[gcc Compilation Optimizations Series] When GCC compiles links, what is the--specs=kernel.specs link property?

1 Source of problem

There's been a little less interest in rt-thread s recently, and today I suddenly see such a forum problem:

Why would you be interested in this?
There are two main reasons:

Recently, we are researching some knowledge about gcc compilation links and making some notes to facilitate our own deeper understanding and memory.
This specs option vaguely remembers where I've seen it, but I don't know where it came from. It still doesn't seem to be memorable enough.

So I decided to take this opportunity to pick up this specs option.

2 Preliminary analysis

2.1 Questions on internal affairs of Baidu and on external affairs of Google

Two things aside, baidu comes first, as follows:

Didn't find the right one, so go google? Helplessly, there is no ladder, then bing it:

The answer to the question was not found, but the question was found by itself.

2.2 Development does not know "man"

It's said that men can be trusted and sows can climb trees, but as a long-term program ape mixed up in the Linux development environment, I can safely tell you that men are the least deceptive, don't believe you man*

recan@ubuntu:~$ man gcc | grep "specs"
           -specs=file  -wrapper @file  -ffile-prefix-map=old=new -fplugin=file  -fplugin-arg-name=arg -fdump-ada-spec[-slim]
           -fconstexpr-loop-limit=n -fconstexpr-ops-limit=n -fno-elide-constructors -fno-enforce-eh-specs -fno-gnu-keywords
           -dletters  -dumpspecs  -dumpmachine  -dumpversion -dumpfullversion  -fchecking  -fchecking=n  -fdbg-cnt-list
           -mshort-calls -nodevicelib  -nodevicespecs -Waddr-space-convert  -Wmisspelled-isr
           declaration).  Such files are also called specs.
       -specs=file
           Process file after the compiler reads in the standard specs file, in order to override the defaults which the gcc
           driver program uses when determining what switches to pass to cc1, cc1plus, as, ld, etc.  More than one -specs=file
           For C and C++ source and include files, generate corresponding Ada specs.
           In conjunction with -fdump-ada-spec[-slim] above, generate Ada specs as child units of parent unit.
       -fno-enforce-eh-specs
           used in filesystem paths and specs. Depending on how the compiler has been configured it can be just a single number
       -dumpspecs
           Print the compiler's built-in specs---and don't do anything else.  (This is used when GCC itself is being built.)
troff: <standard input>:17361: warning [p 110, 20.7i]: can't break line
       -nodevicespecs
           Don't add -specs=device-specs/specs-<mcu> to the compiler driver's command line.  The user takes responsibility for
           (/usr/lpp/ppe.poe/), or the specs file must be overridden with the -specs= option to specify the appropriate

This command line means to search for the specs keyword in the results of man gcc. Look carefully, we find the key message - specs=file. Don't guess, it's it.
To illustrate this better, I'll take this description completely:

-specs=file
           Process file after the compiler reads in the standard specs file, in order to override the defaults which the gcc
           driver program uses when determining what switches to pass to cc1, cc1plus, as, ld, etc.  More than one -specs=file
           can be specified on the command line, and they are processed in order, from left to right.

Need to understand in English, but the meaning is not difficult, it is not really possible, you can do it with translation software:

-specs=file
 The compiler reads in the standard specification file and postprocesses the file to overwrite it gcc Default value used
 Driver is used to determine what to pass to cc1,cc1plus,as,ld Switch of etc. Multiple-specs=file
 It can be specified on the command line and handled in left-to-right order.

OK, which is already clear, is to override the gcc default transfer parameters, which are specified in a new file, such as kernel.specs.

2.3 gcc default specs parameter

If you read the return of man gcc carefully, you will find that there is a -dumpspec option, which records the default specs parameters of gcc. To illustrate what the specs file looks like, I will export it to see: (Note that this is a GCC in x64 environment, if it is a cross-compiled gcc, replace the corresponding gcc, the method is the same.)

recan@ubuntu:~$ gcc -dumpspecs > default.specs
recan@ubuntu:~$ 
recan@ubuntu:~$ cat default.specs 
*asm:
%{m16|m32:--32}  %{m16|m32|mx32:;:--64}  %{mx32:--x32}  %{msse2avx:%{!mavx:-msse2avx}}

