From: Fangrui Song <maskray@google.com>
To: binutils@sourceware.org, Alan Modra <amodra@gmail.com>
Cc: Fangrui Song <maskray@google.com>
Subject: [PATCH] ld: Add -Bsymbolic-non-weak-functions
Date: Sat, 22 May 2021 23:10:21 -0700 [thread overview]
Message-ID: <20210523061021.1671339-1-maskray@google.com> (raw)
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 0e1871aaac9..cbdac95f18a 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -597,14 +597,12 @@ 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 7f1b12dbf37..e1576405007 100644
--- a/include/bfdlink.h
+++ b/include/bfdlink.h
@@ -369,6 +369,9 @@ 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 a5ed9058c04..86bf9a8f9ab 100644
--- a/ld/NEWS
+++ b/ld/NEWS
@@ -10,6 +10,8 @@
* 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 29874688a73..3807ab98f57 100644
--- a/ld/ld.texi
+++ b/ld/ld.texi
@@ -1620,7 +1620,7 @@ 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
@@ -1628,11 +1628,20 @@ 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 e0f0241d9cc..188160c6b9d 100644
--- a/ld/ldlex.h
+++ b/ld/ldlex.h
@@ -64,6 +64,7 @@ enum option_values
OPTION_SORT_SECTION,
OPTION_STATS,
OPTION_SYMBOLIC,
+ OPTION_SYMBOLIC_NON_WEAK_FUNCTIONS,
OPTION_SYMBOLIC_FUNCTIONS,
OPTION_TASK_LINK,
OPTION_TBSS,
diff --git a/ld/lexsup.c b/ld/lexsup.c
index dcb2d9d9ab3..64db6a89460 100644
--- a/ld/lexsup.c
+++ b/ld/lexsup.c
@@ -305,9 +305,11 @@ 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 },
@@ -611,8 +613,9 @@ 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
{
@@ -1309,6 +1312,9 @@ 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;
@@ -1888,6 +1894,11 @@ 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;
}
if (!bfd_link_dll (&link_info))
diff --git a/ld/testsuite/ld-elf/shared.exp b/ld/testsuite/ld-elf/shared.exp
index d00358e47ef..0ddc4b1cfcd 100644
--- a/ld/testsuite/ld-elf/shared.exp
+++ b/ld/testsuite/ld-elf/shared.exp
@@ -457,6 +457,28 @@ 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 00000000000..ef591840f5c
--- /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 00000000000..34228b0627b
--- /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 00000000000..e259f12bfc1
--- /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:
--
2.31.1.818.g46aad6cb9e-goog
next reply other threads:[~2021-05-23 6:10 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-23 6:10 Fangrui Song [this message]
2021-08-23 7:14 ` Fangrui Song
[not found] ` <CAN30aBHgL6QQY_-qzS5+wdOvYSHqQ6tQLFTXfA_WrZ4rHQAdLA@mail.gmail.com>
2021-12-06 4:53 ` Fangrui Song
[not found] ` <CAN30aBFrwa4Un2wV=H7-YorLS690XJj1D1Wa6vSQ_u3tXOAELQ@mail.gmail.com>
2023-09-01 1:10 ` Fangrui Song
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