From: Fangrui Song <i@maskray.me>
To: Fangrui Song <maskray@google.com>
Cc: binutils@sourceware.org, Alan Modra <amodra@gmail.com>
Subject: Re: [PATCH] ld: Add -Bsymbolic-non-weak-functions
Date: Thu, 31 Aug 2023 18:10:43 -0700 [thread overview]
Message-ID: <DS7PR12MB57652041AD2EA1FF5AA17A3DCBE4A@DS7PR12MB5765.namprd12.prod.outlook.com> (raw)
In-Reply-To: <CAN30aBFrwa4Un2wV=H7-YorLS690XJj1D1Wa6vSQ_u3tXOAELQ@mail.gmail.com>
On Sun, Dec 5, 2021 at 8:53 PM Fangrui Song <i@maskray.me> wrote:
>
> On Mon, Aug 23, 2021 at 3:14 AM Fangrui Song <i@maskray.me> wrote:
> >
> > FWIW Android ndk plans to use -Bsymbolic-non-weak-functions.
> > The behavior will be quite similar to Mach-O, so pretty safe.
>
> -Bsymbolic-non-weak-functions or -Bsymbolic-non-weak is still worth considering.
> (The behavior will be similar to Mach-O's model (strong definitions
> are non-interposable by default; weak definitions are coalesced).)
Recently I got interest from Meta (https://reviews.llvm.org/D158322)
and SerenityOS[1] .
I hope that this patch will be considered:)
[1]: "We (SerenityOS) use __attribute__((weak)) to provide stubs for
expensive features (Unicode and Locale data) in libraries, which are
interposed by the real implementation if the application requests it"
> > On Sat, May 22, 2021 at 11:10 PM Fangrui Song via Binutils
> > <binutils@sourceware.org> wrote:
> > >
> > > 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
> > >
prev parent reply other threads:[~2023-09-01 1:10 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-23 6:10 Fangrui Song
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 [this message]
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