Comments on: Software Breakpoints

By: tsp

tsp — Tue, 20 Jul 2010 06:01:25 +0000

At the run time, we are attaching a process to the GDB and at time time we are setting a break point (in a specified file and a specfic line number), how the GDB know the exact opcode in the ELF file.is there any mapping application is there inside GDB

By: Debugging – Modifying Code At Runtime - technochakra.com

Debugging – Modifying Code At Runtime - technochakra.com — Sat, 09 Jan 2010 19:16:38 +0000

[...] The debugger’s access to a program’s memory and registers not only allows users to view the state of the program but also set software breakpoints. Software breakpoints are set by altering and restoring the instructions in memory and has already been covered indepth in an earlier article. [...]

By: tc

tc — Fri, 04 Sep 2009 18:59:24 +0000

@John, Nice approach. It also does not assume Intel as the underlying platform so will work for a lot of Unix variants.

By: John

John — Fri, 04 Sep 2009 09:56:56 +0000

For an alternative approach on a unix platform, assuming gdb, one can use raise(SIGTRAP). In fact, using a signal gives you a way to only stop execution if you are within gdb:

struct sigaction oldAct;
struct sigaction newAct;

newAct.sa_handler = SIG_IGN;
sigaction(SIGTRAP, &newAct, &oldAct);
raise(SIGTRAP);
sigaction(SIGTRAP, &oldAct, NULL);

Wrap that up in a function which takes a bool, and the process will send itself a signal that it will ignore. Crucially, gdb will *not* ignore it, and will take a break.

By: tc

tc — Tue, 18 Aug 2009 18:26:47 +0000

@Rohit,
I am assuming you are asking this for the Windows platform.
Inline assembly (__asm) is not allowed in Visual Studio’s x64 bit compilers. You can either create your own asm file with a function that invokes “int 3″ and call that function from your C/C++ code or simply invoke the ::DebugBreak() Windows API that internally invokes “int 3″.

By: Rohit Kulshreshtha

Rohit Kulshreshtha — Tue, 18 Aug 2009 14:55:03 +0000

Any clue on how one may achieve this on x86_64?