Define various symbols conditionally in shared libraries executables
H.J. Lu
hjl.tools@gmail.com
Wed Jun 6 13:30:00 GMT 2018
On Wed, Jun 06, 2018 at 10:00:43PM +0930, Alan Modra wrote:
> This should be applied on top of the patches attached to
> https://sourceware.org/ml/binutils/2018-06/msg00034.html
>
> The values of symbols in shared libraries like _end, _edata, and
> __bss_start are generally not that useful outside of the shared
> library. This patch defines them conditionally with PROVIDE, since a
> shared library might need the local value. An example is glibc ld.so
> local access to "_begin", "_etext" and "_end". We can't use
> PROVIDE_HIDDEN because the shared library might need the value of the
> symbol in the executable. An example is freebsd libc dynamic access
> to "_end".
>
> PR ld/23161
> * emulparams/aarch64cloudabi.sh: PROVIDE __bss_start__, _bss_end__,
> and __end__ in shared libraries.
> * emulparams/aarch64fbsd.sh: Likewise.
> * emulparams/aarch64linux.sh: Likewise.
> * emulparams/aarch64linux32.sh: Likewise.
> * emulparams/armelf_fuchsia.sh: Likewise.
> * emulparams/armelf_linux.sh: Likewise.
> * emulparams/armelf_phoenix.sh: Likewise.
> * emulparams/aarch64elf.sh: Likewise, and __data_start
> * emulparams/aarch64elf32.sh: Likewise.
> * emulparams/armelf.sh: Likewise.
> * emulparams/armnto.sh: Likewise.
> * emulparams/elf32bmip.sh: Remove duplicate ". = ." from
> OTHER_GOT_SYMBOLS. PROVIDE _ftext, _fdata, and _fbss in shared libs.
> * emulparams/elf32bmipn32-defs.sh: Likewise.
> * emulparams/elf32frv.sh: PROVIDE __end and __data_start in shared libs.
> * emulparams/elf32lriscv-defs.sh: Tidy.
> * emulparams/elf32mcore.sh: PROVIDE __bss_start and _bss_end in
> shared libs
> * emulparams/elf32ppccommon.sh: PROVIDE __end in shared libs.
> * emulparams/elf32rl78.sh: Tidy.
> * emulparams/i386nto.sh: PROVIDE _btext in shared libs.
> * emulparams/shelf_nto.sh: Likewise.
> * emulparams/shlelf_nto.sh: Likewise.
> * emulparams/score3_elf.sh: PROVIDE _gp, _bss_start__, _bss_end__,
> __bss_end__, __end__, _fdata, _sdata_begin, and _bss_start in
> shared libs.
> * scripttempl/elf.sc: Don't use EXECUTABLE_SYMBOLS for shared
> libraries. PROVIDE _edata, edata, __bss_start, and _end in shared
> libraries.
> * testsuite/ld-elf/pr23161.map,
> * testsuite/ld-elf/pr23161.rd,
> * testsuite/ld-elf/pr23161a.c,
> * testsuite/ld-elf/pr23161b.c: New files.
> * testsuite/ld-elf/shared.exp: Run ld/23161 tests.
> * testsuite/ld-elf/pr23162.rd,
Here is a different approach for x86, which includes more testcases
for PR ld/23161. Do they pass with your patch?
H.J.
---
_edata, __bss_start, and _end are defined by linker script. FreeBSD's
libc.so uses executable's _end to initialize curbrk. Glibc's ld.so
references _end as hidden symbol. But there is no good reason to export
unreferenced _edata, __bss_start, and _end defined in shared libraries.
We should hide unreferenced _edata, __bss_start, and _end in shared
libraries.
bfd/
PR ld/23161
* elfxx-x86.c (elf_x86_hide_linker_defined): New function.
(_bfd_x86_elf_link_check_relocs): Use it to hide unrefernced
__bss_start, _end and _edata in shared libraries.
ld/
PR ld/23161
* testsuite/ld-elf/pr23161.map: New file.
* testsuite/ld-elf/pr23161a.c: Likewise.
* testsuite/ld-elf/pr23161a.rd: Likewise.
* testsuite/ld-elf/pr23161b.c: Likewise.
* testsuite/ld-elf/pr23161b.rd: Likewise.
* testsuite/ld-elf/pr23161c.c: Likewise.
* testsuite/ld-elf/pr23161c.rd: Likewise.
* testsuite/ld-elf/pr23161d.rd: Likewise.
* testsuite/ld-elf/pr23162.rd: Remove _edata, __bss_start, and
_end.
* testsuite/ld-elf/shared.exp: Run ld/23161 tests.
