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selftests/x86: build fsgsbase_restore.c with clang

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When building with clang, via:

    make LLVM=1 -C tools/testing/selftests

Fix this by moving the inline asm to "pure" assembly, in two new files:
clang_helpers_32.S, clang_helpers_64.S.

As a bonus, the pure asm avoids the need for ifdefs, and is now very
simple and easy on the eyes.

Acked-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
This commit is contained in:
John Hubbard 2024-07-04 00:24:27 -07:00 committed by Shuah Khan
parent bf967fb39e
commit 1158655317
4 changed files with 30 additions and 6 deletions
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2
tools/testing/selftests/x86/Makefile
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@ -113,6 +113,8 @@ endef
$(eval $(call extra-files,sysret_ss_attrs_64,thunks.S))
$(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))
# 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

11
tools/testing/selftests/x86/clang_helpers_32.S Normal file
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@ -0,0 +1,11 @@
/* SPDX-License-Identifier: GPL-2.0-only */
/*
* 32-bit assembly helpers for asm operations that lack support in both gcc and
* clang. For example, clang asm does not support segment prefixes.
*/
.global dereference_seg_base
dereference_seg_base:
mov %fs:(0), %eax
ret
.section .note.GNU-stack,"",%progbits

12
tools/testing/selftests/x86/clang_helpers_64.S Normal file
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@ -0,0 +1,12 @@
/* SPDX-License-Identifier: GPL-2.0-only */
/*
* 64-bit assembly helpers for asm operations that lack support in both gcc and
* clang. For example, clang asm does not support segment prefixes.
*/
.global dereference_seg_base
dereference_seg_base:
mov %gs:(0), %rax
ret
.section .note.GNU-stack,"",%progbits

11
tools/testing/selftests/x86/fsgsbase_restore.c
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@ -39,12 +39,11 @@
# define SEG "%fs"
#endif
static unsigned int dereference_seg_base(void)
{
int ret;
asm volatile ("mov %" SEG ":(0), %0" : "=rm" (ret));
return ret;
}
/*
* Defined in clang_helpers_[32|64].S, because unlike gcc, clang inline asm does
* not support segmentation prefixes.
*/
unsigned int dereference_seg_base(void);
static void init_seg(void)
{