[Crash-utility] Re: [PATCH] Fix a regression for eppic extension on gdb-16.2

Date: Tue, 8 Jul 2025 13:26:38 +1200 From: Tao Liu <ltao(a)redhat.com&gt; Subject: [Crash-utility] [PATCH] Fix a regression for eppic extension on gdb-16.2 To: devel(a)lists.crash-utility.osci.io Cc: Tao Liu <ltao(a)redhat.com&gt; Message-ID: <20250708012638.97698-1-ltao(a)redhat.com&gt; Content-Type: text/plain; charset="US-ASCII"; x-default=true There is a regression found when testing eppic extension on gdb-16.2 crash: crash> cgroup /root/.eppic/cgroup.c : line 99 : Error: undefined variable 'cgroup_roots' The root cause is when doing gdb upgrading, the replacement of gdb_get_datatype() is incorrect: The original gdb-10.2 version: long value = SYMBOL_VALUE(expr->elts[2].symbol); The incorrect gdb-16.2 replacement: long value = value_as_long(expr->evaluate()); According to gdb/tracepoint.c, the correct gdb-16.2 replacement should be: symbol *sym; expr::var_value_operation *vvop = (gdb::checked_static_cast<expr::var_value_operation *> (exp->op.get ())); sym = vvop->get_symbol (); long value = sym->value_longest (); Otherwise, the value_as_long() will throw an exception when trying to convert a struct into long, such as "cgroup_roots". The reason why this issue only observed on crash extensions, is the faulty code block triggered with "req->tcb", which is a callback for gdb_interface(), and the callback is used by eppic extension, but the normal crash internal calls hardly use it. After: crash> cgroup 0:/user.slice/user-1000.slice/session-2.scope Signed-off-by: Tao Liu <ltao(a)redhat.com&gt; --- gdb-16.2.patch | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/gdb-16.2.patch b/gdb-16.2.patch index 151e4e2..eb620f7 100644 --- a/gdb-16.2.patch +++ b/gdb-16.2.patch

@@ -1952,3 +1952,32 @@ exit 0 } /* Remember the bfd indexes for the .text, .data, .bss and +--- gdb-16.2/gdb/symtab.c.orig ++++ gdb-16.2/gdb/symtab.c +@@ -7690,7 +7690,11 @@ + console("expr->first_opcode(): OP_VAR_VALUE\n"); + type = expr->evaluate_type()->type(); + if (req->tcb) { +- long value = value_as_long(expr->evaluate()); ++ expr::var_value_operation *vvop ++ = (gdb::checked_static_cast<expr::var_value_operation *> ++ (expr->op.get ())); ++ sym = vvop->get_symbol (); ++ long value = sym->value_longest (); + /* callback with symbol value */ + req->typecode = TYPE_CODE(type); + req->tcb(EOP_VALUE, req, &value, 0, 0, 0); +@@ -7701,8 +7705,12 @@ + req->length = type->length(); + } + if (TYPE_CODE(type) == TYPE_CODE_ENUM) { ++ expr::var_value_operation *vvop ++ = (gdb::checked_static_cast<expr::var_value_operation *> ++ (expr->op.get ())); ++ sym = vvop->get_symbol (); + req->typecode = TYPE_CODE(type); +- req->value = value_as_long(expr->evaluate()); ++ req->value = sym->value_longest (); + req->tagname = (char *)TYPE_TAG_NAME(type); + if (!req->tagname) { + val = expr->evaluate_type(); -- 2.47.0