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The BPF trampoline preserves only 8 bytes of the target's return value (R0), so attaching an fexit/fmod_ret/fsession program to a function that returns a >8 byte value is now rejected by the verifier. Add a bpf_testmod function returning __int128 and an fexit program that targets it. The program is expected to fail to load with the "with a >8 byte return value is not supported for this attach type" message. A 128-bit __int128 argument is passed in a register pair and occupies two trampoline context slots. Add a bpf_testmod function taking a leading __int128 argument followed by an int and a long, and an fexit program that reads those two trailing arguments and the return value, verifying that the trampoline reserves enough stack for the 128-bit argument and places the following arguments and the return value at the right context slots. __int128 is only available on 64-bit targets (where the compiler defines __SIZEOF_INT128__). The argument test additionally depends on the calling convention: x86_64 and arm64 pass an __int128 in a register pair as the trampoline expects, while other architectures pass it differently (e.g. s390x passes larger arguments by reference), so that subtest runs only on x86_64 and arm64 and is skipped elsewhere. Signed-off-by: Yonghong Song <yonghong.song@linux.dev> Acked-by: Leon Hwang <leon.hwang@linux.dev> Link: https://lore.kernel.org/bpf/20260729050209.2587581-1-yonghong.song@linux.dev Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
19 lines
413 B
C
19 lines
413 B
C
// SPDX-License-Identifier: GPL-2.0
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/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
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#include <vmlinux.h>
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#include <bpf/bpf_tracing.h>
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#include <bpf/bpf_helpers.h>
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long t_b, t_c, t_ret;
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SEC("fexit/bpf_testmod_test_int128_arg")
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int test_int128_arg_fexit(unsigned long long *ctx)
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{
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t_b = (int)ctx[2];
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t_c = (long)ctx[3];
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t_ret = (long)ctx[4];
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return 0;
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}
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char _license[] SEC("license") = "GPL";
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