[PATCHv2 bpf-next] selftests/bpf: Mark uprobe trigger functions with nocf_check attribute

[PATCHv2 bpf-next] selftests/bpf: Mark uprobe trigger functions with nocf_check attribute

[Jiri Olsa]

Some distros seem to enable the -fcf-protection=branch by default,
which breaks our setup on first instruction of uprobe trigger
functions and place there endbr64 instruction.

Marking them with nocf_check attribute to skip that.

Ignoring unknown attribute warning in gcc for bench objects, because
nocf_check can be used only when -fcf-protection=branch is enabled,
otherwise we get a warning and break compilation.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
v2 changes:
  - posting separately from uretprobe syscall patchset
  - keep the attribute name __nocf_check [Andrii]

 tools/include/linux/compiler.h                     | 4 ++++
 tools/testing/selftests/bpf/benchs/bench_trigger.c | 8 +++++---
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/tools/include/linux/compiler.h b/tools/include/linux/compiler.h
index 7b65566f3e42..8a63a9913495 100644
--- a/tools/include/linux/compiler.h
+++ b/tools/include/linux/compiler.h
@@ -58,6 +58,10 @@
 #define noinline
 #endif
 
+#ifndef __nocf_check
+#define __nocf_check __attribute__((nocf_check))
+#endif
+
 /* Are two types/vars the same type (ignoring qualifiers)? */
 #ifndef __same_type
 # define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
diff --git a/tools/testing/selftests/bpf/benchs/bench_trigger.c b/tools/testing/selftests/bpf/benchs/bench_trigger.c
index b7aea79495ba..c1f8fb8d2dca 100644
--- a/tools/testing/selftests/bpf/benchs/bench_trigger.c
+++ b/tools/testing/selftests/bpf/benchs/bench_trigger.c
@@ -9,6 +9,8 @@
 /* adjust slot shift in inc_hits() if changing */
 #define MAX_BUCKETS 256
 
+#pragma GCC diagnostic ignored "-Wattributes"
+
 /* BPF triggering benchmarks */
 static struct trigger_ctx {
 	struct trigger_bench *skel;
@@ -167,7 +169,7 @@ static void trigger_fmodret_setup(void)
  * GCC doesn't generate stack setup preample for these functions due to them
  * having no input arguments and doing nothing in the body.
  */
-__weak void uprobe_target_nop(void)
+__nocf_check __weak void uprobe_target_nop(void)
 {
 	asm volatile ("nop");
 }
@@ -176,7 +178,7 @@ __weak void opaque_noop_func(void)
 {
 }
 
-__weak int uprobe_target_push(void)
+__nocf_check __weak int uprobe_target_push(void)
 {
 	/* overhead of function call is negligible compared to uprobe
 	 * triggering, so this shouldn't affect benchmark results much
@@ -185,7 +187,7 @@ __weak int uprobe_target_push(void)
 	return 1;
 }
 
-__weak void uprobe_target_ret(void)
+__nocf_check __weak void uprobe_target_ret(void)
 {
 	asm volatile ("");
 }
-- 
2.44.0

Re: [PATCHv2 bpf-next] selftests/bpf: Mark uprobe trigger functions with nocf_check attribute

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Andrii Nakryiko <andrii@kernel.org>:

On Fri, 22 Mar 2024 14:49:36 +0100 you wrote:
> Some distros seem to enable the -fcf-protection=branch by default,
> which breaks our setup on first instruction of uprobe trigger
> functions and place there endbr64 instruction.
> 
> Marking them with nocf_check attribute to skip that.
> 
> Ignoring unknown attribute warning in gcc for bench objects, because
> nocf_check can be used only when -fcf-protection=branch is enabled,
> otherwise we get a warning and break compilation.
> 
> [...]

Here is the summary with links:
  - [PATCHv2,bpf-next] selftests/bpf: Mark uprobe trigger functions with nocf_check attribute
    https://git.kernel.org/bpf/bpf-next/c/af8d27bf15c8

You are awesome, thank you!
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