Add a USDT probe laid out so that its nop10 crosses a page boundary and check that attaching to it succeeds and the probe fires. Without the previous fix libbpf shifts the uprobe onto the nop10 and the attach fails with -ENOTSUPP.
Signed-off-by: Jiayuan Chen <[email protected]> --- tools/testing/selftests/bpf/prog_tests/usdt.c | 54 +++++++++++++++++++ tools/testing/selftests/bpf/usdt_2.c | 16 ++++++ 2 files changed, 70 insertions(+) diff --git a/tools/testing/selftests/bpf/prog_tests/usdt.c b/tools/testing/selftests/bpf/prog_tests/usdt.c index 8004c9568ffa..eff1e57ab13c 100644 --- a/tools/testing/selftests/bpf/prog_tests/usdt.c +++ b/tools/testing/selftests/bpf/prog_tests/usdt.c @@ -250,6 +250,7 @@ static void subtest_basic_usdt(bool optimized) #ifdef __x86_64__ extern void usdt_1(void); extern void usdt_2(void); +extern void usdt_2_cross_page(void); extern void usdt_red_zone_trigger(void); static unsigned char nop1[1] = { 0x90 }; @@ -342,6 +343,57 @@ static void subtest_optimized_attach(void) test_usdt__destroy(skel); } +/* + * Test attachment to a USDT probe whose nop10 crosses a page boundary. + * The kernel can't optimize such nop10, so libbpf keeps the uprobe on + * the preceding 1-byte nop. Do not assume any particular placement + * here, though: however the probe ends up attached, the attachment + * must succeed and the probe must fire. + */ +static void subtest_optimized_attach_cross_page(void) +{ + long page_sz = sysconf(_SC_PAGESIZE); + struct test_usdt *skel; + __u8 *addr = NULL; + long i; + + /* combo is placed up to a page of padding after the function start */ + for (i = 0; i < 2 * page_sz; i++) { + if (!memcmp((void *)usdt_2_cross_page + i, nop1_nop10_combo, 11)) { + addr = (void *)usdt_2_cross_page + i; + break; + } + } + if (!ASSERT_OK_PTR(addr, "find_nop1_nop10_combo")) + return; + + /* layout sanity check: the nop10 must cross the page boundary */ + if (!ASSERT_GT((unsigned long)(addr + 1) % page_sz + 10, page_sz, + "nop10_crosses_page")) + return; + + skel = test_usdt__open_and_load(); + if (!ASSERT_OK_PTR(skel, "test_usdt__open_and_load")) + return; + + skel->bss->my_pid = getpid(); + + skel->links.usdt0 = bpf_program__attach_usdt(skel->progs.usdt0, + 0 /*self*/, "/proc/self/exe", + "optimized_attach", + "usdt_2_cross_page", NULL); + if (!ASSERT_OK_PTR(skel->links.usdt0, "bpf_program__attach_usdt")) + goto cleanup; + + usdt_2_cross_page(); + usdt_2_cross_page(); + + ASSERT_EQ(skel->bss->usdt0_called, 2, "usdt0_called"); + +cleanup: + test_usdt__destroy(skel); +} + /* * Test that USDT arguments survive nop10 optimization in a function where * the compiler places operands in the red zone. @@ -660,6 +712,8 @@ void test_usdt(void) subtest_basic_usdt(true); if (test__start_subtest("optimized_attach")) subtest_optimized_attach(); + if (test__start_subtest("optimized_attach_cross_page")) + subtest_optimized_attach_cross_page(); if (test__start_subtest("optimized_red_zone")) subtest_optimized_red_zone(); #endif diff --git a/tools/testing/selftests/bpf/usdt_2.c b/tools/testing/selftests/bpf/usdt_2.c index 5e38f8605b02..3b7024b9b08b 100644 --- a/tools/testing/selftests/bpf/usdt_2.c +++ b/tools/testing/selftests/bpf/usdt_2.c @@ -13,6 +13,22 @@ void usdt_2(void) USDT(optimized_attach, usdt_2); } +/* + * Force the nop1,nop10 combo of the USDT probe to a spot where the nop10 + * crosses a page boundary: .balign starts the padding exactly at a page + * start regardless of the compiler-generated prologue size, and the 4086 + * one-byte nops put the nop1 at page offset 4086, so the following nop10 + * occupies the last 9 bytes of that page and 1 byte of the next one. + * The kernel can't optimize such nop10, so libbpf must keep the uprobe + * on the 1-byte nop. + */ +__attribute__((noinline)) +void usdt_2_cross_page(void) +{ + asm volatile (".balign 4096, 0x90\n\t.skip 4086, 0x90"); + USDT(optimized_attach, usdt_2_cross_page); +} + static volatile unsigned long usdt_red_zone_arg1 = 0xDEADBEEF; static volatile unsigned long usdt_red_zone_arg2 = 0xCAFEBABE; static volatile unsigned long usdt_red_zone_arg3 = 0xFEEDFACE; -- 2.43.0
