The attached patch adds support for debug info in C++ dynamic initializers. This is subject to -g and also __attribute__((nodebug)) which is now permitted on variables with static storage duration.
The driving reason for this change is to get useful information in
backtraces. For instance, before:
Program received signal SIGSEGV, Segmentation fault.
0x00000000004004de in crash () at gi.cc:3
3 char x = *ptr;
(gdb) bt
#0 0x00000000004004de in crash () at gi.cc:3
#1 0x0000000000400505 in test () at gi.cc:7
#2 0x0000000000400519 in __cxx_global_var_init () at gi.cc:8
#3 0x0000000000400569 in global constructors keyed to a ()
#4 0x0000000000400636 in __do_global_ctors_aux ()
#5 0x00000000004003bb in _init ()
#6 0x00007fffffffe528 in ?? ()
#7 0x00000000004005c5 in __libc_csu_init ()
#8 0x00007ffff7a78be0 in __libc_start_main (main=<optimized out>,
argc=<optimized out>, ubp_av=<optimized out>,
init=0x400580 <__libc_csu_init>, fini=0x7ffff7dd8300 <initial>,
rtld_fini=0x7ffff7dec250 <_dl_fini>, stack_end=0x7fffffffe508)
at libc-start.c:185
#9 0x0000000000400409 in _start ()
which looks fine, but pay attention to the line number info for
__cxx_global_var_init. After:
Program received signal SIGSEGV, Segmentation fault.
0x00000000004004de in crash () at gi.cc:3
3 char x = *ptr;
(gdb) bt
#0 0x00000000004004de in crash () at gi.cc:3
#1 0x00000000004004f9 in test () at gi.cc:7
#2 0x0000000000400519 in __cxx_global_var_init () at gi.cc:11
#3 0x0000000000400559 in global constructors keyed to a ()
#4 0x0000000000400626 in __do_global_ctors_aux ()
#5 0x00000000004003bb in _init ()
#6 0x00007fffffffe528 in ?? ()
#7 0x00000000004005b5 in __libc_csu_init ()
#8 0x00007ffff7a78be0 in __libc_start_main (main=<optimized out>,
argc=<optimized out>, ubp_av=<optimized out>,
init=0x400570 <__libc_csu_init>, fini=0x7ffff7dd8300 <initial>,
rtld_fini=0x7ffff7dec250 <_dl_fini>, stack_end=0x7fffffffe508)
at libc-start.c:185
#9 0x0000000000400409 in _start ()
The before line was wrong. Here's the code for that program.
1 void crash() {
2 volatile char *ptr = 0;
3 char x = *ptr;
4 }
5
6 int test() {
7 crash();
8 return 1;
9 }
10
11 static int i = test();
12 __attribute__((nodebug)) static int j = test();
13
14 int main(void) {}
It's more common to see __cxx_global_var_init given as location foo.cc:0 in
the backtrace, but I wanted to show an example where that doesn't happen.
This patch includes a small cleanup to SemaDeclAttr.cpp. Tabs to spaces.
"!isa<FunctionDecl>(D) && !isa<FunctionTemplateDecl>(D)" became
"!isFunctionOrMethod(D)" because that's what the author actually meant.
Richard Smith suggested that I change the "no address safety" attribute to
use the same logic as nodebug (permitted on certain variables) but that
turns out to be difficult to implement and should be in a separate patch.
Please review!
Nick
gv-debuginfo-1.patch
Description: Binary data
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