forked from Imagelibrary/binutils-gdb
07c1c91de3
On amd64 (at least) if a user sets a watchpoint before the inferior has started then GDB will assume that a hardware watchpoint can be created. When the inferior starts there is a chance that the watchpoint can't actually be create as a hardware watchpoint, in which case (currently) GDB will silently convert the watchpoint to a software watchpoint. Here's an example session: (gdb) p sizeof var $1 = 4000 (gdb) watch var Hardware watchpoint 1: var (gdb) info watchpoints Num Type Disp Enb Address What 1 hw watchpoint keep y var (gdb) starti Starting program: /home/andrew/tmp/watch Program stopped. 0x00007ffff7fd3110 in _start () from /lib64/ld-linux-x86-64.so.2 (gdb) info watchpoints Num Type Disp Enb Address What 1 watchpoint keep y var (gdb) Notice that before the `starti` command the watchpoint is showing as a hardware watchpoint, but afterwards it is showing as a software watchpoint. Additionally, note that we clearly told the user we created a hardware watchpoint: (gdb) watch var Hardware watchpoint 1: var I think this is bad. I used `starti`, but if the user did `start` or even `run` then the inferior is going to be _very_ slow, which will be unexpected -- after all, we clearly told the user that we created a hardware watchpoint, and the manual clearly says that hardware watchpoints are fast (at least compared to s/w watchpoints). In this patch I propose adding a new warning which will be emitted when GDB downgrades a h/w watchpoint to s/w. The session now looks like this: (gdb) p sizeof var $1 = 4000 (gdb) watch var Hardware watchpoint 1: var (gdb) info watchpoints Num Type Disp Enb Address What 1 hw watchpoint keep y var (gdb) starti Starting program: /home/andrew/tmp/watch warning: watchpoint 1 downgraded to software watchpoint Program stopped. 0x00007ffff7fd3110 in _start () from /lib64/ld-linux-x86-64.so.2 (gdb) info watchpoints Num Type Disp Enb Address What 1 watchpoint keep y var (gdb) The important line is: warning: watchpoint 1 downgraded to software watchpoint It's not much, but hopefully it will be enough to indicate to the user that something unexpected has occurred, and hopefully, they will not be surprised when the inferior runs much slower than they expected. I've added an amd64 only test in gdb.arch/, I didn't want to try adding this as a global test as other architectures might be able to support the watchpoint request in h/w. Also the test is skipped for extended-remote boards as there's a different set of options for limiting hardware watchpoints on remote targets, and this test isn't about them. Reviewed-By: Lancelot Six <lancelot.six@amd.com>
30 lines
867 B
C
30 lines
867 B
C
/* This testcase is part of GDB, the GNU debugger.
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Copyright 2023 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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struct struct_type
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{
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unsigned long long array[100];
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};
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struct struct_type global_var;
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int
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main ()
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{
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return 0;
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}
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