*asm_debug:
%{%:debug-level-gt(0):%{gstabs*:--gstabs}%{!gstabs*:%{g*:--gdwarf2}}} %{fdebug-prefix-map=*:--debug-prefix-map %*}

*asm_final:
%{gsplit-dwarf: 
       objcopy --extract-dwo     %{c:%{o*:%*}%{!o*:%b%O}}%{!c:%U%O}      %{c:%{o*:%:replace-extension(%{o*:%*} .dwo)}%{!o*:%b.dwo}}%{!c:%b.dwo} 
       objcopy --strip-dwo       %{c:%{o*:%*}%{!o*:%b%O}}%{!c:%U%O}     }

*asm_options:
%{-target-help:%:print-asm-header()} %{v} %{w:-W} %{I*}  %{gz|gz=zlib:--compress-debug-sections=zlib} %{gz=none:--compress-debug-sections=none} %{gz=zlib-gnu:--compress-debug-sections=zlib-gnu} %a %Y %{c:%W{o*}%{!o*:-o %w%b%O}}%{!c:-o %d%w%u%O}

*invoke_as:
%{!fwpa*:   %{fcompare-debug=*|fdump-final-insns=*:%:compare-debug-dump-opt()}   %{!S:-o %|.s |
 as %(asm_options) %m.s %A }  }

*cpp:
%{posix:-D_POSIX_SOURCE} %{pthread:-D_REENTRANT}

*cpp_options:
%(cpp_unique_options) %1 %{m*} %{std*&ansi&trigraphs} %{W*&pedantic*} %{w} %{f*} %{g*:%{%:debug-level-gt(0):%{g*} %{!fno-working-directory:-fworking-directory}}} %{O*} %{undef} %{save-temps*:-fpch-preprocess} %(distro_defaults)

*cpp_debug_options:
%{d*}

*cpp_unique_options:
%{!Q:-quiet} %{nostdinc*} %{C} %{CC} %{v} %@{I*&F*} %{P} %I %{MD:-MD %{!o:%b.d}%{o*:%.d%*}} %{MMD:-MMD %{!o:%b.d}%{o*:%.d%*}} %{M} %{MM} %{MF*} %{MG} %{MP} %{MQ*} %{MT*} %{!E:%{!M:%{!MM:%{!MT:%{!MQ:%{MD|MMD:%{o*:-MQ %*}}}}}}} %{remap} %{g3|ggdb3|gstabs3|gxcoff3|gvms3:-dD} %{!iplugindir*:%{fplugin*:%:find-plugindir()}} %{H} %C %{D*&U*&A*} %{i*} %Z %i %{E|M|MM:%W{o*}}

*trad_capable_cpp:
cc1 -E %{traditional|traditional-cpp:-traditional-cpp}

*cc1:
%{!mandroid|tno-android-cc:%(cc1_cpu) %{profile:-p};:%(cc1_cpu) %{profile:-p} %{!mglibc:%{!muclibc:%{!mbionic: -mbionic}}} %{!fno-pic:%{!fno-PIC:%{!fpic:%{!fPIC: -fPIC}}}}}

*cc1_options:
%{pg:%{fomit-frame-pointer:%e-pg and -fomit-frame-pointer are incompatible}} %{!iplugindir*:%{fplugin*:%:find-plugindir()}} %1 %{!Q:-quiet} %{!dumpbase:-dumpbase %B} %{d*} %{m*} %{aux-info*} %{fcompare-debug-second:%:compare-debug-auxbase-opt(%b)}  %{!fcompare-debug-second:%{c|S:%{o*:-auxbase-strip %*}%{!o*:-auxbase %b}}}%{!c:%{!S:-auxbase %b}}  %{g*} %{O*} %{W*&pedantic*} %{w} %{std*&ansi&trigraphs} %{v:-version} %{pg:-p} %{p} %{f*} %{undef} %{Qn:-fno-ident} %{Qy:} %{-help:--help} %{-target-help:--target-help} %{-version:--version} %{-help=*:--help=%*} %{!fsyntax-only:%{S:%W{o*}%{!o*:-o %b.s}}} %{fsyntax-only:-o %j} %{-param*} %{coverage:-fprofile-arcs -ftest-coverage} %{fprofile-arcs|fprofile-generate*|coverage:   %{!fprofile-update=single:     %{pthread:-fprofile-update=prefer-atomic}}}

*cc1plus:


