This is the mail archive of the binutils@sourceware.org mailing list for the binutils project.

Index Nav:	[Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav:	[Date Prev] [Date Next]	[Thread Prev] [Thread Next]
Other format:	[Raw text]

Re: [PATCH] Riscv shared libraries should not export __global_pointer$.

From: Palmer Dabbelt <palmer at sifive dot com>
To: Jim Wilson <jimw at sifive dot com>
Cc: Andrew Waterman <andrew at sifive dot com>, binutils at sourceware dot org, Jim Wilson <jimw at sifive dot com>
Date: Mon, 04 Dec 2017 21:56:22 -0800 (PST)
Subject: Re: [PATCH] Riscv shared libraries should not export __global_pointer$.
Authentication-results: sourceware.org; auth=none

On Mon, 04 Dec 2017 17:38:45 PST (-0800), Jim Wilson wrote:

This fixes issue #108 in the riscv-binutils-gdb project on github.
    https://github.com/riscv/riscv-binutils-gdb/issues/108
The problem here is that the riscv linker is exporting __global_pointer$ which
is wrong.  This symbol serves the same function as the mips _gp.  It is set by
the linker script in every executable/shared library and should not be
exported.  Exporting it can lead to linker errors as reported in #108.  The
fix is use HIDDEN for __global_pointer$, same as the mips port uses HIDDEN
for _gp.

I (well, it was really Andrew's idea, but I think he's right) think this mightjust be masking another bug: unlike MIPS, we don't save/restore GP when movingbetween shared libraries on RISC-V. Thus, actually using GP within a sharedlibrary is almost certainly a bug: how to you tell what the GP offset is toload any particular symbol's value? We don't bother having a dynamicrelocation for this because the only benefit of GP is during relaxation, and wecouldn't handle that in the dynamic linker.


For example, in PIC mode we compile this C code

   $ cat test.c
   long global;
   long func(void) { return global; }

to GOT-relative loads.

$ riscv64-unknown-linux-gnu-objdump -d test.so...

   0000000000000468 <func>:
    468:	00002797          	auipc	a5,0x2
    46c:	bc07b783          	ld	a5,-1088(a5) # 2028 <global@@Base-0x20>
    470:	6388                	ld	a0,0(a5)
    472:	8082                	ret

I think the real problem here is that I'm seeing `__global_pointer$` defined ineven the trivial shared library from above


   $ riscv64-unknown-linux-gnu-objdump -t test.so
   ...
   0000000000002840 g       .got	0000000000000000              __global_pointer$

While this commit and the associated test cases aren't wrong, they're just notstrong enough: gp-relative addressing should never appear in shared libraries(it's OK it shared executables), and therefor the presence of`__global_pointer$` probably indicates that something else has gone wrong.This is probably OK for now, as it'll at least let user's code build, but Ithink the real bug here is: why is `__global_pointer$` showing up in sharedlibraries? I'd bet that I screwed something up in glibc...

The mips port has some nice testcases for this, so I borrowed them to use
for the riscv target.  I also noticed that the riscv specific linker tests
weren't being run because of a typo in the target check.  This is fixed by
this patch also.

This was tested with check-binutils/check-gas/check-ld on riscv32 and riscv64.
There were no regressions.  Committed.

