Subject: Re: bug#20614: Segmentation fault when building on Power8 Little Endian

From: Petr Hracek <[email-masked]>
Date: Mon, 5 Oct 2015 09:40:15 +0200

On 10/02/2015 03:46 PM, Eli Zaretskii wrote:
>> Cc: [email-masked]
>> From: Petr Hracek <[email-masked]>
>> Date: Fri, 2 Oct 2015 14:58:56 +0200
>>
>> On 10/02/2015 10:49 AM, Eli Zaretskii wrote:
>>>> Cc: [email-masked]
>>>> From: Petr Hracek <[email-masked]>
>>>> Date: Fri, 2 Oct 2015 10:36:27 +0200
>>>>
>>>> What does this GDB command display in frame #1:
>>>>
>>>>     (gdb) p old_section_names + NEW_SECTION_H (nn).sh_name
>>>>
>>>> ?
>>>>
>>>> It is a really strange.
>>>> in our unexelf.c is NEW_SECTION_H defined as
>>>>
>>>> #define NEW_SECTION_H(n) \
>>>> (*(ElfW (Shdr) *) ((byte *) new_section_h + new_file_h->e_shentsize * (n)))
>>>>
>>>> Paul Eggert did a some patch 1 or 2 year ago and modify it to
>>>> #define NEW_SECTION_H(n) \
>>>>     (*(ElfW (Shdr) *) entry_address (new_section_h, n, new_file_h->e_shentsize))
>>>>
>>>> (gdb) frame 1
>>>> #1 0x00000000102e3724 in unexec (new_name=0x116387e8
>>>> "/home/phracek/rpmbuild/BUILD/emacs-24.3/src/emacs", old_name=0x11638838
>>>> "/home/phracek/rpmbuild/BUILD/emacs-24.3/src/temacs")
>>>> at unexelf.c:1258
>>>> 1258 if (!strcmp (old_section_names + NEW_SECTION_H (nn).sh_name, ".data")
>>>> (gdb) p old_section_names
>>>> $1 = 0x3fffab1dbfcc ""
>>>> (gdb) p old_section_names + NEW_SECTION_H (nn).sh_name
>>>> No symbol "NEW_SECTION_H" in current context.
>>> Use the expansion of that macro instead to display the value.
>> How to use the expansion.
> Just type it by hand:
>
>   (gdb) p old_section_names + (*(ElfW (Shdr) *) ((byte *) new_section_h + new_file_h->e_shentsize * (nn)))
>
>> Are you connected on freenode #emacs.
> No.
First of all thank you for your time.
Well,
(gdb) p (*(ElfW (Shdr) *) ((byte *) new_section_h + 
new_file_h->e_shentsize * (nn)))
No symbol "ElfW" in current context.
(gdb)
Also ElfBitsW does not exists.
(gdb) p ElfBitsW
No symbol "ElfBitsW" in current context.
(gdb)

I tried to find out what could be used from elf.h header file
but no any idea.

I guess that ELFSIZE should be defined from unexec.h, right?
http://git.savannah.gnu.org/cgit/emacs.git/tree/src/unexelf.c?h=emacs-24#n513
(gdb) p ELFSIZE
No symbol "ELFSIZE" in current context.
(gdb)

