[PATCH v5 0/3] selftests/vDSO: fix clang build errors, and Makefile cleanup

[PATCH v5 0/3] selftests/vDSO: fix clang build errors, and Makefile cleanup

[John Hubbard]

Hi Shuah,

These are for 6.10, as we just discussed.

Changes since v4:

1) Subject line on patch #2/3: s/mm/vDSO/

2) Added Muhammad's review tag.

Changes since v3:

1. Rebased onto Linux 6.10-rc6+.

Cover letter for v3:

Jason A. Donenfeld, I've added you because I ended up looking through
your latest "implement getrandom() in vDSO" series [1], which also
touches this Makefile, so just a heads up about upcoming (minor) merge
conflicts.

Changes since v2:

1. Added two patches, both of which apply solely to the Makefile.
These provide a smaller, cleaner, and more accurate Makefile.

2. Added Reviewed-by and Tested-by tags for the original patch, which
fixes all of the clang errors and warnings for this selftest.

3. Removed an obsolete blurb from the commit description of the original
patch, now that Valentin Obst LLVM build fix has been merged.

thanks,
John Hubbard
NVIDIA

John Hubbard (3):
  selftests/vDSO: fix clang build errors and warnings
  selftests/vDSO: remove partially duplicated "all:" target in Makefile
  selftests/vDSO: remove duplicate compiler invocations from Makefile

 tools/testing/selftests/vDSO/Makefile         | 29 ++++++++-----------
 tools/testing/selftests/vDSO/parse_vdso.c     | 16 ++++++----
 .../selftests/vDSO/vdso_standalone_test_x86.c | 18 ++++++++++--
 3 files changed, 39 insertions(+), 24 deletions(-)


base-commit: d270dd21bee023ab627f34cfb77a9b89a688492a
-- 
2.40.1

[PATCH v5 1/3] selftests/vDSO: fix clang build errors and warnings

[John Hubbard]

When building with clang, via:

    make LLVM=1 -C tools/testing/selftests

...there are several warnings, and an error. This fixes all of those and
allows these tests to run and pass.

1. Fix linker error (undefined reference to memcpy) by providing a local
   version of memcpy.

2. clang complains about using this form:

    if (g = h & 0xf0000000)

...so factor out the assignment into a separate step.

3. The code is passing a signed const char* to elf_hash(), which expects
   a const unsigned char *. There are several callers, so fix this at
   the source by allowing the function to accept a signed argument, and
   then converting to unsigned operations, once inside the function.

4. clang doesn't have __attribute__((externally_visible)) and generates
   a warning to that effect. Fortunately, gcc 12 and gcc 13 do not seem
   to require that attribute in order to build, run and pass tests here,
   so remove it.

Reviewed-by: Carlos Llamas <cmllamas@google.com>
Reviewed-by: Edward Liaw <edliaw@google.com>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Tested-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 tools/testing/selftests/vDSO/parse_vdso.c      | 16 +++++++++++-----
 .../selftests/vDSO/vdso_standalone_test_x86.c  | 18 ++++++++++++++++--
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/vDSO/parse_vdso.c b/tools/testing/selftests/vDSO/parse_vdso.c
index 413f75620a35..4ae417372e9e 100644
--- a/tools/testing/selftests/vDSO/parse_vdso.c
+++ b/tools/testing/selftests/vDSO/parse_vdso.c
@@ -55,14 +55,20 @@ static struct vdso_info
 	ELF(Verdef) *verdef;
 } vdso_info;
 
-/* Straight from the ELF specification. */
-static unsigned long elf_hash(const unsigned char *name)
+/*
+ * Straight from the ELF specification...and then tweaked slightly, in order to
+ * avoid a few clang warnings.
+ */
+static unsigned long elf_hash(const char *name)
 {
 	unsigned long h = 0, g;
-	while (*name)
+	const unsigned char *uch_name = (const unsigned char *)name;
+
+	while (*uch_name)
 	{
-		h = (h << 4) + *name++;
-		if (g = h & 0xf0000000)
+		h = (h << 4) + *uch_name++;
+		g = h & 0xf0000000;
+		if (g)
 			h ^= g >> 24;
 		h &= ~g;
 	}
diff --git a/tools/testing/selftests/vDSO/vdso_standalone_test_x86.c b/tools/testing/selftests/vDSO/vdso_standalone_test_x86.c
index 8a44ff973ee1..27f6fdf11969 100644
--- a/tools/testing/selftests/vDSO/vdso_standalone_test_x86.c
+++ b/tools/testing/selftests/vDSO/vdso_standalone_test_x86.c
@@ -18,7 +18,7 @@
 
