tree 1a746dc22ed12badc30198c8eb5065535a76bbb0
parent ac69e973ff0660e455f4ba1ddd4dcce4ae70ed1a
author Linus Torvalds <torvalds@g5.osdl.org> 1145390568 -0700
committer Linus Torvalds <torvalds@g5.osdl.org> 1145390568 -0700

x86: don't allow tail-calls in sys_ftruncate[64]()

Gcc thinks it owns the incoming argument stack, but that's not true for
"asmlinkage" functions, and it corrupts the caller-set-up argument stack
when it pushes the third argument onto the stack.  Which can result in
%ebx getting corrupted in user space.

Now, normally nobody sane would ever notice, since libc will save and
restore %ebx anyway over the system call, but it's still wrong.

I'd much rather have "asmlinkage" tell gcc directly that it doesn't own
the stack, but no such attribute exists, so we're stuck with our hacky
manual "prevent_tail_call()" macro once more (we've had the same issue
before with sys_waitpid() and sys_wait4()).

Thanks to Hans-Werner Hilse <hilse@sub.uni-goettingen.de> for reporting
the issue and testing the fix.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>