[PATCH v2 3/6] selftests/x86: build sysret_rip.c with clang

John Hubbard
2024-05-27T21:01:15Z

First of all, in order to build with clang at all, one must first apply
Valentin Obst's build fix for LLVM [1]. Once that is done, then when
building with clang, via:

make LLVM=1 -C tools/testing/selftests

...the build fails because clang's inline asm doesn't support all of the
features that are used in the asm() snippet in sysret_rip.c.

Fix this by moving the asm code into the clang_helpers_64.S file, where
it can be built with the assembler's full set of features.

[1] https://lore.kernel.org/all/20240329-selftests-libmk-llvm-rfc-v1-1-2f9ed7d1c49f@valentinobst.de/

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
tools/testing/selftests/x86/Makefile | 1 +
.../testing/selftests/x86/clang_helpers_64.S | 16 +++++++++++++++
tools/testing/selftests/x86/sysret_rip.c | 20 ++++++-------------
3 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile
index 99bc2ef84f5a..d0bb32bd5538 100644
--- a/tools/testing/selftests/x86/Makefile
+++ b/tools/testing/selftests/x86/Makefile
@@ -115,6 +115,7 @@ $(eval $(call extra-files,ptrace_syscall_32,raw_syscall_helper_32.S))
$(eval $(call extra-files,test_syscall_vdso_32,thunks_32.S))
$(eval $(call extra-files,fsgsbase_restore_64,clang_helpers_64.S))
$(eval $(call extra-files,fsgsbase_restore_32,clang_helpers_32.S))
+$(eval $(call extra-files,sysret_rip_64,clang_helpers_64.S))

# check_initial_reg_state is special: it needs a custom entry, and it
# needs to be static so that its interpreter doesn't destroy its initial
diff --git a/tools/testing/selftests/x86/clang_helpers_64.S b/tools/testing/selftests/x86/clang_helpers_64.S
index 0d81c71cad97..185a69dbf39c 100644
--- a/tools/testing/selftests/x86/clang_helpers_64.S
+++ b/tools/testing/selftests/x86/clang_helpers_64.S
@@ -9,4 +9,20 @@ dereference_seg_base:
mov %gs:(0), %rax
ret

+.global test_page
+.global test_syscall_insn
+
+.pushsection ".text", "ax"
+.balign 4096
+test_page: .globl test_page
+ .fill 4094,1,0xcc
+
+test_syscall_insn:
+ syscall
+
+.ifne . - test_page - 4096
+ .error "test page is not one page long"
+.endif
+.popsection
+
.section .note.GNU-stack,"",%progbits
diff --git a/tools/testing/selftests/x86/sysret_rip.c b/tools/testing/selftests/x86/sysret_rip.c
index 84d74be1d902..b30de9aaa6d4 100644
--- a/tools/testing/selftests/x86/sysret_rip.c
+++ b/tools/testing/selftests/x86/sysret_rip.c
@@ -22,21 +22,13 @@
#include <sys/mman.h>
#include <assert.h>

-
-asm (
- ".pushsection \".text\", \"ax\"\n\t"
- ".balign 4096\n\t"
- "test_page: .globl test_page\n\t"
- ".fill 4094,1,0xcc\n\t"
- "test_syscall_insn:\n\t"
- "syscall\n\t"
- ".ifne . - test_page - 4096\n\t"
- ".error \"test page is not one page long\"\n\t"
- ".endif\n\t"
- ".popsection"
- );
-
+/*
+ * These items are in clang_helpers_64.S, in order to avoid clang inline asm
+ * limitations:
+ */
+void test_syscall_ins(void);
extern const char test_page[];
+
static void const *current_test_page_addr = test_page;

static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *),
--
2.45.1