Subject: Re: linux-next: manual merge of the tip tree with the bpf-next tree

From: Jiri Olsa <[email-masked]>
Date: Fri, 12 Sep 2025 22:47:52 +0200

On Fri, Sep 12, 2025 at 12:40:59PM +1000, Stephen Rothwell wrote:
> Hi all,
> 
> Today's linux-next merge of the tip tree got a conflict in:
> 
>   tools/testing/selftests/bpf/prog_tests/usdt.c
> 
> between commit:
> 
>   69424097ee10 ("selftests/bpf: Enrich subtest_basic_usdt case in selftests to cover SIB handling logic")
> 
> from the bpf-next tree and commit:
> 
>   875e1705ad99 ("selftests/bpf: Add optimized usdt variant for basic usdt test")
> 
> from the tip tree.
> 
> I fixed it up (see below) and can carry the fix as necessary. This
> is now fixed as far as linux-next is concerned, but any non trivial
> conflicts should be mentioned to your upstream maintainer when your tree
> is submitted for merging.  You may also want to consider cooperating
> with the maintainer of the conflicting tree to minimise any particularly
> complex conflicts.

hi,
fwiw the conflict was mentioned in here:
  https://lore.kernel.org/bpf/aMAiMrLlfmG9FbQ3@krava/

the fix looks good, thanks

jirka

> 
> -- 
> Cheers,
> Stephen Rothwell
> 
> diff --cc tools/testing/selftests/bpf/prog_tests/usdt.c
> index 615e9c3e93bf,833eb87483a1..000000000000
> --- a/tools/testing/selftests/bpf/prog_tests/usdt.c
> +++ b/tools/testing/selftests/bpf/prog_tests/usdt.c
> @@@ -40,73 -40,20 +40,80 @@@ static void __always_inline trigger_fun
>   	}
>   }
>   
>  +#if defined(__x86_64__) || defined(__i386__)
>  +/*
>  + * SIB (Scale-Index-Base) addressing format: "size@(base_reg, index_reg, scale)"
>  + * - 'size' is the size in bytes of the array element, and its sign indicates
>  + *   whether the type is signed (negative) or unsigned (positive).
>  + * - 'base_reg' is the register holding the base address, normally rdx or edx
>  + * - 'index_reg' is the register holding the index, normally rax or eax
>  + * - 'scale' is the scaling factor (typically 1, 2, 4, or 8), which matches the
>  + *    size of the element type.
>  + *
>  + * For example, for an array of 'short' (signed 2-byte elements), the SIB spec would be:
>  + * - size: -2 (negative because 'short' is signed)
>  + * - scale: 2 (since sizeof(short) == 2)
>  + *
>  + * The resulting SIB format: "-2@(%%rdx,%%rax,2)" for x86_64, "-2@(%%edx,%%eax,2)" for i386
>  + */
>  +static volatile short array[] = {-1, -2, -3, -4};
>  +
>  +#if defined(__x86_64__)
>  +#define USDT_SIB_ARG_SPEC -2@(%%rdx,%%rax,2)
>  +#else
>  +#define USDT_SIB_ARG_SPEC -2@(%%edx,%%eax,2)
>  +#endif
>  +
>  +unsigned short test_usdt_sib_semaphore SEC(".probes");
>  +
>  +static void trigger_sib_spec(void)
>  +{
>  +	/*
>  +	 * Force SIB addressing with inline assembly.
>  +	 *
>  +	 * You must compile with -std=gnu99 or -std=c99 to use the
>  +	 * STAP_PROBE_ASM macro.
>  +	 *
>  +	 * The STAP_PROBE_ASM macro generates a quoted string that gets
>  +	 * inserted between the surrounding assembly instructions. In this
>  +	 * case, USDT_SIB_ARG_SPEC is embedded directly into the instruction
>  +	 * stream, creating a probe point between the asm statement boundaries.
>  +	 * It works fine with gcc/clang.
