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

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.


2017-01-10  Yao Qi  <>
	    Pedro Alves  <>

	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.


2017-01-10  Yao Qi  <>

	* gdb.base/ (do_arch_tests): Test
	disassemble on address 0.
 gdb/disasm.c                                    | 13 +++++++++++--
 gdb/disasm.h                                    |  1 +
 gdb/testsuite/gdb.base/ |  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:
   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/ b/gdb/testsuite/gdb.base/
index c7615ac..50a615c 100644
--- a/gdb/testsuite/gdb.base/
+++ b/gdb/testsuite/gdb.base/
@@ -152,6 +152,9 @@ proc print_floats {} {
 proc do_arch_tests {} {
+    gdb_test_internal "disassemble 0x0,+4" \
+	"Cannot access memory at address 0x0"
 # Given we can't change arch, osabi, endianness, etc. atomically, we

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