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On Windows, starting a new process with GDBserver seems to work,
in the sense that the program does get started, and GDBserver
confirms that it is listening for GDB to connect. However, as soon as
GDB establishes the connection with GDBserver, and starts discussing
with it, GDBserver crashes, with a SEGV.
This SEGV occurs in remote-utils.c::prepare_resume_reply...
| regp = current_target_desc ()->expedite_regs;
| [...]
| while (*regp)
... because, in our case, REGP is NULL.
This patches fixes the issues by adding a parameter to init_target_desc,
in order to make sure that we always provide the list of registers when
we initialize a target description.
gdb/ChangeLog:
PR server/23158:
* regformats/regdat.sh: Adjust script, following the addition
of the new expedite_regs parameter to init_target_desc.
gdb/gdbserver/ChangeLog:
PR server/23158:
* tdesc.h (init_target_desc) <expedite_regs>: New parameter.
* tdesc.c (init_target_desc) <expedite_regs>: New parameter.
Use it to set the expedite_regs field in the given tdesc.
* x86-tdesc.h: New file.
* linux-aarch64-tdesc.c (aarch64_linux_read_description):
Adjust following the addition of the new expedite_regs parameter
to init_target_desc.
* linux-tic6x-low.c (tic6x_read_description): Likewise.
* linux-x86-tdesc.c: #include "x86-tdesc.h".
(i386_linux_read_description, amd64_linux_read_description):
Adjust following the addition of the new expedite_regs parameter
to init_target_desc.
* lynx-i386-low.c: #include "x86-tdesc.h".
(lynx_i386_arch_setup): Adjust following the addition of the new
expedite_regs parameter to init_target_desc.
* nto-x86-low.c: #include "x86-tdesc.h".
(nto_x86_arch_setup): Adjust following the addition of the new
expedite_regs parameter to init_target_desc.
* win32-i386-low.c: #include "x86-tdesc.h".
(i386_arch_setup): Adjust following the addition of the new
expedite_regs parameter to init_target_desc.
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Trying to start a program with GDBserver on Windows yields
the following error:
$ gdbserver.exe --once :4444 simple_main.exe
Killing process(es): 5008
No program to debug
Exiting
The error itself comes from the following code shortly after
create_inferior gets called (in server.c::main):
/* Wait till we are at first instruction in program. */
create_inferior (program_path.get (), program_args);
[...]
if (last_status.kind == TARGET_WAITKIND_EXITED
|| last_status.kind == TARGET_WAITKIND_SIGNALLED)
was_running = 0;
else
was_running = 1;
if (!was_running && !multi_mode)
error ("No program to debug");
What happens is that the "last_status" global starts initialized
as zeroes, which means last_status.kind == TARGET_WAITKIND_EXITED,
and we expect create_inferior to be waiting for the inferior to
start until reaching the SIGTRAP, and to set the "last_status"
global to match that last event we received.
I suspect this is an unintended side-effect of the following change...
commit 2090129c36c7e582943b7d300968d19b46160d84
Date: Thu Dec 22 21:11:11 2016 -0500
Subject: Share fork_inferior et al with gdbserver
... which removes some code in server.c that was responsible for
starting the inferior in a functin that was named start_inferior,
and looked like this:
signal_pid = create_inferior (new_argv[0], &new_argv[0]);
[...]
/* Wait till we are at 1st instruction in program, return new pid
(assuming success). */
last_ptid = mywait (pid_to_ptid (signal_pid), &last_status, 0, 0);
The code has been transitioned to using fork_inferior, but sadly,
only for the targets that support it. On Windows, the calls to wait
setting "last_status" simply disappeared.
This patch adds it back in the Windows-specific implementation of
create_inferior.
gdb/gdbserver/ChangeLog:
PR server/23158:
* win32-low.c (win32_create_inferior): Add call to my_wait
setting last_status global.
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Trying to start GDBserver on Windows currently yields the following
error...
$ gdbserver.exe --once :4444 simple_main.exe
glob could not process pattern '(null)'.
Exiting
... after which GDB terminates with a nonzero status.
