[RFA] Fix 'Invalid read of size 4' in search_command_helper

[RFA] Fix 'Invalid read of size 4' in search_command_helper

[Philippe Waroquiers]

Valgrind detects the below error in gdb.base/list.exp.
==14763== Invalid read of size 4
==14763==    at 0x60B584: search_command_helper(char const*, int, bool) [clone .constprop.91] (source.c:1601)
==14763==    by 0x408888: cmd_func(cmd_list_element*, char const*, int) (cli-decode.c:1892)
==14763==    by 0x668550: execute_command(char const*, int) (top.c:630)
==14763==    by 0x4B2F7B: command_handler(char const*) (event-top.c:583)
==14763==    by 0x4B326C: command_line_handler(std::unique_ptr<char, gdb::xfree_deleter<char> >&&) (event-top.c:772)
...
==14763==  Address 0x6d9f09c is 4 bytes before a block of size 156 alloc'd
==14763==    at 0x4C2E2B3: realloc (vg_replace_malloc.c:836)
==14763==    by 0x41904C: xrealloc (common-utils.c:62)
==14763==    by 0x60A300: find_source_lines(symtab*, int) (source.c:1203)
==14763==    by 0x608219: source_cache::get_plain_source_lines(symtab*, int, int, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*) (source-cache.c:51)
==14763==    by 0x60A46B: print_source_lines_base(symtab*, int, int, enum_flags<print_source_lines_flag>) (source.c:1350)
==14763==    by 0x404E2D: list_command(char const*, int) (cli-cmds.c:1080)
....

Add the missing condition to end the loop once line 1 has been
reversed-searched.

gdb/ChangeLog
2019-01-01  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* source.c (search_command_helper): Stop reverse search
	when line 1 has been searched.
---
 gdb/source.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/gdb/source.c b/gdb/source.c
index 5c300db3ad..ad6c6466b4 100644
--- a/gdb/source.c
+++ b/gdb/source.c
@@ -1598,6 +1598,8 @@ search_command_helper (const char *regex, int from_tty, bool forward)
       else
 	{
 	  line--;
+	  if (line < 1)
+	    break;
 	  if (fseek (stream.get (),
 		     current_source_symtab->line_charpos[line - 1], 0) < 0)
 	    {
-- 
2.19.2

Re: [RFA] Fix 'Invalid read of size 4' in search_command_helper

[Tom Tromey]

>>>>> "Philippe" == Philippe Waroquiers <philippe.waroquiers@skynet.be> writes:

Philippe> gdb/ChangeLog
Philippe> 2019-01-01  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

Philippe> 	* source.c (search_command_helper): Stop reverse search
Philippe> 	when line 1 has been searched.

This is ok.  Some of these could probably have gone in under the obvious
rule, though I completely understand if you'd rather not do that.

Tom

Re: [RFA] Fix 'Invalid read of size 4' in search_command_helper

[Philippe Waroquiers]

On Tue, 2019-01-01 at 11:37 -0700, Tom Tromey wrote:
> > > > > > "Philippe" == Philippe Waroquiers <philippe.waroquiers@skynet.be> writes:
> 
> Philippe> gdb/ChangeLog
> Philippe> 2019-01-01  Philippe Waroquiers  <philippe.waroquiers@skynet.be>
> 
> Philippe> 	* source.c (search_command_helper): Stop reverse search
> Philippe> 	when line 1 has been searched.
> 
> This is ok.  Some of these could probably have gone in under the obvious
> rule, though I completely understand if you'd rather not do that.
Effectively, some fixes are easy enough to be obvious, but still sometimes
an explicit review helps to see e.g. when it is time to restructure
the code (e.g. to restructure it using c++).

Thanks for the reviews, I pushed all 3 RFA fixes.

Philippe