*link_gcc_c_sequence:
%{static|static-pie:--start-group} %G %{!nolibc:%L}    %{static|static-pie:--end-group}%{!static:%{!static-pie:%G}}

*distro_defaults:
%{!fno-asynchronous-unwind-tables:-fasynchronous-unwind-tables} %{!fno-stack-protector:%{!fstack-protector-all:%{!ffreestanding:%{!nostdlib:%{!fstack-protector:-fstack-protector-strong}}}}} %{!Wformat:%{!Wformat=2:%{!Wformat=0:%{!Wall:-Wformat} %{!Wno-format-security:-Wformat-security}}}} %{!fno-stack-clash-protection:-fstack-clash-protection} %{!fcf-protection*:%{!fno-cf-protection:-fcf-protection}}

*link_ssp:
%{fstack-protector|fstack-protector-all|fstack-protector-strong|fstack-protector-explicit:}

*endfile:
%{!mandroid|tno-android-ld:%{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s}    %{mpc32:crtprec32.o%s}    %{mpc64:crtprec64.o%s}    %{mpc80:crtprec80.o%s} %{fvtable-verify=none:%s;      fvtable-verify=preinit:vtv_end_preinit.o%s;      fvtable-verify=std:vtv_end.o%s}    %{static:crtend.o%s;      shared|static-pie|!no-pie:crtendS.o%s;      :crtend.o%s} crtn.o%s %{fopenacc|fopenmp:crtoffloadend%O%s};:%{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s}    %{mpc32:crtprec32.o%s}    %{mpc64:crtprec64.o%s}    %{mpc80:crtprec80.o%s} %{shared: crtend_so%O%s;: crtend_android%O%s}}

*link:
%{!r:--build-id} %{!static|static-pie:--eh-frame-hdr} %{!mandroid|tno-android-ld:%{m16|m32|mx32:;:-m elf_x86_64}                    %{m16|m32:-m elf_i386}                    %{mx32:-m elf32_x86_64}   --hash-style=gnu   --as-needed   %{shared:-shared}   %{!shared:     %{!static:       %{!static-pie:     %{rdynamic:-export-dynamic}     %{m16|m32:-dynamic-linker %{muclibc:/lib/ld-uClibc.so.0;:%{mbionic:/system/bin/linker;:%{mmusl:/lib/ld-musl-i386.so.1;:/lib/ld-linux.so.2}}}}       %{m16|m32|mx32:;:-dynamic-linker %{muclibc:/lib/ld64-uClibc.so.0;:%{mbionic:/system/bin/linker64;:%{mmusl:/lib/ld-musl-x86_64.so.1;:/lib64/ld-linux-x86-64.so.2}}}}         %{mx32:-dynamic-linker %{muclibc:/lib/ldx32-uClibc.so.0;:%{mbionic:/system/bin/linkerx32;:%{mmusl:/lib/ld-musl-x32.so.1;:/libx32/ld-linux-x32.so.2}}}}}}     %{static:-static} %{static-pie:-static -pie --no-dynamic-linker -z text}};:%{m16|m32|mx32:;:-m elf_x86_64}                    %{m16|m32:-m elf_i386}                    %{mx32:-m elf32_x86_64}   --hash-style=gnu   --as-needed   %{shared:-shared}   %{!shared:     %{!static:       %{!static-pie:      %{rdynamic:-export-dynamic}     %{m16|m32:-dynamic-linker %{muclibc:/lib/ld-uClibc.so.0;:%{mbionic:/system/bin/linker;:%{mmusl:/lib/ld-musl-i386.so.1;:/lib/ld-linux.so.2}}}}       %{m16|m32|mx32:;:-dynamic-linker %{muclibc:/lib/ld64-uClibc.so.0;:%{mbionic:/system/bin/linker64;:%{mmusl:/lib/ld-musl-x86_64.so.1;:/lib64/ld-linux-x86-64.so.2}}}}     %{mx32:-dynamic-linker %{muclibc:/lib/ldx32-uClibc.so.0;:%{mbionic:/system/bin/linkerx32;:%{mmusl:/lib/ld-musl-x32.so.1;:/libx32/ld-linux-x32.so.2}}}}}}     %{static:-static} %{static-pie:-static -pie --no-dynamic-linker -z text}} %{shared: -Bsymbolic}}

