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: Sun, 5 Dec 2021 23:53:47 -0500 [thread overview]
Message-ID: <MWHPR1201MB01107AF9F6B4959608C0201FCB6D9@MWHPR1201MB0110.namprd12.prod.outlook.com> (raw)
In-Reply-To: <CAN30aBHgL6QQY_-qzS5+wdOvYSHqQ6tQLFTXfA_WrZ4rHQAdLA@mail.gmail.com>
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).)
> 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
> >
next prev parent reply other threads:[~2021-12-06 5:02 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 [this message]
[not found] ` <CAN30aBFrwa4Un2wV=H7-YorLS690XJj1D1Wa6vSQ_u3tXOAELQ@mail.gmail.com>
2023-09-01 1:10 ` Fangrui Song
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