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Re: [patch] Replace most __builtin_expect's with __glibc_{un}likely
- From: "Carlos O'Donell" <carlos at redhat dot com>
- To: Paul Pluzhnikov <ppluzhnikov at google dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Cc: Siddhesh Poyarekar <siddhesh at redhat dot com>
- Date: Wed, 26 Mar 2014 17:21:35 -0400
- Subject: Re: [patch] Replace most __builtin_expect's with __glibc_{un}likely
- Authentication-results: sourceware.org; auth=none
- References: <ye6qha6k7ky8 dot fsf at elbrus2 dot mtv dot corp dot google dot com>
On 03/26/2014 04:40 PM, Paul Pluzhnikov wrote:
> Greetings,
>
> As promised here: https://sourceware.org/ml/libc-alpha/2014-03/msg00676.html
> attached patch converts most of __builtin_expect's into
> __glibc_{un}likely in elf/dl-load.c
>
> This patch produces identical dl-load.{o,os} on Linux/x86_64 (except a
> few line numbers change).
>
> The remaining 7 __builtin_expect's caused the object file to change in
> unexpected ways, which means that either I didn't do them correctly, or
> there is something else at play. I'll try to do them next.
>
> Thanks,
>
> --
>
> 2013-03-26 Paul Pluzhnikov <ppluzhnikov@google.com>
>
> * elf/dl-load.c: Convert __builtin_expect into
> __glibc_{un}likely.
Looks good to me.
OK, modulo one nit, see below (blank line).
Ondrej had some good suggestions for the other 7.
> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index 9455df2..fabe025 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -280,7 +280,7 @@ is_dst (const char *start, const char *name, const char *str,
> && (!is_path || name[len] != ':'))
> return 0;
>
> - if (__builtin_expect (secure, 0)
> + if (__glibc_unlikely (secure)
OK.
> && ((name[len] != '\0' && name[len] != '/'
> && (!is_path || name[len] != ':'))
> || (name != start + 1 && (!is_path || name[-2] != ':'))))
> @@ -381,7 +381,7 @@ _dl_dst_substitute (struct link_map *l, const char *name, char *result,
> /* In SUID/SGID programs, after $ORIGIN expansion the
> normalized path must be rooted in one of the trusted
> directories. */
> - if (__builtin_expect (check_for_trusted, false)
> + if (__glibc_unlikely (check_for_trusted)
OK.
> && !is_trusted_path_normalize (last_elem, wp - last_elem))
> wp = last_elem;
> else
> @@ -395,7 +395,7 @@ _dl_dst_substitute (struct link_map *l, const char *name, char *result,
>
> /* In SUID/SGID programs, after $ORIGIN expansion the normalized
> path must be rooted in one of the trusted directories. */
> - if (__builtin_expect (check_for_trusted, false)
> + if (__glibc_unlikely (check_for_trusted)
OK.
> && !is_trusted_path_normalize (last_elem, wp - last_elem))
> wp = last_elem;
>
> @@ -425,7 +425,7 @@ expand_dynamic_string_token (struct link_map *l, const char *s, int is_path)
> cnt = DL_DST_COUNT (s, is_path);
>
> /* If we do not have to replace anything simply copy the string. */
> - if (__builtin_expect (cnt, 0) == 0)
> + if (__glibc_likely (cnt == 0))
OK.
> return local_strdup (s);
>
> /* Determine the length of the substituted string. */
> @@ -513,7 +513,7 @@ fillin_rpath (char *rpath, struct r_search_path_elem **result, const char *sep,
> cp[len++] = '/';
>
> /* Make sure we don't use untrusted directories if we run SUID. */
> - if (__builtin_expect (check_trusted, 0) && !is_trusted_path (cp, len))
> + if (__glibc_unlikely (check_trusted) && !is_trusted_path (cp, len))
OK.
> {
> free (to_free);
> continue;
> @@ -604,7 +604,7 @@ decompose_rpath (struct r_search_path_struct *sps,
>
> /* First see whether we must forget the RUNPATH and RPATH from this
> object. */
> - if (__builtin_expect (GLRO(dl_inhibit_rpath) != NULL, 0)
> + if (__glibc_unlikely (GLRO(dl_inhibit_rpath) != NULL)
OK.
