On Tue, Dec 16, 2025 at 10:26 PM H. Peter Anvin <[email protected]> wrote: > > Abstract out the calling of true system calls from the vdso into > macros. > > It has been a very long time since gcc did not allow %ebx or %ebp in > inline asm in 32-bit PIC mode; remove the corresponding hacks. > > Remove the use of memory output constraints in gettimeofday.h in favor > of "memory" clobbers. The resulting code is identical for the current > use cases, as the system call is usually a terminal fallback anyway, > and it merely complicates the macroization. > > This patch adds only a handful of more lines of code than it removes, > and in fact could be made substantially smaller by removing the macros > for the argument counts that aren't currently used, however, it seems > better to be general from the start. > > [ v3: remove stray comment from prototyping; remove VDSO_SYSCALL6() > since it would require special handling on 32 bits and is > currently unused. (Uros Biszjak) > > Indent nested preprocessor directives. ] > > Signed-off-by: H. Peter Anvin (Intel) <[email protected]>
Acked-by: Uros Bizjak <[email protected]> > --- > arch/x86/include/asm/vdso/gettimeofday.h | 108 ++--------------------- > arch/x86/include/asm/vdso/sys_call.h | 103 +++++++++++++++++++++ > 2 files changed, 111 insertions(+), 100 deletions(-) > create mode 100644 arch/x86/include/asm/vdso/sys_call.h > > diff --git a/arch/x86/include/asm/vdso/gettimeofday.h > b/arch/x86/include/asm/vdso/gettimeofday.h > index 73b2e7ee8f0f..3cf214cc4a75 100644 > --- a/arch/x86/include/asm/vdso/gettimeofday.h > +++ b/arch/x86/include/asm/vdso/gettimeofday.h > @@ -18,6 +18,7 @@ > #include <asm/msr.h> > #include <asm/pvclock.h> > #include <clocksource/hyperv_timer.h> > +#include <asm/vdso/sys_call.h> > > #define VDSO_HAS_TIME 1 > > @@ -53,130 +54,37 @@ extern struct ms_hyperv_tsc_page hvclock_page > __attribute__((visibility("hidden"))); > #endif > > -#ifndef BUILD_VDSO32 > - > static __always_inline > long clock_gettime_fallback(clockid_t _clkid, struct __kernel_timespec *_ts) > { > - long ret; > - > - asm ("syscall" : "=a" (ret), "=m" (*_ts) : > - "0" (__NR_clock_gettime), "D" (_clkid), "S" (_ts) : > - "rcx", "r11"); > - > - return ret; > + return VDSO_SYSCALL2(clock_gettime,64,_clkid,_ts); > } > > static __always_inline > long gettimeofday_fallback(struct __kernel_old_timeval *_tv, > struct timezone *_tz) > { > - long ret; > - > - asm("syscall" : "=a" (ret) : > - "0" (__NR_gettimeofday), "D" (_tv), "S" (_tz) : "memory"); > - > - return ret; > + return VDSO_SYSCALL2(gettimeofday,,_tv,_tz); > } > > static __always_inline > long clock_getres_fallback(clockid_t _clkid, struct __kernel_timespec *_ts) > { > - long ret; > - > - asm ("syscall" : "=a" (ret), "=m" (*_ts) : > - "0" (__NR_clock_getres), "D" (_clkid), "S" (_ts) : > - "rcx", "r11"); > - > - return ret; > + return