linux-kernel - Re: [RFC PATCH v2 5/6] uprobes/x86: Emulate rip-relative conditional "short" jmp's

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Date:	Mon, 7 Apr 2014 18:41:43 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Anton Arapov <aarapov@...hat.com>,
	David Long <dave.long@...aro.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Jonathan Lebon <jlebon@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 5/6] uprobes/x86: Emulate rip-relative
	conditional "short" jmp's

On 04/07, Oleg Nesterov wrote:
>
> > Incomplete, lacks "jcxz". Simple to fix. Anything else?
>
> Please see v2 below. Simplify the preprocessor hacks.

Finally some testing. This all even seems to work... Although so far
I only tested jz/jnz 8/32bit with this test-case:

	asm (
		".text\n"
		".globl test_0\n"
		"test_0:\n"

		"movq $0, %rax\n"
		"cmpq $0, %rax\n"

		".globl t_0_n; t_0_n:\n"
		"jnz 1f\n"

		".globl t_0_y; t_0_y:\n"
		"jz  2f\n"

		"1: ud2\n"
		"2: retq\n"
	);

	asm (
		".text\n"
		".globl test_1\n"
		"test_1:\n"

		"movq $1, %rax\n"
		"cmpq $0, %rax\n"

		".globl t_1_y; t_1_y:\n"
		"jz 1f\n"

		".globl t_1_n; t_1_n:\n"
		"jnz  2f\n"

		".org . + 1024\n"

		"1: ud2\n"
		"2: retq\n"
	);

	extern void test_0(void), test_1(void);

	int main(void)
	{
		test_0();
		test_1();
		return 0;
	}

it runs fine with t_{0,1}_{y,} probed.

As for "jcxz" support, it must be simple but I am still googling for
"jcxz for dummies". Will do tomorrow, probably I'll make a separate patch
for this to simlify the review.

Oleg.

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