2021-12-09

Tech Programing

程式人小天地

complete garbage gcc producing as linker script in linux my gcc for archetecture x86-64

6 min read


this is the linker script from one tutorial I was reading

ENTRY(_Reset)
SECTIONS
{
 . = 0x10000;
 .startup . : { startup.o(.text) }
 .text : { *(.text) }
 .data : { *(.data) }
 .bss : { *(.bss COMMON) }
 . = ALIGN(8);
 . = . + 0x1000; /* 4kB of stack memory */
 stack_top = .;
}

the above out is use full i.e. if I am flashing my program to flash memory of embedded device but look at my compiled gcc linker script output. complete garbage below

I have no clue where is main function start address and how to know where there is a function in my program called main. no function names. So I like to know I can I produce useful output with gcc for linker script so at least my function and their start addresses plus start address of uninitialized and initialized plus start address address of functions’ stacks get printed. This is following absolute garbage gcc produced. Make no sense. So question is how to produce useful linker script with gcc or any other tool but I prefer gcc I compiled the code with this command [email protected]:~$ gcc -static -o empty sam.c -Wl,--verbose >> ttt.txt

OUTPUT_FORMAT("elf64-x86-64", "elf64-x86-64",
"elf64-x86-64")
OUTPUT_ARCH(i386:x86-64)
ENTRY(_start)
SEARCH_DIR("=/usr/local/lib/x86_64-linux-gnu"); SEARCH_DIR("=/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu64"); SEARCH_DIR("=/usr/local/lib64"); SEARCH_DIR("=/lib64"); SEARCH_DIR("=/usr/lib64"); SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/lib"); SEARCH_DIR("=/usr/lib"); SEARCH_DIR("=/usr/x86_64-linux-gnu/lib64"); SEARCH_DIR("=/usr/x86_64-linux-gnu/lib");
SECTIONS
{
PROVIDE (__executable_start = SEGMENT_START("text-segment", 0x400000)); . = SEGMENT_START("text-segment", 0x400000) + SIZEOF_HEADERS;
.interp         : { *(.interp) }
.note.gnu.build-id  : { *(.note.gnu.build-id) }
.hash           : { *(.hash) }
.gnu.hash       : { *(.gnu.hash) }
.dynsym         : { *(.dynsym) }
.dynstr         : { *(.dynstr) }
.gnu.version    : { *(.gnu.version) }
.gnu.version_d  : { *(.gnu.version_d) }
.gnu.version_r  : { *(.gnu.version_r) }
.rela.dyn       :
{
*(.rela.init)
*(.rela.text .rela.text.* .rela.gnu.linkonce.t.*)
*(.rela.fini)
*(.rela.rodata .rela.rodata.* .rela.gnu.linkonce.r.*)
*(.rela.data .rela.data.* .rela.gnu.linkonce.d.*)
*(.rela.tdata .rela.tdata.* .rela.gnu.linkonce.td.*)
*(.rela.tbss .rela.tbss.* .rela.gnu.linkonce.tb.*)
*(.rela.ctors)
*(.rela.dtors)
*(.rela.got)
*(.rela.bss .rela.bss.* .rela.gnu.linkonce.b.*)
*(.rela.ldata .rela.ldata.* .rela.gnu.linkonce.l.*)
*(.rela.lbss .rela.lbss.* .rela.gnu.linkonce.lb.*)
*(.rela.lrodata .rela.lrodata.* .rela.gnu.linkonce.lr.*)
*(.rela.ifunc)
}
.rela.plt       :
{
*(.rela.plt)
PROVIDE_HIDDEN (__rela_iplt_start = .);
*(.rela.iplt)
PROVIDE_HIDDEN (__rela_iplt_end = .);
}
. = ALIGN(CONSTANT (MAXPAGESIZE));
.init           :
{
KEEP (*(SORT_NONE(.init)))
}
.plt            : { *(.plt) *(.iplt) }
.plt.got        : { *(.plt.got) }
.plt.sec        : { *(.plt.sec) }
.text           :
{
*(.text.unlikely .text.*_unlikely .text.unlikely.*)
*(.text.exit .text.exit.*)
*(.text.startup .text.startup.*)
*(.text.hot .text.hot.*)
*(SORT(.text.sorted.*))
*(.text .stub .text.* .gnu.linkonce.t.*)
/* .gnu.warning sections are handled specially by elf.em.  */
*(.gnu.warning)
}
.fini           :
{
