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An ld_imm64 of a per-CPU map value is followed by a mov_percpu_addr that reuses the same register, so which register the address lands in decides how the JIT encodes the add. Getting the REX prefix wrong there is invisible to a functional test unless the address happens to land in an extended register, which is why this went unnoticed. Load a .percpu variable into every register in one program and match the JITed add against the register each one must resolve into. Signed-off-by: Vineet Gupta <vineet.gupta@linux.dev> Link: https://patch.msgid.link/20260814220254.3797467-3-vineet.gupta@linux.dev Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
73 lines
1.7 KiB
C
73 lines
1.7 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <vmlinux.h>
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#include <bpf/bpf_helpers.h>
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#include "bpf_misc.h"
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#if defined(__TARGET_ARCH_x86)
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int percpu_data SEC(".percpu");
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/*
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* An ld_imm64 of a per-CPU map value is followed by a mov_percpu_addr that
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* reuses the same register, so check that the add resolves into the register
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* the address was loaded into, for every register.
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*/
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SEC("raw_tp")
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__description("per-CPU address resolution")
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__success
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__arch_x86_64
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__jited(" movabsq $0x{{.*}}, %rax")
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__jited(" addq %gs:{{.*}}, %rax")
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__jited(" movabsq $0x{{.*}}, %rdi")
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__jited(" addq %gs:{{.*}}, %rdi")
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__jited(" movabsq $0x{{.*}}, %rsi")
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__jited(" addq %gs:{{.*}}, %rsi")
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__jited(" movabsq $0x{{.*}}, %rdx")
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__jited(" addq %gs:{{.*}}, %rdx")
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__jited(" movabsq $0x{{.*}}, %rcx")
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__jited(" addq %gs:{{.*}}, %rcx")
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__jited(" movabsq $0x{{.*}}, %r8")
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__jited(" addq %gs:{{.*}}, %r8")
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__jited(" movabsq $0x{{.*}}, %rbx")
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__jited(" addq %gs:{{.*}}, %rbx")
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__jited(" movabsq $0x{{.*}}, %r13")
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__jited(" addq %gs:{{.*}}, %r13")
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__jited(" movabsq $0x{{.*}}, %r14")
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__jited(" addq %gs:{{.*}}, %r14")
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__jited(" movabsq $0x{{.*}}, %r15")
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__jited(" addq %gs:{{.*}}, %r15")
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__naked void percpu_addr(void)
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{
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asm volatile (" \
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r0 = %[percpu_data] ll; \
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r1 = %[percpu_data] ll; \
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r2 = %[percpu_data] ll; \
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r3 = %[percpu_data] ll; \
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r4 = %[percpu_data] ll; \
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r5 = %[percpu_data] ll; \
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r6 = %[percpu_data] ll; \
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r7 = %[percpu_data] ll; \
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r8 = %[percpu_data] ll; \
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r9 = %[percpu_data] ll; \
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r0 = 0; \
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exit; \
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" :
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: __imm_addr(percpu_data)
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: __clobber_all);
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}
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#else
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SEC("raw_tp")
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__description("percpu addr dummy")
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__success
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int dummy_test(void)
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{
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return 0;
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}
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#endif
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char _license[] SEC("license") = "GPL";
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