linux/arch/arm/kernel
Russell King 6760b10960 ARM: fix vmlinux.lds.S discarding sections
We are seeing linker errors caused by sections being discarded, despite
the linker script trying to keep them.  The result is (eg):

`.exit.text' referenced in section `.alt.smp.init' of drivers/built-in.o: defined in discarded section `.exit.text' of drivers/built-in.o
`.exit.text' referenced in section `.alt.smp.init' of net/built-in.o: defined in discarded section `.exit.text' of net/built-in.o

This is the relevent part of the linker script (reformatted to make it
clearer):
| SECTIONS
| {
| /*
| * unwind exit sections must be discarded before the rest of the
| * unwind sections get included.
| */
| /DISCARD/ : {
| *(.ARM.exidx.exit.text)
| *(.ARM.extab.exit.text)
| }
| ...
| .exit.text : {
| *(.exit.text)
| *(.memexit.text)
| }
| ...
| /DISCARD/ : {
| *(.exit.text)
| *(.memexit.text)
| *(.exit.data)
| *(.memexit.data)
| *(.memexit.rodata)
| *(.exitcall.exit)
| *(.discard)
| *(.discard.*)
| }
| }

Now, this is what the linker manual says about discarded output sections:

|    The special output section name `/DISCARD/' may be used to discard
| input sections.  Any input sections which are assigned to an output
| section named `/DISCARD/' are not included in the output file.

No questions, no exceptions. It doesn't say "unless they are listed
before the /DISCARD/ section." Now, this is what asn-generic/vmlinux.lds.S
says:
| /*
|  * Default discarded sections.
|  *
|  * Some archs want to discard exit text/data at runtime rather than
|  * link time due to cross-section references such as alt instructions,
|  * bug table, eh_frame, etc. DISCARDS must be the last of output
|  * section definitions so that such archs put those in earlier section
|  * definitions.
|  */

And guess what - the list _always_ includes .exit.text etc.

Now, what's actually happening is that the linker is reading the script,
and it finds the first /DISCARD/ output section at the beginning of the
script. It continues reading the script, and finds the 'DISCARD' macro
at the end, which having been postprocessed results in another
/DISCARD/ output section. As the linker already contains the earlier
/DISCARD/ output section, it adds it to that existing section, so it
effectively is placed at the start. This can be seen by using the -M
option to ld:

| Linker script and memory map
|
|                 0xc037c080                jiffies = jiffies_64
|
| /DISCARD/
|  *(.ARM.exidx.exit.text)
|  *(.ARM.extab.exit.text)
|  *(.exit.text)
|  *(.memexit.text)
|  *(.exit.data)
|  *(.memexit.data)
|  *(.memexit.rodata)
|  *(.exitcall.exit)
|  *(.discard)
|  *(.discard.*)
|
|                 0xc0008000                . = 0xc0008000
|
| .head.text      0xc0008000      0x1d0
|                 0xc0008000                _text = .
|  *(.head.text)
|  .head.text     0xc0008000      0x1d0 arch/arm/kernel/head.o
|                 0xc0008000                stext
|
| .text           0xc0008200   0x2d78d0
|                 0xc0008200                _stext = .
|                 0xc0008200                __exception_text_start = .
|  *(.exception.text)
|  .exception.text
| ...

As you can see, all the discarded sections are grouped together - and
as a result of it being the first output section, they all appear before
any other section.

The result is that not only is the unwind information discarded (as
intended), but also the .exit.text, despite us wanting to have the
.exit.text preserved.

We can't move the unwind information elsewhere, because it'll then be
included even when we do actually discard the .exit.text (and similar)
sections.

So, work around this by avoiding the generic DISCARDS macro, and instead
conditionalize the sections to be discarded ourselves.  This avoids the
ambiguity in how the linker assigns input sections to output sections,
making our script less dependent on undocumented linker behaviour.