---
bfd/elfxx-x86.c | 29 ++++++++++++++++
ld/testsuite/ld-elf/pr23161.map | 4 +++
ld/testsuite/ld-elf/pr23161a.c | 9 +++++
ld/testsuite/ld-elf/pr23161a.rd | 19 +++++++++++
ld/testsuite/ld-elf/pr23161b.c | 23 +++++++++++++
ld/testsuite/ld-elf/pr23161b.rd | 14 ++++++++
ld/testsuite/ld-elf/pr23161c.c | 9 +++++
ld/testsuite/ld-elf/pr23161c.rd | 12 +++++++
ld/testsuite/ld-elf/pr23161d.rd | 8 +++++
ld/testsuite/ld-elf/pr23162.rd | 9 +----
ld/testsuite/ld-elf/shared.exp | 60 +++++++++++++++++++++++++++++++++
11 files changed, 188 insertions(+), 8 deletions(-)
create mode 100644 ld/testsuite/ld-elf/pr23161.map
create mode 100644 ld/testsuite/ld-elf/pr23161a.c
create mode 100644 ld/testsuite/ld-elf/pr23161a.rd
create mode 100644 ld/testsuite/ld-elf/pr23161b.c
create mode 100644 ld/testsuite/ld-elf/pr23161b.rd
create mode 100644 ld/testsuite/ld-elf/pr23161c.c
create mode 100644 ld/testsuite/ld-elf/pr23161c.rd
create mode 100644 ld/testsuite/ld-elf/pr23161d.rd
diff --git a/bfd/elfxx-x86.c b/bfd/elfxx-x86.c
index 3a7573f7a2..e0298edddf 100644
--- a/bfd/elfxx-x86.c
+++ b/bfd/elfxx-x86.c
@@ -876,6 +876,27 @@ elf_x86_linker_defined (struct bfd_link_info *info, const char *name)
}
}
+/* Hide a linker-defined symbol, NAME, if it isn't referenced in a
+ relocatable object file. */
+
+static void
+elf_x86_hide_linker_defined (struct bfd_link_info *info,
+ const char *name)
+{
+ struct elf_link_hash_entry *h;
+
+ h = elf_link_hash_lookup (elf_hash_table (info), name,
+ FALSE, FALSE, FALSE);
+ if (h == NULL)
+ return;
+
+ while (h->root.type == bfd_link_hash_indirect)
+ h = (struct elf_link_hash_entry *) h->root.u.i.link;
+
+ if (!h->ref_regular)
+ _bfd_elf_link_hash_hide_symbol (info, h, TRUE);
+}
+
bfd_boolean
_bfd_x86_elf_link_check_relocs (bfd *abfd, struct bfd_link_info *info)
{
@@ -916,6 +937,14 @@ _bfd_x86_elf_link_check_relocs (bfd *abfd, struct bfd_link_info *info)
elf_x86_linker_defined (info, "_end");
elf_x86_linker_defined (info, "_edata");
}
+ else
+ {
+ /* Hide unreferenced __bss_start, _end and _edata in
+ shared libraries. */
+ elf_x86_hide_linker_defined (info, "__bss_start");
+ elf_x86_hide_linker_defined (info, "_end");
+ elf_x86_hide_linker_defined (info, "_edata");
+ }
}
}
diff --git a/ld/testsuite/ld-elf/pr23161.map b/ld/testsuite/ld-elf/pr23161.map
new file mode 100644
index 0000000000..cc817dc52a
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr23161.map
@@ -0,0 +1,4 @@
+FOO {
+ global:
+ *;
+};
diff --git a/ld/testsuite/ld-elf/pr23161a.c b/ld/testsuite/ld-elf/pr23161a.c
new file mode 100644
index 0000000000..707ed04bfd
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr23161a.c
@@ -0,0 +1,9 @@
+extern char *_end;
+extern char *_edata;
+extern char *__bss_start;
+
+int
+foo (void)
+{
+ return _end[0] + _edata[0] + __bss_start[0];
+}
diff --git a/ld/testsuite/ld-elf/pr23161a.rd b/ld/testsuite/ld-elf/pr23161a.rd
new file mode 100644
index 0000000000..1a7e563949
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr23161a.rd
@@ -0,0 +1,19 @@
+Relocation section '\.rel(a|)\.dyn' at offset 0x[0-9a-f]+ contains [0-9]+ entries:
+ +Offset +Info +Type +Sym.* Value +Sym.* Name( \+ Addend|)
+#...
+[a-f0-9]+ +[0-9a-f]+ +R_.*_GLOB_DAT +[a-f0-9]+ +__bss_start(@@FOO|)( \+ 0|)
+#...
+[a-f0-9]+ +[0-9a-f]+ +R_.*_GLOB_DAT +[a-f0-9]+ +_edata(@@FOO|)( \+ 0|)
+#...