	ld/
	* emulparams/elf32lriscv-defs.sh (SDATA_START_SYMBOLS): Mark
	__global_pointer$ as HIDDEN.
	* testsuite/ld-riscv-elf/gp-hidden-64.rd: New.
	* testsuite/ld-riscv-elf/gp-hidden-lib.rd: New.
	* testsuite/ld-riscv-elf/gp-hidden-lib.s: New.
	* testsuite/ld-riscv-elf/gp-hidden-ver-64.rd: New.
	* testsuite/ld-riscv-elf/gp-hidden-ver.rd: New.
	* testsuite/ld-riscv-elf/gp-hidden-ver.s: New.
	* testsuite/ld-riscv-elf/gp-hidder-ver.ver: New.
	* testsuite/ld-riscv-elf/gp-hidden.rd: New.
	* testsuite/ld-riscv-elf/gp-hidden.s: New.
	* testsuite/ld-riscv-elf/gp-hidden.sd: New.
	* testsuite/ld-riscv-elf/ld-riscv-elf.exp: Change riscv to riscv*.
	Run the new tests with run_ld_link_tests.
---
 ld/emulparams/elf32lriscv-defs.sh             |  2 +-
 ld/testsuite/ld-riscv-elf/gp-hidden-64.rd     |  4 ++++
 ld/testsuite/ld-riscv-elf/gp-hidden-lib.rd    |  5 ++++
 ld/testsuite/ld-riscv-elf/gp-hidden-lib.s     |  6 +++++
 ld/testsuite/ld-riscv-elf/gp-hidden-ver-64.rd |  6 +++++
 ld/testsuite/ld-riscv-elf/gp-hidden-ver.rd    |  6 +++++
 ld/testsuite/ld-riscv-elf/gp-hidden-ver.s     |  7 ++++++
 ld/testsuite/ld-riscv-elf/gp-hidden-ver.ver   |  1 +
 ld/testsuite/ld-riscv-elf/gp-hidden.rd        |  4 ++++
 ld/testsuite/ld-riscv-elf/gp-hidden.s         |  7 ++++++
 ld/testsuite/ld-riscv-elf/gp-hidden.sd        |  9 +++++++
 ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp    | 34 ++++++++++++++++++++++++++-
 12 files changed, 89 insertions(+), 2 deletions(-)
 create mode 100644 ld/testsuite/ld-riscv-elf/gp-hidden-64.rd
 create mode 100644 ld/testsuite/ld-riscv-elf/gp-hidden-lib.rd
 create mode 100644 ld/testsuite/ld-riscv-elf/gp-hidden-lib.s
 create mode 100644 ld/testsuite/ld-riscv-elf/gp-hidden-ver-64.rd
 create mode 100644 ld/testsuite/ld-riscv-elf/gp-hidden-ver.rd
 create mode 100644 ld/testsuite/ld-riscv-elf/gp-hidden-ver.s
 create mode 100644 ld/testsuite/ld-riscv-elf/gp-hidden-ver.ver
 create mode 100644 ld/testsuite/ld-riscv-elf/gp-hidden.rd
 create mode 100644 ld/testsuite/ld-riscv-elf/gp-hidden.s
 create mode 100644 ld/testsuite/ld-riscv-elf/gp-hidden.sd

diff --git a/ld/emulparams/elf32lriscv-defs.sh b/ld/emulparams/elf32lriscv-defs.sh
index ab80333289..5b41d5cd02 100644
--- a/ld/emulparams/elf32lriscv-defs.sh
+++ b/ld/emulparams/elf32lriscv-defs.sh
@@ -23,7 +23,7 @@ TEXT_START_ADDR=0x10000
 MAXPAGESIZE="CONSTANT (MAXPAGESIZE)"
 COMMONPAGESIZE="CONSTANT (COMMONPAGESIZE)"

-SDATA_START_SYMBOLS="__global_pointer$ = . + 0x800;
+SDATA_START_SYMBOLS="HIDDEN (__global_pointer$ = . + 0x800);
     *(.srodata.cst16) *(.srodata.cst8) *(.srodata.cst4) *(.srodata.cst2) *(.srodata .srodata.*)"