Reported-by: Rob Herring <robherring2@gmail.com>
Tested-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2011-09-20 23:42:31 +01:00
..
.gitignore
armksyms.c arm: remove stale export of 'sha_transform' 2011-08-07 15:49:11 -07:00
arthur.c
asm-offsets.c ARM: vfp: fix a hole in VFP thread migration 2011-07-09 17:22:12 +01:00
atags.c
atags.h
bios32.c PCI: Make the struct pci_dev * argument of pci_fixup_irqs const. 2011-07-22 08:26:06 -07:00
calls.S All Arch: remove linkage for sys_nfsservctl system call 2011-08-26 15:09:58 -07:00
compat.c ARM: deprecate support for old way to pass kernel parameters 2010-07-07 16:38:36 +02:00
compat.h ARM: deprecate support for old way to pass kernel parameters 2010-07-07 16:38:36 +02:00
crash_dump.c crash_dump: export is_kdump_kernel to modules, consolidate elfcorehdr_addr, setup_elfcorehdr and saved_max_pfn 2011-03-23 19:47:19 -07:00
crunch-bits.S
crunch.c ARM: Convert VFP/Crunch/XscaleCP thread_release() to exit_thread() 2009-12-18 14:53:41 +00:00
debug.S ARM: 6826/1: Merge v6 and v7 DEBUG_LL DCC support 2011-03-28 19:01:43 +01:00
devtree.c irq: add irq_domain translation infrastructure 2011-07-28 01:32:04 -06:00
dma-isa.c ARM: dma-isa: request cascade channel after registering it 2009-12-24 18:34:08 +00:00
dma.c ARM: dma: add /proc/dma support to arch/arm/kernel/dma.c 2010-04-14 13:13:30 +01:00
early_printk.c ARM: Add an earlyprintk debug console 2009-12-09 10:02:18 +00:00
ecard.c arm: Fold irq_set_chip/irq_set_handler 2011-03-29 14:47:58 +02:00
ecard.h
elf.c ARM: 6878/1: fix personality flag propagation across an exec 2011-04-14 09:15:24 +01:00
entry-armv.S Merge branch 'devel-stable' into for-next 2011-07-22 23:09:07 +01:00
entry-common.S ARM: 6952/1: fix lockdep warning of "unannotated irqs-off" 2011-06-06 10:56:22 +01:00
entry-header.S Merge branch 'devel-stable' into for-next 2011-07-22 23:09:07 +01:00
etm.c ARM: 6838/1: etm: fix section mismatch warning 2011-03-28 19:01:17 +01:00
fiq.c ARM: 6938/1: fiq: Refactor {get,set}_fiq_regs() for Thumb-2 2011-05-26 10:31:06 +01:00
fiqasm.S ARM: 6938/1: fiq: Refactor {get,set}_fiq_regs() for Thumb-2 2011-05-26 10:31:06 +01:00
ftrace.c ARM: ftrace: graph tracer + dynamic ftrace 2010-11-19 21:43:27 +05:30
head-common.S arm/dt: Make __vet_atags also accept a dtb image 2011-05-11 15:12:32 +02:00
head-nommu.S ARM: 6999/1: head, zImage: Always Enter the kernel in ARM state 2011-07-19 12:00:53 +01:00
head.S ARM: 6999/1: head, zImage: Always Enter the kernel in ARM state 2011-07-19 12:00:53 +01:00
hw_breakpoint.c ARM: entry: avoid enabling interrupts in prefetch/data abort handlers 2011-07-02 10:56:00 +01:00
init_task.c
io.c
irq.c Merge branch 'next/devel' of ssh://master.kernel.org/pub/scm/linux/kernel/git/arm/linux-arm-soc 2011-07-26 17:41:04 -07:00
isa.c sysctl: Drop & in front of every proc_handler. 2009-11-18 08:37:40 -08:00
iwmmxt.S ARM: pxa: fix logic error in PJ4 iWMMXt handling 2011-08-11 10:10:26 +08:00
kgdb.c kgdb,arm: fix register dump 2010-10-29 13:14:40 -05:00
kprobes-arm.c ARM: kprobes: Remove now unused code 2011-07-13 17:32:51 +00:00
kprobes-common.c ARM: kprobes: Add alu_write_pc() 2011-07-13 17:32:48 +00:00
kprobes-thumb.c ARM: kprobes: Decode 32-bit Thumb multiply and absolute difference instructions 2011-07-13 17:32:48 +00:00
