[PATCH] PowerPC 32 with Secure PLT

Michael Eager
2012-01-18T03:05:02Z

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This patch adds support for stepping into/over the PLT stubs generated
for secure PLT on PowerPC 32. It requires a recent binutils which
generates symbols for the stubs.

This has been tested on PowerPC 32-bit systems with and without PAX.

2012-01-17 Michael Eager <eager@eagercon.com>

* configure.tgt (powerpc-*-linux*): Add glibc-tdep.o.
* ppc-linux-tdep.c: Include glibc-tdep.h.
(powerpc32_plt_stub, powerpc32_plt_stub_so): Add PLT stub templates.
(powerpc_linux_in_plt_stub): New function.
(powerpc_linux_in_dynsym_resolve_code): New function.
(ppc_skip_trampoline_code): New function.
(ppc_linux_init_abi): Use PPC specific functions rather than generic.
Use glibc_skip_solib_resolver.

--
Michael Eager eager@eagercon.com
1960 Park Blvd., Palo Alto, CA 94306 650-325-8077

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Index: configure.tgt
===================================================================
RCS file: /cvs/src/src/gdb/configure.tgt,v
retrieving revision 1.249
diff -u -p -r1.249 configure.tgt
--- configure.tgt 10 Jan 2012 16:30:43 -0000 1.249
+++ configure.tgt 18 Jan 2012 02:52:00 -0000
@@ -399,7 +399,7 @@ powerpc-*-linux* | powerpc64-*-linux*)
# Target: PowerPC running Linux
gdb_target_obs="rs6000-tdep.o ppc-linux-tdep.o ppc-sysv-tdep.o \
solib-svr4.o solib-spu.o spu-multiarch.o \
- symfile-mem.o linux-tdep.o"
+ glibc-tdep.o symfile-mem.o linux-tdep.o"
gdb_sim=../sim/ppc/libsim.a
build_gdbserver=yes
;;
Index: ppc-linux-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/ppc-linux-tdep.c,v
retrieving revision 1.133
diff -u -p -r1.133 ppc-linux-tdep.c
--- ppc-linux-tdep.c 4 Jan 2012 13:51:36 -0000 1.133
+++ ppc-linux-tdep.c 18 Jan 2012 02:52:01 -0000
@@ -37,6 +37,7 @@
#include "solist.h"
#include "ppc-tdep.h"
#include "ppc-linux-tdep.h"
+#include "glibc-tdep.h"
#include "trad-frame.h"
#include "frame-unwind.h"
#include "tramp-frame.h"
@@ -65,6 +66,9 @@
#include "features/rs6000/powerpc-isa205-vsx64l.c"
#include "features/rs6000/powerpc-e500l.c"

+/* Shared library operations for PowerPC-Linux. */
+static struct target_so_ops powerpc_so_ops;
+
/* The syscall's XML filename for PPC and PPC64. */
#define XML_SYSCALL_FILENAME_PPC "syscalls/ppc-linux.xml"
#define XML_SYSCALL_FILENAME_PPC64 "syscalls/ppc64-linux.xml"
@@ -599,6 +603,87 @@ ppc64_standard_linkage3_target (struct f
return ppc64_desc_entry_point (gdbarch, desc);
}