VDSO_SYSCALL2(clock_getres,_time64,_clkid,_ts); > } > > -#else > - > -static __always_inline > -long clock_gettime_fallback(clockid_t _clkid, struct __kernel_timespec *_ts) > -{ > - long ret; > - > - asm ( > - "mov %%ebx, %%edx \n" > - "mov %[clock], %%ebx \n" > - "call __kernel_vsyscall \n" > - "mov %%edx, %%ebx \n" > - : "=a" (ret), "=m" (*_ts) > - : "0" (__NR_clock_gettime64), [clock] "g" (_clkid), "c" (_ts) > - : "edx"); > - > - return ret; > -} > +#ifndef CONFIG_X86_64 > > static __always_inline > long clock_gettime32_fallback(clockid_t _clkid, struct old_timespec32 *_ts) > { > - long ret; > - > - asm ( > - "mov %%ebx, %%edx \n" > - "mov %[clock], %%ebx \n" > - "call __kernel_vsyscall \n" > - "mov %%edx, %%ebx \n" > - : "=a" (ret), "=m" (*_ts) > - : "0" (__NR_clock_gettime), [clock] "g" (_clkid), "c" (_ts) > - : "edx"); > - > - return ret; > -} > - > -static __always_inline > -long gettimeofday_fallback(struct __kernel_old_timeval *_tv, > - struct timezone *_tz) > -{ > - long ret; > - > - asm( > - "mov %%ebx, %%edx \n" > - "mov %2, %%ebx \n" > - "call __kernel_vsyscall \n" > - "mov %%edx, %%ebx \n" > - : "=a" (ret) > - : "0" (__NR_gettimeofday), "g" (_tv), "c" (_tz) > - : "memory", "edx"); > - > - return ret; > + return VDSO_SYSCALL2(clock_gettime,,_clkid,_ts); > } > > static __always_inline long > -clock_getres_fallback(clockid_t _clkid, struct __kernel_timespec *_ts) > -{ > - long ret; > - > - asm ( > - "mov %%ebx, %%edx \n" > - "mov %[clock], %%ebx \n" > - "call __kernel_vsyscall \n" > - "mov %%edx, %%ebx \n" > - : "=a" (ret), "=m" (*_ts) > - : "0" (__NR_clock_getres_time64), [clock] "g" (_clkid), "c" > (_ts) > - : "edx"); > - > - return ret; > -} > - > -static __always_inline > -long clock_getres32_fallback(clockid_t _clkid, struct old_timespec32 *_ts) > +clock_getres32_fallback(clockid_t _clkid, struct old_timespec32 *_ts) > { > - long ret; > - > - asm ( > - "mov %%ebx, %%edx \n" > - "mov %[clock], %%ebx \n" > - "call __kernel_vsyscall \n" > - "mov %%edx, %%ebx \n" > - : "=a" (ret), "=m" (*_ts) > - : "0" (__NR_clock_getres), [clock] "g" (_clkid), "c" (_ts) > - : "edx"); > - > - return ret; > + return VDSO_SYSCALL2(clock_getres,,_clkid,_ts); > } > > #endif > diff --git a/arch/x86/include/asm/vdso/sys_call.h > b/arch/x86/include/asm/vdso/sys_call.h > new file mode 100644 > index 000000000000..dcfd17c6dd57 > --- /dev/null > +++ b/arch/x86/include/asm/vdso/sys_call.h > @@ -0,0 +1,103 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * Macros for issuing an inline system call from the vDSO. > + */ > + > +#ifndef X86_ASM_VDSO_SYS_CALL_H > +#define X86_ASM_VDSO_SYS_CALL_H > + > +#include <linux/compiler.h> > +#include <asm/cpufeatures.h> > +#include <asm/alternative.h> > + > +#ifdef CONFIG_X86_64 > +# define __sys_instr "syscall" > +# define __sys_clobber "rcx", "r11", "memory" > +# define __sys_nr(x,y) __NR_ ## x > +# define __sys_reg1 "rdi" > +# define __sys_reg2 "rsi" > +# define __sys_reg3 "rdx" > +# define __sys_reg4 "r10" > +# define __sys_reg5 "r8" > +#else > +# define __sys_instr "call __kernel_vsyscall" > +# define __sys_clobber "memory" > +# define __sys_nr(x,y) __NR_ ## x ## y > +# define __sys_reg1 "ebx" > +# define __sys_reg2 "ecx" > +# define __sys_reg3 "edx" > +# define __sys_reg4 "esi" > +# define __sys_reg5 "edi" > +#endif > + > +/* > + * Example usage: > + * > + * result = VDSO_SYSCALL3(foo,64,x,y,z); > + * > + * ... calls foo(x,y,z) on 64 bits, and foo64(x,y,z) on 32 bits. > + * > + * VDSO_SYSCALL6() is currently missing, because it would require > + * special handling for %ebp on 32 bits when the vdso is compiled with > + * frame pointers enabled (the default on 32 bits.) Add it as a special > + * case when and if it becomes necessary. > + */ > +#define _VDSO_SYSCALL(name,suf32,...) \ > + ({ \ > + long _sys_num_ret = __sys_nr(name,suf32); \ > + asm_inline volatile( \ > + __sys_instr \ > + : "+a" (_sys_num_ret) \ > + : __VA_ARGS__ \ > + : __sys_clobber); \ > + _sys_num_ret; \ > + }) > + > +#define VDSO_SYSCALL0(name,suf32) \ > + _VDSO_SYSCALL(name,suf32) > +#define VDSO_SYSCALL1(name,suf32,a1) \ > + ({ \ > + register long _sys_arg1 asm(__sys_reg1) = (long)(a1); \ > + _VDSO_SYSCALL(name,suf32, \ > + "r" (_sys_arg1)); \ > + }) > +#define VDSO_SYSCALL2(name,suf32,a1,a2) \ > + ({ \ > + register long _sys_arg1 asm(__sys_reg1) = (long)(a1); \ > + register long _sys_arg2 asm(__sys_reg2) = (long)(a2); \ > + _VDSO_SYSCALL(name,suf32, \ > + "r" (_sys_arg1), "r" (_sys_arg2)); \ > + }) > +#define VDSO_SYSCALL3(name,suf32,a1,a2,a3) \ > + ({ \ > + register long _sys_arg1 asm(__sys_reg1) = (long)(a1); \ > + register long _sys_arg2 asm(__sys_reg2) = (long)(a2); \ > + register long _sys_arg3 asm(__sys_reg3) = (long)(a3); \ > + _VDSO_SYSCALL(name,suf32, \ > + "r" (_sys_arg1), "r" (_sys_arg2), \ > + "r" (_sys_arg3)); \ > + }) > +#define VDSO_SYSCALL4(name,suf32,a1,a2,a3,a4) \ > + ({ \ > + register long _sys_arg1 asm(__sys_reg1) = (long)(a1); \ > + register long _sys_arg2 asm(__sys_reg2) = (long)(a2); \ > + register long _sys_arg3 asm(__sys_reg3) = (long)(a3); \ > + register long _sys_arg4 asm(__sys_reg4) = (long)(a4); \ > + _VDSO_SYSCALL(name,suf32, \ > + "r" (_sys_arg1), "r" (_sys_arg2), \ > + "r" (_sys_arg3), "r" (_sys_arg4)); \ > + }) > +#define VDSO_SYSCALL5(name,suf32,a1,a2,a3,a4,a5) \ > + ({ \ > + register long _sys_arg1 asm(__sys_reg1) = (long)(a1); \ > + register long _sys_arg2 asm(__sys_reg2) = (long)(a2); \ > + register long _sys_arg3 asm(__sys_reg3) = (long)(a3); \ > + register long _sys_arg4 asm(__sys_reg4) = (long)(a4); \ > + register long _sys_arg5 asm(__sys_reg5) = (long)(a5); \ > + _VDSO_SYSCALL(name,suf32, \ > + "r" (_sys_arg1), "r" (_sys_arg2), \ > + "r" (_sys_arg3), "r" (_sys_arg4), \ > + "r" (_sys_arg5)); \ > + }) > + > +#endif /* X86_VDSO_SYS_CALL_H */ > -- > 2.52.0 >
