Re: [PATCH 6/6] Don't throw exception in dis_asm_memory_error

[Luis Machado <lgustavo@codesourcery.com>]

On 01/16/2017 04:02 AM, Yao Qi wrote:
> Hi,
> GDB calls some APIs from opcodes to do disassembly and provide some
> call backs.  This model makes troubles on C++ exception unwinding,
> because GDB is a C++ program, and opcodes is still compiled as C.
> As we can see, frame #10 and #12 are C++, while #frame 11 is C,
>
>  #10 0x0000000000544228 in memory_error (err=TARGET_XFER_E_IO, memaddr=<optimized out>) at ../../binutils-gdb/gdb/corefile.c:237
>  #11 0x00000000006b0a54 in print_insn_aarch64 (pc=0, info=0xffffffffeeb0) at ../../binutils-gdb/opcodes/aarch64-dis.c:3185
>  #12 0x0000000000553590 in gdb_pretty_print_insn (gdbarch=gdbarch@entry=0xbbceb0, uiout=uiout@entry=0xbc73d0, di=di@entry=0xffffffffeeb0,
>     insn=0xffffffffed40, insn@entry=0xffffffffed90, flags=flags@entry=0,
>
> C++ exception unwinder can't go across frame #11 unless it has
> unwind table.  However, C program on many architectures doesn't
> have it in default.  As a result, GDB aborts, which is described
> in PR 20939.
>
> This is not the first time we see this kind of problem.  We've
> had a commit 89525768cd086a0798a504c81fdf7ebcd4c904e1
> "Propagate GDB/C++ exceptions across readline using sj/lj-based TRY/CATCH".
> We can fix the disassembly bug in a similar way, this is the option one.
>
> Since opcodes is built with gdb, we fix this problem in a different
> way as we did for the same issue with readline.  Instead of throwing
> exception in dis_asm_memory_error, we record the failed memory
> address, and throw exception when GDB returns from opcodes disassemblers.
>
> gdb:
>
> 2017-01-10  Yao Qi  <yao.qi@linaro.org>
> 	    Pedro Alves  <palves@redhat.com>
>
> 	PR gdb/20939
> 	* disasm.c (gdb_disassembler::dis_asm_memory_error): Don't
> 	call memory_error, save memaddr instead.
> 	(gdb_disassembler::print_insn): If gdbarch_print_insn returns
> 	negative, cal memory_error.
> 	* disasm.h (gdb_disassembler) <m_err_memaddr>: New field.
>
> gdb/testsuite:
>
> 2017-01-10  Yao Qi  <yao.qi@linaro.org>
>
> 	* gdb.base/all-architectures.exp.in (do_arch_tests): Test
> 	disassemble on address 0.
> ---
>  gdb/disasm.c                                    | 13 +++++++++++--
>  gdb/disasm.h                                    |  1 +
>  gdb/testsuite/gdb.base/all-architectures.exp.in |  3 +++
>  3 files changed, 15 insertions(+), 2 deletions(-)
>
> diff --git a/gdb/disasm.c b/gdb/disasm.c
> index f31d8d3..8c8c42e 100644
> --- a/gdb/disasm.c
> +++ b/gdb/disasm.c
> @@ -135,7 +135,10 @@ void
>  gdb_disassembler::dis_asm_memory_error (int err, bfd_vma memaddr,
>  					struct disassemble_info *info)
>  {
> -  memory_error (TARGET_XFER_E_IO, memaddr);
> +  gdb_disassembler *self
> +    = static_cast<gdb_disassembler *>(info->application_data);
> +
> +  self->m_err_memaddr = memaddr;
>  }
>
>  /* Like print_address with slightly different parameters.  */
> @@ -765,7 +768,8 @@ fprintf_disasm (void *stream, const char *format, ...)
>  gdb_disassembler::gdb_disassembler (struct gdbarch *gdbarch,
>  				    struct ui_file *file,
>  				    di_read_memory_ftype read_memory_func)
> -  : m_gdbarch (gdbarch)
> +  : m_gdbarch (gdbarch),
> +    m_err_memaddr (0)
>  {
>    init_disassemble_info (&m_di, file, fprintf_disasm);
>    m_di.flavour = bfd_target_unknown_flavour;
> @@ -792,8 +796,13 @@ int
>  gdb_disassembler::print_insn (CORE_ADDR memaddr,
>  			      int *branch_delay_insns)
>  {
> +  m_err_memaddr = 0;
> +
>    int length = gdbarch_print_insn (arch (), memaddr, &m_di);
>
> +  if (length < 0)
> +    memory_error (TARGET_XFER_E_IO, m_err_memaddr);
> +
>    if (branch_delay_insns != NULL)
>      {
>        if (m_di.insn_info_valid)
> diff --git a/gdb/disasm.h b/gdb/disasm.h
> index 5122fa3..8e0b9f9 100644
> --- a/gdb/disasm.h
> +++ b/gdb/disasm.h
> @@ -63,6 +63,7 @@ protected:
>  private:
>    struct gdbarch *m_gdbarch;
>    struct disassemble_info m_di;
> +  CORE_ADDR m_err_memaddr;
>
>    static int dis_asm_read_memory (bfd_vma memaddr, gdb_byte *myaddr,
>  				  unsigned int len,
> diff --git a/gdb/testsuite/gdb.base/all-architectures.exp.in b/gdb/testsuite/gdb.base/all-architectures.exp.in
> index c7615ac..50a615c 100644
> --- a/gdb/testsuite/gdb.base/all-architectures.exp.in
> +++ b/gdb/testsuite/gdb.base/all-architectures.exp.in
> @@ -152,6 +152,9 @@ proc print_floats {} {
>
>  proc do_arch_tests {} {
>      print_floats
> +
> +    gdb_test_internal "disassemble 0x0,+4" \
> +	"Cannot access memory at address 0x0"

I think you missed the comment you had proposed?

# GDB can't access any memory because there is no live inferior.

I take it we have no loaded executable as well? Otherwise we could 
eventually read data from the executable file, which wouldn't yield an 
error.

>  }
>
>  # Given we can't change arch, osabi, endianness, etc. atomically, we
>