[Crash-utility] Re: [PATCH] x86_64: Make ORC_REG_SP and ORC_REG_PREV_SP independent from kernel version

Hi Tao, On 2026/08/04 12:38, Tao Liu wrote: > Previously ORC_REG_SP and ORC_REG_PREV_SP will depend on kernel version > for their value, however this is fragile since distributions will > backport the upstream patch to a lower kernel version, thus break the > version assumption. > > This patch fixes by checking the value of ORC_REG_PREV_SP, which can be > get from orc_fp_entry. Good catch! ORC_REG_PREV_SP's value can work as the indicator > of whether the current kernel have applied the upstream patch 1735858caa4b > ("objtool/x86: Reorder ORC register numbering"). > > Fixes: d0ee428664f9 ("x86_64: Fix "bt" command to use correct ORC register > values on Linux 7.1 and later") > > Signed-off-by: Tao Liu <ltao(a)redhat.com&gt; > --- > x86_64.c | 31 +++++++++++++++++++++++-------- > 1 file changed, 23 insertions(+), 8 deletions(-) > > diff --git a/x86_64.c b/x86_64.c > index 55648697baf3..10e06b942d53 100644 > --- a/x86_64.c > +++ b/x86_64.c > @@ -6661,6 +6661,9 @@ x86_64_ORC_init(void) > NULL > }; > struct ORC_data *orc; > + struct gnu_request request, *req; > + req = &request; > + ulong value = 0; > > MEMBER_OFFSET_INIT(inactive_task_frame_bp, "inactive_task_frame", "bp"); > MEMBER_OFFSET_INIT(inactive_task_frame_ret_addr, "inactive_task_frame", "ret_addr"); > @@ -6736,14 +6739,26 @@ x86_64_ORC_init(void) > if (orc->has_signal && !orc->has_end) > machdep->flags |= ORC_6_4; > > - /* See kernel commit 1735858caa4b */ > - if (THIS_KERNEL_VERSION >= LINUX(7,1,0)) { > - ORC_REG_SP = 3; > - ORC_REG_PREV_SP = 8; > - } else { > - ORC_REG_SP = 5; > - ORC_REG_PREV_SP = 1; > - } > + /* Try get ORC_REG_(PREV)_SP */ > + ORC_REG_SP = 5; > + ORC_REG_PREV_SP = 1; > + > + if (kernel_symbol_exists("orc_fp_entry") && > + get_symbol_type("orc_fp_entry", "bp_reg", req) == TYPE_CODE_INT) { > + get_symbol_data("orc_fp_entry", sizeof(ulong), &value); > + /* > + * orc_fp_entry.bp_reg = ORC_REG_PREV_SP > + * See kernel commit 1735858caa4b. Use ORC_REG_PREV_SP as the > + * indicator of the commit. > + */ > + value >>= req->member_offset; > + value &= ((1UL << req->member_length) - 1); > + if (value == 8) { > + ORC_REG_SP = 3; > + ORC_REG_PREV_SP = 8; > + } > + } else > + error(WARNING, "Cannot get orc_fp_entry info"); orc_fp_entry was introduced by ae6a45a086898, some old kernels with ORC may start to emit this warning. How about emitting it when the symbol exists but cannot get the bp_reg info?

Otherwise, looks good to me. Thanks, Kazu > > machdep->flags |= ORC; > }