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Commit ab9e1858 authored by Daniel Glöckner's avatar Daniel Glöckner Committed by Ingo Molnar
Browse files

x86, math-emu: fix init_fpu for task != current 



Impact: fix math-emu related crash while using GDB/ptrace

init_fpu() calls finit to initialize a task's xstate, while finit always
works on the current task. If we use PTRACE_GETFPREGS on another
process and both processes did not already use floating point, we get
a null pointer exception in finit.

This patch creates a new function finit_task that takes a task_struct
parameter. finit becomes a wrapper that simply calls finit_task with
current. On the plus side this avoids many calls to get_current which
would each resolve to an inline assembler mov instruction.

An empty finit_task has been added to i387.h to avoid linker errors in
case the compiler still emits the call in init_fpu when
CONFIG_MATH_EMULATION is not defined.

The declaration of finit in i387.h has been removed as the remaining
code using this function gets its prototype from fpu_proto.h.

Signed-off-by: default avatarDaniel Glöckner <dg@emlix.com>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: "Pallipadi Venkatesh" <venkatesh.pallipadi@intel.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Bill Metzenthen <billm@melbpc.org.au>
LKML-Reference: <E1Lew31-0004il-Fg@mailer.emlix.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent dd39ecf5

arch/x86/include/asm/i387.h

+7 −1
Original line number Diff line number Diff line
@@ -172,7 +172,13 @@ static inline void __save_init_fpu(struct task_struct *tsk) 


#else  /* CONFIG_X86_32 */



extern void finit(void);

#ifdef CONFIG_MATH_EMULATION

extern void finit_task(struct task_struct *tsk);

#else

static inline void finit_task(struct task_struct *tsk)

{

}

#endif



static inline void tolerant_fwait(void)

{

arch/x86/kernel/i387.c

+1 −1
Original line number Diff line number Diff line
@@ -136,7 +136,7 @@ int init_fpu(struct task_struct *tsk) 
#ifdef CONFIG_X86_32

	if (!HAVE_HWFP) {

		memset(tsk->thread.xstate, 0, xstate_size);

		finit();

		finit_task(tsk);

		set_stopped_child_used_math(tsk);

		return 0;

	}

arch/x86/math-emu/fpu_aux.c

+20 −11
Original line number Diff line number Diff line
@@ -30,20 +30,29 @@ static void fclex(void) 
}



/* Needs to be externally visible */

void finit(void)

void finit_task(struct task_struct *tsk)

{

	control_word = 0x037f;

	partial_status = 0;

	top = 0;		/* We don't keep top in the status word internally. */

	fpu_tag_word = 0xffff;

	struct i387_soft_struct *soft = &tsk->thread.xstate->soft;

	struct address *oaddr, *iaddr;

	soft->cwd = 0x037f;

	soft->swd = 0;

	soft->ftop = 0;	/* We don't keep top in the status word internally. */

	soft->twd = 0xffff;

	/* The behaviour is different from that detailed in

	   Section 15.1.6 of the Intel manual */

	operand_address.offset = 0;

	operand_address.selector = 0;

	instruction_address.offset = 0;

	instruction_address.selector = 0;

	instruction_address.opcode = 0;

	no_ip_update = 1;

	oaddr = (struct address *)&soft->foo;

	oaddr->offset = 0;

	oaddr->selector = 0;

	iaddr = (struct address *)&soft->fip;

	iaddr->offset = 0;

	iaddr->selector = 0;

	iaddr->opcode = 0;

	soft->no_update = 1;

}



void finit(void)

{

	finit_task(current);

}



/*