>  +	 *
>  +	 * Register constraints:
>  +	 * - "d"(array): Binds the 'array' variable to %rdx or %edx register
>  +	 * - "a"(0): Binds the constant 0 to %rax or %eax register
>  +	 * These ensure that when USDT_SIB_ARG_SPEC references %%rdx(%edx) and
>  +	 * %%rax(%eax), they contain the expected values for SIB addressing.
>  +	 *
>  +	 * The "memory" clobber prevents the compiler from reordering memory
>  +	 * accesses around the probe point, ensuring that the probe behavior
>  +	 * is predictable and consistent.
>  +	 */
>  +	asm volatile(
>  +		STAP_PROBE_ASM(test, usdt_sib, USDT_SIB_ARG_SPEC)
>  +		:
>  +		: "d"(array), "a"(0)
>  +		: "memory"
>  +	);
>  +}
>  +#endif
>  +
> - static void subtest_basic_usdt(void)
> + static void subtest_basic_usdt(bool optimized)
>   {
>   	LIBBPF_OPTS(bpf_usdt_opts, opts);
>   	struct test_usdt *skel;
>   	struct test_usdt__bss *bss;
> - 	int err, i;
> + 	int err, i, called;
>  +	const __u64 expected_cookie = 0xcafedeadbeeffeed;
>   
> + #define TRIGGER(x) ({			\
> + 	trigger_func(x);		\
> + 	if (optimized)			\
> + 		trigger_func(x);	\
> + 	optimized ? 2 : 1;		\
> + 	})
> + 
>   	skel = test_usdt__open_and_load();
>   	if (!ASSERT_OK_PTR(skel, "skel_open"))
>   		return;
> @@@ -126,22 -73,13 +133,22 @@@
>   	if (!ASSERT_OK_PTR(skel->links.usdt0, "usdt0_link"))
>   		goto cleanup;
>   
>  +#if defined(__x86_64__) || defined(__i386__)
>  +	opts.usdt_cookie = expected_cookie;
>  +	skel->links.usdt_sib = bpf_program__attach_usdt(skel->progs.usdt_sib,
>  +							 0 /*self*/, "/proc/self/exe",
>  +							 "test", "usdt_sib", &opts);
>  +	if (!ASSERT_OK_PTR(skel->links.usdt_sib, "usdt_sib_link"))
>  +		goto cleanup;
>  +#endif
>  +
> - 	trigger_func(1);
> + 	called = TRIGGER(1);
>   
> - 	ASSERT_EQ(bss->usdt0_called, 1, "usdt0_called");
> - 	ASSERT_EQ(bss->usdt3_called, 1, "usdt3_called");
> - 	ASSERT_EQ(bss->usdt12_called, 1, "usdt12_called");
> + 	ASSERT_EQ(bss->usdt0_called, called, "usdt0_called");
> + 	ASSERT_EQ(bss->usdt3_called, called, "usdt3_called");
> + 	ASSERT_EQ(bss->usdt12_called, called, "usdt12_called");
>   
>  -	ASSERT_EQ(bss->usdt0_cookie, 0xcafedeadbeeffeed, "usdt0_cookie");
>  +	ASSERT_EQ(bss->usdt0_cookie, expected_cookie, "usdt0_cookie");
>   	ASSERT_EQ(bss->usdt0_arg_cnt, 0, "usdt0_arg_cnt");
>   	ASSERT_EQ(bss->usdt0_arg_ret, -ENOENT, "usdt0_arg_ret");
>   	ASSERT_EQ(bss->usdt0_arg_size, -ENOENT, "usdt0_arg_size");
> @@@ -225,18 -163,9 +232,19 @@@
>   	ASSERT_EQ(bss->usdt3_args[1], 42, "usdt3_arg2");
>   	ASSERT_EQ(bss->usdt3_args[2], (uintptr_t)&bla, "usdt3_arg3");
>   
>  +#if defined(__x86_64__) || defined(__i386__)
>  +	trigger_sib_spec();
>  +	ASSERT_EQ(bss->usdt_sib_called, 1, "usdt_sib_called");
>  +	ASSERT_EQ(bss->usdt_sib_cookie, expected_cookie, "usdt_sib_cookie");
>  +	ASSERT_EQ(bss->usdt_sib_arg_cnt, 1, "usdt_sib_arg_cnt");
>  +	ASSERT_EQ(bss->usdt_sib_arg, nums[0], "usdt_sib_arg");
>  +	ASSERT_EQ(bss->usdt_sib_arg_ret, 0, "usdt_sib_arg_ret");
>  +	ASSERT_EQ(bss->usdt_sib_arg_size, sizeof(nums[0]), "usdt_sib_arg_size");
>  +#endif
>  +
>   cleanup:
>   	test_usdt__destroy(skel);
> + #undef TRIGGER
>   }
>   
>   unsigned short test_usdt_100_semaphore SEC(".probes");