Re: [PATCH 1/2] Include the fs_base and gs_base registers in amd64 target descriptions.

Pedro Alves
2017-07-13T19:59:06Z

On 07/13/2017 07:40 PM, Pedro Alves wrote:

> It seems to me that the proper fix is to make sure
> that amd64_linux_init_abi and amd64_init_abi agree. Something like
> this patch below. Fixes the crash for me.

OK, as discussed on IRC, I've pushed this in.

From c55a47e7237ebac17df73183d214d90400a49455 Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Thu, 13 Jul 2017 20:56:42 +0100
Subject: [PATCH] Fix x86-64 GNU/Linux crashes

Ref: https://sourceware.org/ml/gdb-patches/2017-07/msg00162.html

Debugging x86-64 GNU/Linux programs currently crashes GDB in
tdesc_use_registers during gdbarch initialization:

Program received signal SIGSEGV, Segmentation fault.
0x0000000001093eaf in htab_remove_elt_with_hash (htab=0x2ef9fa0, element=0x26af960, hash=557151073) at src/libiberty/hashtab.c:728
728 if (*slot == HTAB_EMPTY_ENTRY)
(top-gdb) p slot
$1 = (void **) 0x0
(top-gdb) bt
#0 0x0000000001093eaf in htab_remove_elt_with_hash (htab=0x2ef9fa0, element=0x26af960, hash=557151073) at src/libiberty/hashtab.c:728
#1 0x0000000001093e79 in htab_remove_elt (htab=0x2ef9fa0, element=0x26af960) at src/libiberty/hashtab.c:714
#2 0x00000000009121b0 in tdesc_use_registers (gdbarch=0x3001240, target_desc=0x2659cb0, early_data=0x2881cb0)
at src/gdb/target-descriptions.c:1328
#3 0x000000000047c93e in i386_gdbarch_init (info=..., arches=0x0) at src/gdb/i386-tdep.c:8634
#4 0x0000000000818d5f in gdbarch_find_by_info (info=...) at src/gdb/gdbarch.c:5394
#5 0x00000000007198a8 in set_gdbarch_from_file (abfd=0x2f48250) at src/gdb/arch-utils.c:618
#6 0x00000000007f21cb in exec_file_attach (filename=0x7fffffffddb0 "/home/pedro/gdb/tests/threads", from_tty=1) at src/gdb/exec.c:380
#7 0x0000000000865c18 in catch_command_errors_const (command=0x7f1d83 <exec_file_attach(char const*, int)>, arg=0x7fffffffddb0 "/home/pedro/gdb/tests/threads",
from_tty=1) at src/gdb/main.c:403
#8 0x00000000008669cf in captured_main_1 (context=0x7fffffffd860) at src/gdb/main.c:1035
#9 0x0000000000866de2 in captured_main (data=0x7fffffffd860) at src/gdb/main.c:1142
#10 0x0000000000866e24 in gdb_main (args=0x7fffffffd860) at src/gdb/main.c:1160
#11 0x000000000041312d in main (argc=3, argv=0x7fffffffd968) at src/gdb/gdb.c:32

The direct cause of the crash is that we tried to remove an element
from the hash which supposedly exists, but does not. (htab_remove_elt
shouldn't really crash in this case, but that's secondary.)

The real problem is that early_data passed to tdesc_use_registers
includes regs from a target description that is not the target_desc,
which violates its assumptions. The registers in question are the
fs_base/gs_base registers, added by amd64_init_abi:

tdesc_numbered_register (feature, tdesc_data_segments,
AMD64_FSBASE_REGNUM, "fs_base");
tdesc_numbered_register (feature, tdesc_data_segments,
AMD64_GSBASE_REGNUM, "gs_base");

and that happens because amd64_linux_init_abi uses amd64_init_abi as
helper, but they don't coordinate on which fallback tdesc to use.

amd64_init_abi does:

if (! tdesc_has_registers (tdesc))
tdesc = tdesc_amd64;

and then adds the fs_base/gs_base registers of the "tdesc_amd64" tdesc
to the tdesc_arch_data.

After amd64_init_abi returns, amd64_linux_init_abi does:

if (! tdesc_has_registers (tdesc))
tdesc = tdesc_amd64_linux;
tdep->tdesc = tdesc;

and we end up tdesc_amd64_linux installed in tdep->tdesc.

The fix is to make sure that amd64_linux_init_abi and amd64_init_abi
agree on default tdesc, by adding a "default tdesc" parameter to
amd64_init_abi, instead of having amd64_init_abi hardcode a default.
With this, amd64_init_abi creates the fs_base/gs_base registers using
the tdesc_amd64_linux tdesc.

Tested on x86-64 GNU/Linux, -m64. I don't have an x32 setup handy.

