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@google.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

diff --git a/arch/arc/Makefile b/arch/arc/Makefile
index 601ed173080b7c7706ba8a149a94e87eab2746c7..fc6ff8f09f236fd764f574fd2f9e5c5f75ce1245 100644 (file)
--- 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 2efb0625331d6d5a6b6f8b1558a05e6e3cc5679e..741712d4d6ff613eb687125f084a87399030283d 100644 (file)
--- 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 576a238434a141d552af52bd6d4f730cb8e5b4a8..9a2849756022c01c2b3c6da9b7b5a0e371ed2e20 100644 (file)
--- 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 4e5dbe7617a1570ebb4e7ad661c6c51337e82b6d..61fd1ce63c56ac499130c6ffcf87471b0398fe06 100644 (file)
--- 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 894e696bddaa3ca3fab6bdca6ed4f7ac451bb290..bb6d8c5ff2e93d989961caf796c7d3c2188cb832 100644 (file)
--- 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) }