KEEP (*(SORT_NONE(.fini)))
}
PROVIDE (__etext = .);
PROVIDE (_etext = .);
PROVIDE (etext = .);
. = ALIGN(CONSTANT (MAXPAGESIZE));
/* Adjust the address for the rodata segment.  We want to adjust up to
the same address within the page on the next page up.  */
. = SEGMENT_START("rodata-segment", ALIGN(CONSTANT (MAXPAGESIZE)) + (. & (CONSTANT (MAXPAGESIZE) - 1)));
.rodata         : { *(.rodata .rodata.* .gnu.linkonce.r.*) }
.rodata1        : { *(.rodata1) }
.eh_frame_hdr   : { *(.eh_frame_hdr) *(.eh_frame_entry .eh_frame_entry.*) }
.eh_frame       : ONLY_IF_RO { KEEP (*(.eh_frame)) *(.eh_frame.*) }
.gcc_except_table   : ONLY_IF_RO { *(.gcc_except_table .gcc_except_table.*) }
.gnu_extab   : ONLY_IF_RO { *(.gnu_extab*) }
/* These sections are generated by the Sun/Oracle C++ compiler.  */
.exception_ranges   : ONLY_IF_RO { *(.exception_ranges*) }
/* Adjust the address for the data segment.  We want to adjust up to
the same address within the page on the next page up.  */
. = DATA_SEGMENT_ALIGN (CONSTANT (MAXPAGESIZE), CONSTANT (COMMONPAGESIZE));
/* Exception handling  */
.eh_frame       : ONLY_IF_RW { KEEP (*(.eh_frame)) *(.eh_frame.*) }
.gnu_extab      : ONLY_IF_RW { *(.gnu_extab) }
.gcc_except_table   : ONLY_IF_RW { *(.gcc_except_table .gcc_except_table.*) }
.exception_ranges   : ONLY_IF_RW { *(.exception_ranges*) }
/* Thread Local Storage sections  */
.tdata      :
{
PROVIDE_HIDDEN (__tdata_start = .);
*(.tdata .tdata.* .gnu.linkonce.td.*)
}
.tbss       : { *(.tbss .tbss.* .gnu.linkonce.tb.*) *(.tcommon) }
.preinit_array    :
{
PROVIDE_HIDDEN (__preinit_array_start = .);
KEEP (*(.preinit_array))
PROVIDE_HIDDEN (__preinit_array_end = .);
}
.init_array    :
{
PROVIDE_HIDDEN (__init_array_start = .);
KEEP (*(SORT_BY_INIT_PRIORITY(.init_array.*) SORT_BY_INIT_PRIORITY(.ctors.*)))
KEEP (*(.init_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .ctors))
PROVIDE_HIDDEN (__init_array_end = .);
}
.fini_array    :
{
PROVIDE_HIDDEN (__fini_array_start = .);
KEEP (*(SORT_BY_INIT_PRIORITY(.fini_array.*) SORT_BY_INIT_PRIORITY(.dtors.*)))
KEEP (*(.fini_array EXCLUDE_FILE (*crtbegin.o *crtbegin?.o *crtend.o *crtend?.o ) .dtors))
PROVIDE_HIDDEN (__fini_array_end = .);
}
.ctors          :
{
/* gcc uses crtbegin.o to find the start of
the constructors, so we make sure it is
first.  Because this is a wildcard, it
doesn't matter if the user does not
actually link against crtbegin.o; the
linker won't look for a file to match a
wildcard.  The wildcard also means that it
doesn't matter which directory crtbegin.o
is in.  */
KEEP (*crtbegin.o(.ctors))
KEEP (*crtbegin?.o(.ctors))
/* We don't want to include the .ctor section from
the crtend.o file until after the sorted ctors.
The .ctor section from the crtend file contains the
end of ctors marker and it must be last */
KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .ctors))
KEEP (*(SORT(.ctors.*)))
KEEP (*(.ctors))
}
.dtors          :
{
KEEP (*crtbegin.o(.dtors))
KEEP (*crtbegin?.o(.dtors))
KEEP (*(EXCLUDE_FILE (*crtend.o *crtend?.o ) .dtors))
KEEP (*(SORT(.dtors.*)))
KEEP (*(.dtors))
}
.jcr            : { KEEP (*(.jcr)) }
.data.rel.ro : { *(.data.rel.ro.local* .gnu.linkonce.d.rel.ro.local.*) *(.data.rel.ro .data.rel.ro.* .gnu.linkonce.d.rel.ro.*) }
.dynamic        : { *(.dynamic) }
.got            : { *(.got) *(.igot) }
. = DATA_SEGMENT_RELRO_END (SIZEOF (.got.plt) >= 24 ? 24 : 0, .);
.got.plt        : { *(.got.plt) *(.igot.plt) }