 #include "parse_vdso.h"
 
-/* We need a libc functions... */
+/* We need some libc functions... */
 int strcmp(const char *a, const char *b)
 {
 	/* This implementation is buggy: it never returns -1. */
@@ -34,6 +34,20 @@ int strcmp(const char *a, const char *b)
 	return 0;
 }
 
+/*
+ * The clang build needs this, although gcc does not.
+ * Stolen from lib/string.c.
+ */
+void *memcpy(void *dest, const void *src, size_t count)
+{
+	char *tmp = dest;
+	const char *s = src;
+
+	while (count--)
+		*tmp++ = *s++;
+	return dest;
+}
+
 /* ...and two syscalls.  This is x86-specific. */
 static inline long x86_syscall3(long nr, long a0, long a1, long a2)
 {
@@ -70,7 +84,7 @@ void to_base10(char *lastdig, time_t n)
 	}
 }
 
-__attribute__((externally_visible)) void c_main(void **stack)
+void c_main(void **stack)
 {
 	/* Parse the stack */
 	long argc = (long)*stack;
-- 
2.40.1

[PATCH v5 2/3] selftests/vDSO: remove partially duplicated "all:" target in Makefile

[John Hubbard]

There were a couple of errors here:

1. TEST_GEN_PROGS was incorrectly prepending $(OUTPUT) to each program
to be built. However, lib.mk already does that because it assumes "bare"
program names are passed in, so this ended up creating
$(OUTPUT)/$(OUTPUT)/file.c, which of course won't work as intended.

2. lib.mk was included before TEST_GEN_PROGS was set, which led to
lib.mk's "all:" target not seeing anything to rebuild.

So nothing worked, which caused the author to force things by creating
an "all:" target locally--while still including ../lib.mk.

Fix all of this by including ../lib.mk at the right place, and removing
the $(OUTPUT) prefix to the programs to be built, and removing the
duplicate "all:" target.

Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 tools/testing/selftests/vDSO/Makefile | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/vDSO/Makefile b/tools/testing/selftests/vDSO/Makefile
index d53a4d8008f9..209ede5de208 100644
--- a/tools/testing/selftests/vDSO/Makefile
+++ b/tools/testing/selftests/vDSO/Makefile
@@ -1,16 +1,15 @@
 # SPDX-License-Identifier: GPL-2.0
-include ../lib.mk
-
 uname_M := $(shell uname -m 2>/dev/null || echo not)
 ARCH ?= $(shell echo $(uname_M) | sed -e s/i.86/x86/ -e s/x86_64/x86/)
 
-TEST_GEN_PROGS := $(OUTPUT)/vdso_test_gettimeofday $(OUTPUT)/vdso_test_getcpu
-TEST_GEN_PROGS += $(OUTPUT)/vdso_test_abi
-TEST_GEN_PROGS += $(OUTPUT)/vdso_test_clock_getres
+TEST_GEN_PROGS := vdso_test_gettimeofday
+TEST_GEN_PROGS += vdso_test_getcpu
+TEST_GEN_PROGS += vdso_test_abi
+TEST_GEN_PROGS += vdso_test_clock_getres
 ifeq ($(ARCH),$(filter $(ARCH),x86 x86_64))
-TEST_GEN_PROGS += $(OUTPUT)/vdso_standalone_test_x86
+TEST_GEN_PROGS += vdso_standalone_test_x86
 endif
-TEST_GEN_PROGS += $(OUTPUT)/vdso_test_correctness
+TEST_GEN_PROGS += vdso_test_correctness
 