This is because create_process in win32-low.c calls gdb_tilde_expand
with the result of a call to get_inferior_cwd without verifying that
the returned directory is not NULL:
| static BOOL
| create_process (const char *program, char *args,
| DWORD flags, PROCESS_INFORMATION *pi)
| {
| const char *inferior_cwd = get_inferior_cwd ();
| std::string expanded_infcwd = gdb_tilde_expand (inferior_cwd);
This patch avoids this by only calling gdb_tilde_expand when
INFERIOR_CWD is not NULL, which is similar to what is done on
GNU/Linux for instance.
gdb/gdbserver/ChangeLog:
PR server/23158:
* win32-low.c (create_process): Only call gdb_tilde_expand if
inferior_cwd is not NULL.
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This patch fixes tagged pointer support for AArch64 GDB. Linux kernel
debugging failure was reported after tagged pointer support was committed.
After a discussion around best path forward to manage tagged pointers
on GDB side we are going to disable tagged pointers support for
aarch64-none-elf-gdb because for non-linux applications we cant be
sure if tagged pointers will be used by MMU or not.
Also for aarch64-linux-gdb we are going to sign extend user-space
address after clearing tag bits. This will help debug both kernel
and user-space addresses based on information from linux kernel
documentation given below:
According to AArch64 memory map:
https://www.kernel.org/doc/Documentation/arm64/memory.txt
"User addresses have bits 63:48 set to 0 while the kernel addresses have
the same bits set to 1."
According to AArch64 tagged pointers document:
https://www.kernel.org/doc/Documentation/arm64/tagged-pointers.txt
The kernel configures the translation tables so that translations made
via TTBR0 (i.e. userspace mappings) have the top byte (bits 63:56) of
the virtual address ignored by the translation hardware. This frees up
this byte for application use.
Running gdb testsuite after applying this patch introduces no regressions
and tagged pointer test cases still pass.
gdb/ChangeLog:
2018-05-10 Omair Javaid <omair.javaid@linaro.org>
PR gdb/23127
* aarch64-linux-tdep.c (aarch64_linux_init_abi): Add call to
set_gdbarch_significant_addr_bit.
* aarch64-tdep.c (aarch64_gdbarch_init): Remove call to
set_gdbarch_significant_addr_bit.
* utils.c (address_significant): Update to sign extend addr.
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Fedora Rawhide started to use -D_GLIBCXX_DEBUG which made gdb-add-index
failing:
gdb: Out-of-bounds vector access while running gdb-add-index
https://bugzilla.redhat.com/show_bug.cgi?id=1540559
/usr/include/c++/7/debug/safe_iterator.h:270:
Error: attempt to dereference a past-the-end iterator.
Objects involved in the operation:
iterator "this" @ 0x0x7fffffffcb90 {
type = __gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<unsigned char*, std::__cxx1998::vector<unsigned char, gdb::default_init_allocator<unsigned char, std::allocator<unsigned char> > > >, std::__debug::vector<unsigned char, gdb::default_init_allocator<unsigned char, std::allocator<unsigned char> > > > (mutable iterator);
state = past-the-end;
references sequence with type 'std::__debug::vector<unsigned char, gdb::default_init_allocator<unsigned char, std::allocator<unsigned char> > >' @ 0x0x7fffffffcc50
}
/usr/include/c++/7/debug/vector:417:
Error: attempt to subscript container with out-of-bounds index 556, but
container only holds 556 elements.
Objects involved in the operation:
sequence "this" @ 0x0x2e87af8 {
type = std::__debug::vector<partial_symbol*, std::allocator<partial_symbol*> >;
}
The two -D_GLIBCXX_DEBUG regressions were made by:
commit bc8f2430e08cc2a520db49a42686e0529be4a3bc
Author: Jan Kratochvil <jan.kratochvil@redhat.com>
Date: Mon Jun 12 16:29:53 2017 +0100
Code cleanup: C++ify .gdb_index producer
commit af5bf4ada48ff65b6658be1fab8f9c8f8ab5f319
Author: Simon Marchi <simon.marchi@ericsson.com>
Date: Sat Oct 14 08:06:29 2017 -0400
Replace psymbol_allocation_list with std::vector
gdb/ChangeLog
2018-04-12 Jan Kratochvil <jan.kratochvil@redhat.com>
PR gdb/23053
* dwarf2read.c (data_buf::grow) (write_one_signatured_type)
(recursively_write_psymbols) (debug_names::recursively_write_psymbols)
(debug_names::write_one_signatured_type): Fix -D_GLIBCXX_DEBUG
regression.
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