Messages in this thread | | | Date | Wed, 18 Oct 2017 18:18:36 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86, syscalls: use SYSCALL_DEFINE() macros for sys_modify_ldt() |
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* Dave Hansen <dave.hansen@linux.intel.com> wrote:
> > We do not have tracepoints for sys_modify_ldt() because we define > it directly instead of using the normal SYSCALL_DEFINEx() macros. > > However, there is a reason sys_modify_ldt() does not use the macros: > it has an 'int' return type instead of 'unsigned long'. This is > a bug, but it's a bug cemented in the ABI. > > What does this mean? If we return -EINVAL from a function that > returns 'int', we have 0x00000000ffffffea in %rax. But, if we > return -EINVAL from a function returning 'unsigned long', we end > up with 0xffffffffffffffea in %rax, which is wrong. > > To work around this and maintain the 'int' behavior while using > the SYSCALL_DEFINEx() macros, so we add a cast to 'unsigned int' > in both implementations of sys_modify_ldt(). > > Cc: x86@kernel.org > Cc: Andy Lutomirski <luto@kernel.org> > Cc: Brian Gerst <brgerst@gmail.com> > > --- > > b/arch/x86/include/asm/syscalls.h | 2 +- > b/arch/x86/kernel/ldt.c | 16 +++++++++++++--- > b/arch/x86/um/ldt.c | 6 ++++-- > 3 files changed, 18 insertions(+), 6 deletions(-)
Fails to build on UML:
/home/mingo/tip/arch/x86/um/ldt.c:372:29: error: expected ‘)’ before ‘int’ SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr , ^ /home/mingo/tip/arch/x86/um/ldt.c:206:13: warning: ‘do_modify_ldt_skas’ defined but not used [-Wunused-function] static long do_modify_ldt_skas(int func, void __user *ptr,
etc.
Thanks,
Ingo
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