Hello,Ran into an odd bug that I am unsure what the solution is. Tested a few kernels versions and they all fail the same.
FUNCTION_GRAPH_FP_TEST was enabled with 953f534a7ed6 ("ARM: ftrace: enable HAVE_FUNCTION_GRAPH_FP_TEST"). This test fails when UNWINDER_FRAME_POINTER is enabled. Enable function_graph tracer and you should see a failure similar to below.
[ 63.817239] ------------[ cut here ]------------[ 63.822006] WARNING: CPU: 3 PID: 1185 at kernel/trace/fgraph.c:195 ftrace_return_to_handler+0x228/0x374
[ 63.831645] Bad frame pointer: expected d1e0df40, received d1e0df48 [ 63.831645] from func packet_setsockopt return to c0b558f4 [ 63.843801] Modules linked in: bdc udc_core[ 63.848246] CPU: 3 PID: 1185 Comm: udhcpc Not tainted 6.1.53-0.1pre-gf0bc552d12f8 #33
[ 63.856209] Hardware name: Broadcom STB (Flattened Device Tree) [ 63.862227] Backtrace: [ 63.864761] dump_backtrace from show_stack+0x20/0x24 [ 63.869982] r7:c031cd8c r6:00000009 r5:00000013 r4:c11c7fac [ 63.875736] show_stack from dump_stack_lvl+0x48/0x54 [ 63.880929] dump_stack_lvl from dump_stack+0x18/0x1c [ 63.886111] r5:000000c3 r4:c11bd92c [ 63.889764] dump_stack from __warn+0x88/0x130 [ 63.894339] __warn from warn_slowpath_fmt+0x140/0x198 [ 63.899631] r8:d1e0deac r7:c11bd958 r6:c031cd8c r5:c11bd92c r4:00000000 [ 63.906431] warn_slowpath_fmt from ftrace_return_to_handler+0x228/0x374 [ 63.913294] r8:c3a8d840 r7:00000002 r6:d1e0df48 r5:c2377a94 r4:c269a400 [ 63.920095] ftrace_return_to_handler from return_to_handler+0xc/0x18 [ 63.926699] r8:c0cd8ed0 r7:00000008 r6:c418c500 r5:00000004 r4:00000107 [ 63.933500] __sys_setsockopt from return_to_handler+0x0/0x18 [ 63.939415] r8:c02002bc r7:00000126 r6:00000003 r5:00000000 r4:00000004 [ 63.946217] sys_setsockopt from return_to_handler+0x0/0x18 [ 63.952053] ---[ end trace 0000000000000000 ]---Sure enough the top of the parent stack is off by 8. (Tested with gcc6.3/gcc8.3/gcc12.3)
00006dcc <packet_setsockopt>: 6dcc: e1a0c00d mov ip, sp 6dd0: e24dd008 sub sp, sp, #8 <======6dd4: e92ddff0 push {r4, r5, r6, r7, r8, r9, sl, fp, ip, lr, pc}
6dd8: e24cb00c sub fp, ip, #12 6ddc: e24dd06c sub sp, sp, #108 @ 0x6c6de0: e52de004 push {lr} @ (str lr, [sp, #-4]!)
6de4: ebfffffe bl 0 <__gnu_mcount_nc>I'm not quite sure why gcc is putting this extra 8 byte frame (maybe some optimization?), but it isn't being accounted for thus the FUNCTION_GRAPH_FP_TEST for arm fails. Note that only some functions do this. Function graph works with FUNCTION_GRAPH_FP_TEST disabled, so it looks the test is hitting false positives.
Thanks, Justin
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