[binutils-gdb] gdb: revert std -> gdb unordered_map change in x86-nat.c

[Simon Marchi]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=017b9771ac003d2138266a877b894cc1bfac0c71

commit 017b9771ac003d2138266a877b894cc1bfac0c71
Author: Simon Marchi <simon.marchi@efficios.com>
Date:   Mon Nov 17 16:32:56 2025 -0500

    gdb: revert std -> gdb unordered_map change in x86-nat.c
    
    This particular change in commit 965deba1208 ("gdb: use
    gdb::unordered_{set,map} at a few places") causes some regressions,
    for instance when running gdb.base/catch-fork-kill.exp:
    
        (gdb) PASS: gdb.base/catch-fork-kill.exp: fork-kind=fork: exit-kind=exit: fork: continue to child fork
        continue^M
        Continuing.^M
        [Attaching after Thread 0x7ffff7e74740 (LWP 490949) fork to child process 490952]^M
        [New inferior 2 (process 490952)]^M
        [Thread debugging using libthread_db enabled]^M
        Using host libthread_db library "/usr/lib/../lib/libthread_db.so.1".^M
        =================================================================^M
        ^[[1m^[[31m==490919==ERROR: AddressSanitizer: heap-use-after-free on address 0x7c9bac051d88 at pc 0x55f46adc7583 bp 0x7ffc862a1e90 sp 0x7ffc862a1e80
    
    Function x86_linux_nat_target::low_new_fork calls function
    x86_debug_reg_state twice in a row.  The first one returns a reference
    to an x86_debug_reg_state object in the map.  The second causes an
    insertion to be made, moving the first object, rendering the first
    reference invalid.
    
    Revert the change and add a comment indicating that the location of
    x86_debug_reg_state objects is important.
    
    Change-Id: I85789d7657bec658a01908117efa25611e660878

Diff:
---
 gdb/x86-nat.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/gdb/x86-nat.c b/gdb/x86-nat.c
index 381364cdd70..43e7764f142 100644
--- a/gdb/x86-nat.c
+++ b/gdb/x86-nat.c
@@ -38,9 +38,13 @@ struct x86_dr_low_type x86_dr_low;
 /* Hash table storing per-process data.  We don't bind this to a
    per-inferior registry because of targets like x86 GNU/Linux that
    need to keep track of processes that aren't bound to any inferior
-   (e.g., fork children, checkpoints).  */
+   (e.g., fork children, checkpoints).
 
-static gdb::unordered_map<pid_t,
+   Use std::unordered_map rather than gdb::unordered_map, because the
+   location of entries must not change across two x86_debug_reg_state(ptid_t)
+   calls.  */
+
+static std::unordered_map<pid_t,
 			  struct x86_debug_reg_state> x86_debug_process_state;
 
 /* See x86-nat.h.  */