+[a-f0-9]+ +[0-9a-f]+ +R_.*_GLOB_DAT +[a-f0-9]+ +_end(@@FOO|)( \+ 0|)
+#...
+Symbol table '\.dynsym' contains [0-9]+ entries:
+ +Num: +Value +Size Type +Bind +Vis +Ndx Name
+ +0: 0+ +0 +NOTYPE +LOCAL +DEFAULT +UND +
+#...
+ +[0-9]+: +[a-f0-9]+ +0 +NOTYPE +GLOBAL +DEFAULT +[0-9]+ +_edata(@@FOO|)
+#...
+ +[0-9]+: +[a-f0-9]+ +0 +NOTYPE +GLOBAL +DEFAULT +[0-9]+ +_end(@@FOO|)
+#...
+ +[0-9]+: +[a-f0-9]+ +0 +NOTYPE +GLOBAL +DEFAULT +[0-9]+ +__bss_start(@@FOO|)
+#...
diff --git a/ld/testsuite/ld-elf/pr23161b.c b/ld/testsuite/ld-elf/pr23161b.c
new file mode 100644
index 0000000000..0112f771b1
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr23161b.c
@@ -0,0 +1,23 @@
+static char *_edata_p;
+static char *_end_p;
+static char *__bss_start_p;
+extern char *_end;
+extern char *_edata;
+extern char *__bss_start;
+
+extern int foo (void);
+
+void
+bar (void)
+{
+ _edata_p = (char*) &_edata;
+ _end_p = (char*) &_end;
+ __bss_start_p = (char*) &__bss_start;
+}
+
+void
+_start ()
+{
+ bar ();
+ foo ();
+}
diff --git a/ld/testsuite/ld-elf/pr23161b.rd b/ld/testsuite/ld-elf/pr23161b.rd
new file mode 100644
index 0000000000..c8529a515f
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr23161b.rd
@@ -0,0 +1,14 @@
+Relocation section '\.rel(a|)\.plt' at offset 0x[0-9a-f]+ contains 1 entry:
+ +Offset +Info +Type +Sym.* Value +Sym.* Name( \+ Addend|)
+[a-f0-9]+ +[0-9a-f]+ +R_.*_JUMP_SLOT +[a-f0-9]+ +foo(@FOO|)( \+ 0|)
+
+Symbol table '\.dynsym' contains [0-9]+ entries:
+ +Num: +Value +Size Type +Bind +Vis +Ndx Name
+ +0: 0+ +0 +NOTYPE +LOCAL +DEFAULT +UND +
+#...
+ +[0-9]+: +[a-f0-9]+ +0 +NOTYPE +GLOBAL +DEFAULT +[0-9]+ +_edata
+#...
+ +[0-9]+: +[a-f0-9]+ +0 +NOTYPE +GLOBAL +DEFAULT +[0-9]+ +_end
+#...
+ +[0-9]+: +[a-f0-9]+ +0 +NOTYPE +GLOBAL +DEFAULT +[0-9]+ +__bss_start
+#...
diff --git a/ld/testsuite/ld-elf/pr23161c.c b/ld/testsuite/ld-elf/pr23161c.c
new file mode 100644
index 0000000000..db5ec4a334
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr23161c.c
@@ -0,0 +1,9 @@
+extern char *_end __attribute__ ((visibility("hidden")));
+extern char *_edata __attribute__ ((visibility("hidden")));
+extern char *__bss_start __attribute__ ((visibility("hidden")));
+
+int
+foo (void)
+{
+ return _end[0] + _edata[0] + __bss_start[0];
+}
diff --git a/ld/testsuite/ld-elf/pr23161c.rd b/ld/testsuite/ld-elf/pr23161c.rd
new file mode 100644
index 0000000000..904f126690
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr23161c.rd
@@ -0,0 +1,12 @@
+There are no relocations in this file.
+
+Symbol table '\.dynsym' contains [0-9]+ entries:
+ +Num: +Value +Size Type +Bind +Vis +Ndx Name
+ +0: 0+ +0 +NOTYPE +LOCAL +DEFAULT +UND +
+#...
+ +[0-9]+: +[a-f0-9]+ +0 +NOTYPE +LOCAL +DEFAULT +[0-9]+ +__bss_start
+#...
+ +[0-9]+: +[a-f0-9]+ +0 +NOTYPE +LOCAL +DEFAULT +[0-9]+ +_edata
+#...