> && !INTUSE(__libc_enable_secure))
> {
> const char *inhp = GLRO(dl_inhibit_rpath);
> @@ -964,7 +964,7 @@ _dl_map_object_from_fd (const char *name, int fd, struct filebuf *fbp,
> #ifdef SHARED
> /* When loading into a namespace other than the base one we must
> avoid loading ld.so since there can only be one copy. Ever. */
> - if (__builtin_expect (nsid != LM_ID_BASE, 0)
> + if (__glibc_unlikely (nsid != LM_ID_BASE)
OK.
> && ((st.st_ino == GL(dl_rtld_map).l_ino
> && st.st_dev == GL(dl_rtld_map).l_dev)
> || _dl_name_match_p (name, &GL(dl_rtld_map))))
> @@ -1026,7 +1026,7 @@ _dl_map_object_from_fd (const char *name, int fd, struct filebuf *fbp,
> #ifdef SHARED
> /* Auditing checkpoint: we are going to add new objects. */
> if ((mode & __RTLD_AUDIT) == 0
> - && __builtin_expect (GLRO(dl_naudit) > 0, 0))
> + && __glibc_unlikely (GLRO(dl_naudit) > 0))
OK.
> {
> struct link_map *head = GL(dl_ns)[nsid]._ns_loaded;
> /* Do not call the functions for any auditing object. */
> @@ -1124,14 +1124,13 @@ _dl_map_object_from_fd (const char *name, int fd, struct filebuf *fbp,
> case PT_LOAD:
> /* A load command tells us to map in part of the file.
> We record the load commands and process them all later. */
> - if (__builtin_expect ((ph->p_align & (GLRO(dl_pagesize) - 1)) != 0,
> - 0))
> + if (__glibc_unlikely ((ph->p_align & (GLRO(dl_pagesize) - 1)) != 0))
OK.
> {
> errstring = N_("ELF load command alignment not page-aligned");
> goto call_lose;
> }
> - if (__builtin_expect (((ph->p_vaddr - ph->p_offset)
> - & (ph->p_align - 1)) != 0, 0))
> + if (__glibc_unlikely (((ph->p_vaddr - ph->p_offset)
> + & (ph->p_align - 1)) != 0))
OK.
> {
> errstring
> = N_("ELF load command address/offset not properly aligned");
> @@ -1184,10 +1183,10 @@ _dl_map_object_from_fd (const char *name, int fd, struct filebuf *fbp,
>
> /* If not loading the initial set of shared libraries,
> check whether we should permit loading a TLS segment. */
> - if (__builtin_expect (l->l_type == lt_library, 1)
> + if (__glibc_likely (l->l_type == lt_library)
OK.
> /* If GL(dl_tls_dtv_slotinfo_list) == NULL, then rtld.c did
> not set up TLS data structures, so don't use them now. */
> - || __builtin_expect (GL(dl_tls_dtv_slotinfo_list) != NULL, 1))
> + || __glibc_likely (GL(dl_tls_dtv_slotinfo_list) != NULL))
OK.
> {
> /* Assign the next available module ID. */
> l->l_tls_modid = _dl_next_tls_modid ();
> @@ -1214,9 +1213,8 @@ _dl_map_object_from_fd (const char *name, int fd, struct filebuf *fbp,
>
> /* The first call allocates TLS bookkeeping data structures.
> Then we allocate the TCB for the initial thread. */
> - if (__builtin_expect (_dl_tls_setup (), 0)
> - || __builtin_expect ((tcb = _dl_allocate_tls (NULL)) == NULL,
> - 0))
> + if (__glibc_unlikely (_dl_tls_setup ())
> + || __glibc_unlikely ((tcb = _dl_allocate_tls (NULL)) == NULL))
OK.
> {
> errval = ENOMEM;
> errstring = N_("\
> @@ -1430,7 +1428,7 @@ cannot allocate TLS data structures for initial thread");
>
> /* Make sure we are not dlopen'ing an object that has the
> DF_1_NOOPEN flag set. */
> - if (__builtin_expect (l->l_flags_1 & DF_1_NOOPEN, 0)
> + if (__glibc_unlikely (l->l_flags_1 & DF_1_NOOPEN)
OK.
> && (mode & __RTLD_DLOPEN))
> {
> /* We are not supposed to load this object. Free all resources. */
> @@ -1469,8 +1467,8 @@ cannot allocate TLS data structures for initial thread");
>
> if (__glibc_unlikely ((stack_flags &~ GL(dl_stack_flags)) & PF_X))
> {
> - if (__builtin_expect (__check_caller (RETURN_ADDRESS (0), allow_ldso),
> - 0) != 0)
> +
> + if (__glibc_unlikely (__check_caller (RETURN_ADDRESS (0), allow_ldso) != 0))
OK.
