[PATCH] ld: Add -Bsymbolic-non-weak-functions
Fangrui Song
i@maskray.me
Mon Aug 23 07:14:23 GMT 2021
FWIW Android ndk plans to use -Bsymbolic-non-weak-functions.
The behavior will be quite similar to Mach-O, so pretty safe.
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
>
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