* skip setting the svr4 shared library breakpoint if there's no execution (Re: Regression loading a tracefile in 7_3)
[not found] ` <201105201257.53942.pedro@codesourcery.com>
@ 2011-05-20 14:03 ` Pedro Alves
2011-05-20 15:35 ` Joel Brobecker
0 siblings, 1 reply; 3+ messages in thread
From: Pedro Alves @ 2011-05-20 14:03 UTC (permalink / raw)
To: gdb-patches; +Cc: Marc Khouzam
Moving to gdb-patches, from
<http://sourceware.org/ml/gdb/2011-05/msg00107.html>
On Friday 20 May 2011 12:57:53, Pedro Alves wrote:
> On Friday 20 May 2011 03:03:20, Marc Khouzam wrote:
> > Hi,
> >
> > I believe I'm seeing a regression loading a tracefile in GDB 7.3
> > I create a simple tracefile using GDB/gdbserver 7.3 but when I try to load
> > that tracefile, I get an error about "PC register is not available", which
> > causes my Eclipse session to abort. This is not happening in 7.2 or 7.2.1.
> >
> > > gdb.7.3 a.out
> > GNU gdb (GDB) 7.2.90.20110519-cvs
> > (gdb) interpreter-exec mi "-target-select tfile trace.7.3"
> > ~"Created tracepoint 1 for target's tracepoint 1 at 0x804851f.\n"
> > ^error,msg="PC register is not available"
> >
>
> Hmm.
>
> #0 throw_error (error=NOT_AVAILABLE_ERROR, fmt=0x7f7908 "PC register is not available") at ../../src/gdb/exceptions.c:423
> #1 0x000000000053de3a in regcache_read_pc (regcache=0xd4b280) at ../../src/gdb/regcache.c:994
> #2 0x0000000000497053 in enable_break (info=0xd0df60, from_tty=1) at ../../src/gdb/solib-svr4.c:1536
> #3 0x00000000004980a8 in svr4_solib_create_inferior_hook (from_tty=1) at ../../src/gdb/solib-svr4.c:2194
> #4 0x000000000046faa7 in solib_create_inferior_hook (from_tty=1) at ../../src/gdb/solib.c:1240
> #5 0x0000000000586de2 in post_create_inferior (target=0xbc7120, from_tty=1) at ../../src/gdb/infcmd.c:427
> #6 0x00000000004d2ca8 in tfile_open (filename=0xd0d790 "/home/pedro/gdb/marck_tfile/build/gdb/./testsuite/basic.tf", from_tty=1)
> at ../../src/gdb/tracepoint.c:3410
>
> Here, in solib-svr4.c:
>
> /* Otherwise we find the dynamic linker's base address by examining
> the current pc (which should point at the entry point for the
> dynamic linker) and subtracting the offset of the entry point.
>
> This is more fragile than the previous approaches, but is a good
> fallback method because it has actually been working well in
> most cases. */
> if (!load_addr_found)
> {
> struct regcache *regcache
> = get_thread_arch_regcache (inferior_ptid, target_gdbarch);
>
> load_addr = (regcache_read_pc (regcache)
> - exec_entry_point (tmp_bfd, tmp_bfd_target));
> }
>
> We could skip this if the PC is not available, but:
>
> - why do we even try to set a shared library breakpoint
> if the target has no execution (e.g., when debugging a core
> file) in the first place? I'll try skipping enable_break in that
> case and see if anything breaks. By inspection, it looks like
> nothing will. svr4_in_dynsym_resolve_code will always
> return false if we skip enable_break, but then again that function
> is only used for run control.
Nothing did break. Here's the patch. Anyone see a problem with
this? I'd like to apply this to mainline and 7.3.
--
Pedro Alves
2011-05-20 Pedro Alves <pedro@codesourcery.com>
gdb/
* solib-svr4.c (svr4_solib_create_inferior_hook): Skip setting
shared library event breakpoint if there's no execution.
gdb/testsuite/
* gdb.trace/tfile.exp: Add test that opening the basic.tf trace
file doesn't error, using MI.
---
gdb/solib-svr4.c | 5 +++++
gdb/testsuite/gdb.trace/tfile.exp | 5 +++++
2 files changed, 10 insertions(+)
Index: src/gdb/solib-svr4.c
===================================================================
--- src.orig/gdb/solib-svr4.c 2011-05-20 14:36:49.428819003 +0100
+++ src/gdb/solib-svr4.c 2011-05-20 14:54:58.548819003 +0100
@@ -2188,6 +2188,11 @@ svr4_solib_create_inferior_hook (int fro
/* Relocate the main executable if necessary. */
svr4_relocate_main_executable ();
+ /* No point setting a breakpoint in the dynamic linker if we can't
+ hit it (e.g., a core file, or a trace file). */
+ if (!target_has_execution)
+ return;
+
if (!svr4_have_link_map_offsets ())
return;
Index: src/gdb/testsuite/gdb.trace/tfile.exp
===================================================================
--- src.orig/gdb/testsuite/gdb.trace/tfile.exp 2011-05-20 14:36:49.428819003 +0100
+++ src/gdb/testsuite/gdb.trace/tfile.exp 2011-05-20 14:54:58.548819003 +0100
@@ -116,3 +116,8 @@ Collected 0 trace frame.*
Trace buffer has 256 bytes of 4096 bytes free \\(93% full\\).*
Not looking at any trace frame.*" \
"tstatus on error trace file"
+
+# Make sure we can reopen without error.
+gdb_test \
+ "interpreter-exec mi \"-target-select tfile basic.tf\"" \
+ "\\^connected.*"
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