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Re: [RFC][PATCH] fix gdb segv when objfile can't be opened
- From: Simon Marchi <simon dot marchi at polymtl dot ca>
- To: Mike Gulick <mike dot gulick at mathworks dot com>
- Cc: gdb-patches at sourceware dot org
- Date: Thu, 19 Oct 2017 13:54:29 -0400
- Subject: Re: [RFC][PATCH] fix gdb segv when objfile can't be opened
- Authentication-results: sourceware.org; auth=none
- References: <59E8B251.4050100@mathworks.com> <8c08307a-94ad-92b8-9c8b-c713cad541fd@mathworks.com>
On 2017-10-19 11:59, Mike Gulick wrote:
I apologize for the improperly formatted patch -- I'm really struggling
to get thunderbird to behave as I want.
Here is an updated patch. I would have sent it with git send-email,
but
I could not figure out the proper way to add this preface before the
patch (without it looking like part of the commit message).
Hi Mike,
Thanks, I was able to apply this version correctly.
If I have a short comment that's not meant to be in the commit message,
I usually
include it in brackets like this:
[Re-sending this patch because the first try was not formatted
correctly.]
If it's longer you can always end it with a line "Actual commit
message:". Either way, it's not really a big deal, as long as it's
clear. You can use the --annotate option of git-send-email to edit the
message before sending it.
---
From 5dee04076518554e4baae864569d6f4faee9b685 Mon Sep 17 00:00:00 2001
From: Mike Gulick <mgulick@mathworks.com>
Date: Wed, 18 Oct 2017 16:04:27 -0400
Subject: [PATCH] fix gdb segv when objfile can't be opened
This fixes PR 16577.
This patch changes gdb_bfd_map_section to issue a warning rather than
an
error if it is unable to read the object file, and sets the size of the
section/frame that it attempted to read to 0 on error.
The description of gdb_bfd_map_section states that it will try to read
or map the contents of the section SECT, and if successful, the section
data is returned and *SIZE is set to the size of the section data.
This
function was throwing an error and leaving *size as-is. Setting the
section size to 0 indicates to dwarf2_build_frame_info that there is no
data to read, otherwise it will try to read from an invalid frame
pointer.
Changing the error to a warning allows this to be handled gracefully.
Additionally, the error was clobbering the breakpoint output indicating
the current frame (function name, arguments, source file, and line
number).
E.g.
Thread 3 "foo" hit Breakpoint 1, BFD: reopening
/tmp/jna-1013829440/jna2973250704389291330.tmp: No such file or
directory
BFD: reopening /tmp/jna-1013829440/jna2973250704389291330.tmp: No such
file or directory
For some reason, I am not able to reproduce the crash using the
instructions in the bug report, and gdb master.
(gdb) up
#1 0x00007ffff78d525a in sleep () from /lib/x86_64-linux-gnu/libc.so.6
(gdb)
BFD: reopening ./badlib.so: No such file or directory
BFD: reopening ./badlib.so: No such file or directory
Can't read data for section '.eh_frame' in file './badlib.so'
(gdb)
Initial frame selected; you cannot go up.
(gdb)
Initial frame selected; you cannot go up.
(gdb)
Initial frame selected; you cannot go up.
(gdb) bt
#0 0x00007ffff78d52f0 in nanosleep () from
/lib/x86_64-linux-gnu/libc.so.6
#1 0x00007ffff78d525a in sleep () from /lib/x86_64-linux-gnu/libc.so.6
Would you be able to create a test case to reproduce it? We would need
one to go in with the fix in the end anyway, and it's easier for
reviewers if they can just run a test file rather than try to reproduce
by hand. You can start by copying an existing solib test, like
gdb.base/solib-display.exp. See here for more details about tests:
http://sourceware.org/gdb/wiki/TestingGDB
http://sourceware.org/gdb/wiki/GDBTestcaseCookbook
Don't hesitate to ask here or on IRC if you need assistance.
(gdb)
While the "BFD: reopening ..." messages will still appear interspersed
in the
breakpoint output, the current frame info is now displayed:
Thread 3 "foo" hit Breakpoint 1, BFD: reopening
/tmp/jna-1013829440/jna1875755897659885075.tmp: No such file or
directory
BFD: reopening /tmp/jna-1013829440/jna1875755897659885075.tmp: No such
file or directory
warning: Can't read data for section '.eh_frame' in file
'/tmp/jna-1013829440/jna1875755897659885075.tmp'
do_something () at file.cpp:80
80 {
(gdb)
---
gdb/gdb_bfd.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff --git a/gdb/gdb_bfd.c b/gdb/gdb_bfd.c
index 29080b8..229f5ae 100644
--- a/gdb/gdb_bfd.c
+++ b/gdb/gdb_bfd.c
@@ -705,9 +705,15 @@ gdb_bfd_map_section (asection *sectp,
bfd_size_type *size)
data = NULL;
if (!bfd_get_full_section_contents (abfd, sectp, &data))
- error (_("Can't read data for section '%s' in file '%s'"),
- bfd_get_section_name (abfd, sectp),
- bfd_get_filename (abfd));
+ {
+ warning (_("Can't read data for section '%s' in file '%s'"),
+ bfd_get_section_name (abfd, sectp),
+ bfd_get_filename (abfd));
+ /* Section is invalid -- set size to 0 and return NULL */
+ descriptor->size = 0;
+ *size = descriptor->size;
+ return (const gdb_byte *) NULL;
+ }
descriptor->data = data;
done:
I don't know if it is really this function's responsibility to clear
*size in case of error, or it would be the callers responsibility to
properly check for errors. But if the function doesn't throw anymore,
the comment in gdb_bfd.h should be updated accordingly.
Thanks,
Simon