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Problem with breakpoint addresses
- From: Andrew STUBBS <andrew dot stubbs at st dot com>
- To: GDB List <gdb at sourceware dot org>
- Date: Thu, 12 Oct 2006 18:54:24 +0100
- Subject: Problem with breakpoint addresses
Hi,
I have a problem setting breakpoints from addresses stored in registers.
Here's an example:
(gdb) set $r1 = 0x80000000
(gdb) b *$r1
Breakpoint 2 at 0x80000000
The breakpoint looks like it is set correctly, but actually, if it is to
work, I have to set it like this:
(gdb) b *($r1 & ~0U)
Breakpoint 3 at 0x80000000
This shows the difference:
(gdb) info breakpoints
Num Type Disp Enb Address What
2 breakpoint keep y 0xffffffff80000000
3 breakpoint keep y 0x80000000
The address has been sign extended. Note that there is no problem with
registers of unsigned type. This is with an sh-elf target hosted on
i686-pc-linux-gnu and using 'target sim'.
The effect of this is that the breakpoint is placed correctly, but, once
hit, the program cannot continue or step any further.
The problem appears to be that the 32 bit address is used to set the
breakpoint (i.e. the 64 bit address is truncated somewhere in the
system), but when it is hit GDB does the address comparison and the
addresses are not the same so the breakpoint is not recognised.
My question is: what is the _correct_ fix for this issue?
Should it never do sign extension? Should it always do sign extension?
Is there some way to identify when it is intended and when not? Or
perhaps the true problem is elsewhere entirely?
Andrew Stubbs