> {
> errstring = N_("invalid caller");
> goto call_lose;
> @@ -1560,7 +1558,7 @@ cannot enable executable stack as shared object requires");
> /* If this object has DT_SYMBOLIC set modify now its scope. We don't
> have to do this for the main map. */
> if ((mode & RTLD_DEEPBIND) == 0
> - && __builtin_expect (l->l_info[DT_SYMBOLIC] != NULL, 0)
> + && __glibc_unlikely (l->l_info[DT_SYMBOLIC] != NULL)
OK.
> && &l->l_searchlist != l->l_scope[0])
> {
> /* Create an appropriate searchlist. It contains only this map.
> @@ -1586,7 +1584,7 @@ cannot enable executable stack as shared object requires");
>
> /* When we profile the SONAME might be needed for something else but
> loading. Add it right away. */
> - if (__builtin_expect (GLRO(dl_profile) != NULL, 0)
> + if (__glibc_unlikely (GLRO(dl_profile) != NULL)
OK.
> && l->l_info[DT_SONAME] != NULL)
> add_name_to_object (l, ((const char *) D_PTR (l, l_info[DT_STRTAB])
> + l->l_info[DT_SONAME]->d_un.d_val));
> @@ -1600,7 +1598,7 @@ cannot enable executable stack as shared object requires");
>
> #ifdef SHARED
> /* Auditing checkpoint: we have a new object. */
> - if (__builtin_expect (GLRO(dl_naudit) > 0, 0)
> + if (__glibc_unlikely (GLRO(dl_naudit) > 0)
OK.
> && !GL(dl_ns)[l->l_ns]._ns_loaded->l_auditing)
> {
> struct audit_ifaces *afct = GLRO(dl_audit);
> @@ -1704,7 +1702,7 @@ open_verify (const char *name, struct filebuf *fbp, struct link_map *loader,
>
> #ifdef SHARED
> /* Give the auditing libraries a chance. */
> - if (__builtin_expect (GLRO(dl_naudit) > 0, 0) && whatcode != 0
> + if (__glibc_unlikely (GLRO(dl_naudit) > 0) && whatcode != 0
OK.
> && loader->l_auditing == 0)
> {
> struct audit_ifaces *afct = GLRO(dl_audit);
> @@ -1748,7 +1746,7 @@ open_verify (const char *name, struct filebuf *fbp, struct link_map *loader,
> break;
> fbp->len += retlen;
> }
> - while (__builtin_expect (fbp->len < sizeof (ElfW(Ehdr)), 0));
> + while (__glibc_unlikely (fbp->len < sizeof (ElfW(Ehdr))));
OK.
>
> /* This is where the ELF header is loaded. */
> ehdr = (ElfW(Ehdr) *) fbp->buf;
> @@ -1830,7 +1828,7 @@ open_verify (const char *name, struct filebuf *fbp, struct link_map *loader,
> goto call_lose;
> }
>
> - if (__builtin_expect (ehdr->e_version, EV_CURRENT) != EV_CURRENT)
> + if (__glibc_unlikely (ehdr->e_version != EV_CURRENT))
OK. Had to think twice about this one :-)
> {
> errstring = N_("ELF file version does not match current one");
> goto call_lose;
> @@ -1854,8 +1852,8 @@ open_verify (const char *name, struct filebuf *fbp, struct link_map *loader,
> errstring = N_("cannot dynamically load executable");
> goto call_lose;
> }
> - else if (__builtin_expect (ehdr->e_phentsize, sizeof (ElfW(Phdr)))
> - != sizeof (ElfW(Phdr)))
> + else if (__glibc_unlikely (ehdr->e_phentsize != sizeof (ElfW(Phdr))))
> +
Added blank line we don't need.
> {
> errstring = N_("ELF file's phentsize not the expected size");
> goto call_lose;
> @@ -1967,7 +1965,7 @@ open_path (const char *name, size_t namelen, int mode,
>
> /* If we are debugging the search for libraries print the path
> now if it hasn't happened now. */
> - if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0)
> + if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS)
OK.
> && current_what != this_dir->what)
> {
> current_what = this_dir->what;
> @@ -2021,7 +2019,7 @@ open_path (const char *name, size_t namelen, int mode,
> /* Remember whether we found any existing directory. */
> here_any |= this_dir->status[cnt] != nonexisting;
>
> - if (fd != -1 && __builtin_expect (mode & __RTLD_SECURE, 0)
> + if (fd != -1 && __glibc_unlikely (mode & __RTLD_SECURE)
OK.
