[PATCH sched_ext/for-7.4 0/2] sched_ext: Clean up -rdynamic and LDFLAGS in Makefiles

[PATCH sched_ext/for-7.4 0/2] sched_ext: Clean up -rdynamic and LDFLAGS in Makefiles

[Cheng-Yang Chou]

Building the demo schedulers and selftests with CC=clang-N fails under
-Werror because CFLAGS passes the link-time flag -rdynamic to compile
steps ($(CC) -c):

    $ make CC=clang-21
    clang-21: error: argument unused during compilation: '-rdynamic'
                     [-Werror,-Wunused-command-line-argument]

Patch 1: Drop the inert -rdynamic from tools/sched_ext. Binaries remain
byte-identical before and after.

Patch 2: Move -rdynamic to LDFLAGS and append with '+=' in selftests.

Thanks,
Cheng-Yang

---

Cheng-Yang Chou (2):
  tools/sched_ext: Drop the no-op -rdynamic from CFLAGS
  selftests/sched_ext: Move -rdynamic to LDFLAGS and append to it

 tools/sched_ext/Makefile                   | 2 +-
 tools/testing/selftests/sched_ext/Makefile | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

-- 
2.43.0

[PATCH 1/2] tools/sched_ext: Drop the no-op -rdynamic from CFLAGS

[Cheng-Yang Chou]

Because CFLAGS only applies to compilation ($(CC) -c), the link-time
flag -rdynamic is inert during the build. Schedulers do not rely on
exported dynamic symbols, and binaries remain byte-identical without it.

Under -Werror, Clang treats this unused argument as a build error:

	$ make CC=clang-21
	clang-21: error: argument unused during compilation: '-rdynamic'
					 [-Werror,-Wunused-command-line-argument]

Drop -rdynamic from CFLAGS to ensure clean builds across Clang versions.

Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 tools/sched_ext/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/sched_ext/Makefile b/tools/sched_ext/Makefile
index 21554f0896923..70d2503b6b330 100644
--- a/tools/sched_ext/Makefile
+++ b/tools/sched_ext/Makefile
@@ -89,7 +89,7 @@ ifneq ($(wildcard $(GENHDR)),)
   GENFLAGS := -DHAVE_GENHDR
 endif
 
-CFLAGS += -g -O2 -rdynamic -pthread -Wall -Werror $(GENFLAGS)			\
+CFLAGS += -g -O2 -pthread -Wall -Werror $(GENFLAGS)				\
 	  -I$(INCLUDE_DIR) -I$(GENDIR) -I$(LIBDIR)				\
 	  -I$(TOOLSINCDIR) -I$(APIDIR) -I$(CURDIR)/include
 
-- 
2.43.0

[PATCH 2/2] selftests/sched_ext: Move -rdynamic to LDFLAGS and append to it

[Cheng-Yang Chou]

CFLAGS passes the link-time flag -rdynamic to compile steps ($(CC) -c),
where it is unused. Under -Werror, Clang fails the build:

    $ make CC=clang-21
    clang-21: error: argument unused during compilation: '-rdynamic'
                     [-Werror,-Wunused-command-line-argument]

Unlike the demo schedulers, the selftest runner requires -rdynamic at
link time to populate .dynsym for testcases. Additionally, LDFLAGS uses
'=' rather than '+=', silently discarding USERLDFLAGS from lib.mk.

Move -rdynamic from CFLAGS to LDFLAGS and append with '+='. This fixes
builds with CC=clang-N while preserving symbol export and USERLDFLAGS.

Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
 tools/testing/selftests/sched_ext/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/sched_ext/Makefile b/tools/testing/selftests/sched_ext/Makefile
index 3cfe90e0f34fa..c756285a4903e 100644
--- a/tools/testing/selftests/sched_ext/Makefile
+++ b/tools/testing/selftests/sched_ext/Makefile
@@ -53,7 +53,7 @@ ifneq ($(wildcard $(GENHDR)),)
   GENFLAGS := -DHAVE_GENHDR
 endif
 
-CFLAGS += -g -O2 -rdynamic -pthread -Wall -Werror $(GENFLAGS)			\
+CFLAGS += -g -O2 -pthread -Wall -Werror $(GENFLAGS)				\
 	  -I$(INCLUDE_DIR) -I$(GENDIR) -I$(LIBDIR)				\
 	  -I$(TOOLSINCDIR) -I$(APIDIR) -I$(CURDIR)/include -I$(SCXTOOLSINCDIR)
 
@@ -62,7 +62,7 @@ ifneq ($(LLVM),)
 CFLAGS += -Wno-unused-command-line-argument
 endif
 
-LDFLAGS = -lelf -lz -lpthread -lzstd
+LDFLAGS += -rdynamic -lelf -lz -lpthread -lzstd
 
 IS_LITTLE_ENDIAN = $(shell $(CC) -dM -E - </dev/null |				\
 			grep 'define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__')
-- 
2.43.0

Re: [PATCH 2/2] selftests/sched_ext: Move -rdynamic to LDFLAGS and append to it

[Tejun Heo]

Hello,

On Tue, Sep 08, 2026 at 09:47:09PM +0800, Cheng-Yang Chou wrote:
> Unlike the demo schedulers, the selftest runner requires -rdynamic at
> link time to populate .dynsym for testcases. Additionally, LDFLAGS uses
> '=' rather than '+=', silently discarding USERLDFLAGS from lib.mk.

The runner doesn't need -rdynamic. Testcases register through constructors
calling scx_test_register() and nothing in the selftests, tools/sched_ext or
libbpf looks up symbols dynamically or prints backtraces. The flag was copied
from the BPF selftests where the test_progs crash handler needs it for
backtrace symbolization. Please drop -rdynamic here too, as in the first
patch. The '=' to '+=' change is good, keep that.

Thanks.

--
tejun

Re: [PATCH 2/2] selftests/sched_ext: Move -rdynamic to LDFLAGS and append to it

[Cheng-Yang Chou]

Hi Tejun,

On Tue, Sep 08, 2026 at 07:09:58AM -1000, Tejun Heo wrote:
> Hello,
> 
> On Tue, Sep 08, 2026 at 09:47:09PM +0800, Cheng-Yang Chou wrote:
> > Unlike the demo schedulers, the selftest runner requires -rdynamic at
> > link time to populate .dynsym for testcases. Additionally, LDFLAGS uses
> > '=' rather than '+=', silently discarding USERLDFLAGS from lib.mk.
> 
> The runner doesn't need -rdynamic. Testcases register through constructors
> calling scx_test_register() and nothing in the selftests, tools/sched_ext or
> libbpf looks up symbols dynamically or prints backtraces. The flag was copied
> from the BPF selftests where the test_progs crash handler needs it for
> backtrace symbolization. Please drop -rdynamic here too, as in the first
> patch. The '=' to '+=' change is good, keep that.

Confirmed here, dropping it takes the runner's .dynsym from 572 to 172
entries, and all testcases still register and run, so nothing was
relying on the exported symbols.

Will send v2 patch soon, thanks!

> 
> Thanks.
> 
> --
> tejun

-- 
Cheers,
Cheng-Yang

Re: [PATCH 1/2] tools/sched_ext: Drop the no-op -rdynamic from CFLAGS

[Tejun Heo]

Hello,

On Tue, Sep 08, 2026 at 09:47:08PM +0800, Cheng-Yang Chou wrote:
> Because CFLAGS only applies to compilation ($(CC) -c), the link-time
> flag -rdynamic is inert during the build. Schedulers do not rely on
> exported dynamic symbols, and binaries remain byte-identical without it.

Applied to sched_ext/for-7.4.

Thanks.

--
tejun