i386 and CFI assembler directives

["Clay Renko" <renkoc@xxxxxxxxx>]

Hi ppl,

I'm really puzzled about those CFI_* directives in system_call handler (i386).
what are them ? i found some red hat documentation, but which really
doesn't help.
I'm really trying to understand the first 4 lines in the system_call handler...
what are them ? what do they do ? why in this order ?
thanks a lot...

Clay

for convenience here's the code:

ENTRY(system_call)
	RING0_INT_FRAME			# can't unwind into user space anyway
	pushl %eax			# save orig_eax
	CFI_ADJUST_CFA_OFFSET 4
	SAVE_ALL
	...rest fo the code

here are the defines:


#define RING0_INT_FRAME \
	CFI_STARTPROC simple;\
	CFI_SIGNAL_FRAME;\
	CFI_DEF_CFA esp, 3*4;\
	/*CFI_OFFSET cs, -2*4;*/\
	CFI_OFFSET eip, -3*4

and in SAVE_ALL there are those CFI lines after each register push:

#define SAVE_ALL \
	cld; \
	pushl %es; \
	CFI_ADJUST_CFA_OFFSET 4;\
	/*CFI_REL_OFFSET es, 0;*/\
	pushl %ds; \
	CFI_ADJUST_CFA_OFFSET 4;\
	/*CFI_REL_OFFSET ds, 0;*/\
	pushl %eax; \
	CFI_ADJUST_CFA_OFFSET 4;\
	CFI_REL_OFFSET eax, 0;\
	pushl %ebp; \
	CFI_ADJUST_CFA_OFFSET 4;\
	CFI_REL_OFFSET ebp, 0;\
	pushl %edi; \
	CFI_ADJUST_CFA_OFFSET 4;\
	CFI_REL_OFFSET edi, 0;\
	pushl %esi; \
	CFI_ADJUST_CFA_OFFSET 4;\
	CFI_REL_OFFSET esi, 0;\
	pushl %edx; \
	CFI_ADJUST_CFA_OFFSET 4;\
	CFI_REL_OFFSET edx, 0;\
	pushl %ecx; \
	CFI_ADJUST_CFA_OFFSET 4;\
	CFI_REL_OFFSET ecx, 0;\
	pushl %ebx; \
	CFI_ADJUST_CFA_OFFSET 4;\
	CFI_REL_OFFSET ebx, 0;\
	movl $(__USER_DS), %edx; \
	movl %edx, %ds; \
	movl %edx, %es;

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