On Thu, Apr 24, 2025 at 6:38 AM Alexis Lothoré alexis.lothore@bootlin.com wrote:
Hi Xu,
On Thu Apr 24, 2025 at 2:00 PM CEST, Xu Kuohai wrote:
On 4/24/2025 3:24 AM, Alexis Lothoré wrote:
Hi Andrii,
On Wed Apr 23, 2025 at 7:15 PM CEST, Andrii Nakryiko wrote:
On Thu, Apr 17, 2025 at 12:14 AM Alexis Lothoré alexis.lothore@bootlin.com wrote:
Hi Andrii,
On Wed Apr 16, 2025 at 11:24 PM CEST, Andrii Nakryiko wrote:
On Fri, Apr 11, 2025 at 1:32 PM Alexis Lothoré (eBPF Foundation) alexis.lothore@bootlin.com wrote:
[...]
Thanks for the pointer, I'll take a look at it. The more we discuss this series, the less member size sounds relevant for what I'm trying to achieve here.
Following Xu's comments, I have been thinking about how I could detect the custom alignments and packing on structures, and I was wondering if I could somehow benefit from __attribute__ encoding in BTF info ([1]). But following your hint, I also see some btf_is_struct_packed() in tools/lib/bpf/btf_dump.c that could help. I'll dig this further and see if I can manage to make something work with all of this.
With DWARF info, we might not need to detect the structure alignment anymore, since the DW_AT_location attribute tells us where the structure parameter is located on the stack, and DW_AT_byte_size gives us the size of the structure.
I am not sure to follow you here, because DWARF info is not accessible from kernel at runtime, right ? Or are you meaning that we could, at build time, enrich the BTF info embedded in the kernel thanks to DWARF info ?
Sounds like arm64 has complicated rules for stack alignment and stack offset computation for passing 9th+ argument.
Since your analysis shows: "there are about 200 functions accept 9 to 12 arguments, so adding support for up to 12 function arguments." I say, let's keep the existing limitation: if (nregs > 8) return -ENOTSUPP;
If there is a simple and dumb way to detect that arg9+ are scalars with simple stack passing rules, then, sure, let's support those too, but fancy packed/align(x)/etc let's ignore.