Re: [Ltt-dev] Linux Kernel Markers : sparc build issue

[Mathieu Desnoyers <compudj@krystal.dyndns.org>]

This issue is "fixed" by disabling KALLSYMS when building the kernel. I
added the following information in the menus :

config MARKERS
        bool "Activate markers"
        select MODULES
        default n
        help
          Place an empty function call at each marker site. Can be
          dynamically changed for a probe function.

          Note that on sparc32, m68k and RS/6000, you may have to disable
          kallsyms (under Configure standard kernel features (for small
          systems), "Load all symbols for debugging/ksymoops") because of
          a GOT size limit of respectively : 8k, 32k and 32k. It can
          otherwise cause linking errors when too much markers appear in
          the code.

Mathieu

* Mathieu Desnoyers (mathieu.desnoyers@polymtl.ca) wrote:
> It seems like I bust the 8k limit for the sparc GOT :
> 
> The kallsyms_addresses is 8614 lines long (for a 33.6kB total) in the .S,
> and, according to
> http://gcc.gnu.org/onlinedocs/gcc-4.1.1/gcc/Code-Gen-Options.html :
> 
> "If the GOT size for the linked executable exceeds a machine-specific
> maximum size, you get an error message from the linker indicating that
> -fpic does not work; in that case, recompile with -fPIC instead. (These
> maximums are 8k on the SPARC and 32k on the m68k and RS/6000. The 386
> has no such limit.)"
> 
> Mathieu
> 
> 
> * Mathieu Desnoyers (mathieu.desnoyers@polymtl.ca) wrote:
> > * Frank Ch. Eigler (fche@redhat.com) wrote:
> > > 
> > > Perhaps you could post excerpts of "objdump -dr <file.o>", to see the
> > > disassembly / relocations in question.
> > > 
> > > - FChE
> > 
> > Hi Frank,
> > 
> > (this message follow up on
> > http://listserv.shafik.org/pipermail/ltt-dev/2007-February/002212.html)
> > 
> > compudj@amd64:~/obj/sparc$ PATH=/opt/crosstool/gcc-4.1.1-glibc-2.3.6/sparc-unknown-linux-gnu/bin sparc-unknown-linux-gnu-objdump -dr .tmp_kallsyms3.o
> > 
> > .tmp_kallsyms3.o:     file format elf32-sparc
> > 
> > (that's all)
> > 
> > By looking at what follows in more depth, it looks like the symbols I
> > keep are relative to the beginning of the _text section and sparc would
> > have a limit regarding this (maximum offset ? number of offsets relative
> > to a symbol ?)
> > 
> > Any insights are welcome,
> > 
> > Mathieu
> > 
> > 
> > link error :
> > 
> > opt/crosstool/gcc-4.1.1-glibc-2.3.6/sparc-unknown-linux-gnu/bin/sparc-unknown-linux-gnu-ld -m elf32_sparc  -T arch/sparc/kernel/vmlinux.lds arch/sparc/kernel/head.o arch/sparc/kernel/init_task.o  init/built-in.o --start-group  usr/built-in.o  arch/sparc/kernel/built-in.o arch/sparc/mm/built-in.o  arch/sparc/math-emu/built-in.o kernel/built-in.o  mm/built-in.o  fs/built-in.o  ipc/built-in.o security/built-in.o  crypto/built-in.o  block/built-in.o  lib/lib.a arch/sparc/prom/lib.a  arch/sparc/lib/lib.a  lib/built-in.o arch/sparc/prom/built-in.o  arch/sparc/lib/built-in.o drivers/built-in.o  sound/built-in.o  net/built-in.o --end-group .tmp_kallsyms3.o arch/sparc/boot/btfix.o -o arch/sparc/boot/image
> > .tmp_kallsyms3.o: In function `kallsyms_addresses':
> > .tmp_kallsyms3.S:(.rodata+0x0): relocation truncated to fit: R_SPARC_32 against symbol `_text' defined in .text section in arch/sparc/boot/image
> > .tmp_kallsyms3.S:(.rodata+0x8): relocation truncated to fit: R_SPARC_32 against symbol `_text' defined in .text section in arch/sparc/boot/image
> > ...
> > .tmp_kallsyms3.S:(.rodata+0x2c): additional relocation overflows omitted
> > from the output
> > make[2]: *** [arch/sparc/boot/image] Error 1
> > 
> > 
> > arch/sparc/kernel/vmlinux.lds
> > ...
> > OUTPUT_FORMAT("elf32-sparc", "elf32-sparc", "elf32-sparc")
> > OUTPUT_ARCH(sparc)
> > ENTRY(_start)
> > jiffies = jiffies_64 + 4;
> > SECTIONS
> > {
> >   . = 0x10000 + SIZEOF_HEADERS;
> >   .text 0xf0004000 :
> >   {
> >     _text = .;
> >     *(.text)
> >     . = ALIGN(8); __sched_text_start = .; *(.sched.text) __sched_text_end = .;
> >     . = ALIGN(8); __lock_text_start = .; *(.spinlock.text) __lock_text_end = .;
