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Date: Mon, 19 Sep 2016 14:49:33 -0700
From: Vineet Gupta <Vineet.Gupta1@...opsys.com>
To: <danielmentz@...gle.com>
CC: <linux-kernel@...r.kernel.org>,
<linux-snps-arc@...ts.infradead.org>,
<Alexey.Brodkin@...opsys.com>,
Vineet Gupta <Vineet.Gupta1@...opsys.com>
Subject: [PATCH 3/3] 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 f52e126cc747 ("ARC: unwind: ensure that
.debug_frame is generated (vs. .eh_frame)") to ensure that we start
getting .eh_frame
Reported-by: Daniel Mentz <danielmentz@...gle.com>
Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
---
arch/arc/Makefile | 2 ++
arch/arc/kernel/entry.S | 12 ------------
arch/arc/kernel/module.c | 13 ++++---------
arch/arc/kernel/unwind.c | 5 ++---
arch/arc/kernel/vmlinux.lds.S | 15 +++++----------
5 files changed, 13 insertions(+), 34 deletions(-)
diff --git a/arch/arc/Makefile b/arch/arc/Makefile
index 601ed173080b..fc6ff8f09f23 100644
--- a/arch/arc/Makefile
+++ b/arch/arc/Makefile
@@ -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
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index 2efb0625331d..741712d4d6ff 100644
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -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 #############################
; ---------------------------------------------
diff --git a/arch/arc/kernel/module.c b/arch/arc/kernel/module.c
index 576a238434a1..9a2849756022 100644
--- a/arch/arc/kernel/module.c
+++ b/arch/arc/kernel/module.c
@@ -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;
}
diff --git a/arch/arc/kernel/unwind.c b/arch/arc/kernel/unwind.c
index 4e5dbe7617a1..61fd1ce63c56 100644
--- a/arch/arc/kernel/unwind.c
+++ b/arch/arc/kernel/unwind.c
@@ -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;
}
diff --git a/arch/arc/kernel/vmlinux.lds.S b/arch/arc/kernel/vmlinux.lds.S
index 894e696bddaa..bb6d8c5ff2e9 100644
--- a/arch/arc/kernel/vmlinux.lds.S
+++ b/arch/arc/kernel/vmlinux.lds.S
@@ -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) }
--
2.7.4
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