 INITIAL_READONLY_SECTIONS=".interp         : { *(.interp) } ${CREATE_PIE-${INITIAL_READONLY_SECTIONS}}"
diff --git a/ld/testsuite/ld-riscv-elf/gp-hidden-64.rd b/ld/testsuite/ld-riscv-elf/gp-hidden-64.rd
new file mode 100644
index 0000000000..aaaec93d8e
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-hidden-64.rd
@@ -0,0 +1,4 @@
+
+Relocation section '\.rela\.dyn' at offset .* contains 1 entry:
+ *Offset * Info * Type * Sym\. *Value * Sym\. *Name \+ Addend
+[0-9a-f]+ * [0-9a-f]+02 * R_RISCV_64 * [0-9a-f]+ * foo \+ 0
diff --git a/ld/testsuite/ld-riscv-elf/gp-hidden-lib.rd b/ld/testsuite/ld-riscv-elf/gp-hidden-lib.rd
new file mode 100644
index 0000000000..59b4442190
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-hidden-lib.rd
@@ -0,0 +1,5 @@
+
+Relocation section '\.rela\.dyn' at offset .* contains 1 entry:
+ *Offset * Info * Type * Sym\. *Value * Sym\. *Name \+ Addend
+# This must be an absolute relocation, there must not be a _gp reference.
+[0-9a-f]+ * 0+03 * R_RISCV_RELATIVE * [0-9a-f]+
diff --git a/ld/testsuite/ld-riscv-elf/gp-hidden-lib.s b/ld/testsuite/ld-riscv-elf/gp-hidden-lib.s
new file mode 100644
index 0000000000..04f0655857
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-hidden-lib.s
@@ -0,0 +1,6 @@
+	.data
+	.globl	bar
+	.type	bar, @object
+bar:
+	.dc.a	__global_pointer$
+	.size	bar, . - bar
diff --git a/ld/testsuite/ld-riscv-elf/gp-hidden-ver-64.rd b/ld/testsuite/ld-riscv-elf/gp-hidden-ver-64.rd
new file mode 100644
index 0000000000..57cb13fc4a
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-hidden-ver-64.rd
@@ -0,0 +1,6 @@
+
+Relocation section '\.rela\.dyn' at offset .* contains 2 entries:
+ *Offset * Info * Type * Sym\. *Value * Sym\. *Name \+ Addend
+# This must be an absolute relocation, there must not be a _gp reference.
+[0-9a-f]+ * 0+03 * R_RISCV_RELATIVE * [0-9a-f]+
+[0-9a-f]+ * [0-9a-f]+02 * R_RISCV_64 * [0-9a-f]+ * bar \+ 0
diff --git a/ld/testsuite/ld-riscv-elf/gp-hidden-ver.rd b/ld/testsuite/ld-riscv-elf/gp-hidden-ver.rd
new file mode 100644
index 0000000000..dbed24f81e
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-hidden-ver.rd
@@ -0,0 +1,6 @@
+
+Relocation section '\.rela\.dyn' at offset .* contains 2 entries:
+ *Offset * Info * Type * Sym\. *Value * Sym\. *Name \+ Addend
+# This must be an absolute relocation, there must not be a _gp reference.
+[0-9a-f]+ * 0+03 * R_RISCV_RELATIVE * [0-9a-f]+
+[0-9a-f]+ * [0-9a-f]+01 * R_RISCV_32 * [0-9a-f]+ * bar \+ 0
diff --git a/ld/testsuite/ld-riscv-elf/gp-hidden-ver.s b/ld/testsuite/ld-riscv-elf/gp-hidden-ver.s
new file mode 100644
index 0000000000..a197bacd9b
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-hidden-ver.s
@@ -0,0 +1,7 @@
+	.data
+	.globl	foo
+	.type	foo, @object
+foo:
+	.dc.a	bar
+	.dc.a	__global_pointer$
+	.size	foo, . - foo
diff --git a/ld/testsuite/ld-riscv-elf/gp-hidden-ver.ver b/ld/testsuite/ld-riscv-elf/gp-hidden-ver.ver
new file mode 100644
index 0000000000..b6b2365188
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-hidden-ver.ver
@@ -0,0 +1 @@
+{ global: foo; local: *; };
diff --git a/ld/testsuite/ld-riscv-elf/gp-hidden.rd b/ld/testsuite/ld-riscv-elf/gp-hidden.rd
new file mode 100644
index 0000000000..dc29f7d058
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-hidden.rd
@@ -0,0 +1,4 @@
+
+Relocation section '\.rela\.dyn' at offset .* contains 1 entry:
+ *Offset * Info * Type * Sym\. *Value * Sym\. *Name \+ Addend
+[0-9a-f]+ * [0-9a-f]+01 * R_RISCV_32 * [0-9a-f]+ * foo \+ 0
diff --git a/ld/testsuite/ld-riscv-elf/gp-hidden.s b/ld/testsuite/ld-riscv-elf/gp-hidden.s
new file mode 100644
index 0000000000..18d3ca3d98
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-hidden.s
@@ -0,0 +1,7 @@
+	.data
+	.globl	blah
+	.type	blah, @object
+blah:
+	.dc.a	foo
+	.dc.a	__global_pointer$
+	.size	blah, . - blah
diff --git a/ld/testsuite/ld-riscv-elf/gp-hidden.sd b/ld/testsuite/ld-riscv-elf/gp-hidden.sd
new file mode 100644
index 0000000000..f4321c2b1f
--- /dev/null
+++ b/ld/testsuite/ld-riscv-elf/gp-hidden.sd
@@ -0,0 +1,9 @@
+
+Symbol table '.dynsym' contains [0-9]+ entries:
+ * Num: * Value * Size * Type * Bind * Vis * Ndx * Name
+#...
+Symbol table '.symtab' contains [0-9]+ entries:
+ * Num: * Value * Size * Type * Bind * Vis * Ndx * Name
+#...
+ * [0-9a-f]+: * [0-9a-f]+ * 0 * NOTYPE * LOCAL * DEFAULT .* __global_pointer\$
+#pass
diff --git a/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp b/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
index c219b18159..9f5959cc3b 100644
--- a/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
+++ b/ld/testsuite/ld-riscv-elf/ld-riscv-elf.exp
@@ -19,6 +19,38 @@
 # MA 02110-1301, USA.
 #

