Actual default linker script and gcc settings

Question

Where can I find the actual linker script and gcc settings use?

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Things I tried:

For concreteness, consider a small program: empty.c

int main(void) { return 0; } 

build it statically and look at the result:

 $ gcc -static -o empty empty.c $ readelf -W -l empty Elf file type is EXEC (Executable file) Entry point 0x400f4e There are 6 program headers, starting at offset 64 Program Headers: Type Offset VirtAddr PhysAddr FileSiz MemSiz Flg Align LOAD 0x000000 0x0000000000400000 0x0000000000400000 0x0bf581 0x0bf581 RE 0x200000 LOAD 0x0bfeb0 0x00000000006bfeb0 0x00000000006bfeb0 0x001d80 0x0042d8 RW 0x200000 NOTE 0x000190 0x0000000000400190 0x0000000000400190 0x000044 0x000044 R 0x4 TLS 0x0bfeb0 0x00000000006bfeb0 0x00000000006bfeb0 0x000020 0x000058 R 0x10 GNU_STACK 0x000000 0x0000000000000000 0x0000000000000000 0x000000 0x000000 RW 0x10 GNU_RELRO 0x0bfeb0 0x00000000006bfeb0 0x00000000006bfeb0 0x000150 0x000150 R 0x1 Section to Segment mapping: Segment Sections... 00 .note.ABI-tag .note.gnu.build-id .rela.plt .init .plt .text __libc_freeres_fn __libc_thread_freeres_fn .fini .rodata __libc_subfreeres __libc_atexit __libc_thread_subfreeres .eh_frame .gcc_except_table 01 .tdata .init_array .fini_array .jcr .data.rel.ro .got .got.plt .data .bss __libc_freeres_ptrs 02 .note.ABI-tag .note.gnu.build-id 03 .tdata .tbss 04 05 .tdata .init_array .fini_array .jcr .data.rel.ro .got 

Pay attention to the various sections, grouped by segment and placed in memory areas of different resolutions.

Now try to get as much information as possible about how this was related.

 $ gcc -static -o empty empty.c -Wl,--verbose GNU ld (GNU Binutils for Ubuntu) 2.24 Supported emulations: elf_x86_64 elf32_x86_64 elf_i386 i386linux elf_l1om elf_k1om i386pep i386pe using internal linker script: ================================================== /* Script for -z combreloc: combine and sort reloc sections */ OUTPUT_FORMAT("elf64-x86-64", "elf64-x86-64", "elf64-x86-64") OUTPUT_ARCH(i386:x86-64) ENTRY(_start) SEARCH_DIR("/usr/x86_64-linux-gnu/lib64"); SEARCH_DIR("=/usr/local/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/local/lib64"); SEARCH_DIR("=/lib/x86_64-linux-gnu"); SEARCH_DIR("=/lib64"); SEARCH_DIR("=/usr/lib/x86_64-linux-gnu"); SEARCH_DIR("=/usr/lib64"); SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/lib"); SEARCH_DIR("=/usr/lib"); SECTIONS { /* Read-only sections, merged into text segment: */ 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 = .); } .init : { KEEP (*(SORT_NONE(.init))) } .plt : { *(.plt) *(.iplt) } .text : { *(.text.unlikely .text.*_unlikely .text.unlikely.*) *(.text.exit .text.exit.*) *(.text.startup .text.startup.*) *(.text.hot .text.hot.*) *(.text .stub .text.* .gnu.linkonce.t.*) /* .gnu.warning sections are handled specially by elf32.em. */ *(.gnu.warning) } .fini : { KEEP (*(SORT_NONE(.fini))) } PROVIDE (__etext = .); PROVIDE (_etext = .); PROVIDE (etext = .); .rodata : { *(.rodata .rodata.* .gnu.linkonce.r.*) } .rodata1 : { *(.rodata1) } .eh_frame_hdr : { *(.eh_frame_hdr) } .eh_frame : ONLY_IF_RO { KEEP (*(.eh_frame)) } .gcc_except_table : ONLY_IF_RO { *(.gcc_except_table .gcc_except_table.*) } /* These sections are generated by the Sun/Oracle C++ compiler. */ .exception_ranges : ONLY_IF_RO { *(.exception_ranges .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. */ . = ALIGN (CONSTANT (MAXPAGESIZE)) - ((CONSTANT (MAXPAGESIZE) - .) & (CONSTANT (MAXPAGESIZE) - 1)); . = DATA_SEGMENT_ALIGN (CONSTANT (MAXPAGESIZE), CONSTANT (COMMONPAGESIZE)); /* Exception handling */ .eh_frame : ONLY_IF_RW { KEEP (*(.eh_frame)) } .gcc_except_table : ONLY_IF_RW { *(.gcc_except_table .gcc_except_table.*) } .exception_ranges : ONLY_IF_RW { *(.exception_ranges .exception_ranges*) } /* Thread Local Storage sections */ .tdata : { *(.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 don't 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) } /* 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 Extension. */ .debug_macro 0 : { *(.debug_macro) } .gnu.attributes 0 : { KEEP (*(.gnu.attributes)) } /DISCARD/ : { *(.note.GNU-stack) *(.gnu_debuglink) *(.gnu.lto_*) } } ================================================== ... <snip searching and linking actual object files> 

But the script, although long, lacks much of the import information that was specified earlier.

How do I know which partitions are going to different load segments?
There is no PHDRS command, and although using SEGMENT_START requires some standard segments for this system, defined elsewhere, none of the sections are listed in the corresponding segment.

Also, how do you know where to load these segments, or what permissions do these memory areas have?
There is no MEMORY command. And again, if there are some standard memory areas for this system defined elsewhere, none of the sections show which memory area to use.

When I saw the default linker scripts before for microcontrollers, they were incredibly detailed. However, this conclusion suggests that it has more scripts and settings.

Where are the definitions and settings of other script builders stored?