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[Bug breakpoints/16087] New: cannot step in catch block after exception is thrown
- From: "toma.bilius at enea dot com" <sourceware-bugzilla at sourceware dot org>
- To: gdb-prs at sourceware dot org
- Date: Fri, 25 Oct 2013 15:51:47 +0000
- Subject: [Bug breakpoints/16087] New: cannot step in catch block after exception is thrown
- Auto-submitted: auto-generated
https://sourceware.org/bugzilla/show_bug.cgi?id=16087
Bug ID: 16087
Summary: cannot step in catch block after exception is thrown
Product: gdb
Version: 7.4
Status: NEW
Severity: normal
Priority: P2
Component: breakpoints
Assignee: unassigned at sourceware dot org
Reporter: toma.bilius at enea dot com
We're using a test application for ARM (cortex a9) compiled with GCC 4.6.3 and
thumb2. We use GDB 7.4 to debug the target. We have trouble stepping over the
code in a try/catch block. After setting a breakpoint on throw, it is hit but
when issuing a next command GDB will just resume execution.
Here's the initial c++ code:
try
{
throw 4711; /* GDB Test (cplusplus.cpp,1) */
}
catch (int i) /* GDB Test (cplusplus.cpp,2) */
{
blue::fibonacci(5); /* GDB Test (cplusplus.cpp,3) */
} /* GDB Test (cplusplus.cpp,9) */
After disassembling we noticed that this code is split, having the actual catch
clause somewhere at the end of the function:
try
{
throw 4711; /* GDB Test (cplusplus.cpp,1) */
17b3ae: f04f 0004 mov.w r0, #4
17b3b2: f09c fba9 bl 217b08 <__cxa_allocate_exception>
17b3b6: 4603 mov r3, r0
17b3b8: f241 2267 movw r2, #4711 ; 0x1267
17b3bc: 601a str r2, [r3, #0]
17b3be: 4618 mov r0, r3
17b3c0: f64c 0118 movw r1, #51224 ; 0xc818
17b3c4: f04f 0302 mov.w r3, #2
17b3c8: 623b str r3, [r7, #32]
17b3ca: f2c0 012c movt r1, #44 ; 0x2c
17b3ce: f04f 0200 mov.w r2, #0
17b3d2: f09d fc45 bl 218c60 <__cxa_throw>
....
try
{
throw 4711; /* GDB Test (cplusplus.cpp,1) */
}
catch (int i) /* GDB Test (cplusplus.cpp,2) */
17b530: 4618 mov r0, r3
17b532: f09c fd59 bl 217fe8 <__cxa_begin_catch>
17b536: 4603 mov r3, r0
17b538: 681b ldr r3, [r3, #0]
17b53a: 677b str r3, [r7, #116] ; 0x74
{
blue::fibonacci(5); /* GDB Test (cplusplus.cpp,3) */
17b53c: f04f 0005 mov.w r0, #5
17b540: f7ff fcc2 bl 17aec8 <_ZN4blue9fibonacciEi>
On Powerpc GDB installs a second breakpoint on the "_Unwind_DebugHook"
function. Then, after stepping over this hook GDB will install another 3
breakpoints: one after the call to _cxa_throw in the first block, one on the
catch block in the second (which is of interest) and another breakpoint on
DebugHook. Thus at some point the breakpoint on fibonacci will be reached. On
ARM there is no DebugHook so the target will not know when to stop. The "next"
command will only issue a step through range 17b3ae-17b3d2. How can the GDB
stub on the target side reach the branch to the fibonacci function at 17b540?
Perhaps we need to install additional breakpoints like on PPC?
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