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btrace: preserve call stack on function switch 

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.

gdb/
	* btrace.c (ftrace_new_switch): Preserve up link and flags.
This commit is contained in:
Markus Metzger 2017-01-30 09:16:27 +01:00
parent 61697d017e
commit 4c2c7ac69d
2 changed files with 8 additions and 2 deletions
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4
gdb/ChangeLog
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@ -1,3 +1,7 @@
2017-02-14 Markus Metzger <markus.t.metzger@intel.com>
* btrace.c (ftrace_new_switch): Preserve up link and flags.
2017-02-13 Luis Machado <lgustavo@codesourcery.com>
* symfile (_initialize_symfile): Add usage text to the load command's

6
gdb/btrace.c
View File

@ -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");