 CFLAGS := -std=gnu99
 CFLAGS_vdso_standalone_test_x86 := -nostdlib -fno-asynchronous-unwind-tables -fno-stack-protector
@@ -19,7 +18,7 @@ ifeq ($(CONFIG_X86_32),y)
 LDLIBS += -lgcc_s
 endif
 
-all: $(TEST_GEN_PROGS)
+include ../lib.mk
 $(OUTPUT)/vdso_test_gettimeofday: parse_vdso.c vdso_test_gettimeofday.c
 $(OUTPUT)/vdso_test_getcpu: parse_vdso.c vdso_test_getcpu.c
 $(OUTPUT)/vdso_test_abi: parse_vdso.c vdso_test_abi.c
-- 
2.40.1

[PATCH v5 3/3] selftests/vDSO: remove duplicate compiler invocations from Makefile

[John Hubbard]

The Makefile open-codes compiler invocations that ../lib.mk already
provides.

Avoid this by using a Make feature that allows setting per-target
variables, which in this case are: CFLAGS and LDFLAGS. This approach
generates the exact same compiler invocations as before, but removes all
of the code duplication, along with the quirky mangled variable names.
So now the Makefile is smaller, less unusual, and easier to read.

The new dependencies are listed after including lib.mk, in order to
let lib.mk provide the first target ("all:"), and are grouped together
with their respective source file dependencies, for visual clarity.

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 tools/testing/selftests/vDSO/Makefile | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/tools/testing/selftests/vDSO/Makefile b/tools/testing/selftests/vDSO/Makefile
index 209ede5de208..98d8ba2afa00 100644
--- a/tools/testing/selftests/vDSO/Makefile
+++ b/tools/testing/selftests/vDSO/Makefile
@@ -12,8 +12,7 @@ endif
 TEST_GEN_PROGS += vdso_test_correctness
 
 CFLAGS := -std=gnu99
-CFLAGS_vdso_standalone_test_x86 := -nostdlib -fno-asynchronous-unwind-tables -fno-stack-protector
-LDFLAGS_vdso_test_correctness := -ldl
+
 ifeq ($(CONFIG_X86_32),y)
 LDLIBS += -lgcc_s
 endif
@@ -23,12 +22,9 @@ $(OUTPUT)/vdso_test_gettimeofday: parse_vdso.c vdso_test_gettimeofday.c
 $(OUTPUT)/vdso_test_getcpu: parse_vdso.c vdso_test_getcpu.c
 $(OUTPUT)/vdso_test_abi: parse_vdso.c vdso_test_abi.c
 $(OUTPUT)/vdso_test_clock_getres: vdso_test_clock_getres.c
+
 $(OUTPUT)/vdso_standalone_test_x86: vdso_standalone_test_x86.c parse_vdso.c
-	$(CC) $(CFLAGS) $(CFLAGS_vdso_standalone_test_x86) \
-		vdso_standalone_test_x86.c parse_vdso.c \
-		-o $@
+$(OUTPUT)/vdso_standalone_test_x86: CFLAGS +=-nostdlib -fno-asynchronous-unwind-tables -fno-stack-protector
+
 $(OUTPUT)/vdso_test_correctness: vdso_test_correctness.c
-	$(CC) $(CFLAGS) \
-		vdso_test_correctness.c \
-		-o $@ \
-		$(LDFLAGS_vdso_test_correctness)
+$(OUTPUT)/vdso_test_correctness: LDFLAGS += -ldl
-- 
2.40.1

Re: [PATCH v5 0/3] selftests/vDSO: fix clang build errors, and Makefile cleanup

[Shuah Khan]

On 7/5/24 13:57, John Hubbard wrote:
> Hi Shuah,
> 
> These are for 6.10, as we just discussed.
> 
> Changes since v4:
> 
> 1) Subject line on patch #2/3: s/mm/vDSO/
> 
> 2) Added Muhammad's review tag.
> 

Applied to
https://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest.git/?h=fixes
for Linux 6.10

thanks,
-- Shuah