-if [istarget "riscv-*-*"] {
+if [istarget "riscv*-*-*"] {
     run_dump_test "c-lui"
+
+    set abis { rv32gc ilp32 elf32lriscv rv64gc lp64 elf64lriscv }
+    foreach { arch abi emul } $abis {
+	# This checks whether our linker scripts get the scope of
+	# __global_pointer$ right, and thus must therefore use default scripts.
+	set suff64 [string map {ilp32 "" lp64 -64} $abi]
+	run_ld_link_tests [list \
+			       [list "gp scope test ($abi shared library)" \
+				    "-m$emul -shared" "" \
+				    "-march=$arch -mabi=$abi -fpic" \
+				    { gp-hidden-lib.s } \
+				    [list \
+					 "readelf --relocs gp-hidden-lib.rd" \
+					 "readelf --syms gp-hidden.sd"] \
+				    "gp-hidden-lib-${abi}.so"] \
+			       [list "gp scope test ($abi versioned lib)" \
+				    "-m$emul -shared -version-script gp-hidden-ver.ver tmpdir/gp-hidden-lib-${abi}.so" "" \
+				    "-march=$arch -mabi=$abi -fpic" \
+				    { gp-hidden-ver.s } \
+				    [list \
+					 "readelf --relocs gp-hidden-ver${suff64}.rd" \
+					 "readelf --syms gp-hidden.sd"] \
+				    "gp-hidden-ver-${abi}.so"] \
+			       [list "gp scope test ($abi executable)" \
+				    "-m$emul -e 0 -rpath-link . tmpdir/gp-hidden-ver-${abi}.so" "" \
+				    "-march=$arch -mabi=$abi" \
+				    {gp-hidden.s} \
+				    [list \
+					 "readelf --relocs gp-hidden${suff64}.rd" \
+					 "readelf --syms gp-hidden.sd"]\
+				    "gp-hidden-${abi}"]]
+    }
 }

References:
- [PATCH] Riscv shared libraries should not export __global_pointer$.
  - From: Jim Wilson

Index Nav:	[Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav:	[Date Prev] [Date Next]	[Thread Prev] [Thread Next]