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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Fangrui Song <maskray@google.com>
Date: Sat, 22 May 2021 23:10:21 -0700
Subject: [PATCH] ld: Add -Bsymbolic-non-weak-functions
This option is a subset of -Bsymbolic-functions: only STB_GLOBAL are
considered. Vague linkage functions are STB_WEAK. A vague linkage
function may have different addresses in a -Bsymbolic-functions linked
shared object and outside the shared object.
-Bsymbolic-non-weak-functions can keep pointer equality while providing
most benefits: (a) fewer JUMP_SLOT (symbol lookups) (b) avoid PLT
entries for default visibility defined functions.
PR 27871
include/
* bfdlink.h (struct bfd_link_info): Add dynamic_weak_functions.
ld/
* ldlex.h (enum option_values): Add OPTION_SYMBOLIC_NON_WEAK_FUNCTIONS.
* lexsup.c (struct ld_options): Add -Bsymbolic-non-weak-functions.
(enum symbolic_enum): Add symbolic_non_weak_functions.
(parse_args): Handle -Bsymbolic-non-weak-functions.
* ld.texi: Document -Bsymbolic-non-weak-functions.
* NEWS: Mention -Bsymbolic-non-weak-functions.
* testsuite/ld-elf/shared.exp: Add tests.
* testsuite/ld-elf/symbolic-non-weak-func.s: New file.
* testsuite/ld-elf/symbolic-non-weak-func-a.rd: Likewise.
* testsuite/ld-elf/symbolic-non-weak-func-b.rd: Likewise.
---
bfd/elflink.c | 12 +++++-----
include/bfdlink.h | 3 +++
ld/NEWS | 2 ++
ld/ld.texi | 15 ++++++++++---
ld/ldlex.h | 1 +
ld/lexsup.c | 17 +++++++++++---
ld/testsuite/ld-elf/shared.exp | 22 +++++++++++++++++++
.../ld-elf/symbolic-non-weak-func-a.rd | 4 ++++
.../ld-elf/symbolic-non-weak-func-b.rd | 4 ++++
ld/testsuite/ld-elf/symbolic-non-weak-func.s | 18 +++++++++++++++
10 files changed, 85 insertions(+), 13 deletions(-)
create mode 100644 ld/testsuite/ld-elf/symbolic-non-weak-func-a.rd
create mode 100644 ld/testsuite/ld-elf/symbolic-non-weak-func-b.rd
create mode 100644 ld/testsuite/ld-elf/symbolic-non-weak-func.s
diff --git a/bfd/elflink.c b/bfd/elflink.c
index 91c77c211ef065a77883004eb696adacd92a00be..558e2a74061452083fd6bcdc99541b535e134aed 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -637,14 +637,12 @@ bfd_elf_link_mark_dynamic_symbol (struct bfd_link_info *info,
if(h->dynamic || bfd_link_relocatable (info))
return;
+ int type = sym != NULL ? ELF_ST_TYPE (sym->st_info) : STT_NOTYPE;
if ((info->dynamic_data
- && (h->type == STT_OBJECT
- || h->type == STT_COMMON
- || (sym != NULL
- && (ELF_ST_TYPE (sym->st_info) == STT_OBJECT
- || ELF_ST_TYPE (sym->st_info) == STT_COMMON))))
- || (d != NULL
- && h->non_elf
+ && (type == STT_OBJECT || type == STT_COMMON))
+ || (info->dynamic_weak_functions && type == STT_FUNC
+ && ELF_ST_BIND (sym->st_info) == STB_WEAK)
+ || (d != NULL && h->non_elf
&& (*d->match) (&d->head, NULL, h->root.root.string)))
{
h->dynamic = 1;
diff --git a/include/bfdlink.h b/include/bfdlink.h
index ae451075996498eb2c20ea28180dd67489724583..5b5d059b17b62d5f48eede1583638f216f64bb37 100644
--- a/include/bfdlink.h
+++ b/include/bfdlink.h
@@ -371,6 +371,9 @@ struct bfd_link_info
/* TRUE if all data symbols should be dynamic. */
unsigned int dynamic_data: 1;
+ /* TRUE if all weak function symbols should be dynamic. */
+ unsigned int dynamic_weak_functions: 1;
+
/* TRUE if section groups should be resolved. */
unsigned int resolve_section_groups: 1;
diff --git a/ld/NEWS b/ld/NEWS
index 17fb20a6b9f7813748dc3346075291ce7ad13f56..b05cbd77a9c4492e32a0cea6a54d05af58e090f7 100644
--- a/ld/NEWS
+++ b/ld/NEWS
@@ -185,6 +185,8 @@ Changes in 2.37:
* Add -Bno-symbolic to cancel -Bsymbolic and -Bsymbolic-functions.
+* Add -Bsymbolic-non-weak-functions as a safe subset of -Bsymbolic-functions.
