Re: [PATCH bpf 2/7] bpf/x86: prevent trampoline attachment when args location on stack is uncertain
From: Alexis Lothoré <hidden>
Date: 2025-06-13 08:59:37
Also in:
bpf, linux-kselftest, linux-riscv, linux-s390, lkml, netdev
On Fri Jun 13, 2025 at 10:32 AM CEST, Peter Zijlstra wrote:
On Fri, Jun 13, 2025 at 10:26:37AM +0200, Alexis Lothoré wrote:quoted
Hi Peter, On Fri Jun 13, 2025 at 10:11 AM CEST, Peter Zijlstra wrote:quoted
On Fri, Jun 13, 2025 at 09:37:11AM +0200, Alexis Lothoré (eBPF Foundation) wrote:
[...]
quoted
Maybe my commit wording is not precise enough, but indeed, there's not doubt about whether the struct value is passed on the stack or through a register/a pair of registers. The doubt is rather about the struct location when it is passed _by value_ and _on the stack_: the ABI indeed clearly states that "Structures and unions assume the alignment of their most strictly aligned component" (p.13), but this rule is "silently broken" when a struct has an __attribute__((packed)) or and __attribute__((aligned(X))), and AFAICT this case can not be detected at runtime with current BTF info.Ah, okay. So it is a failure of BTF. That was indeed not clear.
If I need to respin, I'll rewrite the commit message to include the details above. Alexis -- Alexis Lothoré, Bootlin Embedded Linux and Kernel engineering https://bootlin.com