Thanks to John Baldwin, Yao Qi and Simon Marchi for the investigation.

gdb/ChangeLog:
2017-07-13 Pedro Alves <palves@redhat.com>

* amd64-darwin-tdep.c (x86_darwin_init_abi_64): Pass tdesc_amd64
as default tdesc.
* amd64-dicos-tdep.c (amd64_dicos_init_abi):
* amd64-fbsd-tdep.c (amd64fbsd_init_abi):
* amd64-linux-tdep.c (amd64_linux_init_abi): Pass
tdesc_amd64_linux as default tdesc. Get final tdesc from the
tdep.
(amd64_x32_linux_init_abi): Pass tdesc_x32_linux as default tdesc.
Get final tdesc from the tdep.
* amd64-nbsd-tdep.c (amd64nbsd_init_abi): Pass tdesc_amd64 as
default tdesc.
* amd64-obsd-tdep.c (amd64obsd_init_abi): Likewise.
* amd64-sol2-tdep.c (amd64_sol2_init_abi): Likewise.
* amd64-tdep.c (amd64_init_abi): Add 'default_tdesc' parameter.
Use it as default tdesc.
(amd64_x32_init_abi): Add 'default_tdesc' parameter, and pass it
down to amd_init_abi. No longer handle fallback tdesc here.
* amd64-tdep.h (tdesc_x32): Declare.
(amd64_init_abi, amd64_x32_init_abi): Add 'default_tdesc'
parameter.
* amd64-windows-tdep.c (amd64_windows_init_abi): Pass tdesc_amd64
as default tdesc.
---
gdb/ChangeLog | 25 +++++++++++++++++++++++++
gdb/amd64-darwin-tdep.c | 2 +-
gdb/amd64-dicos-tdep.c | 2 +-
gdb/amd64-fbsd-tdep.c | 2 +-
gdb/amd64-linux-tdep.c | 16 +++++-----------
gdb/amd64-nbsd-tdep.c | 2 +-
gdb/amd64-obsd-tdep.c | 2 +-
gdb/amd64-sol2-tdep.c | 2 +-
gdb/amd64-tdep.c | 15 ++++++---------
gdb/amd64-tdep.h | 13 +++++++++++--
gdb/amd64-windows-tdep.c | 2 +-
11 files changed, 54 insertions(+), 29 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 37fe06e..3210957 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,28 @@
+2017-07-13 Pedro Alves <palves@redhat.com>
+
+ * amd64-darwin-tdep.c (x86_darwin_init_abi_64): Pass tdesc_amd64
+ as default tdesc.
+ * amd64-dicos-tdep.c (amd64_dicos_init_abi):
+ * amd64-fbsd-tdep.c (amd64fbsd_init_abi):
+ * amd64-linux-tdep.c (amd64_linux_init_abi): Pass
+ tdesc_amd64_linux as default tdesc. Get final tdesc from the
+ tdep.
+ (amd64_x32_linux_init_abi): Pass tdesc_x32_linux as default tdesc.
+ Get final tdesc from the tdep.
+ * amd64-nbsd-tdep.c (amd64nbsd_init_abi): Pass tdesc_amd64 as
+ default tdesc.
+ * amd64-obsd-tdep.c (amd64obsd_init_abi): Likewise.
+ * amd64-sol2-tdep.c (amd64_sol2_init_abi): Likewise.
+ * amd64-tdep.c (amd64_init_abi): Add 'default_tdesc' parameter.
+ Use it as default tdesc.
+ (amd64_x32_init_abi): Add 'default_tdesc' parameter, and pass it
+ down to amd_init_abi. No longer handle fallback tdesc here.
+ * amd64-tdep.h (tdesc_x32): Declare.
+ (amd64_init_abi, amd64_x32_init_abi): Add 'default_tdesc'
+ parameter.
+ * amd64-windows-tdep.c (amd64_windows_init_abi): Pass tdesc_amd64
+ as default tdesc.
+
2017-07-13 Andreas Arnez <arnez@linux.vnet.ibm.com>

* s390-linux-tdep.c (s390_process_record): Add support for
diff --git a/gdb/amd64-darwin-tdep.c b/gdb/amd64-darwin-tdep.c
index db400cd..be26d9e 100644
--- a/gdb/amd64-darwin-tdep.c
+++ b/gdb/amd64-darwin-tdep.c
@@ -99,7 +99,7 @@ x86_darwin_init_abi_64 (struct gdbarch_info info, struct gdbarch *gdbarch)
{
struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);

