From: Fangrui Song <maskray@google.com>
To: libc-alpha@sourceware.org
Cc: Fangrui Song <maskray@google.com>
Subject: [PATCH] elf: Add the soname to the libname_list eagerly on loading a library
Date: Thu, 27 Apr 2023 23:26:34 -0700 [thread overview]
Message-ID: <20230428062634.2152615-1-maskray@google.com> (raw)
Original author is Ambrose Feinstein while working at Google.
_dl_map_object iterates over loaded objects and calls _dl_name_match_p.
If l->l_soname_added is 0, we incur two costs.
First, loading l->l_info[DT_SONAME]->d_un.d_val has TLB pressure as
every library's string table is in a different page. The cost will be
avoided if the string is on the heap.
Second, add_name_to_object repeats the l_libname comparison already done
by the _dl_name_match_p call.
To remove these costs, we eagerly add the SONAME to the libname_list.
l_soname_added is typically 1, so laziness doesn't provide savings.
---
elf/dl-load.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/elf/dl-load.c b/elf/dl-load.c
index 9a0e40c0e9..1b17410ce0 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1451,10 +1451,11 @@ 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 (__glibc_unlikely (GLRO(dl_profile) != NULL)
- && l->l_info[DT_SONAME] != NULL)
+ if (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));
+ l->l_soname_added = 1;
+ }
/* If we have newly loaded libc.so, update the namespace
description. */
--
2.40.1.495.gc816e09b53d-goog
next reply other threads:[~2023-04-28 6:26 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-28 6:26 Fangrui Song [this message]
2023-04-28 8:42 ` Florian Weimer
2023-05-02 23:08 ` Fangrui Song
2023-07-05 6:17 ` Florian Weimer
2023-07-05 18:22 ` Fangrui Song
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