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bf14ef193b
commit 4486c579cb disabled vdso
clock_gettime on arm due to a Linux kernel bug that was not understood
at the time, whereby the vdso function silently produced
catastrophically wrong results on some systems.
since then, the bug was tracked down to the way the arm kernel
disabled use of vdso clock_gettime on kernels where the necessary
timer was not available or was disabled. it simply patched out the
symbols, but it only did this for the legacy time32 functions, and
left the time64 function in place but non-operational. kernel commit
4405bdf3c57ec28d606bdf5325f1167505bfdcd4 (first present in 5.8)
provided the fix.
if this were a bug that impacted all users of the broken kernel
versions, we could probably ignore it and assume it had been patched
or replaced. however, it's very possible that these kernels appear in
the wild in devices running time32 userspace (glibc, musl 1.1.x, or
some other environment) where they appear to work fine, but where our
new binaries would fail catastrophically if we used the time64 vdso
function.
since the kernel has not (yet?) given us a way to probe for the
working time64 vdso function semantically, we work around the problem
by refusing to use the time64 one unless the time32 one is also
present. this will revert to not using vdso at all if the time32 one
is ever removed, but at least that's safe against wrong results and is
just a missed optimization.
111 lines
3.2 KiB
C
111 lines
3.2 KiB
C
#define __SYSCALL_LL_E(x) \
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((union { long long ll; long l[2]; }){ .ll = x }).l[0], \
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((union { long long ll; long l[2]; }){ .ll = x }).l[1]
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#define __SYSCALL_LL_O(x) 0, __SYSCALL_LL_E((x))
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#ifdef __thumb__
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/* Avoid use of r7 in asm constraints when producing thumb code,
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* since it's reserved as frame pointer and might not be supported. */
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#define __ASM____R7__
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#define __asm_syscall(...) do { \
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__asm__ __volatile__ ( "mov %1,r7 ; mov r7,%2 ; svc 0 ; mov r7,%1" \
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: "=r"(r0), "=&r"((int){0}) : __VA_ARGS__ : "memory"); \
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return r0; \
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} while (0)
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#else
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#define __ASM____R7__ __asm__("r7")
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#define __asm_syscall(...) do { \
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__asm__ __volatile__ ( "svc 0" \
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: "=r"(r0) : __VA_ARGS__ : "memory"); \
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return r0; \
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} while (0)
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#endif
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/* For thumb2, we can allow 8-bit immediate syscall numbers, saving a
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* register in the above dance around r7. Does not work for thumb1 where
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* only movs, not mov, supports immediates, and we can't use movs because
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* it doesn't support high regs. */
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#ifdef __thumb2__
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#define R7_OPERAND "rI"(r7)
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#else
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#define R7_OPERAND "r"(r7)
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#endif
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static inline long __syscall0(long n)
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{
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register long r7 __ASM____R7__ = n;
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register long r0 __asm__("r0");
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__asm_syscall(R7_OPERAND);
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}
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static inline long __syscall1(long n, long a)
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{
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register long r7 __ASM____R7__ = n;
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register long r0 __asm__("r0") = a;
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__asm_syscall(R7_OPERAND, "0"(r0));
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}
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static inline long __syscall2(long n, long a, long b)
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{
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register long r7 __ASM____R7__ = n;
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register long r0 __asm__("r0") = a;
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register long r1 __asm__("r1") = b;
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__asm_syscall(R7_OPERAND, "0"(r0), "r"(r1));
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}
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static inline long __syscall3(long n, long a, long b, long c)
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{
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register long r7 __ASM____R7__ = n;
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register long r0 __asm__("r0") = a;
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register long r1 __asm__("r1") = b;
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register long r2 __asm__("r2") = c;
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__asm_syscall(R7_OPERAND, "0"(r0), "r"(r1), "r"(r2));
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}
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static inline long __syscall4(long n, long a, long b, long c, long d)
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{
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register long r7 __ASM____R7__ = n;
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register long r0 __asm__("r0") = a;
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register long r1 __asm__("r1") = b;
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register long r2 __asm__("r2") = c;
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register long r3 __asm__("r3") = d;
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__asm_syscall(R7_OPERAND, "0"(r0), "r"(r1), "r"(r2), "r"(r3));
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}
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static inline long __syscall5(long n, long a, long b, long c, long d, long e)
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{
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register long r7 __ASM____R7__ = n;
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register long r0 __asm__("r0") = a;
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register long r1 __asm__("r1") = b;
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register long r2 __asm__("r2") = c;
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register long r3 __asm__("r3") = d;
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register long r4 __asm__("r4") = e;
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__asm_syscall(R7_OPERAND, "0"(r0), "r"(r1), "r"(r2), "r"(r3), "r"(r4));
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}
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static inline long __syscall6(long n, long a, long b, long c, long d, long e, long f)
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{
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register long r7 __ASM____R7__ = n;
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register long r0 __asm__("r0") = a;
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register long r1 __asm__("r1") = b;
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register long r2 __asm__("r2") = c;
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register long r3 __asm__("r3") = d;
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register long r4 __asm__("r4") = e;
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register long r5 __asm__("r5") = f;
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__asm_syscall(R7_OPERAND, "0"(r0), "r"(r1), "r"(r2), "r"(r3), "r"(r4), "r"(r5));
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}
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#define SYSCALL_FADVISE_6_ARG
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#define SYSCALL_IPC_BROKEN_MODE
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#define VDSO_USEFUL
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#define VDSO_CGT32_SYM "__vdso_clock_gettime"
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#define VDSO_CGT32_VER "LINUX_2.6"
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#define VDSO_CGT_SYM "__vdso_clock_gettime64"
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#define VDSO_CGT_VER "LINUX_2.6"
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#define VDSO_CGT_WORKAROUND 1
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