(gdb) frame 1
#1  0x00000000102e4174 in unexec (new_name=0x115c2868 
"/home/phracek/rpmbuild/BUILD/emacs-24.3/src/emacs", old_name=0x115c28b8 
"/home/phracek/rpmbuild/BUILD/emacs-24.3/src/temacs")
     at unexelf.c:1257
1257          if (!strcmp (old_section_names + NEW_SECTION_H 
(nn).sh_name, ".data")
(gdb) i locals
section = {sh_name = 122, sh_type = 4, sh_flags = 2, sh_addr = 
268483520, sh_offset = 48064, sh_size = 768, sh_link = 5, sh_info = 0, 
sh_addralign = 8, sh_entsize = 24}
new_file = 10
old_file = 9
new_file_size = 30325149
new_break = 0x11690000
old_base = 0x3fffaa7a0000 "\177ELF\002\001\001"
new_base = 0x3fffa8ab0000 "\177ELF\002\001\001"
old_file_h = 0x3fffaa7a0000
new_file_h = 0x3fffa8ab0000
old_program_h = 0x3fffaa7a0040
new_program_h = 0x3fffa8ab0040
old_section_h = 0x3fffab17a798
new_section_h = 0x3fffaa72a798
old_section_names = 0x3fffab17a657 ""
old_bss_addr = 272564224
new_bss_addr = 292093952
old_bss_size = 563096
new_data2_size = 19529728
new_data2_offset = 4063232
new_data2_addr = 272564224
old_bss_offset = 4063232
new_data2_incr = 19529728
n = 9
nn = 0
old_bss_index = 22
old_sbss_index = -1
old_plt_index = 20
old_data_index = 21
new_data2_index = 20
stat_buf = {st_dev = 2050, st_ino = 5119868, st_nlink = 1, st_mode = 
33261, st_uid = 20582, st_gid = 20582, __pad2 = 0, st_rdev = 0, st_size 
= 10795357, st_blksize = 4096,
   st_blocks = 20976, st_atim = {tv_sec = 1444028953, tv_nsec = 
509013261}, st_mtim = {tv_sec = 1444028953, tv_nsec = 379013248}, 
st_ctim = {tv_sec = 1444028953, tv_nsec = 379013248},
   __unused4 = 0, __unused5 = 0, __unused6 = 0}
old_file_size = 10795357
(gdb)

It seems like some compilation directives are missing. But of course I 
am guessing.

Local exec file:
     `/home/phracek/rpmbuild/BUILD/emacs-24.3/src/temacs', file type 
elf64-powerpcle.
     Entry point: 0x10016100
     0x0000000010000238 - 0x0000000010000249 is .interp
     0x000000001000024c - 0x000000001000026c is .note.ABI-tag
     0x000000001000026c - 0x0000000010000290 is .note.gnu.build-id
     0x0000000010000290 - 0x000000001000036c is .gnu.hash
     0x0000000010000370 - 0x0000000010006790 is .dynsym
     0x0000000010006790 - 0x000000001000b204 is .dynstr
     0x000000001000b204 - 0x000000001000ba5c is .gnu.version
     0x000000001000ba60 - 0x000000001000bbc0 is .gnu.version_r
     0x000000001000bbc0 - 0x000000001000bec0 is .rela.toc
     0x000000001000bec0 - 0x0000000010011ff8 is .rela.plt
     0x0000000010012000 - 0x000000001001204c is .init
     0x0000000010012060 - 0x000000001037d398 is .text
     0x000000001037d398 - 0x000000001037d3bc is .fini
     0x000000001037d3c0 - 0x00000000103a08e2 is .rodata
     0x00000000103a08e4 - 0x00000000103a9178 is .eh_frame_hdr
     0x00000000103a9178 - 0x00000000103d0258 is .eh_frame
     0x00000000103ef100 - 0x00000000103ef530 is .data.rel.ro
     0x00000000103ef530 - 0x00000000103ef970 is .dynamic
     0x00000000103ef970 - 0x00000000103f0000 is .got
     0x00000000103f0000 - 0x00000000103f2078 is .plt
     0x00000000103f2078 - 0x00000000106b91b8 is .data
     0x00000000106b91c0 - 0x00000000107408e0 is .bss
     0x00003fffb7fb0200 - 0x00003fffb7fb0224 is .note.gnu.build-id in 
/lib64/ld64.so.2
     0x00003fffb7fb0228 - 0x00003fffb7fb02e4 is .hash in /lib64/ld64.so.2

-- 
Petr Hracek
Software Engineer
Developer Experience
Red Hat, Inc
Mob: +420777056169
email: [email-masked]