Fix stepping past GNU ifunc resolvers (introduce lookup_msym_prefer)
authorPedro Alves <palves@redhat.com>
Thu, 26 Apr 2018 12:01:27 +0000 (13:01 +0100)
committerPedro Alves <palves@redhat.com>
Thu, 26 Apr 2018 12:08:47 +0000 (13:08 +0100)
commit20944a6e20324cd897bf6c4c5fd20ef7224dacaa
tree968bead0171a67545a55be23811d7ba0ee8d5439
parent1adeb822668d3bd7182ca9b8cf42a7261deb3c7f
Fix stepping past GNU ifunc resolvers (introduce lookup_msym_prefer)

When we're stepping (with "step"), we want to skip trampoline-like
functions automatically, including GNU ifunc resolvers.  That is done
by infrun.c calling into:

  in_solib_dynsym_resolve_code
    -> svr4_in_dynsym_resolve_code
      -> in_gnu_ifunc_stub

A problem here is that if there's a regular text symbol at the same
address as the ifunc symbol, the minimal symbol lookup in
in_gnu_ifunc_stub may miss the GNU ifunc symbol:

(...)
    41: 000000000000071a    53 FUNC    GLOBAL DEFAULT   11 gnu_ifunc_resolver
(...)
    50: 000000000000071a    53 IFUNC   GLOBAL DEFAULT   11 gnu_ifunc
(...)

This causes this FAIL in the tests added later in the series:

 (gdb) PASS: gdb.base/gnu-ifunc.exp: resolver_attr=1: resolver_debug=0: final_debug=0: resolver received HWCAP
 set step-mode on
 (gdb) PASS: gdb.base/gnu-ifunc.exp: resolver_attr=1: resolver_debug=0: final_debug=0: set step-mode on
 step
 0x00007ffff7bd371a in gnu_ifunc_resolver () from build/gdb/testsuite/outputs/gdb.base/gnu-ifunc/gnu-ifunc-lib-1-0-0.so
 (gdb) FAIL: gdb.base/gnu-ifunc.exp: resolver_attr=1: resolver_debug=0: final_debug=0: step

Above, GDB simply thought that it stepped into a regular function, so
it stopped stepping, while it should have continued stepping past the
resolver.

The fix is to teach minimal symbol lookup to prefer GNU ifunc symbols
if desired.

gdb/ChangeLog:
2018-04-26  Pedro Alves  <palves@redhat.com>

* minsyms.c (lookup_minimal_symbol_by_pc_section_1): Rename to ...
(lookup_minimal_symbol_by_pc_section): ... this.  Replace
'want_trampoline' parameter by a lookup_msym_prefer parameter.
Handle it.
(lookup_minimal_symbol_by_pc_section): Delete old implementation.
(lookup_minimal_symbol_by_pc): Adjust.
(in_gnu_ifunc_stub): Prefer GNU ifunc symbols.
(lookup_solib_trampoline_symbol_by_pc): Adjust.
* minsyms.h (lookup_msym_prefer): New enum.
(lookup_minimal_symbol_by_pc_section): Replace 'want_trampoline'
parameter by a lookup_msym_prefer parameter.
gdb/ChangeLog
gdb/minsyms.c
gdb/minsyms.h