> >     *(.gnu.warning)
> >   } =0
> >   _etext = .;
> > ...
> > 
> > 
> > A look at .tmp_kallsyms3.S, symbol kallsyms_addresses which seems to cause
> > linking error on sparc :
> > 
> > 
> > #include <asm/types.h>
> > #if BITS_PER_LONG = 64
> > #define PTR .quad
> > #define ALGN .align 8
> > #else
> > #define PTR .long
> > #define ALGN .align 4
> > #endif
> >         .section .rodata, "a"
> > .globl kallsyms_addresses
> >         ALGN
> > kallsyms_addresses:
> >         PTR     _text - 0xeffd7000
> >         PTR     0x2d000
> >         PTR     _text - 0xeffd6fb8
> >         PTR     _text - 0xeffd6f50
> >         PTR     _text - 0xeffd6ed0
> >         PTR     _text - 0xeffd6eac
> >         PTR     _text - 0xeffd6b84
> >         PTR     _text - 0xeffd6860
> >         PTR     _text - 0xeffd6830
> >         PTR     _text - 0xeffd6814
> >         PTR     _text - 0xeffd6794
> >         PTR     _text - 0xeffd6788
> >         PTR     _text - 0xeffd6778
> >         PTR     _text - 0xeffd6764
> >         PTR     _text - 0xeffd673c
> >         PTR     _text - 0xeffd6714
> >         PTR     _text - 0xeffd66e4
> >         PTR     _text - 0xeffd66b4
> >         PTR     _text - 0xeffd66ac
> >         PTR     _text - 0xeffd6698
> >         PTR     _text - 0xeffd6674
> >         PTR     _text - 0xeffd6650
> >         PTR     _text - 0xeffd63dc
> >         PTR     _text - 0xeffd637c
> >         PTR     _text - 0xeffd6304
> >         PTR     _text - 0xeffd6060
> >         PTR     _text - 0xeffd6034
> >         PTR     _text - 0xeffd6008
> >         PTR     _text - 0xeffd5ff8
> > .....
> > 
> >         PTR     _text - 0xeffbc7a0
> >         PTR     _text - 0xeffbc730
> >         PTR     0x47930
> >         PTR     _text + 0
> >         PTR     _text + 0
> >         PTR     _text + 0
> >         PTR     _text + 0
> >         PTR     _text + 0
> >         PTR     _text + 0
> >         PTR     _text + 0
> >         PTR     _text + 0x10
> >         PTR     _text + 0x20
> >         PTR     _text + 0x30
> >         PTR     _text + 0x40
> >         PTR     _text + 0x50
> >         PTR     _text + 0x60
> >         PTR     _text + 0x70
> >         PTR     _text + 0x80
> >         PTR     _text + 0x90
> >         PTR     _text + 0xa0
> >         PTR     _text + 0xb0
> >         PTR     _text + 0xc0
> >         PTR     _text + 0x110
> >         PTR     _text + 0x120
> >         PTR     _text + 0x130
> >         PTR     _text + 0x140
> >         PTR     _text + 0x150
> > ....
> > 
> > 
> >         PTR     _text + 0x1b67c4
> >         PTR     _text + 0x1b67d8
> >         PTR     0xf01ba890
> > 
> > 
> > And by the way, I also add my own section to 
> > include/asm-generic/vmlinux.lds.h in RODATA :
> > adds at line 124, kernel 2.6.20 :
> >         /* Kernel markers : pointers */                                 \
> >         .markers : AT(ADDR(.markers) - LOAD_OFFSET) {                   \
> >                 VMLINUX_SYMBOL(__start___markers) = .;                  \
> >                 *(.markers)                                             \
> >                 VMLINUX_SYMBOL(__stop___markers) = .;                   \
> >         }                                                               \
> > 
> > 
> > 
> > -- 
> > Mathieu Desnoyers
> > Computer Engineering Graduate Student, École Polytechnique de Montréal
> > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
> > _______________________________________________
> > Ltt-dev mailing list
> > Ltt-dev@listserv.shafik.org
> > http://listserv.shafik.org/mailman/listinfo/ltt-dev
> > 
> 
> -- 
> Mathieu Desnoyers
> Computer Engineering Graduate Student, École Polytechnique de Montréal
> OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
> _______________________________________________
> Ltt-dev mailing list
> Ltt-dev@listserv.shafik.org
> http://listserv.shafik.org/mailman/listinfo/ltt-dev
> 

-- 
Mathieu Desnoyers
Computer Engineering Graduate Student, École Polytechnique de Montréal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68