Descriptionsyscall: keep allocated C string live across call to Syscall
Given:
p := alloc()
fn_taking_ptr(p)
p is NOT recorded as live at the call to fn_taking_ptr:
it's not needed by the code following the call.
p was passed to fn_taking_ptr, and fn_taking_ptr must keep
it alive as long as it needs it.
In practice, fn_taking_ptr will keep its own arguments live
for as long as the function is executing.
But if instead you have:
p := alloc()
i := uintptr(unsafe.Pointer(p))
fn_taking_int(i)
p is STILL NOT recorded as live at the call to fn_taking_int:
it's not needed by the code following the call.
fn_taking_int is responsible for keeping its own arguments
live, but fn_taking_int is written to take an integer, so even
though fn_taking_int does keep its argument live, that argument
does not keep the allocated memory live, because the garbage
collector does not dereference integers.
The shorter form:
p := alloc()
fn_taking_int(uintptr(unsafe.Pointer(p)))
and the even shorter form:
fn_taking_int(uintptr(unsafe.Pointer(alloc())))
are both the same as the 3-line form above.
syscall.Syscall is like fn_taking_int: it is written to take a list
of integers, and yet those integers are sometimes pointers.
If there is no other copy of those pointers being kept live,
the memory they point at may be garbage collected during
the call to syscall.Syscall.
This is happening on Solaris: for whatever reason, the timing
is such that the garbage collector manages to free the string
argument to the open(2) system call before the system call
has been invoked.
Change the system call wrappers to insert explicit references
that will keep the allocations alive in the original frame
(and therefore preserve the memory) until after syscall.Syscall
has returned.
Should fix Solaris flakiness.
This is not a problem for cgo, because cgo wrappers have
correctly typed arguments.
Patch Set 1 #Patch Set 2 : diff -r 9e30a2df4e1d3babaf09895488730b26f829d768 https://code.google.com/p/go/ #Patch Set 3 : diff -r 9e30a2df4e1d3babaf09895488730b26f829d768 https://code.google.com/p/go/ #Patch Set 4 : diff -r 9e30a2df4e1d3babaf09895488730b26f829d768 https://code.google.com/p/go/ #Patch Set 5 : diff -r 9e30a2df4e1d3babaf09895488730b26f829d768 https://code.google.com/p/go/ #Patch Set 6 : diff -r ad5d9f8f9be743e72f89d85d8bd6348807bdac90 https://code.google.com/p/go/ #
MessagesTotal messages: 23
|