.data           :
{
*(.data .data.* .gnu.linkonce.d.*)
SORT(CONSTRUCTORS)
}
.data1          : { *(.data1) }
_edata = .; PROVIDE (edata = .);
. = .;
__bss_start = .;
.bss            :
{
*(.dynbss)
*(.bss .bss.* .gnu.linkonce.b.*)
*(COMMON)
/* Align here to ensure that the .bss section occupies space up to
_end.  Align after .bss to ensure correct alignment even if the
.bss section disappears because there are no input sections.
FIXME: Why do we need it? When there is no .bss section, we do not
pad the .data section.  */
. = ALIGN(. != 0 ? 64 / 8 : 1);
}
.lbss   :
{
*(.dynlbss)
*(.lbss .lbss.* .gnu.linkonce.lb.*)
*(LARGE_COMMON)
}
. = ALIGN(64 / 8);
. = SEGMENT_START("ldata-segment", .);
.lrodata   ALIGN(CONSTANT (MAXPAGESIZE)) + (. & (CONSTANT (MAXPAGESIZE) - 1)) :
{
*(.lrodata .lrodata.* .gnu.linkonce.lr.*)
}
.ldata   ALIGN(CONSTANT (MAXPAGESIZE)) + (. & (CONSTANT (MAXPAGESIZE) - 1)) :
{
*(.ldata .ldata.* .gnu.linkonce.l.*)
. = ALIGN(. != 0 ? 64 / 8 : 1);
}
. = ALIGN(64 / 8);
_end = .; PROVIDE (end = .);
. = DATA_SEGMENT_END (.);
/* Stabs debugging sections.  */
.stab          0 : { *(.stab) }
.stabstr       0 : { *(.stabstr) }
.stab.excl     0 : { *(.stab.excl) }
.stab.exclstr  0 : { *(.stab.exclstr) }
.stab.index    0 : { *(.stab.index) }
.stab.indexstr 0 : { *(.stab.indexstr) }
.comment       0 : { *(.comment) }
.gnu.build.attributes : { *(.gnu.build.attributes .gnu.build.attributes.*) }
/* DWARF debug sections.
Symbols in the DWARF debugging sections are relative to the beginning
of the section so we begin them at 0.  */
/* DWARF 1.  */
.debug          0 : { *(.debug) }
.line           0 : { *(.line) }
/* GNU DWARF 1 extensions.  */
.debug_srcinfo  0 : { *(.debug_srcinfo) }
.debug_sfnames  0 : { *(.debug_sfnames) }
/* DWARF 1.1 and DWARF 2.  */
.debug_aranges  0 : { *(.debug_aranges) }
.debug_pubnames 0 : { *(.debug_pubnames) }
/* DWARF 2.  */
.debug_info     0 : { *(.debug_info .gnu.linkonce.wi.*) }
.debug_abbrev   0 : { *(.debug_abbrev) }
.debug_line     0 : { *(.debug_line .debug_line.* .debug_line_end) }
.debug_frame    0 : { *(.debug_frame) }
.debug_str      0 : { *(.debug_str) }
.debug_loc      0 : { *(.debug_loc) }
.debug_macinfo  0 : { *(.debug_macinfo) }
/* SGI/MIPS DWARF 2 extensions.  */
.debug_weaknames 0 : { *(.debug_weaknames) }
.debug_funcnames 0 : { *(.debug_funcnames) }
.debug_typenames 0 : { *(.debug_typenames) }
.debug_varnames  0 : { *(.debug_varnames) }
/* DWARF 3.  */
.debug_pubtypes 0 : { *(.debug_pubtypes) }
.debug_ranges   0 : { *(.debug_ranges) }
/* DWARF 5.  */
.debug_addr     0 : { *(.debug_addr) }
.debug_line_str 0 : { *(.debug_line_str) }
.debug_loclists 0 : { *(.debug_loclists) }
.debug_macro    0 : { *(.debug_macro) }
.debug_names    0 : { *(.debug_names) }
.debug_rnglists 0 : { *(.debug_rnglists) }
.debug_str_offsets 0 : { *(.debug_str_offsets) }
.debug_sup      0 : { *(.debug_sup) }
.gnu.attributes 0 : { KEEP (*(.gnu.attributes)) }
/DISCARD/ : { *(.note.GNU-stack) *(.gnu_debuglink) *(.gnu.lto_*) }
}

the above garbage produced with this smallest program

#include <stdio.h>
#include <stdint.h>
void hello()
{
printf("hellon");
}
int main()
{
hello();
/*
int *i=(int[]){10000000,2,3,4,5};
uint8_t *c=(uint8_t *)(i);
printf("-%x-",*c);*/
int *i=(int[]){1,2,3,4,5};
int *x=(void *)(i+1);
printf("-%d-",*x);
}



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資料來源:Stackoverflow

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