I found when I press `list ,,` by mistake (the correct command should be `list ,N`, and N is a line number), gdb will `Aborted (core dumped)`. So I would like to create a bug for gdb. Environment information is as following: ```shell $ uname -r 5.15.11-arch2-1 $ pacman -Qi gdb|rg Version Version : 11.1-4 ``` This C file can be a test file. ```c #include <stdio.h> int main(int argc, char *argv[]) { int a = 1; int b = 2; a = a + b; printf("%s\n"); return 0; } ``` ``` gcc -g main.c -o main gdb main ``` Then press `l ,,`. gdb will `Aborted (core dumped)` Thanks.
This is related, but not an exact duplicate of this bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28665 for which I posted some patches here: https://sourceware.org/pipermail/gdb-patches/2021-December/184314.html unfortunately, those patches don't fix this issue, but they do change the failure mode from an abort, to an assertion failure. I'll take a look and update that series to cover this issue too.
The master branch has been updated by Andrew Burgess <aburgess@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=8e454b9c61b6d3a80ea4bc840e808e1564d94ec7 commit 8e454b9c61b6d3a80ea4bc840e808e1564d94ec7 Author: Andrew Burgess <aburgess@redhat.com> Date: Tue Dec 7 13:25:47 2021 +0000 gdb: add empty string check in parse_linespec If parse_linespec (linespec.c) is passed ARG as an empty string then we end up calling `strchr (linespec_quote_characters, '\0')`, which will return a pointer to the '\0' at the end of linespec_quote_characters. This then results in GDB calling skip_quote_char with `ARG + 1`, which is undefined behaviour (as ARG only contained a single character, the '\0'). Fix this by checking for the first character of ARG being '\0' before the call to strchr. I have additionally added an assertion that ARG can't itself be nullptr, as calling is_ada_operator with nullptr can end up calling 'startswith' on the nullptr, which is undefined behaviour. Finally, I moved the declaration of TOKEN into the body of parse_linespec, to where TOKEN is defined. This patch came about while I was working on fixes for PR cli/28665 and PR gdb/28797. The actual fixes for these two issues will be in a later commit in this series, but, with this patch in place, both of the above bugs would hit the new assertion rather than accessing invalid memory and crashing. The '\0' check is not currently ever hit, but just makes the code a little safer. Because this patch only changes the nature of the failure for the above two bugs, there's no tests here. A later commit will fix the above two issues, at which point I'll add some tests. Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28665 Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28797
The master branch has been updated by Andrew Burgess <aburgess@sourceware.org>: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=3c5fcec6dccb0e598d1e64640e55d50ed3ddedb6 commit 3c5fcec6dccb0e598d1e64640e55d50ed3ddedb6 Author: Andrew Burgess <aburgess@redhat.com> Date: Tue Dec 7 14:01:23 2021 +0000 gdb: handle calls to list command passing only a linespec condition In PR cli/28665, it was reported that GDB would crash when given a command like: (gdb) list task 123 The problem here is that in cli/cli-cmd.c:list_command, the string 'task 123' is passed to string_to_event_location in find a location specification. However, this location parsing understands about breakpoint conditions, and so, will stop parsing when it sees something that looks like a condition, in this case, the 'task 123' looks like a breakpoint condition. As a result, the location we get back from string_to_event_location has no actual location specification attached to it. The actual call path is: list_command string_to_event_location string_to_event_location_basic new_linespec_location In new_linespec_location we call linespec_lex_to_end, which looks at 'task 123' and decides that there's nothing there that describes a location. As such, in new_linespec_location, the spec_string field of the location is left as nullptr. Back in list_command we then call decode_line_1, which calls event_location_to_sals, which calls parse_linespec, which takes the spec_string we found earlier, and tries to converts this into a list of sals. However, parse_linespec is not intended to be passed a nullptr, for example, calling is_ada_operator will try to access through the nullptr, causing undefined behaviour. But there are other cases within parse_linespec which don't expect to see a nullptr. When looking at how to fix this issue, I first considered having linespec_lex_to_end detect the problem. That function understands when the first thing in the linespec is a condition keyword, and so, could throw an error saying something like: "no linespec before condition keyword", however, this is not going to work, at least, not without additional changes to GDB, it is valid to place a breakpoint like: (gdb) break task 123 This will place a breakpoint at the current location with the condition 'task 123', and changing linespec_lex_to_end breaks this behaviour. So, next, I considered what would happen if I added a condition to an otherwise valid list command, this is what I see: (gdb) list file.c:1 task 123 Junk at end of line specification. (gdb) So, then I wondered, could we just pull the "Junk" detection forward, so that we throw the error earlier, before we call decode_line_1? It turns out that yes we can. Well, sort of. It is simpler, I think, to add a separate check into the list_command function, after calling string_to_event_location, but before calling decode_line_1. We know when we call string_to_event_location that the string in question is not empty, so, after calling string_to_event_location, if non of the string has been consumed, then the content of the string must be junk - it clearly doesn't look like a location specification. I've reused the same "Junk at end of line specification." error for consistency, and added a few tests to cover this issue. While the first version of this patch was on the mailing list, a second bug PR gdb/28797 was raised. This was for a very similar issue, but this time the problem command was: (gdb) list ,, Here the list command understands about the first comma, list can have two arguments separated by a comma, and the first argument can be missing. So we end up trying to parse the second command "," as a linespec. However, in linespec_lex_to_end, we will stop parsing a linespec at a comma, so, in the above case we end up with an empty linespec (between the two commas), and, like above, this results in the spec_string being nullptr. As with the previous case, I've resolved this issue by adding an extra check for junk at the end of the line - after parsing (or failing to parse) the nothing between the two commas, we still have the "," left at the end of the list command line - when we see this we can throw the same "junk at the end of the line" error, and all is good. I've added tests for this case too. Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28665 Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28797
I believe this issue is now fixed. If you are still seeing any failures in this area, please feel free to reopen the bug.