| Message ID | ye6qeh1o7ab8.fsf@elbrus2.mtv.corp.google.com |
|---|---|
| State | New |
| Headers | show |
On Wed, Mar 26, 2014 at 05:30:03PM -0700, Paul Pluzhnikov wrote: > Greetings, > > This patch cleans up remaining uses of __builtin_expect. > > It does change elf/dl-load.o in non-trivial ways, but > - the tests still pass on Linux/x86_64 and > - is much smaller, and easier to verify. > Looks mostly ok. > @@ -2104,8 +2103,7 @@ _dl_map_object (struct link_map *loader, const char *name, > /* If the requested name matches the soname of a loaded object, > use that object. Elide this check for names that have not > yet been opened. */ > - if (__glibc_unlikely (l->l_faked != 0) > - || __builtin_expect (l->l_removed, 0) != 0) > + if (__glibc_unlikely (l->l_faked != 0 || l->l_removed != 0)) > continue; > if (!_dl_name_match_p (name, l)) > { Here it might decrease performance (see below), do you have profile data it migth make sense even to drop this one. As written now its optimized to if (__glibc_unlikely (l->l_faked != 0) continue; if (__builtin_expect (l->l_removed, 0) != 0) continue; with your change compiler could assume that first part happens in 49% time and 49% for other part. So its better to trasform that expression that requires only one jump, here best one is if (__glibc_unlikely (l->l_faked | l->l_removed != 0)) continue; > @@ -2230,7 +2228,7 @@ _dl_map_object (struct link_map *loader, const char *name, > > #ifdef USE_LDCONFIG > if (fd == -1 > - && (__builtin_expect (! (mode & __RTLD_SECURE), 1) > + && (__glibc_likely ((mode & __RTLD_SECURE) == 0) > || ! INTUSE(__libc_enable_secure)) > && __glibc_likely (GLRO(dl_inhibit_cache) == 0)) > { Extra parens here.
Ondřej Bílka <neleai@seznam.cz> writes: > if (__glibc_unlikely (l->l_faked != 0) > continue; > if (__builtin_expect (l->l_removed, 0) != 0) > continue; __builtin_expect should really only be used in boolean context, ie. this should be written as: if (__builtin_expect (l->l_removed != 0, 0)) continue; Andreas.
On Thu, Mar 27, 2014 at 4:42 AM, Ondřej Bílka <neleai@seznam.cz> wrote: > On Wed, Mar 26, 2014 at 05:30:03PM -0700, Paul Pluzhnikov wrote: >> @@ -2104,8 +2103,7 @@ _dl_map_object (struct link_map *loader, const char *name, >> /* If the requested name matches the soname of a loaded object, >> use that object. Elide this check for names that have not >> yet been opened. */ >> - if (__glibc_unlikely (l->l_faked != 0) >> - || __builtin_expect (l->l_removed, 0) != 0) >> + if (__glibc_unlikely (l->l_faked != 0 || l->l_removed != 0)) >> continue; >> if (!_dl_name_match_p (name, l)) >> { ... > if (__glibc_unlikely (l->l_faked | l->l_removed != 0)) > continue; Done. >> @@ -2230,7 +2228,7 @@ _dl_map_object (struct link_map *loader, const char *name, >> >> #ifdef USE_LDCONFIG >> if (fd == -1 >> - && (__builtin_expect (! (mode & __RTLD_SECURE), 1) >> + && (__glibc_likely ((mode & __RTLD_SECURE) == 0) >> || ! INTUSE(__libc_enable_secure)) >> && __glibc_likely (GLRO(dl_inhibit_cache) == 0)) >> { > > Extra parens here. Are there? I don't see them :-( Thanks,
On Thu, Mar 27, 2014 at 09:42:54AM -0700, Paul Pluzhnikov wrote: > > >> @@ -2230,7 +2228,7 @@ _dl_map_object (struct link_map *loader, const char *name, > >> > >> #ifdef USE_LDCONFIG > >> if (fd == -1 > >> - && (__builtin_expect (! (mode & __RTLD_SECURE), 1) > >> + && (__glibc_likely ((mode & __RTLD_SECURE) == 0) > >> || ! INTUSE(__libc_enable_secure)) > >> && __glibc_likely (GLRO(dl_inhibit_cache) == 0)) > >> { > > > > Extra parens here. > > Are there? I don't see them :-( > Never mind, when I saw that I forgotten that & has weird precedence.