*lib:
%{!mandroid|tno-android-ld:%{pthread:-lpthread} %{shared:-lc}    %{!shared:%{profile:-lc_p}%{!profile:-lc}};:%{shared:-lc}    %{!shared:%{profile:-lc_p}%{!profile:-lc}} %{!static: -ldl}}

*link_gomp:


*libgcc:
%{static|static-libgcc|static-pie:-lgcc -lgcc_eh}%{!static:%{!static-libgcc:%{!static-pie:%{!shared-libgcc:-lgcc --push-state --as-needed -lgcc_s --pop-state}%{shared-libgcc:-lgcc_s%{!shared: -lgcc}}}}}

*startfile:
%{!mandroid|tno-android-ld:%{shared:;      pg|p|profile:%{static-pie:grcrt1.o%s;:gcrt1.o%s};      static:crt1.o%s;      static-pie:rcrt1.o%s;      !no-pie:Scrt1.o%s;      :crt1.o%s} crti.o%s    %{static:crtbeginT.o%s;      shared|static-pie|!no-pie:crtbeginS.o%s;      :crtbegin.o%s}    %{fvtable-verify=none:%s;      fvtable-verify=preinit:vtv_start_preinit.o%s;      fvtable-verify=std:vtv_start.o%s} %{fopenacc|fopenmp:crtoffloadbegin%O%s};:%{shared: crtbegin_so%O%s;:  %{static: crtbegin_static%O%s;: crtbegin_dynamic%O%s}}}

*cross_compile:
0

*version:
9.3.0

*multilib:
. !m32 !m64 !mx32;32:../lib32:i386-linux-gnu m32 !m64 !mx32;64:../lib:x86_64-linux-gnu !m32 m64 !mx32;x32:../libx32:x86_64-linux-gnux32 !m32 !m64 mx32;

*multilib_defaults:
m64

*multilib_extra:


*multilib_matches:
m32 m32;m64 m64;mx32 mx32;

*multilib_exclusions:


*multilib_options:
m32/m64/mx32

*multilib_reuse:


*linker:
collect2

*linker_plugin_file:


*lto_wrapper:


*lto_gcc:


*post_link:


*link_libgcc:
%D

*md_exec_prefix:


*md_startfile_prefix:


*md_startfile_prefix_1:


*startfile_prefix_spec:


*sysroot_spec:
--sysroot=%R

*sysroot_suffix_spec:


*sysroot_hdrs_suffix_spec:


*self_spec:


*cc1_cpu:
%{march=native:%>march=native %:local_cpu_detect(arch)   %{!mtune=*:%>mtune=native %:local_cpu_detect(tune)}} %{mtune=native:%>mtune=native %:local_cpu_detect(tune)}

