[patch] Fix gdb.cp/gdb2495.exp regression with gcc-4.7

Jan Kratochvil
2011-12-22T20:21:07Z

Hi,

(gdb) p exceptions.throw_function()
Program received signal SIGSEGV, Segmentation fault.
x86_64_fallback_frame_state (fs=0x7fffffffdc80, context=0x7fffffffdef0) at ../../../gcc/config/i386/linux-unwind.h:47
47 if (*(unsigned char *)(pc+0) == 0x48
The program being debugged was signaled while in a function called from GDB.
[...]
(gdb) FAIL: gdb.cp/gdb2495.exp: Call a function that raises an exception without a handler.

This happens with
gcc (GCC) 4.7.0 20111222 (experimental)
on Fedora Rawhide (pre-17) x86_64 as the function before _start is PLT and
PLTs have no proper .eh_frame entries. Still such .eh_frame PLT entry sure
does not apply for the <function called from gdb> frame. Therefore it unwinds
into garbage and then crashes on it (PC is 0x1 abo-ve).

No regressions on {x86_64,x86_64-m32}-fedora16-linux-gnu.

Thanks,
Jan

gdb/
2011-12-22 Jan Kratochvil <jan.kratochvil@redhat.com>

Fix regression for gdb.cp/gdb2495.exp with gcc-4.7.
* gdbarch.sh (max_insn_length): Set the default length to 31.
* gdbarch.c: Regenerate.
* gdbarch.h: Regenerate.
* infcall.c: Include disasm.h.
(call_function_by_hand) <AT_ENTRY_POINT>: New variables insn and
insn_len. Adjust DUMMY_ADDR with them if possible.

--- a/gdb/gdbarch.sh
+++ b/gdb/gdbarch.sh
@@ -655,7 +655,8 @@ v:int:vbit_in_delta:::0:0::0
F:void:skip_permanent_breakpoint:struct regcache *regcache:regcache

# The maximum length of an instruction on this architecture.
-V:ULONGEST:max_insn_length:::0:0
+# It should be at least as maximum of all the supported architectures.
+V:ULONGEST:max_insn_length:::31:31

# Copy the instruction at FROM to TO, and make any adjustments
# necessary to single-step it at that address.
--- a/gdb/infcall.c
+++ b/gdb/infcall.c
@@ -38,6 +38,7 @@
#include "ada-lang.h"
#include "gdbthread.h"
#include "exceptions.h"
+#include "disasm.h"

/* If we can't find a function's name from its address,
we print this instead. */
@@ -634,9 +635,32 @@ call_function_by_hand (struct value *function, int nargs, struct value **args)
case AT_ENTRY_POINT:
{
CORE_ADDR dummy_addr;
+ gdb_byte *insn;
+ CORE_ADDR insn_len;

real_pc = funaddr;
dummy_addr = entry_point_address ();
+
+ /* If the inferior call throws an uncaught C++ exception the inferior
+ unwinder will try to unwind all the frames incl. the dummy frame.
+ Using the entry_point_address directly will try to find FDE at the
+ function right before the entry_point_address address as the
+ unwinder subtracts 1 to get at the call instruction. FDE of the
+ preceding function, if found, would be invalid for the dummy frame
+ and it would crash the inferior's unwinder. Therefore attempt to
+ skip the very first instruction of entry_point_address. */
+
+ insn_len = gdbarch_max_insn_length (gdbarch);
+ insn = alloca (insn_len);
+ if (target_read_memory (dummy_addr, insn, insn_len) == 0)
+ dummy_addr += gdb_buffered_insn_length (gdbarch, insn, insn_len,
+ dummy_addr);
+ else
+ {
+ /* No problem probably occurs without this adjustment. INSN_LEN
+ may be for example larger than the entry_point_address code. */
+ }
+
/* A call dummy always consists of just a single breakpoint, so
its address is the same as the address of the dummy. */
bp_addr = dummy_addr;