- amd64_init_abi (info, gdbarch);
+ amd64_init_abi (info, gdbarch, tdesc_amd64);

tdep->struct_return = reg_struct_return;

diff --git a/gdb/amd64-dicos-tdep.c b/gdb/amd64-dicos-tdep.c
index ee40891..7bdb167 100644
--- a/gdb/amd64-dicos-tdep.c
+++ b/gdb/amd64-dicos-tdep.c
@@ -25,7 +25,7 @@
static void
amd64_dicos_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
- amd64_init_abi (info, gdbarch);
+ amd64_init_abi (info, gdbarch, tdesc_amd64);

dicos_init_abi (gdbarch);
}
diff --git a/gdb/amd64-fbsd-tdep.c b/gdb/amd64-fbsd-tdep.c
index 48bb209..ad4d787 100644
--- a/gdb/amd64-fbsd-tdep.c
+++ b/gdb/amd64-fbsd-tdep.c
@@ -217,7 +217,7 @@ amd64fbsd_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
tdep->gregset_num_regs = ARRAY_SIZE (amd64fbsd_r_reg_offset);
tdep->sizeof_gregset = 22 * 8;

- amd64_init_abi (info, gdbarch);
+ amd64_init_abi (info, gdbarch, tdesc_amd64);

tdep->sigtramp_p = amd64fbsd_sigtramp_p;
tdep->sigtramp_start = amd64fbsd_sigtramp_start_addr;
diff --git a/gdb/amd64-linux-tdep.c b/gdb/amd64-linux-tdep.c
index 4ef0f78..cf24789 100644
--- a/gdb/amd64-linux-tdep.c
+++ b/gdb/amd64-linux-tdep.c
@@ -1863,7 +1863,6 @@ static void
amd64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
- const struct target_desc *tdesc = info.target_desc;
struct tdesc_arch_data *tdesc_data
= (struct tdesc_arch_data *) info.tdep_info;
const struct tdesc_feature *feature;
@@ -1875,15 +1874,13 @@ amd64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
tdep->gregset_num_regs = ARRAY_SIZE (amd64_linux_gregset_reg_offset);
tdep->sizeof_gregset = 27 * 8;

- amd64_init_abi (info, gdbarch);
+ amd64_init_abi (info, gdbarch, tdesc_amd64_linux);
+
+ const target_desc *tdesc = tdep->tdesc;

/* Reserve a number for orig_rax. */
set_gdbarch_num_regs (gdbarch, AMD64_LINUX_NUM_REGS);

- if (! tdesc_has_registers (tdesc))
- tdesc = tdesc_amd64_linux;
- tdep->tdesc = tdesc;
-
feature = tdesc_find_feature (tdesc, "org.gnu.gdb.i386.linux");
if (feature == NULL)
return;
@@ -2080,7 +2077,6 @@ static void
amd64_x32_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
- const struct target_desc *tdesc = info.target_desc;
struct tdesc_arch_data *tdesc_data
= (struct tdesc_arch_data *) info.tdep_info;
const struct tdesc_feature *feature;
@@ -2092,14 +2088,12 @@ amd64_x32_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
tdep->gregset_num_regs = ARRAY_SIZE (amd64_linux_gregset_reg_offset);
tdep->sizeof_gregset = 27 * 8;

- amd64_x32_init_abi (info, gdbarch);
+ amd64_x32_init_abi (info, gdbarch, tdesc_x32_linux);

/* Reserve a number for orig_rax. */
set_gdbarch_num_regs (gdbarch, AMD64_LINUX_NUM_REGS);

- if (! tdesc_has_registers (tdesc))
- tdesc = tdesc_x32_linux;
- tdep->tdesc = tdesc;
+ const target_desc *tdesc = tdep->tdesc;

feature = tdesc_find_feature (tdesc, "org.gnu.gdb.i386.linux");
if (feature == NULL)
diff --git a/gdb/amd64-nbsd-tdep.c b/gdb/amd64-nbsd-tdep.c
index db6f19f..02bf427 100644
--- a/gdb/amd64-nbsd-tdep.c
+++ b/gdb/amd64-nbsd-tdep.c
@@ -103,7 +103,7 @@ amd64nbsd_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
tdep->gregset_num_regs = ARRAY_SIZE (amd64nbsd_r_reg_offset);
tdep->sizeof_gregset = 26 * 8;

- amd64_init_abi (info, gdbarch);
+ amd64_init_abi (info, gdbarch, tdesc_amd64);

tdep->jb_pc_offset = 7 * 8;

diff --git a/gdb/amd64-obsd-tdep.c b/gdb/amd64-obsd-tdep.c
index 72895b6..ad90c20 100644
--- a/gdb/amd64-obsd-tdep.c
+++ b/gdb/amd64-obsd-tdep.c
@@ -419,7 +419,7 @@ amd64obsd_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
{
struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);