+
Changes in 2.36:
* Add libdep plugin, for linking dependencies of static libraries that
diff --git a/ld/ld.texi b/ld/ld.texi
index f6384ad82dd943a1a7e71ed560793d6ab8bdd6f4..7d5d736c32c7011478e7f422d6ca3ea6d2cf9293 100644
--- a/ld/ld.texi
+++ b/ld/ld.texi
@@ -1853,7 +1853,7 @@ libraries.
@kindex -Bsymbolic
@item -Bsymbolic
-When creating a shared library, bind references to global symbols to the
+When creating a shared library, bind references to non-local symbols to the
definition within the shared library, if any. Normally, it is possible
for a program linked against a shared library to override the definition
within the shared library. This option is only meaningful on ELF
@@ -1861,11 +1861,20 @@ platforms which support shared libraries.
@kindex -Bsymbolic-functions
@item -Bsymbolic-functions
-When creating a shared library, bind references to global function
-symbols to the definition within the shared library, if any.
+When creating a shared library, bind references to non-local function
+symbols to the definition within the shared library, if any. A vague linkage
+function definition is weak. It may have different addresses in the linked
+shared library and outside the shared library.
This option is only meaningful on ELF platforms which support shared
libraries.
+@kindex -Bsymbolic-non-weak-functions
+@item -Bsymbolic-non-weak-functions
+When creating a shared library, bind references to @code{STB_GLOBAL} function
+symbols to the definition within the shared library, if any. Noticeably this
+option skips C++ vague linkage functions and is thus safe.
+This option is only meaningful on ELF platforms which support shared libraries.
+
@kindex -Bno-symbolic
@item -Bno-symbolic
This option can cancel previously specified @samp{-Bsymbolic} and
diff --git a/ld/ldlex.h b/ld/ldlex.h
index b8b7d6b6829d9e7427ebd99eb556237005538940..1e60d3f8b7a1aa1280e725eebdf2eed1470ba1fb 100644
--- a/ld/ldlex.h
+++ b/ld/ldlex.h
@@ -65,6 +65,7 @@ enum option_values
OPTION_SECTION_ORDERING_FILE,
OPTION_STATS,
OPTION_SYMBOLIC,
+ OPTION_SYMBOLIC_NON_WEAK_FUNCTIONS,
OPTION_SYMBOLIC_FUNCTIONS,
OPTION_TASK_LINK,
OPTION_IMAGE_BASE,
diff --git a/ld/lexsup.c b/ld/lexsup.c
index 5399aa45b724e61008686d607a1f3a8e360e2c7f..21e542886ec9a83bb764209affacc0aa4d47bdc3 100644
--- a/ld/lexsup.c
+++ b/ld/lexsup.c
@@ -318,9 +318,11 @@ static const struct ld_option ld_options[] =
{ {"Bno-symbolic", no_argument, NULL, OPTION_NO_SYMBOLIC},
'\0', NULL, N_("Don't bind global references locally"), ONE_DASH },
{ {"Bsymbolic", no_argument, NULL, OPTION_SYMBOLIC},
- '\0', NULL, N_("Bind global references locally"), ONE_DASH },
+ '\0', NULL, N_("Bind default visibility defined symbols locally for -shared"), ONE_DASH },
+ { {"Bsymbolic-non-weak-functions", no_argument, NULL, OPTION_SYMBOLIC_NON_WEAK_FUNCTIONS},
+ '\0', NULL, N_("Bind default visibility defined STB_GLOBAL function symbols locally for -shared"), ONE_DASH },
{ {"Bsymbolic-functions", no_argument, NULL, OPTION_SYMBOLIC_FUNCTIONS},
- '\0', NULL, N_("Bind global function references locally"), ONE_DASH },
+ '\0', NULL, N_("Bind default visibility defined function symbols locally for -shared"), ONE_DASH },
{ {"check-sections", no_argument, NULL, OPTION_CHECK_SECTIONS},
'\0', NULL, N_("Check section addresses for overlaps (default)"),
TWO_DASHES },
@@ -668,8 +670,9 @@ parse_args (unsigned argc, char **argv)
enum symbolic_enum
{
symbolic_unset = 0,
- symbolic,
+ symbolic_non_weak_functions,
symbolic_functions,
