On Tue, Mar 24, 2026 at 08:03:30AM -0700, Alexei Starovoitov wrote:
On Mon, Mar 23, 2026 at 9:49 AM Sasha Levin <[email protected]> wrote:Embed DWARF-derived function parameter name and type information in the kernel image so that oops and WARN dumps display the crashing function's register-passed arguments with their names, types, and values. A new build-time tool (scripts/gen_paraminfo.c) parses DW_TAG_subprogram and DW_TAG_formal_parameter entries from DWARF .debug_info, extracting parameter names and human-readable type strings. The resulting tables are stored in .rodata using the same two-phase link approach as lineinfo. At runtime, kallsyms_show_paraminfo() performs a binary search on the paraminfo tables, maps parameters to x86-64 calling convention registers (RDI, RSI, RDX, RCX, R8, R9), and prints each parameter's name, type, and value from pt_regs. If a parameter value matches the page fault address (CR2), it is highlighted with "<-- fault address". Integration at show_regs() means this works for both oops and WARN() automatically, since both paths provide full pt_regs at the exception point. Example output: Function parameters (ext4_readdir): file (struct file *) = 0xffff888123456000 ctx (struct dir_context *) = 0x0000000000001234 <-- fault address Gated behind CONFIG_KALLSYMS_PARAMINFO (depends on CONFIG_KALLSYMS_LINEINFO). Adds approximately 1-2 MB to the kernel image for ~58K functions. Assisted-by: Claude:claude-opus-4-6 Signed-off-by: Sasha Levin <[email protected]>Nack. You asked claude to reinvent pahole and BTF and it did it completely missing years of fine tuning that pahole does.
Let's keep this on the technical side please.
dwarf cannot be trusted as-is. pahole converts it carefully by analyzing optimized out arguments and dropping signatures
Fair point about pahole and optimized-out args. The problem is that BTF depends on BPF_SYSCALL, and the environments I care about can't enable either. Automotive, robotics, and safety configs all have DWARF and KALLSYMS but no path to BTF.
from BTF that are not accurate. This work is still ongoing. For example see this set: https://lore.kernel.org/bpf/[email protected]/
Ack. I wasn't familiar with this, and looks like it makes the 2nd patch in this series unnecessary.
pahole isn't perfect, but what you attempted to do here is just broken.
I hear you that raw DWARF isn't perfect with optimized code, but I'd rather show best-effort info than nothing. Happy to mark it as such in the output. Open to suggestions on improving accuracy without the BTF dependency. -- Thanks, Sasha
