Re: [patch 08/24] x86/entry: Convert Divide Error to IDTENTRY

Alexandre Chartre
2020-02-28T14:58:53Z

On 2/25/20 11:16 PM, Thomas Gleixner wrote:
> Convert #DE to IDTENTRY:
> - Implement the C entry point with DEFINE_IDTENTRY
> - Emit the ASM stub with DECLARE_IDTENTRY
> - Remove the ASM idtentry in 64bit
> - Remove the open coded ASM entry code in 32bit
> - Fixup the XEN/PV code
>
> No functional change.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> arch/x86/entry/entry_32.S | 7 -------
> arch/x86/entry/entry_64.S | 1 -
> arch/x86/include/asm/idtentry.h | 3 +++
> arch/x86/include/asm/traps.h | 3 ---
> arch/x86/kernel/idt.c | 2 +-
> arch/x86/kernel/traps.c | 7 ++++++-
> arch/x86/xen/enlighten_pv.c | 7 ++++++-
> arch/x86/xen/xen-asm_64.S | 2 +-
> 8 files changed, 17 insertions(+), 15 deletions(-)
>
> --- a/arch/x86/entry/entry_32.S
> +++ b/arch/x86/entry/entry_32.S
> @@ -1386,13 +1386,6 @@ SYM_CODE_START(alignment_check)
> jmp common_exception
> SYM_CODE_END(alignment_check)
>
> -SYM_CODE_START(divide_error)
> - ASM_CLAC
> - pushl $0 # no error code
> - pushl $do_divide_error
> - jmp common_exception
> -SYM_CODE_END(divide_error)
> -
> #ifdef CONFIG_X86_MCE
> SYM_CODE_START(machine_check)
> ASM_CLAC
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -1061,7 +1061,6 @@ apicinterrupt IRQ_WORK_VECTOR irq_work
> * Exception entry points.
> */
>
> -idtentry X86_TRAP_DE divide_error do_divide_error has_error_code=0
> idtentry X86_TRAP_OF overflow do_overflow has_error_code=0
> idtentry X86_TRAP_BP int3 do_int3 has_error_code=0
> idtentry X86_TRAP_BR bounds do_bounds has_error_code=0
> --- a/arch/x86/include/asm/idtentry.h
> +++ b/arch/x86/include/asm/idtentry.h
> @@ -76,4 +76,7 @@ static __always_inline void __##func(str
>
> #endif /* __ASSEMBLY__ */
>
> +/* Simple exception entries: */
> +DECLARE_IDTENTRY(X86_TRAP_DE, exc_divide_error);
> +

I think this macro has a tricky behavior because it will declare C functions
when included in a C file, and define assembly idtentry when included in an
assembly file.

I see your point which is to have a single statement which provides both C
and assembly functions, but this dual behavior is not obvious when reading
the code. Maybe add a comment to explain this behavior?

Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>

alex.

> #endif
> --- a/arch/x86/include/asm/traps.h
> +++ b/arch/x86/include/asm/traps.h
> @@ -11,7 +11,6 @@
>
> #define dotraplinkage __visible
>
> -asmlinkage void divide_error(void);
> asmlinkage void debug(void);
> asmlinkage void nmi(void);
> asmlinkage void int3(void);
> @@ -38,7 +37,6 @@ asmlinkage void machine_check(void);
> asmlinkage void simd_coprocessor_error(void);
>
> #if defined(CONFIG_X86_64) && defined(CONFIG_XEN_PV)
> -asmlinkage void xen_divide_error(void);
> asmlinkage void xen_xennmi(void);
> asmlinkage void xen_xendebug(void);
> asmlinkage void xen_int3(void);
> @@ -62,7 +60,6 @@ asmlinkage void xen_machine_check(void);
> asmlinkage void xen_simd_coprocessor_error(void);
> #endif
>
> -dotraplinkage void do_divide_error(struct pt_regs *regs, long error_code);
> dotraplinkage void do_debug(struct pt_regs *regs, long error_code);
> dotraplinkage void do_nmi(struct pt_regs *regs, long error_code);
> dotraplinkage void do_int3(struct pt_regs *regs, long error_code);
> --- a/arch/x86/kernel/idt.c
> +++ b/arch/x86/kernel/idt.c
> @@ -70,7 +70,7 @@ static const __initconst struct idt_data
> * set up TSS.
> */
> static const __initconst struct idt_data def_idts[] = {
> - INTG(X86_TRAP_DE, divide_error),
> + INTG(X86_TRAP_DE, asm_exc_divide_error),
> INTG(X86_TRAP_NMI, nmi),
> INTG(X86_TRAP_BR, bounds),
> INTG(X86_TRAP_UD, invalid_op),
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -279,6 +279,12 @@ static inline void __user *error_get_tra
> return (void __user *)uprobe_get_trap_addr(regs);
> }
>
> +DEFINE_IDTENTRY(exc_divide_error)
> +{
> + do_error_trap(regs, 0, "divide_error", X86_TRAP_DE, SIGFPE,
> + FPE_INTDIV, error_get_trap_addr(regs));
> +}
> +
> #define IP ((void __user *)uprobe_get_trap_addr(regs))
> #define DO_ERROR(trapnr, signr, sicode, addr, str, name) \
> dotraplinkage void do_##name(struct pt_regs *regs, long error_code) \
> @@ -286,7 +292,6 @@ dotraplinkage void do_##name(struct pt_r
> do_error_trap(regs, error_code, str, trapnr, signr, sicode, addr); \
> }
>
> -DO_ERROR(X86_TRAP_DE, SIGFPE, FPE_INTDIV, IP, "divide error", divide_error)
> DO_ERROR(X86_TRAP_OF, SIGSEGV, 0, NULL, "overflow", overflow)
> DO_ERROR(X86_TRAP_UD, SIGILL, ILL_ILLOPN, IP, "invalid opcode", invalid_op)
> DO_ERROR(X86_TRAP_OLD_MF, SIGFPE, 0, NULL, "coprocessor segment overrun", coprocessor_segment_overrun)
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -602,6 +602,11 @@ struct trap_array_entry {
> bool ist_okay;
> };
>
> +#define TRAP_ENTRY(func, ist_ok) { \
> + .orig = asm_##func, \
> + .xen = xen_asm_##func, \
> + .ist_okay = ist_ok }
> +
> static struct trap_array_entry trap_array[] = {
> { debug, xen_xendebug, true },
> { double_fault, xen_double_fault, true },
> @@ -615,7 +620,7 @@ static struct trap_array_entry trap_arra
> { entry_INT80_compat, xen_entry_INT80_compat, false },
> #endif
> { page_fault, xen_page_fault, false },
> - { divide_error, xen_divide_error, false },
> + TRAP_ENTRY(exc_divide_error, false ),
> { bounds, xen_bounds, false },
> { invalid_op, xen_invalid_op, false },
> { device_not_available, xen_device_not_available, false },
> --- a/arch/x86/xen/xen-asm_64.S
> +++ b/arch/x86/xen/xen-asm_64.S
> @@ -28,7 +28,7 @@ SYM_CODE_END(xen_\name)
> _ASM_NOKPROBE(xen_\name)
> .endm
>
> -xen_pv_trap divide_error
> +xen_pv_trap asm_exc_divide_error
> xen_pv_trap debug
> xen_pv_trap xendebug
> xen_pv_trap int3
>
>