+ symbolic,
} opt_symbolic = symbolic_unset;
enum dynamic_list_enum
{
@@ -1420,6 +1423,9 @@ parse_args (unsigned argc, char **argv)
case OPTION_SYMBOLIC:
opt_symbolic = symbolic;
break;
+ case OPTION_SYMBOLIC_NON_WEAK_FUNCTIONS:
+ opt_symbolic = symbolic_non_weak_functions;
+ break;
case OPTION_SYMBOLIC_FUNCTIONS:
opt_symbolic = symbolic_functions;
break;
@@ -2038,6 +2044,11 @@ parse_args (unsigned argc, char **argv)
link_info.dynamic = true;
link_info.dynamic_data = true;
break;
+ case symbolic_non_weak_functions:
+ link_info.dynamic = true;
+ link_info.dynamic_data = true;
+ link_info.dynamic_weak_functions = true;
+ break;
}
/* -z nosectionheader implies --strip-all. */
diff --git a/ld/testsuite/ld-elf/shared.exp b/ld/testsuite/ld-elf/shared.exp
index bf8952a843cf31bdca7032511c3b0a7e74452a63..0d125653e6e9814c35421ee8d552ab25396db69b 100644
--- a/ld/testsuite/ld-elf/shared.exp
+++ b/ld/testsuite/ld-elf/shared.exp
@@ -459,6 +459,28 @@ run_ld_link_tests [list \
"symbolic-func.so"] \
]
+if {[istarget "aarch64*-*-*"] || [istarget "powerpc*-*-*"] ||
+ [istarget "i?86-*-*"] || [istarget "x86_64-*-*"]} {
+ run_ld_link_tests [list \
+ [list "-Bsymbolic-non-weak-functions -Bsymbolic" \
+ "-shared -Bsymbolic-non-weak-functions -Bsymbolic" "" "$AFLAGS_PIC" \
+ {symbolic-non-weak-func.s} {{readelf {-r --wide} symbolic-non-weak-func-a.rd}} \
+ "symbolic-non-weak-func-a.so"] \
+ ]
+ run_ld_link_tests [list \
+ [list "-Bsymbolic-non-weak-functions" \
+ "-shared -Bsymbolic-non-weak-functions" "" "$AFLAGS_PIC" \
+ {symbolic-non-weak-func.s} {{readelf {-r --wide} symbolic-non-weak-func-b.rd}} \
+ "symbolic-non-weak-func-b.so"] \
+ ]
+ run_ld_link_tests [list \
+ [list "-Bsymbolic-functions -Bsymbolic-non-weak-functions" \
+ "-shared -Bsymbolic-functions -Bsymbolic-non-weak-functions" "" "$AFLAGS_PIC" \
+ {symbolic-non-weak-func.s} {{readelf {-r --wide} symbolic-non-weak-func-b.rd}} \
+ "symbolic-non-weak-func-b.so"] \
+ ]
+}
+
run_ld_link_tests [list \
[list "Build pr20995.so" \
"-shared" "" "$AFLAGS_PIC" \
diff --git a/ld/testsuite/ld-elf/symbolic-non-weak-func-a.rd b/ld/testsuite/ld-elf/symbolic-non-weak-func-a.rd
new file mode 100644
index 0000000000000000000000000000000000000000..ef591840f5c338a55f6d44fc372568569011c430
--- /dev/null
+++ b/ld/testsuite/ld-elf/symbolic-non-weak-func-a.rd
@@ -0,0 +1,4 @@
+#...
+[0-9a-f]+ +[0-9a-f]+ +R_.*_RELATIVE .*
+[0-9a-f]+ +[0-9a-f]+ +R_.*_RELATIVE .*
+[0-9a-f]+ +[0-9a-f]+ +R_.*_RELATIVE .*
diff --git a/ld/testsuite/ld-elf/symbolic-non-weak-func-b.rd b/ld/testsuite/ld-elf/symbolic-non-weak-func-b.rd
new file mode 100644
index 0000000000000000000000000000000000000000..34228b0627b226cfdc76e3cedff6f515b7c27872
--- /dev/null
+++ b/ld/testsuite/ld-elf/symbolic-non-weak-func-b.rd
@@ -0,0 +1,4 @@
+#...
+[0-9a-f]+ +[0-9a-f]+ +R_.*_RELATIVE .*
+[0-9a-f]+ +[0-9a-f]+ +R_.*_RELATIVE .*
+[0-9a-f]+ +[0-9a-f]+ +R_.* weak_fun.*
diff --git a/ld/testsuite/ld-elf/symbolic-non-weak-func.s b/ld/testsuite/ld-elf/symbolic-non-weak-func.s
new file mode 100644
index 0000000000000000000000000000000000000000..e259f12bfc126bf2ef9bf16aba64667ca4e2bfd5
--- /dev/null
+++ b/ld/testsuite/ld-elf/symbolic-non-weak-func.s
@@ -0,0 +1,18 @@
+ .text
+ .global global_fun
+ .type global_fun, %function
+global_fun:
+ .space 4
+ .weak weak_fun
+ .type weak_fun, %function
+weak_fun:
+ .space 4
+
+ .section .data,"aw",%progbits
+ .p2align 3
+ .dc.a global_data
+ .dc.a global_fun
+ .dc.a weak_fun
+
+ .global global_data
+global_data: