Is there a gfortran equivalent to gcc's __attribute__((section("name")))? - gcc

Question

I am using the nestedvm package, which includes a patched Gnu gcc compiler. For this package, callable user methods/functions have to annotated with __attribute__((section(".text"))), as shown in the C example below.
void echo(const char *string, int count) __attribute__((section(".text")));
void echo(const char *string, int count) {
int i;
for(i=0;i<count;i++)
printf("%d: %s\n",i,string);
}
I don't know about the inner workings of the patched compiler, but without this annotation, the user function is not visible to outside callers.
If using gfortran, how can I accomplish this annotation for Fortran subroutines and functions? Could this be done with a linker script file? I could write a C wrapper to the Fortran functions, but would like to avoid this if possible.
** UPDATE 1 **
Using nm to investigate the .o file sheds some light on the issue...a C method without the attribute looks like the suckram function (which is not callable in nestedvm), while the echo function has the attribute and is callable in nestedvm:
Name Value Class Type Size Line Section
suckram |00000000| T | FUNC|00000078| |.text.suckram
echo |00000200| T | FUNC|00000074| |.text
The test1 subroutine in my Fortran object looks like the suckram method without the attribute:
test1_ |00000000| T | FUNC|00000080| |.text.test1_
According to some nestedvm documentation I found, in order for a user function to be callable in nestedvm, it has to end up in the .text section.
** UPDATE 2 **
A link command line is below. It is too long to put in a comment. I removed some of the many .o files (…)
mips-unknown-elf-gfortran -O3 -mmemcpy -ffunction-sections -fdata-sections -falign-functions=512 -fno-rename-registers -fno-schedule-insns -fno-delayed-branch -march=mips1 -specs=/home/jhuber/Documents/source/nestedvm/upstream/install/mips-unknown-elf/lib/crt0-override.spec -I. -Wall -Wno-unused -o build/refprop/Refprop.mips build/refprop/NVM.o (...) build/refprop/TRNS_VIS.o build/refprop/MAIN.o -march=mips1 -specs=/home/jhuber/Documents/source/nestedvm/upstream/install/mips-unknown-elf/lib/crt0-override.spec --static -Wl,--gc-sections -Wl,-Map=output1.map -Wl,--cref -lc -Wl,-Map=output.map -Wl,--cref
Also, even though I am calling the code as a library, nestedvm requires the library to have a MAIN routine for initialization. If I make some dummy calls to the library functions in the MAIN routine, those functions that are called in MAIN are moved the .text section, and become callable.
** UPDATE 3 **
Verbose output from make. I removed some of the many .o files (…)
mips-unknown-elf-gfortran -O3 -mmemcpy -ffunction-sections -fdata-sections -falign-functions=512 -fno-rename-registers -fno-schedule-insns -fno-delayed-branch -march=mips1 -specs=/home/jhuber/Documents/source/nestedvm/upstream/install/mips-unknown-elf/lib/crt0-override.spec -I. -Wall -Wno-unused -o build/refprop/Refprop.mips build/refprop/NVM.o (…) build/refprop/TRNS_VIS.o build/refprop/MAIN.o -march=mips1 -specs=/home/jhuber/Documents/source/nestedvm/upstream/install/mips-unknown-elf/lib/crt0-override.spec --static -Wl,--gc-sections -Wl,-Map=output1.map -Wl,--cref -lc -Wl,-Map=output.map -Wl,--cref -v
Driving: mips-unknown-elf-gfortran -O3 -mmemcpy -ffunction-sections -fdata-sections -falign-functions=512 -fno-rename-registers -fno-schedule-insns -fno-delayed-branch -march=mips1 -specs=/home/jhuber/Documents/source/nestedvm/upstream/install/mips-unknown-elf/lib/crt0-override.spec -I. -Wall -Wno-unused -o build/refprop/Refprop.mips build/refprop/NVM.o (…) build/refprop/TRNS_VIS.o build/refprop/MAIN.o -march=mips1 -specs=/home/jhuber/Documents/source/nestedvm/upstream/install/mips-unknown-elf/lib/crt0-override.spec --static -Wl,--gc-sections -Wl,-Map=output1.map -Wl,--cref -lc -Wl,-Map=output.map -Wl,--cref -v -l gfortran -l m
Using built-in specs.
Reading specs from /home/jhuber/Documents/source/nestedvm/upstream/install/mips-unknown-elf/lib/crt0-override.spec
Reading specs from /home/jhuber/Documents/source/nestedvm/upstream/install/mips-unknown-elf/lib/crt0-override.spec
COLLECT_GCC=mips-unknown-elf-gfortran
COLLECT_LTO_WRAPPER=/home/jhuber/Documents/source/nestedvm/upstream/install/libexec/gcc/mips-unknown-elf/4.8.5/lto-wrapper
Target: mips-unknown-elf
Configured with: ../gcc-4.8.5/configure --prefix=/home/jhuber/Documents/source/nestedvm/upstream/install --target=mips-unknown-elf --disable-threads --disable-libssp --with-gnu-ld --with-gnu-as --with-newlib=yes --enable-sjlj-exceptions --enable-languages=c : (reconfigured) ../gcc-4.8.5/configure --prefix=/home/jhuber/Documents/source/nestedvm/upstream/install --target=mips-unknown-elf --disable-threads --disable-libssp --with-gnu-ld --with-gnu-as --with-newlib=yes --enable-sjlj-exceptions --enable-languages=c --enable-languages=c,c++,fortran
Thread model: single
gcc version 4.8.5 (GCC)
Reading specs from /home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/4.8.5/../../../../mips-unknown-elf/lib/libgfortran.spec
rename spec lib to liborig
COLLECT_GCC_OPTIONS='-O3' '-mmemcpy' '-ffunction-sections' '-fdata-sections' '-falign-functions=512' '-fno-rename-registers' '-fno-schedule-insns' '-fno-delayed-branch' '-march=mips1' '-specs=/home/jhuber/Documents/source/nestedvm/upstream/install/mips-unknown-elf/lib/crt0-override.spec' '-I' '.' '-Wall' '-Wno-unused' '-o' 'build/refprop/Refprop.mips' '-march=mips1' '-specs=/home/jhuber/Documents/source/nestedvm/upstream/install/mips-unknown-elf/lib/crt0-override.spec' '-static' '-v'
COMPILER_PATH=/home/jhuber/Documents/source/nestedvm/upstream/install/libexec/gcc/mips-unknown-elf/4.8.5/:/home/jhuber/Documents/source/nestedvm/upstream/install/libexec/gcc/mips-unknown-elf/4.8.5/:/home/jhuber/Documents/source/nestedvm/upstream/install/libexec/gcc/mips-unknown-elf/:/home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/4.8.5/:/home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/:/home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/4.8.5/../../../../mips-unknown-elf/bin/
LIBRARY_PATH=/home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/4.8.5/:/home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/4.8.5/../../../../mips-unknown-elf/lib/
COLLECT_GCC_OPTIONS='-O3' '-mmemcpy' '-ffunction-sections' '-fdata-sections' '-falign-functions=512' '-fno-rename-registers' '-fno-schedule-insns' '-fno-delayed-branch' '-march=mips1' '-specs=/home/jhuber/Documents/source/nestedvm/upstream/install/mips-unknown-elf/lib/crt0-override.spec' '-I' '.' '-Wall' '-Wno-unused' '-o' 'build/refprop/Refprop.mips' '-march=mips1' '-specs=/home/jhuber/Documents/source/nestedvm/upstream/install/mips-unknown-elf/lib/crt0-override.spec' '-static' '-v'
/home/jhuber/Documents/source/nestedvm/upstream/install/libexec/gcc/mips-unknown-elf/4.8.5/collect2 -EB -o build/refprop/Refprop.mips /home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/4.8.5/crti.o /home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/4.8.5/crtbegin.o /home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/4.8.5/../../../../mips-unknown-elf/lib/crt0.o -L/home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/4.8.5 -L/home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/4.8.5/../../../../mips-unknown-elf/lib build/refprop/NVM.o (…) build/refprop/TRNS_VIS.o build/refprop/MAIN.o --gc-sections -Map=output1.map --cref -lc -Map=output.map --cref -lgfortran -lm -lgcc -lm -lgcc -lgcc /home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/4.8.5/crtend.o /home/jhuber/Documents/source/nestedvm/upstream/install/lib/gcc/mips-unknown-elf/4.8.5/crtn.o