*link_command:
%{!fsyntax-only:%{!c:%{!M:%{!MM:%{!E:%{!S:    %(linker) %{!fno-use-linker-plugin:%{!fno-lto:     -plugin %(linker_plugin_file)     -plugin-opt=%(lto_wrapper)     -plugin-opt=-fresolution=%u.res     %{flinker-output=*:-plugin-opt=-linker-output-known}     %{!nostdlib:%{!nodefaultlibs:%:pass-through-libs(%(link_gcc_c_sequence))}}     }}%{flto|flto=*:%<fcompare-debug*}     %{flto} %{fno-lto} %{flto=*} %l %{static|shared|r:;!no-pie:-pie -z now} %{fuse-ld=*:-fuse-ld=%*}  %{gz|gz=zlib:--compress-debug-sections=zlib} %{gz=none:--compress-debug-sections=none} %{gz=zlib-gnu:--compress-debug-sections=zlib-gnu}  -z relro %X %{o*} %{e*} %{N} %{n} %{r}    %{s} %{t} %{u*} %{z} %{Z} %{!nostdlib:%{!r:%{!nostartfiles:%S}}}     %{static|no-pie|static-pie:} %@{L*} %(mfwrap) %(link_libgcc) %{fvtable-verify=none:} %{fvtable-verify=std:   %e-fvtable-verify=std is not supported in this configuration} %{fvtable-verify=preinit:   %e-fvtable-verify=preinit is not supported in this configuration} %{!nostdlib:%{!r:%{!nodefaultlibs:%{%:sanitize(address):%{!shared:libasan_preinit%O%s} %{static-libasan:%{!shared:-Bstatic --whole-archive -lasan --no-whole-archive -Bdynamic}}%{!static-libasan:%{!fuse-ld=gold:--push-state} --no-as-needed -lasan %{fuse-ld=gold:--as-needed;:--pop-state}}}     %{%:sanitize(thread):%{!shared:libtsan_preinit%O%s} %{static-libtsan:%{!shared:-Bstatic --whole-archive -ltsan --no-whole-archive -Bdynamic}}%{!static-libtsan:%{!fuse-ld=gold:--push-state} --no-as-needed -ltsan %{fuse-ld=gold:--as-needed;:--pop-state}}}     %{%:sanitize(leak):%{!shared:liblsan_preinit%O%s} %{static-liblsan:%{!shared:-Bstatic --whole-archive -llsan --no-whole-archive -Bdynamic}}%{!static-liblsan:%{!fuse-ld=gold:--push-state} --no-as-needed -llsan %{fuse-ld=gold:--as-needed;:--pop-state}}}}}} %o      %{fopenacc|fopenmp|%:gt(%{ftree-parallelize-loops=*:%*} 1):      %:include(libgomp.spec)%(link_gomp)}    %{fgnu-tm:%:include(libitm.spec)%(link_itm)}    %(mflib)  %{fsplit-stack: --wrap=pthread_create}    %{fprofile-arcs|fprofile-generate*|coverage:-lgcov} %{!nostdlib:%{!r:%{!nodefaultlibs:%{%:sanitize(address): %{static-libasan|static:%:include(libsanitizer.spec)%(link_libasan)}    %{static:%ecannot specify -static with -fsanitize=address}}    %{%:sanitize(thread): %{static-libtsan|static:%:include(libsanitizer.spec)%(link_libtsan)}    %{static:%ecannot specify -static with -fsanitize=thread}}    %{%:sanitize(undefined):%{static-libubsan:-Bstatic} %{!static-libubsan:--push-state --no-as-needed} -lubsan  %{static-libubsan:-Bdynamic} %{!static-libubsan:--pop-state} %{static-libubsan|static:%:include(libsanitizer.spec)%(link_libubsan)}}    %{%:sanitize(leak): %{static-liblsan|static:%:include(libsanitizer.spec)%(link_liblsan)}}}}}     %{!nostdlib:%{!r:%{!nodefaultlibs:%(link_ssp) %(link_gcc_c_sequence)}}}    %{!nostdlib:%{!r:%{!nostartfiles:%E}}} %{T*}  
%(post_link) }}}}}}

Since the specs file is really a blind spot for me, and I have to remember the shoulders of giants, I found a reference that is of great value. Article.
Specifically, I will not elaborate on it any more. You can learn by comparing it. You will be more impressed by a simple stroke.

Where are the 2.4 specs files?

At first, when we knew that kernel.specs in -specs=kernel.specs was a file, my first feeling was, "Well, it should be in the bsp directory of the source code." As a result, I pulled out the rt-smart source and searched it all but once:

takeout@newnew MINGW64 /c/llc/git_repos/rt-thread-share/rt-thread (rt-smart)
$ find . -name "kernel.specs"

takeout@newnew MINGW64 /c/llc/git_repos/rt-thread-share/rt-thread (rt-smart)
$ find . -name "*.specs"

Some BSPs refer to nano.specs:

Now that some bsp linking options are available, the nano.specs file is explicitly introduced and compiled without errors, there must be a place to find it.
Since it's not in the source directory, another possibility is that we'll look in the directory of the cross-compilation tool chain.
With gcc-arm-none-eabi-5_in my hand 4-2016q3 as an example:

So I think about why I had some impressions of specs before, these two nano.specs and nosys.specs. baidu, there is a lot of information, here are some useful reference links:

Looking at the second nosys.specs and recalling it again, there was a problem in the RRT forum that had to be solved by joining nosys.specs. Of course, I also saw its solution, which was a bit impressive, that's all.
Find the one I answered at the time That question You can also take a look at my thoughts at that time.

In addition, I'll give you a link to related issues, so you can go and see them whenever you have time, maybe it will solve some of your questions.

2.5 Happy End

Seeing here, the questions of the landlord have been answered, and I have a better understanding of this knowledge point. It seems that I still need to take more notes, what really enters my mind is my own, otherwise it will always exist only in search engines.