diff --git a/elf/dl-load.c b/elf/dl-load.c index 2d15e41..0ae0ad1 100644 --- a/elf/dl-load.c +++ b/elf/dl-load.c @@ -1269,7 +1269,7 @@ cannot allocate TLS data structures for initial thread"); /* Length of the sections to be loaded. */ maplength = loadcmds[nloadcmds - 1].allocend - c->mapstart; - if (__builtin_expect (type, ET_DYN) == ET_DYN) + if (__glibc_likely (type == ET_DYN)) { /* This is a position-independent shared object. We can let the kernel map it anywhere it likes, but we must have space for all @@ -1767,14 +1767,13 @@ open_verify (const char *name, struct filebuf *fbp, struct link_map *loader, } /* See whether the ELF header is what we expect. */ - if (__builtin_expect (! VALID_ELF_HEADER (ehdr->e_ident, expected, + if (__glibc_unlikely (! VALID_ELF_HEADER (ehdr->e_ident, expected, EI_ABIVERSION) || !VALID_ELF_ABIVERSION (ehdr->e_ident[EI_OSABI], ehdr->e_ident[EI_ABIVERSION]) || memcmp (&ehdr->e_ident[EI_PAD], &expected[EI_PAD], - EI_NIDENT - EI_PAD) != 0, - 0)) + EI_NIDENT - EI_PAD) != 0)) { /* Something is wrong. */ const Elf32_Word *magp = (const void *) ehdr->e_ident; @@ -1832,10 +1831,10 @@ open_verify (const char *name, struct filebuf *fbp, struct link_map *loader, errstring = N_("ELF file version does not match current one"); goto call_lose; } - if (! __builtin_expect (elf_machine_matches_host (ehdr), 1)) + if (! __glibc_likely (elf_machine_matches_host (ehdr))) goto close_and_out; - else if (__builtin_expect (ehdr->e_type, ET_DYN) != ET_DYN - && __builtin_expect (ehdr->e_type, ET_EXEC) != ET_EXEC) + else if (__glibc_unlikely (ehdr->e_type != ET_DYN + && ehdr->e_type != ET_EXEC)) { errstring = N_("only ET_DYN and ET_EXEC can be loaded"); goto call_lose; @@ -2104,8 +2103,7 @@ _dl_map_object (struct link_map *loader, const char *name, /* If the requested name matches the soname of a loaded object, use that object. Elide this check for names that have not yet been opened. */ - if (__glibc_unlikely (l->l_faked != 0) - || __builtin_expect (l->l_removed, 0) != 0) + if (__glibc_unlikely (l->l_faked != 0 || l->l_removed != 0)) continue; if (!_dl_name_match_p (name, l)) { @@ -2230,7 +2228,7 @@ _dl_map_object (struct link_map *loader, const char *name, #ifdef USE_LDCONFIG if (fd == -1 - && (__builtin_expect (! (mode & __RTLD_SECURE), 1) + && (__glibc_likely ((mode & __RTLD_SECURE) == 0) || ! INTUSE(__libc_enable_secure)) && __glibc_likely (GLRO(dl_inhibit_cache) == 0)) {
Greetings, This patch cleans up remaining uses of __builtin_expect. It does change elf/dl-load.o in non-trivial ways, but - the tests still pass on Linux/x86_64 and - is much smaller, and easier to verify. Thanks, -- 2014-03-26 Paul Pluzhnikov <ppluzhnikov@google.com> * elf/dl-load.c: Finish __builtin_expect into __glibc_{un}likely conversion.