> && INTUSE(__libc_enable_secure))
> {
> /* This is an extra security effort to make sure nobody can
> @@ -2108,14 +2106,14 @@ _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 (__builtin_expect (l->l_faked, 0) != 0
> + if (__glibc_unlikely (l->l_faked != 0)
OK.
> || __builtin_expect (l->l_removed, 0) != 0)
> continue;
> if (!_dl_name_match_p (name, l))
> {
> const char *soname;
>
> - if (__builtin_expect (l->l_soname_added, 1)
> + if (__glibc_likely (l->l_soname_added)
OK.
> || l->l_info[DT_SONAME] == NULL)
> continue;
>
> @@ -2134,7 +2132,7 @@ _dl_map_object (struct link_map *loader, const char *name,
> }
>
> /* Display information if we are debugging. */
> - if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_FILES, 0)
> + if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_FILES)
OK.
> && loader != NULL)
> _dl_debug_printf ((mode & __RTLD_CALLMAP) == 0
> ? "\nfile=%s [%lu]; needed by %s [%lu]\n"
> @@ -2144,7 +2142,7 @@ _dl_map_object (struct link_map *loader, const char *name,
> #ifdef SHARED
> /* Give the auditing libraries a chance to change the name before we
> try anything. */
> - if (__builtin_expect (GLRO(dl_naudit) > 0, 0)
> + if (__glibc_unlikely (GLRO(dl_naudit) > 0)
OK.
> && (loader == NULL || loader->l_auditing == 0))
> {
> struct audit_ifaces *afct = GLRO(dl_audit);
> @@ -2236,7 +2234,7 @@ _dl_map_object (struct link_map *loader, const char *name,
> if (fd == -1
> && (__builtin_expect (! (mode & __RTLD_SECURE), 1)
> || ! INTUSE(__libc_enable_secure))
> - && __builtin_expect (GLRO(dl_inhibit_cache) == 0, 1))
> + && __glibc_likely (GLRO(dl_inhibit_cache) == 0))
OK.
> {
> /* Check the list of libraries in the file /etc/ld.so.cache,
> for compatibility with Linux's ldconfig program. */
> @@ -2254,7 +2252,7 @@ _dl_map_object (struct link_map *loader, const char *name,
>
> /* If the loader has the DF_1_NODEFLIB flag set we must not
> use a cache entry from any of these directories. */
> - if (__builtin_expect (l->l_flags_1 & DF_1_NODEFLIB, 0))
> + if (__glibc_unlikely (l->l_flags_1 & DF_1_NODEFLIB))
OK.
> {
> const char *dirp = system_dirs;
> unsigned int cnt = 0;
> @@ -2297,7 +2295,7 @@ _dl_map_object (struct link_map *loader, const char *name,
> /* Finally, try the default path. */
> if (fd == -1
> && ((l = loader ?: GL(dl_ns)[nsid]._ns_loaded) == NULL
> - || __builtin_expect (!(l->l_flags_1 & DF_1_NODEFLIB), 1))
> + || __glibc_likely (!(l->l_flags_1 & DF_1_NODEFLIB)))
OK.
> && rtld_search_dirs.dirs != (void *) -1)
> fd = open_path (name, namelen, mode, &rtld_search_dirs,
> &realname, &fb, l, LA_SER_DEFAULT, &found_other_class);
> @@ -2319,7 +2317,7 @@ _dl_map_object (struct link_map *loader, const char *name,
> fd = open_verify (realname, &fb,
> loader ?: GL(dl_ns)[nsid]._ns_loaded, 0, mode,
> &found_other_class, true);
> - if (__builtin_expect (fd, 0) == -1)
> + if (__glibc_unlikely (fd == -1))
OK.
> free (realname);
> }
> }
> @@ -2333,10 +2331,10 @@ _dl_map_object (struct link_map *loader, const char *name,
> if (mode & __RTLD_CALLMAP)
> loader = NULL;
>
> - if (__builtin_expect (fd, 0) == -1)
> + if (__glibc_unlikely (fd == -1))
OK.
> {
> if (trace_mode
> - && __builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_PRELINK, 0) == 0)
> + && __glibc_likely ((GLRO(dl_debug_mask) & DL_DEBUG_PRELINK) == 0))
OK.
> {
> /* We haven't found an appropriate library. But since we
> are only interested in the list of libraries this isn't
>
Cheers,
Carlos.