- amd64_init_abi (info, gdbarch);
+ amd64_init_abi (info, gdbarch, tdesc_amd64);
obsd_init_abi (info, gdbarch);

/* Initialize general-purpose register set details. */
diff --git a/gdb/amd64-sol2-tdep.c b/gdb/amd64-sol2-tdep.c
index 51fe9db..ca474db 100644
--- a/gdb/amd64-sol2-tdep.c
+++ b/gdb/amd64-sol2-tdep.c
@@ -99,7 +99,7 @@ amd64_sol2_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
tdep->gregset_num_regs = ARRAY_SIZE (amd64_sol2_gregset_reg_offset);
tdep->sizeof_gregset = 28 * 8;

- amd64_init_abi (info, gdbarch);
+ amd64_init_abi (info, gdbarch, tdesc_amd64);

tdep->sigtramp_p = amd64_sol2_sigtramp_p;
tdep->sigcontext_addr = amd64_sol2_mcontext_addr;
diff --git a/gdb/amd64-tdep.c b/gdb/amd64-tdep.c
index 9ff7dfc..6171bc5 100644
--- a/gdb/amd64-tdep.c
+++ b/gdb/amd64-tdep.c
@@ -3005,7 +3005,8 @@ static const int amd64_record_regmap[] =
};

void
-amd64_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
+amd64_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch,
+ target_desc *default_tdesc)
{
struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
const struct target_desc *tdesc = info.target_desc;
@@ -3022,7 +3023,7 @@ amd64_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
tdep->fpregset = &amd64_fpregset;

if (! tdesc_has_registers (tdesc))
- tdesc = tdesc_amd64;
+ tdesc = default_tdesc;
tdep->tdesc = tdesc;

tdep->num_core_regs = AMD64_NUM_GREGS + I387_NUM_REGS;
@@ -3196,16 +3197,12 @@ amd64_x32_pseudo_register_type (struct gdbarch *gdbarch, int regnum)
}

void
-amd64_x32_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
+amd64_x32_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch,
+ target_desc *default_tdesc)
{
struct gdbarch_tdep *tdep = gdbarch_tdep (gdbarch);
- const struct target_desc *tdesc = info.target_desc;
-
- amd64_init_abi (info, gdbarch);

- if (! tdesc_has_registers (tdesc))
- tdesc = tdesc_x32;
- tdep->tdesc = tdesc;
+ amd64_init_abi (info, gdbarch, default_tdesc);

tdep->num_dword_regs = 17;
set_tdesc_pseudo_register_type (gdbarch, amd64_x32_pseudo_register_type);
diff --git a/gdb/amd64-tdep.h b/gdb/amd64-tdep.h
index 87f0ba3..d4c6c9a 100644
--- a/gdb/amd64-tdep.h
+++ b/gdb/amd64-tdep.h
@@ -88,6 +88,7 @@ enum amd64_regnum
#define AMD64_NUM_REGS (AMD64_GSBASE_REGNUM + 1)

extern struct target_desc *tdesc_amd64;
+extern struct target_desc *tdesc_x32;

extern struct displaced_step_closure *amd64_displaced_step_copy_insn
(struct gdbarch *gdbarch, CORE_ADDR from, CORE_ADDR to,
@@ -97,9 +98,17 @@ extern void amd64_displaced_step_fixup (struct gdbarch *gdbarch,
CORE_ADDR from, CORE_ADDR to,
struct regcache *regs);

-extern void amd64_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch);
+/* Initialize the ABI for amd64. Uses DEFAULT_TDESC as fallback
+ tdesc, if INFO does not specify one. */
+extern void amd64_init_abi (struct gdbarch_info info,
+ struct gdbarch *gdbarch,
+ target_desc *default_tdesc);
+
+/* Initialize the ABI for x32. Uses DEFAULT_TDESC as fallback tdesc,
+ if INFO does not specify one. */
extern void amd64_x32_init_abi (struct gdbarch_info info,
- struct gdbarch *gdbarch);
+ struct gdbarch *gdbarch,
+ target_desc *default_tdesc);
extern const struct target_desc *amd64_target_description (uint64_t xcr0);

/* Fill register REGNUM in REGCACHE with the appropriate
diff --git a/gdb/amd64-windows-tdep.c b/gdb/amd64-windows-tdep.c
index f1acdb9..9158282 100644
--- a/gdb/amd64-windows-tdep.c
+++ b/gdb/amd64-windows-tdep.c
@@ -1224,7 +1224,7 @@ amd64_windows_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
*/
frame_unwind_append_unwinder (gdbarch, &amd64_windows_frame_unwind);

- amd64_init_abi (info, gdbarch);
+ amd64_init_abi (info, gdbarch, tdesc_amd64);

windows_init_abi (info, gdbarch);

--
2.5.5