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[PATCH 1/1] [RFC] gdb: corelow: make possible to modify (set) registers for a corefile
- From: Roman Pen <roman dot penyaev at profitbricks dot com>
- To:
- Cc: Roman Pen <roman dot penyaev at profitbricks dot com>, Pedro Alves <palves at redhat dot com>, Daniel Jacobowitz <dan at codesourcery dot com>, Jan Kratochvil <jan dot kratochvil at redhat dot com>, gdb-patches at sourceware dot org, Stefan Hajnoczi <stefanha at redhat dot com>, Paolo Bonzini <pbonzini at redhat dot com>
- Date: Tue, 14 Mar 2017 11:08:37 +0100
- Subject: [PATCH 1/1] [RFC] gdb: corelow: make possible to modify (set) registers for a corefile
- Authentication-results: sourceware.org; auth=none
Despite the fact that this is a hairy hack this change eases debugging
of a jmp_buf (setjmp()) and user contexts (makecontext()), which are
highly used in QEMU project as a part of coroutines.
This change allows setting registers for a corefile, thus QEMU gdb
script (qemu/scripts/qemugdb/coroutine.py) is allowed to investigate
backtrace of a preempted coroutine context. Previously only debugging
of a live process was allowed.
This patch caches all register on a first attempt to modify register
'(gdb) set $REG = ADDR' and then cached copy is always returned from
get_core_registers().
This change should not break previous behaviour if nobody sets any
register, i.e. on each get_core_registers() call registers from a
corefile will be reread.
Signed-off-by: Roman Pen <roman.penyaev@profitbricks.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Daniel Jacobowitz <dan@codesourcery.com>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: gdb-patches@sourceware.org
QEMU guys who can be interested in this new gdb behaviour:
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
---
gdb/corelow.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 51 insertions(+)
diff --git a/gdb/corelow.c b/gdb/corelow.c
index c46af0a8a59d..4a4b20ed57a0 100644
--- a/gdb/corelow.c
+++ b/gdb/corelow.c
@@ -74,6 +74,15 @@ static struct gdbarch *core_gdbarch = NULL;
unix child targets. */
static struct target_section_table *core_data;
+/* Cached registers. Once registers are modified (set) for a corefile,
+ they are cached and then are always fetched from get_core_registers().
+ This hairy hack is used only for one purpose: give a possibility to
+ debug jmp_buf (setjmp()) and user contexts (makecontext()). */
+
+static struct cached_reg {
+ char regp[MAX_REGISTER_SIZE];
+} *core_cachedregs;
+
static void core_files_info (struct target_ops *);
static struct core_fns *sniff_core_bfd (bfd *);
@@ -213,6 +222,11 @@ core_close (struct target_ops *self)
}
core_vec = NULL;
core_gdbarch = NULL;
+ if (core_cachedregs)
+ {
+ xfree(core_cachedregs);
+ core_cachedregs = NULL;
+ }
}
static void
@@ -620,6 +634,18 @@ get_core_registers (struct target_ops *ops,
}
gdbarch = get_regcache_arch (regcache);
+
+ if (core_cachedregs)
+ {
+ /* If registers were once modified (set) for a corefile,
+ follow this path and always return cached registers */
+
+ for (i = 0; i < gdbarch_num_regs(gdbarch); i++)
+ regcache_raw_supply(regcache, i, &core_cachedregs[i]);
+
+ return;
+ }
+
if (gdbarch_iterate_over_regset_sections_p (gdbarch))
gdbarch_iterate_over_regset_sections (gdbarch,
get_core_registers_cb,
@@ -639,6 +665,29 @@ get_core_registers (struct target_ops *ops,
}
static void
+set_core_registers (struct target_ops *self, struct regcache *regcache,
+ int regnum)
+{
+ struct gdbarch *gdbarch;
+ int i;
+
+ gdbarch = get_regcache_arch(regcache);
+
+ if (core_cachedregs == NULL)
+ core_cachedregs = (struct cached_reg*)xcalloc(gdbarch_num_regs(gdbarch),
+ sizeof(*core_cachedregs));
+
+ for (i = 0; i < gdbarch_num_regs(gdbarch); i++)
+ regcache_raw_collect(regcache, i, &core_cachedregs[i]);
+}
+
+static void
+prepare_core_registers (struct target_ops *self, struct regcache *arg1)
+{
+ /* nothing here */
+}
+
+static void
core_files_info (struct target_ops *t)
{
print_section_info (core_data, core_bfd);
@@ -1050,6 +1099,8 @@ init_core_ops (void)
core_ops.to_close = core_close;
core_ops.to_detach = core_detach;
core_ops.to_fetch_registers = get_core_registers;
+ core_ops.to_store_registers = set_core_registers;
+ core_ops.to_prepare_to_store = prepare_core_registers;
core_ops.to_xfer_partial = core_xfer_partial;
core_ops.to_files_info = core_files_info;
core_ops.to_insert_breakpoint = ignore;
--
2.11.0