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Commit 6716dbbd authored by Vineet Gupta's avatar Vineet Gupta
Browse files

ARC: dw2 unwind: switch to .eh_frame based unwinding 



So finally after almost 8 years of dealing with .debug_frame, we are
finally switching to .eh_frame. The reason being stripped kernel
binaries had non-functional unwinder as .debug_frame was gone.
Also, in general .eh_frame seems more common way of doing unwinding.

This also folds a revert of f52e126c ("ARC: unwind: ensure that
.debug_frame is generated (vs. .eh_frame)") to ensure that we start
getting .eh_frame

Reported-by: default avatarDaniel Mentz <danielmentz@google.com>
Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
parent d040876b

arch/arc/Makefile

+2 −0
Original line number Diff line number Diff line
@@ -66,6 +66,8 @@ endif 


endif



cflags-$(CONFIG_ARC_DW2_UNWIND)		+= -fasynchronous-unwind-tables



# By default gcc 4.8 generates dwarf4 which kernel unwinder can't grok

ifeq ($(atleast_gcc48),y)

cflags-$(CONFIG_ARC_DW2_UNWIND)		+= -gdwarf-2

arch/arc/kernel/entry.S

+0 −12
Original line number Diff line number Diff line
@@ -61,18 +61,6 @@ ENTRY(ret_from_fork) 
	b    ret_from_exception

END(ret_from_fork)



#ifdef CONFIG_ARC_DW2_UNWIND

; Workaround for bug 94179 (STAR ):

; Despite -fasynchronous-unwind-tables, linker is not making dwarf2 unwinder

; section (.debug_frame) as loadable. So we force it here.

; This also fixes STAR 9000487933 where the prev-workaround (objcopy --setflag)

; would not work after a clean build due to kernel build system dependencies.

.section .debug_frame, "wa",@progbits



; Reset to .text as this file is included in entry-<isa>.S

.section .text, "ax",@progbits

#endif



;################### Non TLB Exception Handling #############################



; ---------------------------------------------

arch/arc/kernel/module.c

+4 −9
Original line number Diff line number Diff line
@@ -22,13 +22,9 @@ static inline void arc_write_me(unsigned short *addr, unsigned long value) 
	*(addr + 1) = (value & 0xffff);

}



/* ARC specific section quirks - before relocation loop in generic loader

 *

 * For dwarf unwinding out of modules, this needs to

 * 1. Ensure the .debug_frame is allocatable (ARC Linker bug: despite

 *    -fasynchronous-unwind-tables it doesn't).

 * 2. Since we are iterating thru sec hdr tbl anyways, make a note of

 *    the exact section index, for later use.

/*

 * This gets called before relocation loop in generic loader

 * Make a note of the section index of unwinding section

 */

int module_frob_arch_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs,

			      char *secstr, struct module *mod)
@@ -40,8 +36,7 @@ int module_frob_arch_sections(Elf_Ehdr *hdr, Elf_Shdr *sechdrs, 
	mod->arch.unw_info = NULL;



	for (i = 1; i < hdr->e_shnum; i++) {

		if (strcmp(secstr+sechdrs[i].sh_name, ".debug_frame") == 0) {

			sechdrs[i].sh_flags |= SHF_ALLOC;

		if (strcmp(secstr+sechdrs[i].sh_name, ".eh_frame") == 0) {

			mod->arch.unw_sec_idx = i;

			break;

		}

arch/arc/kernel/unwind.c

+2 −3
Original line number Diff line number Diff line
@@ -111,7 +111,7 @@ UNW_REGISTER_INFO}; 
#define DW_EH_PE_indirect 0x80

#define DW_EH_PE_omit     0xff



#define CIE_ID	0xffffffffUL

#define CIE_ID	0



typedef unsigned long uleb128_t;

typedef signed long sleb128_t;
@@ -510,8 +510,7 @@ static const u32 *__cie_for_fde(const u32 *fde) 
{

	const u32 *cie;



	/* cie = fde + 1 - fde[1] / sizeof(*fde); */

	cie = (u32 *) fde[1];

	cie = fde + 1 - fde[1] / sizeof(*fde);



	return cie;

}

arch/arc/kernel/vmlinux.lds.S

+5 −10
Original line number Diff line number Diff line
@@ -84,7 +84,7 @@ SECTIONS 


	/*

	 * .exit.text is discard at runtime, not link time, to deal with

	 * references from .debug_frame

	 * references from unwinding sections

	 * It will be init freed, being inside [__init_start : __init_end]

	 */

	.exit.text : { EXIT_TEXT }
@@ -120,18 +120,13 @@ SECTIONS 


#ifdef CONFIG_ARC_DW2_UNWIND

	. = ALIGN(PAGE_SIZE);

	.debug_frame  : {

	.eh_frame  : {

		__start_unwind = .;

		*(.debug_frame)

		*(.eh_frame)

		__end_unwind = .;

	}

	/*

	 * gcc 4.8 generates this for -fasynchonous-unwind-tables,

	 * while we still use the .debug_frame based unwinder

	 */

	/DISCARD/ : {	*(.eh_frame) }

#else

	/DISCARD/ : {	*(.debug_frame) }

	/DISCARD/ : {	*(.eh_frame) }

#endif



	NOTES
@@ -148,7 +143,7 @@ SECTIONS 
	}



#ifndef CONFIG_DEBUG_INFO

	/* open-coded because we need .debug_frame seperately for unwinding */

	/DISCARD/ : { *(.debug_frame) }

	/DISCARD/ : { *(.debug_aranges) }

	/DISCARD/ : { *(.debug_pubnames) }

	/DISCARD/ : { *(.debug_info) }