kprobes.c ARM: kprobes: Extend arch_specific_insn to add pointer to emulated instruction 2011-07-13 17:32:42 +00:00
kprobes.h ARM: kprobes: Add alu_write_pc() 2011-07-13 17:32:48 +00:00
leds.c ARM: Use struct syscore_ops instead of sysdevs for PM in common code 2011-04-24 19:16:08 +02:00
machine_kexec.c [ARM] add machine-specific hook to machine_kexec 2011-03-03 16:26:55 -05:00
Makefile ARM: kprobes: Add Thumb instruction decoding stubs 2011-07-13 17:32:41 +00:00
module.c ARM: Fix build error for SMP=n builds 2011-08-04 08:24:29 +01:00
perf_event.c Merge branch 'devel-stable' into for-next 2011-07-22 23:09:07 +01:00
perf_event_v6.c perf, arch: Add generic NODE cache events 2011-07-01 11:06:38 +02:00
perf_event_v7.c Merge branch 'for-linus' of master.kernel.org:/home/rmk/linux-2.6-arm 2011-07-24 10:20:54 -07:00
perf_event_xscale.c perf, arch: Add generic NODE cache events 2011-07-01 11:06:38 +02:00
pj4-cp0.c ARM: pxa: add iwmmx support for PJ4 2010-12-20 23:07:36 +08:00
pmu.c ARM: perf: make name of arm_pmu_type consistent 2011-08-12 15:40:21 +01:00
process.c cpuidle: Consistent spelling of cpuidle_idle_call() 2011-08-04 16:35:34 -10:00
ptrace.c Merge branch 'for-linus' of master.kernel.org:/home/rmk/linux-2.6-arm 2011-07-24 10:20:54 -07:00
relocate_kernel.S ARM: 7065/1: kexec: ensure new kernel is entered in ARM state 2011-08-28 10:39:41 +01:00
return_address.c ARM: fix some sparse errors in generic ARM code 2011-02-23 17:24:12 +00:00
sched_clock.c ARM: sched_clock: make minsec argument to clocks_calc_mult_shift() zero 2011-01-11 16:44:02 +00:00
setup.c ARM: cache: detect VIPT aliasing I-cache on ARMv6 2011-08-12 15:41:15 +01:00
signal.c ARM: 6892/1: handle ptrace requests to change PC during interrupted system calls 2011-05-12 10:52:00 +01:00
signal.h
sleep.S ARM: pm: allow suspend finisher to return error codes 2011-07-02 09:54:01 +01:00
smp.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
smp_scu.c ARM: 7091/1: errata: D-cache line maintenance operation by MVA may not succeed 2011-09-17 12:47:17 +01:00
smp_tlb.c ARM: SMP: split out software TLB maintainence broadcasting 2010-12-20 15:09:17 +00:00
smp_twd.c ARM: twd: register clockevents device before enabling PPI 2011-08-12 15:41:08 +01:00
stacktrace.c ARM: fix /proc/$PID/stack on SMP 2011-01-15 09:27:04 +00:00
swp_emulate.c perf: Remove the nmi parameter from the swevent and overflow interface 2011-07-01 11:06:35 +02:00
sys_arm.c Make do_execve() take a const filename pointer 2010-08-17 18:07:43 -07:00
sys_oabi-compat.c ARM: 6891/1: prevent heap corruption in OABI semtimedop 2011-04-29 15:53:14 +01:00
tcm.c ARM: 6985/1: export functions to determine the presence of I/DTCM 2011-07-06 20:49:45 +01:00
tcm.h
thumbee.c
time.c ARM: Use struct syscore_ops instead of sysdevs for PM in common code 2011-04-24 19:16:08 +02:00
traps.c atomic: use <linux/atomic.h> 2011-07-26 16:49:47 -07:00
unwind.c ARM: 6468/1: backtrace: fix calculation of thread stack base 2010-11-07 16:12:37 +00:00
vmlinux.lds.S ARM: fix vmlinux.lds.S discarding sections 2011-09-20 23:42:31 +01:00
xscale-cp0.c ARM: Convert VFP/Crunch/XscaleCP thread_release() to exit_thread() 2009-12-18 14:53:41 +00:00