Hi, here is the diagnosis for SIGSEGV in recordmcount.c on MIPS64:
On 10/23/2010, wu zhangjin wrote:
> CC init/main.o
> /bin/sh: line 1: 21835 Segmentation fault scripts/recordmcount "init/main.o"
> make[1]: *** [init/main.o] Error 139
> make: *** [init] Error 2
>
> I traced the problem and found it was triggered by the 201 line of
> scripts/recordmcount.h:
>
> 198 if (!mcountsym) {
> 199 Elf_Sym const *const symp =
> 200 &sym0[ELF_R_SYM(_w(relp->r_info))];
> *201 char const *symname = &str0[w(symp->st_name)];*
> 202
> 203 if ('.' == symname[0])
> 204 ++symname; /* ppc64 hack */
>
> Exactly, it was triggered by: symp->st_name, symp is normal address,
> i.e. 0xa01831f0, but perhaps the content pointed by this address may
> not exist or is not allocated before?
>
> Did I miss something for MIPS specific support?
The layout of a MIPS structure Elf64_Rela is not described correctly
by the macros ELF64_R_SYM and ELF64_R_TYPE of <elf.h>:
-----
#define ELF64_R_SYM(i) ((i) >> 32)
#define ELF64_R_TYPE(i) ((i) & 0xffffffff)
-----
"readelf main.o" says:
-----
Relocation section '.rela.text' at offset 0x5b68 contains 59 entries:
Offset Info Type Sym. Value Sym. Name + Addend
000000000020 004200000004 R_MIPS_26 0000000000000000 _mcount + 0
Type2: R_MIPS_NONE
Type3: R_MIPS_NONE
-----
The actual bytes are [performed on a little-endian machine,
which is the same as main.o, namely ELFDATA2LSB]:
-----
$ od -Ax -tx8 -j0x5b68 main.o | sed 2q
005b68 0000000000000020 0400000000000042
005b78 0000000000000000
-----
So it looks like the data actually corresponds to:
-----
#define MIPS_ELF64_R_TYPE(i) (0xff & ((i)>>56))
#define MIPS_ELF64_R_TYPE2(i) (0xff & ((i)>>48))
#define MIPS_ELF64_R_TYPE3(i) (0xff & ((i)>>40))
#define MIPS_ELF64_R_SYM(i) (0xffffffff & (i)) /* perhaps 40 bits? */
-----
What this means for recordmcount.c is that ELF_R_SYM and ELF_R_TYPE
should become pointers to functions with default bodies given by
the macros in <elf.h>, and which EM_MIPS overrides.
> for kernel:
> # 14: 0c000000 jal 0
> # 14: R_MIPS_26 _mcount
> for module:
> # c: 3c030000 lui v1,0x0
> # c: R_MIPS_HI16 _mcount
I suggest that the argv command line for recordcmount.c have an
optional flag -m or --module, such that the correct reltype can
be chosen when .e_machine is decoded.
> (Note: The above patch is not enough, for the modules with
> -mlong-calls, the reltype should be R_MIPS_HI16, and we may also need
> to add our specific code for sift_rel_mcount() to get the right
> location of the _mcount calling site)
"-mlong-calls" must set .e_flags, or otherwise provide enough
description to that the correct reltype can be chosen at the time
when .e_machine is decoded. Adjusting the address for the location
of the call to _mcount should be another function pointer that is
overridden for EM_MIPS.
Regards,
--
John Reiser, jreiser@xxxxxxxxxxxx