+/* PLT stub in executable. */
+static struct insn_pattern powerpc32_plt_stub[] =
+ {
+ { 0xffff0000, 0x3d600000, 0 }, /* lis r11, xxxx */
+ { 0xffff0000, 0x816b0000, 0 }, /* lwz r11, xxxx(r11) */
+ { 0xffffffff, 0x7d6903a6, 0 }, /* mtctr r11 */
+ { 0xffffffff, 0x4e800420, 0 }, /* bctr */
+ { 0, 0, 0 }
+ };
+
+/* PLT stub in shared library. */
+static struct insn_pattern powerpc32_plt_stub_so[] =
+ {
+ { 0xffff0000, 0x817e0000, 0 }, /* lwz r11, xxxx(r30) */
+ { 0xffffffff, 0x7d6903a6, 0 }, /* mtctr r11 */
+ { 0xffffffff, 0x4e800420, 0 }, /* bctr */
+ { 0xffffffff, 0x60000000, 0 }, /* nop */
+ { 0, 0, 0 }
+ };
+#define POWERPC32_PLT_STUB_LEN \
+ (sizeof powerpc32_plt_stub / sizeof (powerpc32_plt_stub[0]))
+
+/* Check if PC is in PLT stub. For non-secure PLT, stub is in .plt
+ section. For secure PLT, stub is in .text and we need to check
+ instruction patterns. */
+
+static int
+powerpc_linux_in_dynsym_resolve_code (CORE_ADDR pc)
+{
+ struct objfile *objfile;
+ struct minimal_symbol *sym;
+
+ /* Check whether PC is in the dynamic linker. This also checks
+ whether it is in the .plt section, used by non-PIC executables. */
+ if (svr4_in_dynsym_resolve_code (pc))
+ return 1;
+
+ /* Check if we are in the resolver. */
+ sym = lookup_minimal_symbol_by_pc (pc);
+ if ((strcmp (SYMBOL_LINKAGE_NAME (sym), "__glink") == 0)
+ || (strcmp (SYMBOL_LINKAGE_NAME (sym), "__glink_PLTresolve") == 0))
+ return 1;
+
+ return 0;
+}
+
+/* Follow PLT stub to actual routine. */
+
+static CORE_ADDR
+ppc_skip_trampoline_code (struct frame_info *frame, CORE_ADDR pc)
+{
+ int insnbuf[POWERPC32_PLT_STUB_LEN];
+ struct gdbarch *gdbarch = get_frame_arch (frame);
+ struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
+ enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
+ CORE_ADDR target = 0;
+
+ if (insns_match_pattern (pc, powerpc32_plt_stub, insnbuf))
+ {
+ /* Insn pattern is
+ lis r11, xxxx
+ lwz r11, xxxx(r11)
+ Branch target is in r11. */
+
+ target = (insn_d_field (insnbuf[0]) << 16) | insn_d_field (insnbuf[1]);
+ target = (CORE_ADDR) read_memory_unsigned_integer (target, 4, byte_order);
+ }
+
+ if (insns_match_pattern (pc, powerpc32_plt_stub_so, insnbuf))
+ {
+ /* Insn pattern is
+ lwz r11, xxxx(r30)
+ Branch target is in r11. */
+ target = (CORE_ADDR) get_frame_register_unsigned (frame,
+ tdep->ppc_gp0_regnum + 30)
+ + insn_d_field (insnbuf[0]);
+ target = (CORE_ADDR) read_memory_unsigned_integer (target, 4, byte_order);
+ }
+
+ return target;
+}

/* Given that we've begun executing a call trampoline at PC, return
the entry point of the function the trampoline will go to. */
@@ -1524,7 +1609,7 @@ ppc_linux_init_abi (struct gdbarch_info
ppc_linux_memory_remove_breakpoint);

/* Shared library handling. */
- set_gdbarch_skip_trampoline_code (gdbarch, find_solib_trampoline_target);
+ set_gdbarch_skip_trampoline_code (gdbarch, ppc_skip_trampoline_code);
set_solib_svr4_fetch_link_map_offsets
(gdbarch, svr4_ilp32_fetch_link_map_offsets);

@@ -1555,6 +1640,17 @@ ppc_linux_init_abi (struct gdbarch_info
else
set_gdbarch_core_regset_sections (gdbarch,
ppc_linux_fp_regset_sections);
+
+ if (powerpc_so_ops.in_dynsym_resolve_code == NULL)
+ {
+ powerpc_so_ops = svr4_so_ops;
+ /* Override dynamic resolve function. */
+ powerpc_so_ops.in_dynsym_resolve_code =
+ powerpc_linux_in_dynsym_resolve_code;
+ }
+ set_solib_ops (gdbarch, &powerpc_so_ops);
+
+ set_gdbarch_skip_solib_resolver (gdbarch, glibc_skip_solib_resolver);
}

if (tdep->wordsize == 8)