+ +[0-9]+: +[a-f0-9]+ +0 +NOTYPE +LOCAL +DEFAULT +[0-9]+ +_end
+#...
diff --git a/ld/testsuite/ld-elf/pr23161d.rd b/ld/testsuite/ld-elf/pr23161d.rd
new file mode 100644
index 0000000000..338cfad336
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr23161d.rd
@@ -0,0 +1,8 @@
+Relocation section '\.rel(a|)\.plt' at offset 0x[0-9a-f]+ contains 1 entry:
+ +Offset +Info +Type +Sym.* Value +Sym.* Name( \+ Addend|)
+[a-f0-9]+ +[0-9a-f]+ +R_.*_JUMP_SLOT +[a-f0-9]+ +foo( \+ 0|)
+
+Symbol table '\.dynsym' contains [0-9]+ entries:
+ +Num: +Value +Size Type +Bind +Vis +Ndx Name
+ +0: 0+ +0 +NOTYPE +LOCAL +DEFAULT +UND +
+ +[0-9]+: +[a-f0-9]+ +0 +FUNC +GLOBAL +DEFAULT +UND +foo
diff --git a/ld/testsuite/ld-elf/pr23162.rd b/ld/testsuite/ld-elf/pr23162.rd
index 3ac848fe05..48351ffea7 100644
--- a/ld/testsuite/ld-elf/pr23162.rd
+++ b/ld/testsuite/ld-elf/pr23162.rd
@@ -1,12 +1,5 @@
There are no relocations in this file\.
-Symbol table '\.dynsym' contains [0-9]+ entries:
+Symbol table '\.dynsym' contains 1 entry:
+Num: +Value +Size Type +Bind +Vis +Ndx Name
+0: 0+ +0 +NOTYPE +LOCAL +DEFAULT +UND +
-#...
- +[0-9]+: +[a-f0-9]+ +0 +NOTYPE +GLOBAL +DEFAULT +[0-9]+ +_edata
-#...
- +[0-9]+: +[a-f0-9]+ +0 +NOTYPE +GLOBAL +DEFAULT +[0-9]+ +_end
-#...
- +[0-9]+: +[a-f0-9]+ +0 +NOTYPE +GLOBAL +DEFAULT +[0-9]+ +__bss_start
-#...
diff --git a/ld/testsuite/ld-elf/shared.exp b/ld/testsuite/ld-elf/shared.exp
index ef517bac42..f357b867c3 100644
--- a/ld/testsuite/ld-elf/shared.exp
+++ b/ld/testsuite/ld-elf/shared.exp
@@ -1393,5 +1393,65 @@ if { ([istarget "i?86-*-*"]
"pr23162b" \
"-fPIC -O0" \
] \
+ [list \
+ "Build libpr23161a.so" \
+ "-shared" \
+ "" \
+ "$AFLAGS_PIC" \
+ { pr23161a.c } \
+ {{readelf {--dyn-syms -rW} pr23161a.rd}} \
+ "libpr23161a.so" \
+ "-fPIC -O2" \
+ ] \
+ [list \
+ "Build pr23161a" \
+ "-pie --no-as-needed tmpdir/libpr23161a.so" \
+ "" \
+ "-mrelax-relocations=yes" \
+ { pr23161b.c } \
+ {{readelf {--dyn-syms -rW} pr23161b.rd}} \
+ "pr23161a" \
+ "-fPIC -O0" \
+ ] \
+ [list \
+ "Build libpr23161b.so" \
+ "-shared --version-script=pr23161.map" \
+ "" \
+ "$AFLAGS_PIC" \
+ { pr23161a.c } \
+ {{readelf {--dyn-syms -rW} pr23161a.rd}} \
+ "libpr23161b.so" \
+ "-fPIC -O2" \
+ ] \
+ [list \
+ "Build pr23161b" \
+ "-pie --no-as-needed tmpdir/libpr23161b.so" \
+ "" \
+ "-mrelax-relocations=yes" \
+ { pr23161b.c } \
+ {{readelf {--dyn-syms -rW} pr23161b.rd}} \
+ "pr23161b" \
+ "-fPIC -O0" \
+ ] \
+ [list \
+ "Build libpr23161c.so" \
+ "-shared" \
+ "" \
+ "$AFLAGS_PIC" \
+ { pr23161c.c } \
+ {{readelf {--dyn-syms -rW} pr23161c.rd}} \
+ "libpr23161c.so" \
+ "-fPIC -O2" \
+ ] \
+ [list \
+ "Build pr23161c" \
+ "-pie --no-as-needed tmpdir/libpr23161c.so" \
+ "" \
+ "-mrelax-relocations=yes" \
+ { pr23161b.c } \
+ {{readelf {--dyn-syms -rW} pr23161d.rd}} \
+ "pr23161c" \
+ "-fPIC -O0" \
+ ] \
]
}
--
2.17.1
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