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[PATCH] btrace: preserve call stack on function switch
- From: Markus Metzger <markus dot t dot metzger at intel dot com>
- To: gdb-patches at sourceware dot org
- Date: Wed, 1 Feb 2017 10:12:23 +0100
- Subject: [PATCH] btrace: preserve call stack on function switch
- Authentication-results: sourceware.org; auth=none
On 64-bit FC25, the _dl_runtime_resolve function uses a conditional branch to
'call' a particular variant optimized for that system:
(gdb) disas _dl_runtime_resolve_avx_opt
Dump of assembler code for function _dl_runtime_resolve_avx_opt:
0x00007ffff7deeb60 <+0>: push %rax
0x00007ffff7deeb61 <+1>: push %rcx
0x00007ffff7deeb62 <+2>: push %rdx
0x00007ffff7deeb63 <+3>: mov $0x1,%ecx
0x00007ffff7deeb68 <+8>: xgetbv
0x00007ffff7deeb6b <+11>: mov %eax,%r11d
0x00007ffff7deeb6e <+14>: pop %rdx
0x00007ffff7deeb6f <+15>: pop %rcx
0x00007ffff7deeb70 <+16>: pop %rax
0x00007ffff7deeb71 <+17>: and $0x4,%r11d
0x00007ffff7deeb75 <+21>: bnd je 0x7ffff7def4a0 <_dl_runtime_resolve_sse_vex>
End of assembler dump.
When computing the function-level trace, btrace treats this as a switch from
_dl_runtime_resolve_avx_opt to _dl_runtime_resolve_sse_vex. We know that we
switched functions but we can't really say in which caller/callee relationship
those two functions are.
In addition to preserving the indentaion level, also preserve the caller
information. This is a heuristic since we don't really know. But at least in
this case, this seems to be the right thing to do.
This fixes a fail in gdb.btrace/rn-dl-bind.exp on 64-bit FC25.
2017-02-01 Markus Metzger <markus.t.metzger@intel.com>
* btrace.c (ftrace_new_switch): Preserve up link and flags.
---
gdb/btrace.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/gdb/btrace.c b/gdb/btrace.c
index 6d621e4..ddf6692 100644
--- a/gdb/btrace.c
+++ b/gdb/btrace.c
@@ -448,9 +448,11 @@ ftrace_new_switch (struct btrace_function *prev,
{
struct btrace_function *bfun;
- /* This is an unexplained function switch. The call stack will likely
- be wrong at this point. */
+ /* This is an unexplained function switch. We can't really be sure about the
+ call stack, yet the best I can think of right now is to preserve it. */
bfun = ftrace_new_function (prev, mfun, fun);
+ bfun->up = prev->up;
+ bfun->flags = prev->flags;
ftrace_debug (bfun, "new switch");
--
1.8.3.1