Answer 1

I did some local tests, and -ffunction-sections puts each fortran function its own section, as expected. Compare:
$ gfortran -c -O3 -o hello.o hello.f90
$ objdump -h hello.o
hello.o: file format elf64-x86-64
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 000000aa 0000000000000000 0000000000000000 00000040 2**4
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
1 .data 00000000 0000000000000000 0000000000000000 000000ea 2**0
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000000 0000000000000000 0000000000000000 000000ea 2**0
ALLOC
3 .rodata.str1.1 0000000a 0000000000000000 0000000000000000 000000ea 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .text.startup 00000026 0000000000000000 0000000000000000 00000100 2**4
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
5 .rodata 0000001c 0000000000000000 0000000000000000 00000130 2**4
CONTENTS, ALLOC, LOAD, READONLY, DATA
6 .comment 00000026 0000000000000000 0000000000000000 0000014c 2**0
CONTENTS, READONLY
7 .note.GNU-stack 00000000 0000000000000000 0000000000000000 00000172 2**0
CONTENTS, READONLY
8 .eh_frame 00000068 0000000000000000 0000000000000000 00000178 2**3
CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
to:
$ gfortran -ffunction-sections -c -O3 -o hello.o hello.f90
$ objdump -h hello.o
hello.o: file format elf64-x86-64
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00000000 0000000000000000 0000000000000000 00000040 2**0
CONTENTS, ALLOC, LOAD, READONLY, CODE
1 .data 00000000 0000000000000000 0000000000000000 00000040 2**0
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000000 0000000000000000 0000000000000000 00000040 2**0
ALLOC
3 .rodata.str1.1 0000000a 0000000000000000 0000000000000000 00000040 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .text.MAIN__ 00000097 0000000000000000 0000000000000000 00000050 2**4
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
5 .text.foo_ 0000000a 0000000000000000 0000000000000000 000000f0 2**4
CONTENTS, ALLOC, LOAD, READONLY, CODE
6 .text.startup.main 00000026 0000000000000000 0000000000000000 00000100 2**4
CONTENTS, ALLOC, LOAD, RELOC, READONLY, CODE
7 .rodata 0000001c 0000000000000000 0000000000000000 00000130 2**4
CONTENTS, ALLOC, LOAD, READONLY, DATA
8 .comment 00000026 0000000000000000 0000000000000000 0000014c 2**0
CONTENTS, READONLY
9 .note.GNU-stack 00000000 0000000000000000 0000000000000000 00000172 2**0
CONTENTS, READONLY
10 .eh_frame 00000068 0000000000000000 0000000000000000 00000178 2**3
CONTENTS, ALLOC, LOAD, RELOC, READONLY, DATA
The builtin linker script on my local machine rolls all of these into .text by default. It appears whatever you're linking with doesn't. You should be able to modify that script to do what you're trying. It's a bit more difficult than the attribute extensions, since you'll have to maintain the list in a separate file, but you should be able to locate things however you like. I can work up an example here if you give some more context about that in your question.