-10-11 15:10 ` Mark Wielaard
2023-10-17 19:57 ` Heather McIntyre
2023-10-19 22:06 ` Mark Wielaard
2023-10-10 13:42 ` [PATCH 12/16] libdw: Make libdw_find_split_unit thread-safe Mark Wielaard
2023-10-11 17:17 ` Mark Wielaard
2023-10-17 20:01 ` Heather McIntyre
2023-10-10 13:42 ` [PATCH 13/16] libdw: Make libdw_findcu thread-safe Mark Wielaard
2023-10-12 22:02 ` Mark Wielaard
2023-10-17 20:10 ` Heather McIntyre
2023-10-10 13:42 ` [PATCH 14/16] libdw,libdwfl: Use eu-search for thread-safety Mark Wielaard
2023-10-12 22:05 ` Mark Wielaard
2023-10-10 13:42 ` [PATCH 15/16] tests: Add eu-search tests Mark Wielaard
2023-10-13 14:38 ` Mark Wielaard
2023-10-10 13:43 ` [PATCH 16/16] configure: No longer mark --enable-thread-safety as EXPERIMENTAL Mark Wielaard
2023-10-12 22:09 ` Mark Wielaard
2023-10-10 13:54 ` [PATCH 01/16] lib: Add new once_define and once macros to eu-config.h Mark Wielaard
2023-10-14 15:39 ` [PATCH] Fix thread-safety for elfutils Mark Wielaard
2023-10-14 18:29 ` Heather McIntyre
2023-10-17 15:04 ` Mark Wielaard
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